Mark O Gessner"

Marielle Thomast

Anne-Marie Jean-Louis And

Eric Chauvet

Stable successional patterns of aquatic hyphomycetes on leaves decaying in a summer cool stream

The colonization of leaf litter (A/nus glutinosa) by aquatic hyphomycetes was studied in a summer cool stream of the French Pyrenees. In spite of the rapid decomposition of leaves, the fungal community exhibited a characteristic successional pattern with three phases. The initial colonization stage was defined by a dense sporulation of the five species Tetrachaetum elegans, Lemonniera aquatica, L. centrosphaera, L. terres/ris, and in particular Flagellospora curvula. After four weeks of colonization, a mature community had established. It was characterized by high species diversity and peak fungal biomass, which was measured as ergosterol content, and coincided with about 50 % Joss in leaf mass. With leaf decay progressing further, diversity diminished concomitant with a slight reduction in fungal biomass and a sharp decrease in the rate of conidial production. Typical species of this late successional stage were Clavatospora longibrachiata, Heliscella stel/ata and Goniopila monticola. This successional pattern proved to be stable bath within the period of leaf fall in one year and between two successive yea rs. Betweenseasons differences were quite small as well, the striking Jack of species replacement apparently being due to not exceeding the threshold temperature of 16-18 °C as previously defined in literature. In spite of this general stability in community structure, correspondence analysis discriminated the communities on leaf packs with equal exposure times according to season, with the cyclical arrangement of leaf packs on the principal factorial plane reflecting the seasonal cycle. The colonization of fresh (non-dried) leaf litter by aquatic hyphomycetes was delayed compared to air-dried litter; however, the lead diminished with progressing leaf decay, resulting in nearly identical communities on fresh and dried leaves after four weeks of decomposition.

Since the discovery of a unique fungal flora associated with decaying leaf litter in streams and rivers, a considerable body of literature has accumulated on the ecology of these fungi that [START_REF] Ingold | Aquatic hyphomycetes of decaying alder leaves[END_REF] has termed aquatic hyphomycetes and that are now sometimes referred to as Ingoldian fungi (Barlocher, 1982). A number of studies have dealt with the seasonal dynamics of aquatic hyphomycetes by examining the composition of conidia in foam [START_REF] Chauvet | Dynamique saisonnière des spores d'hyphomycètes aquatiques de quatre rivières[END_REF], in river water (Shearer & Webster, 1985 a; [START_REF] Thomas | Changes in concentration of aquatic hyphomycete spores in Lees Creek. ACT, Australia[END_REF], or on decaying leaves that were randomly picked from the stream bed [START_REF] Shearer | Comparison of three techniques for the study of aquatic hyphomycete communities[END_REF]Shearer & Webster, 1985 a; [START_REF] Chauvet | Dynamique saisonnière des spores d'hyphomycètes aquatiques de quatre rivières[END_REF]. In other investigations, leaf litter was introduced to streams experimentally so as to study the colonization patterns of aquatic hyphomycetes on their natural substrate (e.g. Barlocