Stéphane Costa
email: stephane.costa@unicaen.fr

Olivier Maquaire

Pauline Letortu

Guillaume Thirard

Vincent Compain

Thomas Roulland

Mohand Medjkane

Robert Davidson

Kevin Graff

Candide Lissak

Christophe Delacourt

Timothée Duguet

Cyril Fauchard

Raphael Antoine

Sedimentary coastal cliffs of Normandy: Modalities and quantification of retreat

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction:

Before the 1990s, the vast majority of coastal geomorphology work focused on accumulation coasts, due to the presence of many economic challenges threatened by rapid regressive changes, or potentially accelerated by contemporary mean sea level rise [START_REF] Trenhaile | Modeling the development of wave-cut shore platforms[END_REF][START_REF] Woodroffe | Coasts: Form, process and evolution[END_REF][START_REF] Kennedy | The temporal and spatial scales of rocky coast geomorphology: a commentary[END_REF]. However, rocky and cliffy coasts are said to represent more than 75% of the world's coastline [START_REF] Emery | Sea cliffs: their processes, profiles, and classification[END_REF][START_REF] Davis | Beaches and Coasts[END_REF], and are now one of the few sources of sediment for beaches. It is only in the last two to three decades that studies on these retreating coasts have increased [START_REF] Kennedy | Rock coast geomorphology: A global synthesis[END_REF][START_REF] Kennedy | The temporal and spatial scales of rocky coast geomorphology: a commentary[END_REF]. This is probably due to the rising impact of their retreat on coastal activities and populations, and to the development of tools and methods to understand the slow but abrupt dynamics of these complex rocky coastal systems [START_REF] Sunamura | Geomorphology of Rocky Coasts[END_REF][START_REF] Paskoff | Les littoraux : impact des aménagements sur leur évolution[END_REF][START_REF] Bird | Coastal Geomorphology. An introduction[END_REF][START_REF] Brunsden | Behaviour of coastal landslide systems: an interdisciplinary view[END_REF][START_REF] Young | Rain, waves, and shortterm evolution of composite seacliffs in southern California[END_REF]Costa et al., 2004;[START_REF] Costa | Quantification of the Normandy and Picardy chalk cliff retreat by photogrammetric analysis[END_REF]Gomez-Puyol et al., 2014;Letortu et al., 2015b;Guiliano, 2015). The Norman morphostructural environment (between the Bay of Mont Saint Michel and the Tréport) is favorable to the development of retreating coasts, the evolution of which can be very important [START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF][START_REF] Costa | Dynamique littorale et risques naturels : l'impact des aménagements, des variations du niveau marin et des modifications climatiques entre la Baie de Seine et la Baie de Somme[END_REF][START_REF] Costa | Quantification of the Normandy and Picardy chalk cliff retreat by photogrammetric analysis[END_REF][START_REF] Lissak | Les glissements de terrain des versants côtiers du pays d'Auge (Calvados) : morphologie, fonctionnement et gestion du risque[END_REF][START_REF] Elineau | Le risque naturel côtier sur la communauté d'agglomération du Havre (Haute-Normandie) : Une évaluation des aléas[END_REF][START_REF] Lissak | Analyse spatio-temporelle de glissements de terrain littoraux par l'exploitation de données géospatiales multi-sources[END_REF]Letortu et al., 2015b;[START_REF] Maquaire | Evolution à long terme des falaises des 'Vaches Noires' et occurrence des glissements (Calvados, Basse-Normandie, France)[END_REF][START_REF] Medjkane | High resolution monitoring of complex coastal morphology changes: crossefficiency of SfM and TLS-based survey (Vaches-Noires cliffs, Normandy, France)[END_REF]. To the extreme west of the study area (Cotentin) appears the Armorican Massif (Fig. 1) composed of ancient sedimentary, metamorphic and volcanic soils (crossed locally by granitic intrusions). Rocky coasts are made up with these Paleozoic materials [START_REF] Dugué | Le Jurassique des Côtes du Calvados. Biostratigraphie, sédimentologie, paléoécologie, paléogéographie et stratigraphie séquentielle[END_REF] with very slow retreat. In the rest of the study area, to the north, the ancient Armorican lands are covered, sometimes in discordance, by the northwestern termination of the Paris sedimentary basin [START_REF] Juignet | La transgression crétacée sur la bordure orientale du Massif armoricain[END_REF][START_REF] Lasseur | La Craie du Bassin de Paris (Cénomanien-Campanien, Crétacé supérieur). Sédimentologie de faciès, stratigraphie séquentielle et géométrie 3D[END_REF][START_REF] Le Cossec | La déformation gravitaire des côtes à falaises sédimentaires : modélisation numériques et expérimentales du secteur côtier Le Havre-Antifer (Haute-Normandie)[END_REF][START_REF] Benabdellouahed | Nouvelle cartographie du substratum de la baie de Seine et synthèse géologique terre-mer : apports de nouvelles données sismiques et biostratigraphiques[END_REF]. The latter is characterized by the existence of more or less high, undulating and sometimes faulted plateaus, explaining the lithostratigraphic diversity of the outcrops, and the variety of types of gravitational landslides encountered. Thus, in contact with the epicontinental sea that is the Eastern and Central Channel, these plateaus are carved into cliffs with a much faster retreat due to the outcropping of sedimentary formations (from the Jurassic to the Upper Cretaceous) favorable to weathering. This article has a twofold objective: first, to provide, on a historical scale and using traditional photo-interpretation methods, the values of the retreat of Norman sedimentary cliffs. In a second step, and on specific sites monitored at high frequency and resolution (SNO-Dynalit and SNO-OMIV sites, photogrammetric and lasergrammetric monitoring), the objective is to provide initial results on some of the main issues that drive the research community working on cliff coasts, namely, the spatial distribution of the retreat or evolution rates on the cliff face, the evolution rhythms, and the factors responsible for triggering gravitational landslides (rockfall, slide, debris fall).

1/ Study area

The coastal cliffs studied in this paper exclude cliffs carved from Paleozoic rocks in the Cotentin region (from Saint Vaast la Hougue to Bay of Veys). The Norman cliffs studied therefore correspond to the north-western termination of the Paris sedimentary basin and have an average amplitude of about fifty meters, even if they can exceed 100 m in the Seine Maritime area. At the foot of the latter is a large shore platform (150 to 700 m wide), with a low slope (0.2 to 2%), sometimes covered with thin sandy veneers. In their upper part, the shore platforms are hidden by a flint gravel barrier in Seine-Maritime or resistant limestones and sands of multi-metric thickness in Calvados [START_REF] Costa | The gravel beaches of North-West France and their contribution to the dynamic of the coastal cliff-shore platform system[END_REF]. With regard to the morphostructural characteristics of the study area, we can observe (Fig. 1):

1-To the west of Calvados, between Grandcamp-Maisy and Saint-Côme de Fresné, lie the active cliffs of the Bessin plateau, which range in height from 10 to 75 m (section C-D, Fig. 1). These cliffs are composite in their topographical aspects and geological structures. The profiles are variable from one end to the other and in relation to the relative thicknesses between the limestones (Bajocian and Bathonian stages) and the marls of Port-en-Bessin (Bathonian stage). Three types of cliffs have been defined [START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF]): a cliff with a soft marly pedestal topped by a limestone cornice, a cliff with a resistant pedestal in the marly limestone of the Lower Bathonian or the limestone of the Bajocian, and a simple subvertical cliff reinforced by the Bathonian limestone.

2-In the 'Caen Countryside', the similar system is reproduced between Saint-Aubin-sur-Mer and Lionsur-Mer with a plateau at lower altitudes. Several small areas of low active cliffs (Bathonian limestone) do not exceed 10 m in height.

3-Along the plateau of the 'Pays d'Auge', the cliffs carved into the Jurassic and the Lower and Upper Cretaceous are discontinuous and looser (section E-F, fig. 1). The cliffs of the 'Vaches Noires', carved into the Oxfordian stage where some limestone beds are interstratified, are called mudflow cliffs, forming a landscape of badlands and pinnacles. In Benerville-sur-Mer, at the right of Mont Canisy (110 m), and especially between Trouville-sur-Mer and Honfleur, the cliffs reappear (section E-F, fig. 1). Their foot is made of Jurassic age materials (limestone and marl) topped with Albian sand (Lower Cretaceous) and Cenomanian chalk (Upper Cretaceous) suitable for deep-seated landslides [START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF][START_REF] Lissak | Les glissements de terrain des versants côtiers du pays d'Auge (Calvados) : morphologie, fonctionnement et gestion du risque[END_REF]. 4-From Cap d'Antifer to Tréport, the cliffs are carved mainly into Upper Cretaceous chalk (from Cenomanian to Campanian stages) whose facies are more or less rich in flint beds (section A-B, fig. 1). The local tectonic deformations of the Caux plateaus also explain the outcropping of some lower Jurassic and Cretaceous strata (between Octeville-sur-Mer and Le Havre), or the conservation of sandy and clay terrains of Tertiary age (Cap d'Ailly;Bignot, 1962). The different chalk layers [START_REF] Pomerol | Lithostratigraphy and biostratigraphy of the Lewes and Seaford chalks : a link across the Anglo-Paris basin at the Turonian-Senonian boundary[END_REF][START_REF] Mortimore | Coastal cliff geohazards in weak rock: the UK Chalk cliffs of Sussex[END_REF][START_REF] Lasseur | La Craie du Bassin de Paris (Cénomanien-Campanien, Crétacé supérieur). Sédimentologie de faciès, stratigraphie séquentielle et géométrie 3D[END_REF] show subtle variations in resistance, also found in the cliff profile (Fig. 1). Thus, between Cap d'Antifer and Le Tréport, three types of cliffs have been defined [START_REF] Costa | Dynamique littorale et risques naturels : l'impact des aménagements, des variations du niveau marin et des modifications climatiques entre la Baie de Seine et la Baie de Somme[END_REF]: simple vertical cliffs (main type) composed mainly of Coniacien-Santonian chalk; cliffs with resistant pedestal, with a "basal" jump corresponding to the outcrop of the Turonian stage or even the more resistant Cenomanian stage; and complex cliffs. For the latter, the Coniacien and Santonian chalk (~ 30 m) are topped by clayey and sandy loose formations (~ 40 m), forming three back cliffs (Cap d'Ailly).

Variations in resistance between the various outcrops [START_REF] Juignet | La transgression crétacée sur la bordure orientale du Massif armoricain[END_REF][START_REF] Dugué | Géodynamique d'une bordure de massifs anciens. La bordure occidentale du bassin anglo-péruvien au Callovo-Oxfordien. Pulsations épirogéniques et cycles eustatiques[END_REF][START_REF] Juignet | Mid-Cretaceous sequence stratigraphy and sedimentary cyclicity in the western Paris Basin[END_REF][START_REF] Laignel | Les altérites à silex de l'ouest du Bassin de Paris: caractérisation lithologique, genèse et utilisation potentielle comme granulats[END_REF][START_REF] Dugué | Le Jurassique des Côtes du Calvados. Biostratigraphie, sédimentologie, paléoécologie, paléogéographie et stratigraphie séquentielle[END_REF][START_REF] Lasseur | La Craie du Bassin de Paris (Cénomanien-Campanien, Crétacé supérieur). Sédimentologie de faciès, stratigraphie séquentielle et géométrie 3D[END_REF], visible in cliff profiles, reflect various gravitational mechanisms (falls, slide, flow, etc.), but also different retreat rates and evolution rhythms. The difficulty in quantifying cliff retreat lies in the slowness of the dynamics (a time taken to prepare the rock material, often several decades before the rupture), the multiplicity and sometimes the combination of marine and sub-aerial factors responsible for the dynamics, and the punctual dimension of the evolution (spatially localized phenomenon). Normandy is located in the northwestern part of France, on both sides of the 50 th northern parallel, along the English Channel (epicontinental sea, 86 m deep on average). The environment is macrotidal (Table 1) with a tidal range of 8 m (south) to 10 m (north). Waves (Table 2), which impact the cliff foot during high tide, are limited but the wind sea can produce significant wave heights of up to 4 m at Dieppe (annual return period). 2: Significant wave (H 1/3 ) along the Normandy coast (in [START_REF] Augris | Évolution morphosédimentaire du domaine littoral et marin de la Seine-Maritime. Collection « Bilan and prospectives[END_REF]Cerema, in press).

Location

Normandy has a marine west coast climate. According to data from Météo-France (1971-2000), average winter temperatures are positive but an average of 26 daily freeze/thaw cycles is recorded per year (minimal temperature can reach -15°C). Rainfall is distributed over the year (≈800 mm) although fall and winter are the wettest seasons (51 mm in August and 94 mm in November). Daily rainfall can exceed 77 mm in October.

2/ Methodology, material and documents

With regard to the objectives of this paper, the diachronic approach is central. Indeed, two main techniques and documents are used (Fig. 2). This quantification (several decades) was carried out by classical photo-interpretation, then for the Calvados, by comparison with ancient cartographic documents (cadastral register and "Terrier plan" of the 19th century). The main documents used are vertical aerial photographs provided by the IGN (National Geographic Institute), sometimes produced by photogrammetric method. The time interval between the two series of aerial photographs is nearly 50 years for the various territories (Table 3). This diachronic approach is classic [START_REF] May | The nature and rates of change on chalk coastlines[END_REF][START_REF] Moore | Shoreline mapping techniques[END_REF][START_REF] Moore | Long-term cliff retreat and erosion hotspots along the central shores of the Monterey Bay National Marine Sanctuary[END_REF][START_REF] Lahousse | The retreat of chalk cliffs at Cape Blanc-Nez (France): Autopsy of an erosion crisis[END_REF][START_REF] Hénaff | Le recul des falaises crayeuses du Pays de Caux: détermination des processus d'érosion et quantification des rythmes d'évolution/Retreat of chalk cliffs in the Pays de Caux: processes and rates[END_REF][START_REF] Costa | Quantification of the Normandy and Picardy chalk cliff retreat by photogrammetric analysis[END_REF][START_REF] Marques | Rates, patterns and timing of cliff retreat. A case study on the west of Portugal[END_REF][START_REF] Dornbusch | Temporal and spatial variations of chalk cliff retreat in East Sussex, 1873 to 2001[END_REF][START_REF] Brooks | Temporal and spatial variations in recession rates and sediment release from soft rock cliffs, Suffolk coast, UK[END_REF][START_REF] Moses | Chalk coast dynamics: Implications for understanding rock coast evolution[END_REF][START_REF] Letortu | Le recul des falaises crayeuses haut-normandes et les inondations par la mer en Manche centrale et orientale : de la quantification de l'aléa à la caractérisation des risques induits[END_REF][START_REF] Cerema | Développer la connaissance et l'observation du trait de côte -Contribution nationale pour une gestion intégrée[END_REF]. After georeferencing and rectification of the images at from 1:10,000 to 1:20,000 scale [START_REF] Costa | Quantification of the Normandy and Picardy chalk cliff retreat by photogrammetric analysis[END_REF][START_REF] Letortu | Vitesses et modalités de recul des falaises crayeuses de Haute-Normandie (France): méthodologie et variabilité du recul[END_REF][START_REF] Lissak | Analyse spatio-temporelle de glissements de terrain littoraux par l'exploitation de données géospatiales multi-sources[END_REF][START_REF] Maquaire | Evolution à long terme des falaises des 'Vaches Noires' et occurrence des glissements (Calvados, Basse-Normandie, France)[END_REF][START_REF] Vioget | Analyse de l'évolution morpho-structurale des falaises littorales du Bessin[END_REF][START_REF] Roulland | Dynamique des falaises des Vaches Noires : analyse diachronique historique et récente à l'aide de documents multi-sources[END_REF], the digitization of the coastline was carried out (cliff top for the Seine Maritime, top and bottom for the Calvados cliffs). The margins of error of the results are not negligible (+/-0.50 m to +/-4 m). Associated with these aerial photographs, we benefited from airborne lidar data (RGE Alti-IGN) to provide a new layer of more accurate information (margin of error +/-20 cm) that completes the analysis. Finally, for the cliffs of Calvados, old documents (cadastral registers) have been integrated. France has a single document, which is the cadastral map of all the municipalities. The first of these cadastral registers, called Napoleonic, was established in the 19th century by order of Napoleon I. Carried out on a very large scale (from 1/1,000 to 1/2,500), this document has been updated to this day. The principle is attractive, but these documents exclusively express the limit of taxable parcels, which alone are perfectly mapped from one document to another. Consequently, the correct setting of these plots is logical, but it does not in any way ensure, given the danger of the measurement, the exact position of a very unstable steep slope of several tens of meters. Even if the margins of error around the position of the shoreline are large, the loss of perfectly located plots of land by erosion makes it possible to replace the cliff retreat rates obtained over a few decades in a wider time period. In addition, the multiplicity of aerial images used for different dates (Table 3) also makes it possible to provide initial information on the evolution rates of the studied cliffs.

2.2/ Quantification at high resolution and frequency diachronic monitoring

In order to participate in the current debate on (1) the evolution of the cliff face, for which it is preferable, for analysis, to monitor the height or basal coastline [START_REF] Lim | Combined digital photogrammetry and time-of-flight laser scanning for monitoring cliff evolution[END_REF][START_REF] Lim | The rock coast of the British Isles: cliffs[END_REF][START_REF] Young | Rain, waves, and shortterm evolution of composite seacliffs in southern California[END_REF][START_REF] Dewez | Laser survey and mechanical modeling of chalky sea cliff collapse in Normandy, France[END_REF]2013;[START_REF] Michoud | Landslides Detection and Monitoring Capability of Boat-based Mobile Laser Scanning along Dieppe Coastal Cliffs[END_REF]Letortu et al, 2015b;[START_REF] Rosser | Coastline retreat via progressive failure of rocky coastal cliffs[END_REF] (2) the rates of evolution (3) the processes responsible for the trigger of gravitational movements, a high resolution and frequency diachronic monitoring is carried out on some sites by lasergrammetric (TLS) and photogrammetric (SfM-MVS, Structure-from-Motion -Multi-View-Stereo) methods, completed on two sites by several continuous or permanent GPS stations. This work was undertaken within the framework of the SNO-Dynalit, but also SNO-OMIV.

Two sites are subject to these 3D monitoring in SNO Dynalit survey. These are the cap d'Ailly-Dieppe site (Seine Maritime), which has been performed since 2010 (surveys 3 to 4 times a year), and the Vaches Noires cliff near Villers-sur-Mer site since 2014 (surveys 3 to 4 times a year). On the third site of the Villerville slow-moving landslide, the monitoring system is based on twenty-four cemented benchmarks, three permanent GNSS receivers and several hydro-meteorological observation points [START_REF] Lissak | Piezometric thresholds for triggering landslides along the Normandy coast, France[END_REF]. The first site is Cap d'Ailly-Dieppe (Fig. 3a). From October 2010 (Fig. 3d), surveys using terrestrial laser scanning were carried out to monitor erosion on three chalk cliff faces with close lithological characteristics. The active cliff of Varengeville-sur-Mer is along the cap d'Ailly (6 km from Dieppe) on either side of the Petit Ailly dry valley (250 m long, 40 m high, facing 010°N, subvertical). The abandoned cliffs of Dieppe are located on the right bank of the Arques river mouth, behind an extension of the northeastern part of the harbor, land reclaimed from the sea. Dieppe 1 W (45 m long, 35 m high, facing 310°N, subvertical) became abandoned during the nineteenth century whereas Dieppe 2 N (80 m long, 35 m high, facing 010°N, subvertical) became abandoned in the 1980s (Fig. 3a andc). The western cliff is in front of the quay for the Newhaven-Dieppe ferry crossings. The cliff lithology in cap d'Ailly is made up with Santonian chalk, covered by a bed of clay and sand of Paleogene period (due to the syncline prone to strata preservation), which are very prone to erosion (Fig. 3b). The cliff section of Dieppe is made up of Coniacian chalk covered with residual flint formation (Fig. 3c). Even if each facies within a stage can have some subtle resistance contrasts, the Coniacian chalk is close to Santonian chalk [START_REF] Laignel | Caractérisation et dynamique érosive de systèmes géomorphologiques continentaux sur substrat crayeux. Exemple de l'Ouest du Bassin de Paris dans le contexte[END_REF]. The SNO-OMIV survey is focused on the Villerville slope site. This site is affected by a deep-seated rotational-translational complex landslide. It is monitored since the early 1980s, following the major event of 1982 [START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF]. In order to measure the seasonal displacements affecting the landslide from upstream to downstream, 24 cemented landmarks were installed and their positions are regularly measured by GNSS. Since 2009, this equipment is completed by the installation of 3 GNSS receivers in the East part of the unstable area, which record their XYZ position every hour and provides a better knowledge of the evolution rhythms (velocity, distance, direction and thresholds) [START_REF] Lissak | Les glissements de terrain des versants côtiers du pays d'Auge (Calvados) : morphologie, fonctionnement et gestion du risque[END_REF][START_REF] Lissak | Analyse spatio-temporelle de glissements de terrain littoraux par l'exploitation de données géospatiales multi-sources[END_REF]. Groundwater fluctuations are observed across a network composed by a set of 20 piezometers and inclinometers, mainly distributed on the eastern two thirds of the landslide, which is known as the most active area [START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF][START_REF] Lissak | Les glissements de terrain des versants côtiers du pays d'Auge (Calvados) : morphologie, fonctionnement et gestion du risque[END_REF][START_REF] Lissak | Analyse spatio-temporelle de glissements de terrain littoraux par l'exploitation de données géospatiales multi-sources[END_REF]. Among those devices, six are continuously tracked with multiparameter sensors (temperature and depth), the others are surveyed monthly with a contact gauge to highlight seasonal trends. Lastly, various hydrometeorological parameters are registered by meteorological stations that records rainfall, temperature, solar radiation, wind speed and wind direction, nearby the unstable slopes at Villerville and on the plateau located at Saint-Gatien-des-Bois from 5 kilometres of the cliffs.

Along the Bessin cliff, on a local scale, four sites are surveyed by TLS and terrestrial photogrammetry SfM (4-5 times per year) since December 2017 in order to assess the rate of the retreat of the cliff base following the triggering factors. These sites are representative of the diversity of the landslide (falls, rotational and translational landslides …) occurred in marly and limestone environments [START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF][START_REF] Vioget | Analyse de l'évolution morpho-structurale des falaises littorales du Bessin[END_REF]. In addition, on a regional scale, the evolution of Bessin cliffs is study by comparison of oblique aerial photographs taken since 1983 (thesis of Vincent Compain in progress).

The TLS instrument used in this study is a RIEGL VZ-400 emitting a wavelength laser of 1,550 nm, which records unique echo digitization (RIEGL Laser Measurement Systems, 2014). The laser beam covers the environment with vertical scanning by an oscillating mirror and horizontal scanning by rotating the head. The point cloud is therefore centered on the position of the scanner. To have georeferenced data, the process of data acquisition requires additional equipment: target(s), a total station or a DGPS. The total station or the DGPS station is used to register the point cloud acquired in a relative coordinate system to an absolute coordinate system thanks to target(s) (RGF93/Lambert93, EPSG:2154). Data processing has 4 steps: (1) georeferencing and point cloud alignment; (2) manual point cloud filtering (vegetation, people, foreshore); (3) meshing using Delaunay triangulation and generation of a 3D Digital Elevation Model (DEM); (4) creating a DEM of Difference (DoD). Precision is the most important parameter in our monitoring, thus all the point clouds are fitted to a selected reference point cloud using best fit alignment algorithms (Cloudcompare® or 3DReshaper®). This adjustment reduces the error margin because it includes the TLS instrumental error (0.005 m at a range of 100 m, RIEGL Laser Measurement Systems, 2014) and the cloud adjustment error (fitting) only. To assess precision, fixed parts of the point cloud are compared using the usual data processing. The precision in planimetry is 0.03 m for cap d'Ailly and Dieppe 2 N, 0.02 m for Dieppe 1 W and Villers-sur-mer. The volume precision is ± 156 m3 in cap d'Ailly (surface of 5,214 m²), ± 9 m 3 in Dieppe 1 W (434 m²) and ± 30 m 3 in Dieppe 2 N (1,018 m²), and ± 3 m 3 in Villers-sur-Mer (111 m²) [START_REF] Medjkane | High resolution monitoring of complex coastal morphology changes: crossefficiency of SfM and TLS-based survey (Vaches-Noires cliffs, Normandy, France)[END_REF]. These improved resolutions, particularly over the whole cliff face, and the higher frequency of acquisitions provide valuable information on ablation rates, spatial distribution, temporalities and the processes and factors responsible for triggering of gravitational movements.

The models obtained by SfM processing followed the method presented in [START_REF] Medjkane | High resolution monitoring of complex coastal morphology changes: crossefficiency of SfM and TLS-based survey (Vaches-Noires cliffs, Normandy, France)[END_REF]. The processing steps, carried out with Agisoft Photoscan, can be summarized as follows: (1) Image matching and orientation of cameras; (2) densification of the 3D point cloud; (3) triangulation/meshing of the point cloud; (4) texturing of the model; (5) creation of a DoD. The same targets used to georeference lasergrammetric models were used in photogrammetric models. Photographs were obtained with an advance grade camera to further improve model precision: Nikon D810 (36 million pixels, sensor size 36x24 mm) and a Sigma 35 mm fixed optics. Finally, to assess precision, the accuracy of control points on the model was compared with the precisely measured GCPs by calculating the RMSE (Root Mean Square Error, [START_REF] Eltner | Image-based surface reconstruction in geomorphometry -merits, limits and developments[END_REF][START_REF] Kaiser | Small-scale surface reconstruction and volume calculation of soil erosion in complex moroccan gully morphology using Structure-from-Motion[END_REF]).

3/ Results

3.1/ Historical approach for all Norman sedimentary cliffs

The study of the Norman sedimentary cliffs shows that their retreat is decimetric, from 0.1 to 0.5 m/yr during the last decades. These values are in line with the literature (Woodroff, 2002). The spatial variations of the cliff retreat rates, at the scale of Normandy, can be explained by geological structure from which the cliffs were formed) (Fig. 5). However, the differences are not excessive while various materials, of significantly different resistance, are exposed (limestones, chalks, marls, clays). The greatest variations of retreat appear for the cliffs of Seine Maritime which are nevertheless carved in materials, a priori more homogeneous, Cretaceous chalks.

Example of lithodependance: the chalk cliff of Seine Maritime

Various authors have proposed cliff typologies that relate profile, resistance and disposition of rocks (Guilcher, 1954;Trenhaile, 1987;[START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF][START_REF] Costa | Dynamique littorale et risques naturels : l'impact des aménagements, des variations du niveau marin et des modifications climatiques entre la Baie de Seine et la Baie de Somme[END_REF][START_REF] Woodroffe | Coasts: Form, process and evolution[END_REF][START_REF] Senfaute | Micro-seismic precursory cracks prior to rockfall on coastal chalk cliffs: a case study at Mesnil-Val, Normandie, NW France[END_REF][START_REF] Dornbusch | Temporal and spatial variations of chalk cliff retreat in East Sussex, 1873 to 2001[END_REF][START_REF] Kennedy | Rock coast geomorphology: A global synthesis[END_REF]. These classifications sometimes make it possible to deduce the effectiveness of the marine and continental processes involved [START_REF] Emery | Sea cliffs: their processes, profiles, and classification[END_REF][START_REF] Kuhn | Coastal cliff monitoring and analysis of mass wasting processes with the application of terrestrial laser scanning: A case study of Rügen, Germany[END_REF]. Behind a lithological homogeneity that is only apparent, the variability of the facies of the Seine Maritime chalk [START_REF] Pomerol | Lithostratigraphy and biostratigraphy of the Lewes and Seaford chalks : a link across the Anglo-Paris basin at the Turonian-Senonian boundary[END_REF][START_REF] Mortimore | Coastal cliff geohazards in weak rock: the UK Chalk cliffs of Sussex[END_REF][START_REF] Lasseur | La Craie du Bassin de Paris (Cénomanien-Campanien, Crétacé supérieur). Sédimentologie de faciès, stratigraphie séquentielle et géométrie 3D[END_REF] very clearly influences the modalities and evolution rates of the Seine-Maritime cliffs. Photogrammetry analyses were carried out to quantify the retreat of chalk cliffs. The 1966 and 1995 vertical aerial photographic surveys (1:10,000) from the French National Geographic Institute have been used [START_REF] Costa | Le littoral haut normand et picard : une gestion concertée[END_REF]2004). The mean retreat rate of the entire shoreline under study is approximately 6 m between 1966 and 1995, which yields a rate of 0.21 m/yr. This average rate, however, masks a very high spatial variability of cliff retreat (Fig. 6). Figure 6: Relationship between chalk rates cliff retreat and lithology (from [START_REF] Costa | Le littoral haut normand et picard : une gestion concertée[END_REF]2004;[START_REF] Letortu | Vitesses et modalités de recul des falaises crayeuses de Haute-Normandie (France): méthodologie et variabilité du recul[END_REF]. In fact, the analysis allows three distinct areas to be distinguished: (i) an area of low retreat rate (0.8 to 0.13 m/yr) between Antifer and Fécamp; (ii) an area of moderate retreat rate (approximately 0.19 m/yr) between Fécamp and Saint-Valéry-en-Caux, and between Dieppe and Le Tréport; (iii) an area of rapid retreat (0.21 to 0.28 m/yr) between Saint-Valéry-en-Caux and Dieppe [START_REF] Costa | Le littoral haut normand et picard : une gestion concertée[END_REF]2004;[START_REF] Letortu | Vitesses et modalités de recul des falaises crayeuses de Haute-Normandie (France): méthodologie et variabilité du recul[END_REF].

3.2/ Contributions of high resolution and frequency measurements

Ablation rates and spatial distribution of the cliff face evolutions

For fast retreating cliffs, the emergence of techniques such as airborne or terrestrial lidars, terrestrial or UAV photogrammetry have made it possible to better estimate cliff retreat rates by integrating a fundamental dimension, the cliff face [START_REF] Lim | Combined digital photogrammetry and time-of-flight laser scanning for monitoring cliff evolution[END_REF][START_REF] Rosser | Terrestrial laser scanning for monitoring the process of hard rock coastal cliff erosion[END_REF][START_REF] Young | Application of airborne LIDAR for seacliff volumetric change and beach sediment contributions[END_REF][START_REF] Costa | Le littoral haut normand et picard : une gestion concertée[END_REF]2004;[START_REF] Lahousse | The retreat of chalk cliffs at Cape Blanc-Nez (France): Autopsy of an erosion crisis[END_REF][START_REF] Dewez | Laser survey and mechanical modeling of chalky sea cliff collapse in Normandy, France[END_REF]2013;[START_REF] Young | Rain, waves, and shortterm evolution of composite seacliffs in southern California[END_REF][START_REF] Lim | Erosional processes in the hard rock coastal cliffs at Staithes, North Yorkshire[END_REF][START_REF] Olsen | New automated Point-Cloud Alignement for Ground-Based Ligth Detection and Ranging Data of Long Coastal Sections[END_REF]Letortu et al., 2015b;[START_REF] Michoud | Landslides Detection and Monitoring Capability of Boat-based Mobile Laser Scanning along Dieppe Coastal Cliffs[END_REF][START_REF] Kuhn | Coastal cliff monitoring and analysis of mass wasting processes with the application of terrestrial laser scanning: A case study of Rügen, Germany[END_REF][START_REF] Giuliano | Erosion des falaises de la région Provence-Alpes-Côte d'Azur : évolution et origine de la morphologie côtière en Méditerranée : télédétection, géochronologie, géomorphologie[END_REF][START_REF] Rosser | Coastline retreat via progressive failure of rocky coastal cliffs[END_REF]. This work (Fig. 7), carried out approximately every 3-5 months on active and abandoned chalk cliffs (cap d'Ailly and Dieppe, respectively), but with similar lithology, shows that over the period studied (2010-2017): (1) The ablation rate evaluated by TLS on active cliffs over a period of 7 years corroborates that established by photo-interpretation (observed over nearly 50 years), i.e. around 36 cm/year for the cap d'Ailly and almost zero for the abandoned cliffs of Dieppe; (2) in 7 years, the entire front of the active cliff is affected by debris or mass movements; (3) scree movements (debris falls) represent 100% of the evolution of the abandoned cliff faces (for the moment!), while they represent 2% of the total retreat of the active cliff of cap d'Ailly. This quantification highlights the poor contribution of debris falls, and explains in a more detailed way the first assessments made on the same Norman chalk cliffs and East Sussex [START_REF] Lageat | The retreat of the chalk cliffs of the Pays de Caux (France): erosion processes and patterns[END_REF][START_REF] May | The nature and rates of change on chalk coastlines[END_REF]; (4) Abandoned cliffs have evolved up to 36 times more slowly than active one, highlighting the importance of marine actions in the active cliff retreat (Letortu et al., 2015b). Those in accumulation are visible at the outlet of the gullies and very locally at the top of the basal scarp. However, in detail, we note that the erosion and accumulation sectors follow one another spatially in the gullies, at their outlet and at the level of the basal scarp. These values reveal the seasonal activity of the cliffs of the "Vaches Noires" with a contribution of materials upstream of the cliffs and the finest elements that will then be partially cleaned and swallowed by the sea. After these observations, the high temporal frequency survey allowed to assess the different accumulated / eroded volumes according to the processes and associated morphologies (ablation zone and accumulation zone) between the different dates in order to better understand the seasonal temporality and the role and the weight of each controlled factors (sea erosion and groundwater elevation) (Thomas Roulland thesis in progress).

4.1/ Rhythms of evolutions

The identification of several sectors with distinctive retreat rates raises questions about the causes of this spatial distribution of the cliff retreat rates (especially its relation to the outcropping of different chalk strata), and more, the temporalities between two cliff collapses at the same location [START_REF] Evrard | Stabilité des falaises du Pays de Caux[END_REF]Trenhaile, 1987;[START_REF] Trenhaile | Cliffs and Rock Coasts[END_REF][START_REF] Sunamura | Geomorphology of Rocky Coasts[END_REF][START_REF] Prager | Age distribution of fossil landslides in the Tyrol (Austria) and its surrounding areas[END_REF][START_REF] Kennedy | Rock coast geomorphology: A global synthesis[END_REF]. The knowledge of the cliffs evolution rhythms is as fundamental as that of their rates, especially in the context of the timing of the movement of properties and people threatened by the decline. As the Figure 9 shows for the chalk cliffs of Seine Maritime, the sectors with "low" and "moderate" retreat, are affected by infrequent but voluminous rockfalls [START_REF] Costa | Dynamique littorale et risques naturels : l'impact des aménagements, des variations du niveau marin et des modifications climatiques entre la Baie de Seine et la Baie de Somme[END_REF][START_REF] Costa | Origine de la variabilité spatiale du recul des falaises crayeuses du nord-ouest du Bassin de Paris. L'exemple du littoral haut normand (France)[END_REF]2004;[START_REF] Letortu | Le recul des falaises crayeuses haut-normandes et les inondations par la mer en Manche centrale et orientale : de la quantification de l'aléa à la caractérisation des risques induits[END_REF], and correspond to cliff foot cut into Turonian, Cenomanian, and even Coniacian outcrops (Antifer/Fécamp ; Fécamp/Saint-Valéry-en-Caux ; Dieppe/Le Tréport). By contrast, the rapidly retreating sectors, affected by frequent but less voluminous rockfalls, correspond to Santonian and Campanian outcrops (Saint-Valéry-en-Caux/Dieppe). Even within each of these coastal sections, important variations do exist. These sharp variations are linked with the influence of cliff collapses or anthropogenic obstacles, such as harbour arms or major groynes that disrupt the gravel transit from the south-west to the north-east. Then down current from these obstacles, the cliff retreat can be multiplied by 2 [START_REF] Costa | The gravel beaches of North-West France and their contribution to the dynamic of the coastal cliff-shore platform system[END_REF]. These observations are confirmed by the analysis of the retreat at 50 m intervals (Fig. 10). Figure 10: Impact of major cliff falls or anthropogenic obstacles on chalk cliff retreat of Seine Maritime (A), and some examples of measures at 50 m intervals (B).

For the "Vaches Noires" cliffs, by comparing old documents (terrier plan, land register map, aerial photographs, postcard photography) and more contemporary data (orthophotographs, satellite images, dGPS surveys, LIDAR survey) between 1759 and 2016 (257 years), the results show a marked decline in the main scarp estimated at -0.39 m/year, but also an average annual decline of -0.27 m/year between 1837 and 2016 (179 years). The secondary scarp declined more modestly by -0.23 m/year between 1759 and 2016 (257 years), then by -0.48 m/year over the period 1837 and 2016 (179 years). The basal scarp has a more contrasted evolution, with some sectors in erosion, others in progradation, and some sectors without significant evolution (or included in the margins of error). The erosion values are generally between -0.02 m/year to -0.15 m/year between the different periods. The progradation values range from + 0.02 m/year to + 0.15 m/year, often included in front of the locality "Hermitage". Comparison with the average evolution rates (in m/year) of other Normandy clay and marl cliffs (ranging from -0.15 m/year to -0.30 m/year) showed that the foot of the basal scarp suffered a slight overall decline. These studies showed that nuances needed to be made in the evaluation of shorter time step velocities due to the reactivation and progression of major landslides on the foreshore that alter the coastline. In the cliffs of the "Vaches Noires", this is visible in the area known as "l'Hermitage" where a large landslide occurred between 1837 and 1947, causing the main scarp to retreat by more than 120 m and the coastline to advance by more than 50 m [START_REF] Maquaire | Evolution à long terme des falaises des 'Vaches Noires' et occurrence des glissements (Calvados, Basse-Normandie, France)[END_REF]Roulland et al., in press).

Thus, on sectors with cliffs evolving by landslides and mudflows, nuances in the evolutions must be made according to the sectors and according to the periods considered. The evolution calculated over a long period is probably more significant when taking into account the "cycle" of evolution of the cliff. For marl cliffs of different configurations, evolution can occur within cycles of 30 to 40 years in London clays [START_REF] Hutchinson | The response of London Clay cliffs to different rates of toe erosion[END_REF], or of a hundred years in the Gault clay cliffs of Dorset [START_REF] Brunsden | Relative time scales and formative events in coastal landslide systems[END_REF] where the activation of summit flows depends largely on the retreat of the lower part of the cliff (Pierre, 2005). Thus, for the "Vaches Noires" cliffs, the duration of the "cycle" to be taken into account would be at least around 250 to 300 years to be able to set a long-term evolutionary trend of decline.

4.2/ Factors responsible for triggering gravitational landslides (rockfall, slide, debris fall) and thresholds

The cross-referencing of multi-date and multi-document data as well as that of some agents as erosion processes can provide information about the factors responsible for triggering gravitational landslides. At the SNO-OMIV landslide of Villerville, the link was clearly established between efficient rainfall, groundwater level and displacements of the unstable slopes [START_REF] Maquaire | Les mouvements de terrain de la côte du Calvados -Recherche et prévention[END_REF][START_REF] Lissak | Role of hydrological process in landslide occurrence: Villerville-Cricqueboeuf landslides (Normandy coast, France)[END_REF][START_REF] Lissak | Les glissements de terrain des versants côtiers du pays d'Auge (Calvados) : morphologie, fonctionnement et gestion du risque[END_REF]. Efficient rainfall increase the roof level of the groundwater until it exceed a threshold rain quantity, considered in the literature as the main triggering factor of worldwide landslides (Zezere, 2002;Zezere et al., 2015;[START_REF] Guzzetti | The rainfall intensity-duration control of shallow landslides and debris flows: an update[END_REF][START_REF] Peruccacci | Rainfall Thresholds for Possible Landslide Occurrence in Italy[END_REF]. The link intensity/duration has a particular impact on the overtaking of this threshold (Zezere et al., 2015).

In order to highlight the relationship between rain, groundwater and displacement of the Villerville deep-seeted landslide, long-term chronicles of data should be used (Fig. 11). To this end, data from a piezometer of the national network located in Danestal (in the hinterland, on the Pays d'Auge plateau) were crossed-analysed with efficient rainfall data measured at the Météo-France weather station of Saint-Gatien-des-Bois (located 5 km backwards the landslide). Then, those chronicles were linked to the major events known which affected this great coastal landslide. This correlation analysis, initially expressed by [START_REF] Lissak | Les glissements de terrain des versants côtiers du pays d'Auge (Calvados) : morphologie, fonctionnement et gestion du risque[END_REF], revealed a small-scale causal relationship between the hinterland groundwater level and the four major accelerations observed on the coast (Fig. 11). From this observation, a regional warning threshold have been proposed in cases in which the piezometer of Danestal exceed a depth of 11m/GL and the effective rain on a 4-monthsperiod is over 250 mm [START_REF] Lissak | Analyse spatio-temporelle de glissements de terrain littoraux par l'exploitation de données géospatiales multi-sources[END_REF].

For the chalk cliffs of Seine Maritime, determination of the triggering factors of rock falls is more difficult. Based on a census of 331 chalk cliff rock falls collected weekly between 2002 and 2009 from Veules-les-Roses to Le Treport the relationship between dates of cliff rock falls and external factors commonly agreed as triggering (rainfall, temperature variations, tide and wind) is studied (Fig. 12). The combination of multivariate statistical and empirical analyses indicates (Letortu et al., 2015a) that, (1) the high rainfall are an essential triggering factors and especially the most massive chalk rock falls (mostly larger than 10,000 m 3 ) (confirmed studied of [START_REF] Pierre | The role of groundwater in cliff instability: an example at Cape Blanc-Nez (Pas-de-Calais, France)[END_REF][START_REF] Duperret | Coastal rock cliff erosion by collapse at Puys, France: The role of impervious marl seams within chalk of NW Europe[END_REF]2004;2005), (2) but also the freeze/thaw cycles which are responsible for scree production phenomena (individual particles), (3) marine factors are not negligible but their influence is difficult to quantify because rock falls of small volumes may be quickly removed during a turbulent period. However, the contribution of each factor to triggering is difficult to determine because of combinations of factors (84 % of 331 cases), relays of processes and hysteresis phenomena. In view of these first results, it is still presumptuous to predict the location and time of triggering of rock falls. However, the statistical and naturalistic approaches adopted and the observations made in this study are from an original database, and constitute a real starting point for the prediction and prevention of the hazard of coastal chalk cliff rock falls.

Conclusion

The retreat rates of the sedimentary cliffs of Normandy are about 20-30 cm/year. These values are in line with what is generally observed for this type of geology (Woodroff, 2002;Dunrbush et al., 2008;Mooses and Robinson, 2011;[START_REF] Kennedy | The temporal and spatial scales of rocky coast geomorphology: a commentary[END_REF]. Spatial disparities are due to lithological variations (outcrop less resistant at the foot of cliffs), but also and above all to the existence of obstacles to coastal drift (structures or cliff falls) which considerably and locally increase the retreat rates. These values are also comparable to what has been observed on the English coasts for similar materials (Durnbush et al., 2008) while the orientation towards swells is different. However, beyond the lithological variations there may be other factors that explain the spatial variation in retreat rates. Among these factors not exposed in this work are the width of the platform, the height of the cliff, the width of the beaches at the foot of the cliffs, the intensity of the fracturing of the rocks, the presence of more or less important groundwater... This work also shows the interest of diachronic analysis using a multisource and multitemporal approach (comparison of historical documents of modest precision, but allowing observation over large areas with high frequency and high resolution data, allowing the cliff face to be studied locally). This work provides information on the "periodicities" of the evolution of the various cliffs that are essential for the temporal management of the movement of goods and people.

The high frequency and high resolution monitoring carried out as part of SNO-Dynalit and SNO-OMIV greatly improves the knowledge of these sites. Even if the monitoring is carried out only in fairly small areas, it allows to finely spatialize the evolutions, especially on the cliff face. It makes it possible to distinguish between screes and mass movements, to quantify the production of debris brought to the sea. However, the development of these new techniques (laser and photogrammetry) is recent (a decade). The results therefore have a limited temporal representativeness. To be exhaustive, high-resolution data will have to be acquired over the entire cliff evolution periodicity ("evolution cycle"), which for some of them is at least two decades. Similarly, the frequency of surveys should be well above 3-4 per year to define the agents and processes responsible for weathering cliffs or triggering gravity movements. It is also for these reasons that it is very difficult to estimate the impact of climate change and sea level rise on cliff recession rates. Moreover, the extent of anthropization on coastal dynamics in recent decades masks the possible influence of these global changes.

Figure 1 :

 1 Figure 1: Simplified geological map of the Normandy (from BRGM, French geological survey) and litho-stratigraphic profiles of cliffs on the study site.

Figure 2 :

 2 Figure 2: Techniques and documents used to study the evolution of Norman sedimentary coastal cliffs 2.1/ Quantification on historical scale and for all Norman sedimentary cliffs

Figure 4 :

 4 Figure 4: Scheme of the measurement tools and equipment used for the monitoring of the "Vaches Noires" cliffs

Figure 5 :

 5 Figure 5: Synthesis of historical rates retreat of the Normandy sedimentary cliffs (in cm/year).

Figure 7 :

 7 Figure 7: Erosion results of DoD over 7-years of monitoring of "cap d'Ailly/Varengeville-Dieppe" site. For the "Vaches noires" cliffs, the TLS differential model (March 2015 and October 2017) clearly identifies erosion areas (red color) and accretion areas (blue color) (Fig. 8) at high spatial resolution. The main eroding areas are the upstream scarp, the flanks of the interfluve ridges, and the basal scarp.

Figure 8 :

 8 Figure 8: Erosion and accretion areas: TLS differential model of "Vaches noires" cliffs (March 2015 -October 2017) 4/ Discussion

Figure 9 :

 9 Figure 9: Cliff retreat, average retreat per fall and average time between two cliff falls for cliffs chalk of Seine Maritime.

Figure 11 :

 11 Figure 11: Evolution of the groundwater level of the Danestal well and of the effective annual rainfall of the St-Gatien-des-Bois climatic station from 1974 to 2018

Figure 12 :

 12 Figure 12: Example of relationship between cliff falls inventoried and external factors shows combinations and relays of processes (A), and multivariate statistical analyses (PCA) of 331 chalk cliff rock falls (Letortu et al., 2015a) of Seine Maritime (B).

Table 1 :

 1 Tide level along the Normandy coast(Shom, 2007).

	Barfleur	Le Havre	Dieppe	Le Tréport

This work also shows the importance of setting up observatories for long-term monitoring such as INSU's SNO-Dynalit and SNO-OMIV, or INEE's "workshop zones" ("Zones Ateliers" of National Institute on Ecology and Environment studies).

Acknowledgements

This research was supported by several projects: the project "Developing Geomorphological mapping skills and datasets in anticipation of subsequent Susceptibility, Vulnerability, Hazard and Risk Mapping" funded by the EUR-OPA European Major Hazards Agreement of the Council of Europe; the ANR project "RICOCHET: multi-RIsk assessment on Coastal territory in a global CHange context" funded by the French Research National Agency (ANR-16-CE03-0008); the project "RAiv Cot: flood and storm surge Risk and Hazard of coastal towns : quantitative and virtual reality approach funded by Normandy Regional Council and by Fondation de France; the project "Teledetac: Télédection par DronE du TrAit de Côte" funded by Normandy Regional Council; the project "TOSCA CNES -SWOT 2013 and SWOT COTEST 2018 funded by the CNES.


Andrea " S " Meseguer
email: asanchezmeseguer@gmail.com

Pierre6olivier " Antoine

Antoine " Fouquet

Frédéric " Delsuc

" Fabien

" Condamine

Andrea ! S ! Meseguer

The'role'of'the'Neotropics'as'a'source'of'world'tetrapod'biodiversity' 2

Keywords: "speciation, "extinction, "dispersal, "phylogeny, "tetrapods, "biogeography, "fossils.' 43" 4

Aim:"The"Neotropics"currently"host"outstanding"levels"of"species"richness,"with"one"third"of"the"

17"

global" tetrapod" species." The" underlying" causes" of" these" extraordinary" levels" of" biodiversity" 18" represent" a" debated" topic" in" evolutionary" ecology," but" the" main" processes" at" work" remain" 19" elusive."

190"

when"high"tip"ratio"bias"is"observed" [START_REF] Davis | Exploring"power"and"parameter"estimation"of" 529" the"BiSSE"method"for"analyzing"species"diversification[END_REF][START_REF] Alves | Geographical"diversification"and"the" 494" effect"of"model"and"data"inadequacies:"the"bat"diversity"gradient"as"a"case"study[END_REF]."Unfortunately,"most" 191" species"in"our"trees"are"endemic"to"one"region"(widespread"species"representing"less"than"10%" 192" of" our" dataset)." The" same" limitations" prevented" us" from" using" the" multistate" model" and"

193"

decompose" the" "Elsewhere"" character" into" different" continental" units." In" addition," BiSSE.td" 194" approaches" have" not" yet" been" implemented" for" GeoSSE." Although" the" time6variable" GeoSSE.t" 195" function" allows" diversification" parameters" to" vary" continuously" through" time" (Rolland" et! al.," 196" 2014),"time"variation"in"this"model"is"constant,"such"that"parameters"either"increase"or"decrease" 197" all"the"way"from"the"origin"of"the"clade"to"the"present."In"this"sense,"this"model"is"not"adapted"to" 198" infer"whether"the"Neotropical"region"was"a"prolonged"source"of"world"diversity"or"the"dynamic" 199" changed"at"specific"time"periods."

200"

Issues" associated" with" model" adequacy" and" rejection" in" SSE" approaches" have" been"

201"

recently" raised" [START_REF] Rabosky | Model"Inadequacy"and"Mistaken"Inferences"of"Trait6 616" Dependent"Speciation[END_REF]." We" explored" the" relationship" between" 202" geographical" distribution" and" diversification" using" the" Hidden" State" Speciation" and" Extinction"

203"

(HiSSE)" model" in" the" R6package" HiSSE" 1.9.1" [START_REF] Beaulieu | Detecting"hidden"diversification"shifts"in"models"of"trait6 512" dependent"speciation"and"extinction[END_REF]," which" accounts" for"

204"

unmeasured"factors"("hidden""states)"that"could"impact"diversification"rates"in"addition"to"the" 205" 10" " trait" of" interest," a" method" that" provides" a" solution" to" the" issues" detected" with" SSE" models" 206" [START_REF] Beaulieu | Detecting"hidden"diversification"shifts"in"models"of"trait6 512" dependent"speciation"and"extinction[END_REF]." We" implemented" a" full" hidden6state" speciation" and" extinction" 207" model"(full"HiSSE)"and"two"additional"null"models"where"diversification"was"allowed"to"vary"but" 208" was"not"impacted"by"species"distributions:"a"character6independent"diversification"model"with" 209" two"hidden"states"(CID62)"and"a"character6independent"diversification"model"with"four"hidden" 210"

states"(CID64).""

211"

Finally," we" used" a" time6variable" (trait6independent)" birth6death" model" to" detect" 212" diversification"rate"shifts"at"specific"branches"of"the"tree"as"implemented"in"BAMM"2.5" (Rabosky" 213" et!al.," 2013)." We" ran" four" independent" MCMC" for" 20" million" generations," sampling" event" data" 214" every"2000"steps."Global"incomplete"sampling"was"accounted"for"by"providing"the"proportion"of" 215" species" sampled" in" the" tree." Appropriate" priors" were" estimated" with" the" setBAMMpriors"

216"

command" in" the" R6package" BAMMtools" [START_REF] Rabosky | BAMM"tools:"an"R"package"for"the"analysis"of"evolutionary"dynamics"on" 619" phylogenetic"trees[END_REF]." MCMC" outputs" were" processed" 217" using"effective"sample"sizes"to"check"convergence,"including"the"visualization"of"phylorate"plots"

218"

and"rate6through6time"plots"for"the"history"of"the"species"currently"distributed"in"the"Neotropics"

219"

and"Elsewhere."

220"

#

221" (c)"Colonisations#into#and#out#of#the#Neotropics#

222"

We" estimated" when" tetrapods" colonised" the" Neotropics" using" two" different" approaches." First,"

223"

the" maximum6likelihood" model" 'dispersal-extinction-cladogenesis'" (DEC)" implemented" in"

224"

Lagrange"(Ree"&"Smith,"2008)"and"considered"that"all"ranges"comprised"of"two"areas"could"be"

225"

ancestral"states."Second,"since"ancestral"state"estimations"can"be"misleading"when"the"potential" 226" impact" of" the" trait" on" the" diversification" process" is" ignored" [START_REF] Maddison | Estimating"a"binary"character's"effect"on" 585" speciation"and"extinction[END_REF]," we" 227" estimated" the" likeliest" "Neotropical"" and" "Elsewhere"" states" for" internal" nodes" of" a" phylogeny" 228" using" the" function" asrXbisse" in" diversitree" and" the" best6fitting" BiSSE" model" (ancestral" 229" reconstructions"are"not"implemented"for"BiSSE.td"in"diversitree)."

230"

" 231"

Results'

232"

11" " (a)#Neotropical#tetrapod#diversity#

233"

According" to" current" distribution" data," the" Neotropics" contain" a" substantial" part" of" the" world" 234" species" diversity" for" tetrapods" with" more" than" a" third" of" described" species" for" amphibians," 235" birds,"and"lepidosaurs,"and"25%"for"mammals"(average"of"34.2%;"Table'1)."The"tetrapod"time6 236" calibrated"phylogenies"currently"available"include"24.2%"of"the"described"Neotropical"species," 237" on"average."

240"

TimeBconstant# diversification# models.' The" best6fitting" time6constant" BiSSE" model" for"

241"

amphibians" (Table" S1)" is" the" one" with" speciation" and" dispersal" parameters" differing" between" 242" regions,"while"extinction"remains"equal"(λN"≠"λE;"dNE"≠"dEN;"μN!=!μE)."In"this"model,"speciation"rates" 243" in"the"Neotropics"are"higher"than"in"the"rest"of"the"world"(λN!=!0.078"vs."λE!=!0.062),"and"dispersal" 244" rates" out" of" the" Neotropics" are" higher" than" into" the" Neotropics" (dEN!=!0.0" vs.! dNE!=!0.001)." The"

245"

best6fitting" BiSSE" model" for" lepidosaurs" has" speciation" and" extinction" rates" differing" between" 246" regions," while" dispersal" rates" are" similar" (λN"≠" λE;" μN!≠!μE;" dNE"="dEN;" Table" S1)." Both" speciation"

247"

and"extinction"rates"are"higher"in"the"Neotropics"(λE!=!0.064"vs."λN!=!0.169,!μE!=!0.0"vs."μN!=!0.101)."

248"

For" birds," the" best6fitting" BiSSE" model" is" the" one" with" speciation" and" dispersal" parameters"

249"

differing"between"regions,"while"extinction"remains"equal"(λN"≠"λE;"dNE"≠"dEN;"μN!=!μE)."Speciation" 250" rates" in" the" Neotropics" (λN!=!0. 161)" are" higher" than" in" the" rest" of" the" world" (λE!=!0. 092)," and" 251" dispersal" rates" out" of" the" Neotropics" (dNE!=!0. 0193)" are" higher" than" into" the" Neotropics" (dEN!=! 252" 0.0057)." For" mammals," the" best6fitting" BiSSE" model" is" the" one" with" all" parameters" differing"

253"

between"regions"(Table"S1)."In"this"model,"speciation"rates"in"the"Neotropics"are"higher"than"in" 254" the"rest"of"the"world"(λN!=!0.152"vs."λE!=!0.117),"and"extinction"rates"too"(μE!=!0.011"vs."μN!=!0.094)."

255"

Dispersal"rates"from"the"Neotropics"to"other"regions"are"higher"than"the"other"way"around"(dNE!=! 256" 0.010"vs.!dEN!=!0.003)."Very"similar"results"are"obtained"with"the"two"alternative"rooting"schemes" 257" of" the" placental" mammal" phylogeny" tested" (Table" S1)." Bayesian" MCMC" analyses" of" the" best6 258" fitting"models"for"each"group"are"portrayed"in"

4"

the" outstanding" species" richness" in" the" Neotropics" today." Species" richness" is" the" result" of" 5" different"speciation"(λ),"extinction"(μ),"and"dispersal"(d)"rates"on"each"area,"with"black"arrows" 6" indicating" the" prevailing" parameters." "Source"" areas" are" characterized" by" high" in-situ0

7"

diversification" rates," as" the" product" of" high" speciation" and/or" low" extinction," accompanied" by" 8" high"rates"of"dispersal"from"the"region"to"other"areas."Conversely,""Sink""areas"are"characterized" 9" by" low" speciation" and/or" high" extinction" rates," with" high" dispersal" rates" from" other" regions" 10" increasing"the"net"number"of"species.

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 3 Figure(3(

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Tables'

688"

28" " ' 689" ' 690" '

717"

Table' 4.' Fossil"evidence"for"the"early"presence"of"modern"amphibians,"birds,"lepidosaurs,"and"

718"

mammals"in"the"Neotropics"and"outside"the"Neotropical"region."We"considered"fossils"that"are"

719"

assigned" as" crown6group" lineage" relatives" (otherwise" sister6group" stem" relatives" to" modern" 720" amphibians," birds," lepidosaurs," and" mammals" are" indicated" in" the" Fossil" taxon" column" in" 721" brackets)."


Hannah L Owens
email: hannah.owens@bio.ku.dk

D S Lewis

F L Condamine

A Y Kawahara

R P Guralnick

Comparative phylogenetics of Papilio butterfly wing shape and size demonstrates independent hindwing and forewing evolution RUNNING TITLE: Comparative phylogenetics of Papilio wing morphology

Keywords: geometric morphometrics, museum specimens, Lepidoptera, Batesian mimicry

The complex forces that shape butterfly wings have long been a subject of experimental and comparative research. Butterflies use their wings for flight, camouflage, mate recognition, warning and mimicry. However, general patterns and correlations among wing shape and size evolution are still poorly understood. We collected geometric morphometric measurements from over 1400 digitized museum specimens of Papilio swallowtails and combined them with phylogenetic data to test two hypotheses: 1) forewing shape and size evolve independently of hindwing shape and size, and 2) wing size evolves more quickly than wing shape. We also determined the major axes of wing shape variation and discovered that most shape variability occurs in hindwing tails and adjacent areas. We conclude that forewing shape and size are functionally and biomechanically constrained, while hindwings are more labile, perhaps in response to disruptive selective pressure for Batesian mimicry or against predation. The development of a significant, re-usable, digitized data resource will enable further investigation on tradeoffs between flight performance and ecological selective pressures, along with the degree to which intraspecific, local-scale selection may explain macroevolutionary patterns.

"…[O]n these expanded membranes Nature writes, as on a tablet, the story of the modifications of species, so truly do all changes of the organization register themselves thereon." -Henry Walter Bates on butterfly wings, 1863

For decades, researchers have examined butterfly wing diversity through lenses of functional adaptation, evolutionary history, and development. For nearly all Lepidoptera species, wings power flight to search for larval host plants, nectar sources, mates, and new territory [START_REF] Scoble | The Lepidoptera: form, function and diversity[END_REF]). The physical requirements for powered flight are thought to exert natural selective pressure on lepidopteran wing size and shape; indeed, artificial selection experiments on wing and body size allometries have demonstrated significant fitness advantages for wild-type males compared those selectively bred for alternative allometries [START_REF] Frankino | Natural selection and developmental constraints in the evolution of allometries[END_REF]. However, evidence suggests that forewings and hindwings unequally contribute to flight performance: in a study of 19 species of butterflies and 25 species of moths, all could fly with their hindwings removed, although at the cost of speed and maneuverability [START_REF] Jantzen | Hindwings are unnecessary for flight but essential for execution of normal evasive flight in Lepidoptera[END_REF]. Therefore, forewing shape and size may result from stabilizing selection imposed by the biomechanical requirements of flight, whereas hindwing shape and size may respond more readily to neutral or selective processes such as sexual selection [START_REF] Chazot | Morpho morphometrics: shared ancestry and selection drive the evolution of wing size and shape in Morpho butterflies[END_REF], and predation pressure [START_REF] Sourakov | Two heads are better than one: false head allows Calycopis cecrops (Lycaenidae) to escape predation by a Jumping Spider, Phidippus pulcherrimus (Salticidae)[END_REF][START_REF] Barber | Moth tails divert bat attack: evolution of acoustic deflection[END_REF][START_REF] Willmott | Maintaining mimicry diversity: Optimal warning colour patterns differ among microhabitats in Amazonian clearwing butterflies[END_REF][START_REF] Rubin | The evolution of anti-bat sensory illusions in moths[END_REF].

Still, experimental manipulations (e.g. [START_REF] Jantzen | Hindwings are unnecessary for flight but essential for execution of normal evasive flight in Lepidoptera[END_REF] cannot characterize processes at evolutionary time scales and across lineages. Comparative analysis of data from natural history collections may ameliorate this shortcoming by bridging the gap between experimental manipulation and observed macroevolutionary patterns. [START_REF] Strauss | Patterns of quantitative variation in lepidopteran wing morphology: the convergent groups Heliconiinae and Ithomiinae[END_REF] quantified variation in wing morphology in select heliconiine and ithomiine butterflies and found hindwings were much more variable than forewings, providing a tantalizing link between functional studies and the impact of aerodynamic constraints on wing shape evolution. In contrast, a recent study of Morpho butterflies found a strong correlation between fore-and hindwing sizes as well as shapes [START_REF] Chazot | Morpho morphometrics: shared ancestry and selection drive the evolution of wing size and shape in Morpho butterflies[END_REF]. Such datasets can also be used to identify morphological "paths of least resistance," axes along which diversification happens most quickly [START_REF] Schluter | Adaptive radiation along genetic lines of least resistance[END_REF]. Comparative studies of Myotis bat skulls [START_REF] Dzeverin | The stasis and possible patterns of selection in evolution of a group of related species from the bat genus Myotis (Chiroptera, Vespertilionidae)[END_REF]) and whole Pheidole ants [START_REF] Pie | Size and shape in the evolution of ant worker morphology[END_REF] found size evolved more quickly than shape, but size variation as an evolutionary path of least resistance remains untested in Lepidoptera.

We built on this groundwork to test two predictions via examination of swallowtail butterflies in one clade of the genus Papilio (subgenera Agehana, Alexanoria, Chilasa, Heraclides and Pterourus, hereafter "swallowtails in the clade of interest"): 1) forewing shape and size evolve independently of hindwing shape and size, and 2) wing size evolves more quickly than wing shape (Table 1). Our first prediction is based on the presumption that the forewing is functionally constrained while other selective pressures (e.g. predation, sexual selection) operate on hindwing shape. The second is based on the presumption that overall size change is an evolutionary path of least resistance. To test these hypotheses, we took morphometric measurements from digitized museum specimens and analyzed them in a comparative phylogenetic framework with a well-sampled and resolved species-level phylogeny [START_REF] Owens | The latitudinal diversity gradient in New World swallowtail butterflies is caused by contrasting patterns of out-of-and into-the-tropics dispersal[END_REF].

METHODS

Morphometrics

Standardized dorsal and ventral images of Papilio butterfly specimens with scale and color bars were obtained from four natural history museums (Supplemental Fig. 1): the American Museum of Natural History (AMNH), Field Museum (FMNH), Florida Museum of Natural History, McGuire Center for Lepidoptera and Biodiversity (MGCL), and the Smithsonian Institution National Museum of Natural History (NMNH; Supplemental Table 1). Images were taken with a NIKON D300S with an AF Micro-Nikkor 60mm f/2.8D lens (AMNH), Canon EOS 70D with a Canon EF 50mm f/1.4 USM lens (FMNH), Canon EOS 70D with a Canon EF-S 60mm f/2.8 Macro USM lens (MGCL), or a Canon EOS 6D with a Canon EF 28-80mm f/3.5-5.6 lens (NMNH) mounted on either a copy stand or tripod and operated manually (AMNH) or tethered to a MacBook Air with the Canon EOS Utility (FMNH, MGCL, NMNH; Supplemental Fig. 2). Photographs were centered with white-space around images, where labels and color bar are located, to limit lens distortion. Specimen label data, collection date, location and sex of specimen (where available) were transcribed by volunteers via the Notes from Nature platform [START_REF] Hill | The notes from nature tool for unlocking biodiversity records from museum records through citizen science[END_REF]. All standardized images used in this study have been made publicly available (AMNH: https://datadryad.org/stash/share/Lq-XOj-IAFl-PyvNF3Es77l3n4WgsEKE6XrKTjPH7z8; FMNH: https://pj.fieldmuseum.org/event/626b0f98-98e7-49c8-903e-d67017fe2356; MGCL: LINK PENDING; NMNH: LINK PENDING).

Landmarks for morphometric measurement were based on previous morphological work on Heraclides swallowtails [START_REF] Lewis | Role of Caribbean Islands in the diversification and biogeography of Neotropical Heraclides swallowtails[END_REF]; Fig. 1). One forewing landmark (F1 in Fig. 1), was removed from final analysis due to particularly high rate of measurement error; this was largely due to curling of the anterior wing margin in many specimens. To allow full view of otherwise overlapping wing elements, we used 10 forewing landmarks from dorsal images and 12 hindwing landmarks from ventral images (Fig. 1). PyvNF3Es77l3n4WgsEKE6XrKTjPH7z8). Forewing and hindwing landmark data with scale information were superimposed using Procrustes alignment; species represented by fewer than 10 specimens and statistical outlier landmark sets were removed, and the final datasets were realigned. We tested for allometric effects in fore-and hindwing shape variation using the homogeneity of slopes test (grouping specimens by species) and a subsequent Procrustes ANOVA to determine the contribution of size in determining shape variation. Mean species shape was calculated, the resulting dataset was re-aligned, gross outliers were removed, and allometric effects (grouping species into two subclades: Agehana + Pterourus, Alexanoria, Chilasa, and Heraclides, Fig. 1) were examined. Finally, mean intraspecific Procrustes distance from mean shape, morphospace volume occupied by each species (the product of the range of each principal component excluding values more than 1.5 times greater or less than the interquartile range), mean intraspecific centroid size, and intraspecific centroid variance were calculated from the specimen-level dataset. These four shape summary statistics were each rescaled to values between 0 and 1 using min-max normalization to render them comparable for downstream analyses. All shape analyses were performed using the R package geomorph 3.1.2 [START_REF] Adams | geomorph: An R package for the collection and analysis of geometric morphometric shape data[END_REF], except for intraspecific Procrustes distance from mean shape, which was calculated using Evomorph 0.9 (Cabrera and Giri 2016; details can be found in Appendix 2).

Testing independence of forewing and hindwing shape evolution

Using a recently-published time-calibrated phylogeny for swallowtails in the clade of interest (Fig. 1; Appendix 1; [START_REF] Owens | The latitudinal diversity gradient in New World swallowtail butterflies is caused by contrasting patterns of out-of-and into-the-tropics dispersal[END_REF], we performed a suite of comparative phylogenetic analyses of forewing and hindwing morphology to test the independence of foreand hindwing shape and size evolution. These analyses were all done in R 3.5.1 (R Core Team 2012; details of the analyses can be found in Appendix 2). We estimated phylogenetic signal of fore-and hindwing shapes using K mult , [START_REF] Blomberg | Testing for phylogenetic signal in comparative data: behavioral traits are more labile[END_REF], a generalization of Blomberg's K implemented in the R package geomorph 3.1.2 [START_REF] Adams | geomorph: An R package for the collection and analysis of geometric morphometric shape data[END_REF]). Just as with the traditional Blomberg's K statistic, the closer K mult is to 1, the more variation in species' characters can be explained by their phylogenetic relationships under a Brownian motion (BM) model of evolution, and values of K< 1 indicate more variation than expected under BM [START_REF] Blomberg | Testing for phylogenetic signal in comparative data: behavioral traits are more labile[END_REF]. We then used geomorph to calculate the modular rate ratio (function:

compare.multi.evol.rates) for the fore-and hindwing datasets (Denton and Adams 2015), and test whether fore-and hindwing shape evolution was correlated (also known as phylogenetic integration, function: phylo.integration; Adams and Felice 2014). Both tests were conducted under an assumption of BM, as this is the only model currently available for such multidimensional datasets implemented in geomorph [START_REF] Adams | Multivariate Phylogenetic Comparative Methods: Evaluations, Comparisons, and Recommendations[END_REF].

Testing independence of fore-and hindwing size evolution

We also tested the independence of forewing and hindwing size evolution. First, we estimated the phylogenetic signal (univariate Blomberg's K), then estimated the evolutionary rates of fore-and hindwing shape based on the best-fit evolutionary model for each dataset, and finally, tested for significant fore-and hindwing centroid size correlation. These analyses were done using the R packages phytools 0.6-60 [START_REF] Revell | phytools: an R package for phylogenetic comparative biology (and other things)[END_REF], geiger 2.0.6 [START_REF] Harmon | GEIGER: investigating evolutionary radiations[END_REF], and phylolm 2.6 (Tung Ho and Ané 2014); additional details can be found in Appendix 2.

Correlations were assessed using a linear-time algorithm developed by Tung [START_REF] Ho | A linear-time algorithm for Gaussian and non-Gaussian trait evolution models[END_REF].

For the correlation between fore-and hindwing centroid size, we fit a series of phylogenetic linear regressions with different evolutionary models-BM, Ornstein-Uhlenbeck (OU) with root ancestral state estimated from the data, and early burst (EB). We chose the best-fit model for the relationship between fore-and hindwing centroid size based on its minimum corrected Akaike Information Criterion (AICc) score as calculated using the R package MuMIn 1.42.1 (Barton 2018) and examined the ratio of hindwing to forewing evolutionary rates (σ 2 ) under these best-fit models using geomorph. To get a clear picture of the degree to which fore-and hindwing centroid sizes were correlated, we calculated R 2 pred for hindwing size as explained by forewing size; this is an extension of the traditional R 2 that weighs the residuals by variance and covariance [START_REF] Ives | R 2 s for correlated data: phylogenetic models, LMMs, and GLMMs[END_REF]). These calculations were done using the R package rr2 1.0.1 (Ives and Li 2018; Appendix 2).

Differences in speed of shape and size evolution

We made a final comparison of rates of fore-and hindwing shape and size evolution (σ 2 ) as obtained from the analyses described above to determine the relative evolutionary lability of these four characteristics. Appendix 2 provides an R markdown script of all analyses performed.

RESULTS

Morphometrics

Forewing measurements for 1,449 specimens representing 60 species and hindwing measurements for 1,404 specimens representing 59 species were analyzed after specimen-level datasets were cleaned. When the datasets were reduced to species for which there were available measurements for at least 10 individuals, 49 species remained in the forewing dataset and 47 in the hindwing dataset. Principal component (PC) 1 of the forewing describes elongation of the wing from the apex to the base, explaining 45% of species' mean shape variation; PC 2 describes wing margin angularity, explaining 20% of species' mean shape variation (Fig. 2). PC 1 of the hindwing primarily describes tail length, explaining 67% of variation, while PC 2 describes scalloping of the outer margin, explaining 8% of variation (Fig. 2).

Shape does not covary with size consistently for all species in the specimen-level dataset and for all subgenera in the mean species shape dataset (homogeneity of slopes test, P < 0.05), which suggests interspecific allometric effects likely do not play a complicating role in the patterns we examined in this study. However, correlations between log size and shape are significant (P < 0.05), albeit small, for all datasets (forewing specimen-level: R 2 = 0.02; hindwing specimen-level: R 2 = 0.15; forewing mean shape: R 2 = 0.15; hindwing mean shape: R 2 = 0.21). Summary statistics quantifying intraspecific shape variation (mean Procrustes distance of individuals from mean shape, morphospace volume occupied by each species, mean centroid size, and centroid size variance) can be found in Supplemental Table 2.

Independence of Fore-and Hindwing shape

Comparative phylogenetic analyses of mean species wing shape indicate a stronger phylogenetic signal in forewing than hindwing shape datasets (Table 2, Fig. 2). The evolutionary rate of the hindwing shape (under an assumption of BM) was also 9 times faster (a statistically significant difference, P < 0.05) than that of the forewing (forewing σ 2 = 6.6 × 10 -5 ; hindwing σ 2 = 6.01 × 10 -4 ). However, despite this disparity in evolutionary rates, fore-and hindwing shapes at the species-level are strongly integrated (r PLS : 0. 75; P < 0.05).

Independence of Fore-and Hindwing size

Comparative phylogenetic analyses of wing centroid size yielded similar patterns.

Phylogenetic signal for both fore-and hindwing centroid size is low to moderate (Table 2, Supplemental Fig. 3), but the statistical significance of these estimates is marginal for the forewing and not significant for the hindwing (P = 0.04, P = 0.18, respectively). The OU model fits the forewing dataset best, while the white noise model fits the hindwing dataset best.

However, for forewing size, the white noise model was the next-best fit, while for hindwing size, the OU model was the next-best fit (Supplemental Table 4). Therefore, we calculated evolutionary rate based on the OU model for both hindwing and forewing, as this was the best-fit model for both datasets from which evolutionary rate can be calculated [START_REF] Harmon | GEIGER: investigating evolutionary radiations[END_REF].

Hindwing centroid size evolution is 90 times the forewing rate; this difference is statistically significant (forewing σ 2 = 8.4 × 10 -8 , hindwing σ 2 = 1.1 × 10 -5 , P < 0.05). Fore-and hindwing centroid size are mildly but positively and significantly (P < 0.05) correlated (R 2 = 0.22; β= 3.58).

Differences in speed of shape and size evolution

Based on our σ 2 estimates, hindwing shape is evolving fastest (σ 2 = 6.01 × 10 -4 ), followed by forewing shape (σ 2 = 6.6 × 10 -5 ), hindwing size (σ 2 = 1.1 × 10 -5 ), and forewing size (σ 2 = 8.4 × 10 -8 ), in that order (Table 2). Appendix 3 is an R Markdown report of the corresponding results of analytical code supplied in Appendix 2.

DISCUSSION

Our results demonstrate that fore-and hindwings are subject to different selective pressures and are evolving autonomously from each other, although there is also evidence of balancing constraint. Notably, phylogenetic signal is stronger in the forewing compared to the hindwing. This pattern is consistent with findings from an early comparative study that demonstrated much higher hindwing shape variation compared to forewings in ithomiine and heliconiine butterflies [START_REF] Strauss | Patterns of quantitative variation in lepidopteran wing morphology: the convergent groups Heliconiinae and Ithomiinae[END_REF]. Our findings also provide evidence that swallowtail forewing shape and size evolve more slowly than respective hindwing measures, perhaps due to stabilizing selection imposed by dependence on forewings for flight [START_REF] Jantzen | Hindwings are unnecessary for flight but essential for execution of normal evasive flight in Lepidoptera[END_REF]. If so, hindwings may be responding more readily to stochastic forces than forewings as the result of factors that can be geographically quite localized and variable (e.g. predation pressure; [START_REF] Barber | Moth tails divert bat attack: evolution of acoustic deflection[END_REF][START_REF] Rubin | The evolution of anti-bat sensory illusions in moths[END_REF]). However, further comparative scrutiny of this trend among butterflies with differing flight behaviors would be beneficial. A recent study in experimental wing reduction in Pierella helvina, a floor-gliding heteriine butterfly, demonstrated enlarged hindwings greatly improved flight performance (Stylman et al. 2019).

In contrast to previous studies on bats and ants that found size evolved more quickly than shape [START_REF] Dzeverin | The stasis and possible patterns of selection in evolution of a group of related species from the bat genus Myotis (Chiroptera, Vespertilionidae)[END_REF][START_REF] Pie | Size and shape in the evolution of ant worker morphology[END_REF], swallowtails in the clade of interest, shape has evolved at least an order of magnitude more quickly than size in both the hindwing and forewing (Table 2). Indeed, for the full clade of interest as well as both subclades, hindwing shape has the fastest rate of evolution, followed by forewing shape, hindwing size, and forewing size, in that order. This suggests that for butterflies, and in contrast to predictions (Table 1), hindwing shape is the path of least resistance to morphological diversification. This is not to say the evolution of shape and size in the clade is necessarily adaptiveindeed, the difference between hindwing and forewing evolutionary rate ratios for centroid size and wing shape, while dramatic, may also bear the signal of stochasticity in hindwing evolution. Our results should also be interpreted carefully due to a methodological limitation-evolutionary rates for the shape datasets could only be inferred under a BM model using existing methods [START_REF] Adams | Multivariate Phylogenetic Comparative Methods: Evaluations, Comparisons, and Recommendations[END_REF]. If the fit of an OU model could be assessed and was found to be a better fit than BM, it is likely that lower evolutionary rates would be inferred for shape than those found here, as the OU model constrains character evolution around a central location.

One of the most labile characteristics of hindwing shape is presence and size of tails, as can be seen examining our hindwing shape deformation grids in relation to PC1 (Fig. 2), which explains 77% of hindwing shape variation. While it is tempting to think of tails as a presenceabsence trait, there are a wide range of tail shapes and relative sizes compared to the rest of the wing (e.g. Fig. 1), ranging from highly prominent to entirely absent. Tail form lability, visible both in the wide range of tail shapes and sizes and in models of hindwing evolution that appear primarily stochastic, remains understudied. Longer tails have been argued to increase aerodynamic performance for lepidopterans [START_REF] Park | Aerodynamic performance of a gliding swallowtail butterfly wing model[END_REF] as well as improving the odds of escaping predators [START_REF] Barber | Moth tails divert bat attack: evolution of acoustic deflection[END_REF]. However, the tradeoff between costs associated with producing tails versus their benefit requires closer examination, as it is likely dependent on complex interactions among flight behavior characteristics, biotic interactions, and microhabitat.

Mimicry may be especially critical as a driver of hindwing shape evolution and tail shape differences. Mimicry selection in Papilio butterflies, often for dramatically different models, appears to have had a profound effect across the clade. This is particularly true for hindwings in swallowtails in the clade of interest, and especially in relation to tail shape because most species with strongly reduced tails (e.g. those species with positive values along PC1) are also mimetic (Supplemental Fig. 4). Overall, 39 of the 60 taxa included in our study have at least one mimetic sex (Supplemental Table 5; Supplemental Fig. 4). Examples of putative Batesian mimic taxa include P. (Pterourus) zagreus, which mimics Heliconius and a number of genera in Danainae [START_REF] Tyler | Swallowtail butterflies of the Americas. A study in biological dynamics, ecological diversity, biosystematics and conservation[END_REF]; P. (Chilasa) clytia, which mimics Euploea [START_REF] Kunte | The diversity and evolution of Batesian mimicry in Papilio swallowtail butterflies[END_REF], and Heraclides of the anchisiades group, which mimics Parides [START_REF] Srygley | Flight morphology of neotropical butterflies: palatability and distribution of mass to the thorax and abdomen[END_REF][START_REF] Tyler | Swallowtail butterflies of the Americas. A study in biological dynamics, ecological diversity, biosystematics and conservation[END_REF].

Additional mimetic taxa that were not well-sampled enough to incorporate into our final analyses or were removed because they were strong outliers, such as P. (Chilasa) laglaizei, a mimic of the uraniid moth Alcidis agarthyrsus [START_REF] Collins | Threatened Swallowtail Butterflies of the World[END_REF], and P. (Pterourus) euterpinus, a mimic of heliconiine butterflies [START_REF] Tyler | Swallowtail butterflies of the Americas. A study in biological dynamics, ecological diversity, biosystematics and conservation[END_REF].

Our results suggest that for swallowtails, selective pressure for mimicry is a much stronger driver of morphology than shared phylogenetic history. This highlights the importance of predation interactions for the evolution of these lineages. [START_REF] Kunte | The diversity and evolution of Batesian mimicry in Papilio swallowtail butterflies[END_REF] demonstrated Papilio butterflies do not appear to have co-evolved with their models, but instead may have adapted to existing models after colonizing new areas. This result is consistent with the findings of studies in other organisms, such as ant-mimic jumping spiders [START_REF] Ceccarelli | Dynamics of the evolution of Batesian mimicry: molecular phylogenetic analysis of ant-mimicking Myrmarachne (Araneae: Salticidae) species and their ant models[END_REF], coral-snake-mimic colubrid snakes [START_REF] Rabosky | Coral snakes predict the evolution of mimicry across New World snakes[END_REF], and army-ant-mimic rove beetles [START_REF] Maruyama | Deep-time convergence in rove beetle symbionts of army ants[END_REF]. None of these groups appear to have co-evolved with their models, but instead may have taken advantage of already-established model patterns. This hypothesis deserves further study by reconstructing the evolution of shape in mimetic Papilio lineages (and outward into the family Papilionidae) and comparing the result to the inferred biogeographic history of these lineages and their putative models.

Owing to a preponderance of male and unsexed specimens in our study (and natural history collections in general), we were unable to fully explore differential patterns of wing shape evolution in the context of sexual dimorphism. Previous studies of evolutionary processes related to sex-limited mimicry have not focused on wing shape; instead, studies have diagnosed mimics based on coloration [START_REF] Kunte | The diversity and evolution of Batesian mimicry in Papilio swallowtail butterflies[END_REF] or examined evolution of key mimicry-relevant genes [START_REF] Timmermans | Independent evolution of sexual dimorphism and female-limited mimicry in swallowtail butterflies (Papilio dardanus and Paplio phorcas)[END_REF]. Thus, a critical, unanswered question is how different drivers of dimorphism operate across the clade, and we hope that this can be addressed in the future by leveraging our growing database of landmarked Papilio wings. Despite current sample limitations, we were able to examine two species (P. androgeus and P. scamander) for which we had data to make statistically relevant comparisons between male and female specimens. For those two species, we found no evidence of sexual dimorphism in shape or size in forewings or hindwings (script Appendix 3; R Markdown report Appendix 4).

In conclusion, our study demonstrates how digitized museum specimens can bridge the gap between taxonomically-and temporally-limited experimental manipulations (e.g. [START_REF] Frankino | Natural selection and developmental constraints in the evolution of allometries[END_REF][START_REF] Jantzen | Hindwings are unnecessary for flight but essential for execution of normal evasive flight in Lepidoptera[END_REF] and broad-scale macroevolutionary hypotheses. We recovered evidence that Papilio forewings and hindwings are evolving independently, which is consistent with experimental observations that fore-and hindwings have different effects on butterfly flight dynamics. Furthermore, hindwing shape may be an evolutionary path of least resistance for morphological diversification in butterflies and may reflect strong disruptive selection for mimicry and/or for predation defense. Still, this study is a first glance at the evolutionary relationships between hindwing and forewing shape and size in insects, and future studies are needed to investigate these patterns more thoroughly within swallowtails and more generally across the insect tree of life. Such work will require detailed information on species' phylogenetic relationships and wing morphologies, as well as factors including mimetic systems, within-species geographic variation, and flight behavior. Fortunately, with the systematic digitization of museum specimens and the increasing capacity of researchers to manage large, complex datasets, the answers to these questions are closer to our reach than ever before.

SUPPLEMENTARY MATERIAL

Data available from the Dryad Digital Repository: https://datadryad.org/stash/share/Lq-XOj-IAFl-PyvNF3Es77l3n4WgsEKE6XrKTjPH7z8

Hypothesis Predictions

Forewing shape is evolving independently of hindwing shape Forewing K mult > Hindwing K mult Forewing σ 2 ≠ Hindwing σ 2 (Forewing σ 2 / Hindwing σ 2 ) > 1

Forewing and hindwing r PLS < 1

Forewing size is evolving independently of hindwing size Forewing K mult > Hindwing K mult Forewing σ 2 ≠ Hindwing σ 2 (Forewing σ 2 / Hindwing σ 2 ) > 1

Forewing and hindwing R 2 < 1 Size is evolving more quickly than shape Forewing shape σ 2 < Forewing size σ 2 Hindwing shape σ 2 shape < Hindwing size σ 2

FIGURESFigure 1 .

 1 FIGURES

Figure 2 .

 2 Figure 2. Forewing and hindwing phylomorphospace plots; species' forewing shapes tend

Figure 3 .

 3 Figure 3. Mean species centroid size in phylomorphospace; Chilasa fore-and hindwing

Table 1 : Hypotheses examined in this study, with predictions regarding phylogenetic signal and evolutionary rate.

 1 TABLES

Table 2 : Comparative phylogenetics statistics for species-level shape and size.

 2 Wing shape generally has more significant phylogenetic signal and evolves more quickly than centroid size; forewing size and shape generally shows stronger phylogenetic signal and evolves more slowly than hindwing size and shape. Full clade: Agehana + Alexanoria + Chilasa + Heraclides +

	Pterourus; Non-Heraclides: Agehana + Alexanoria + Chilasa + Pterourus. Statistically
	significant values (p < 0.05) are bolded.
					Non-
			Full Clade Heraclides	Heraclides
	Shape	Forewing K mult	0.4977	0.2870	0.5495
		Hindwing K mult	0.3234	0.2448	0.5691
		Forewing σ 2 †	6.59 × 10 -5	7.03 × 10 -5	5.88 × 10 -5
		Hindwing σ 2 †	6.00 × 10 -4	7.09 × 10 -4	4.59 × 10 -4
		Evolutionary Rate Ratio	9.1106	10.0861	7.8094
		Fore-and hindwing correlation (r PLS )	0.7534	0.8182	0.7518
	Centroid	Forewing K	0.4511	0.1787	0.6636
	Size	Hindwing K	0.2172	0.0960	0.2635
		Forewing σ 2	8.50 × 10 -8 5.70 × 10 -8 1.12 × 10 -7
		Hindwing σ 2	1.10 × 10 -5 8.60 × 10 -6 1.31 × 10 -5
		Evolutionary Rate Ratio	130.2796	151.2126	116.9315
		Fore-and hindwing correlation (R 2 ) †	0.2174	0.0147	0.1455
		† Does not have a p value

ACKNOWLEDGEMENTS

We are very grateful to the curators and collections managers that granted us access to their collections in order to image specimens, particularly David Grimaldi, Courtney Richenbacher, and Suzanne Rab Green (AMNH); Crystal Maier (FMNH, now MCZ); Andrew Warren and Laurel Kaminsky (MGCL); and Robert K. Robbins and Brian Harris (NMNH). Laura Brenskelle, Josh Dieringer, Toshita Barve, and Vijay Barve (University of Florida) were instrumental in data collection. Chris Hamilton (University of Idaho) engineered the portable light box used on museum visits.

FUNDING

This work was supported by National Science Foundation grant no. DEB 1523732 to H.L.O., DEB 1557007 to A.Y.K. and R.P.G., and an "Investissements d'Avenir" grant managed by Agence Nationale de la Recherche (CEBA, ref. ANR-10-LABX-25-01) to F.L.C.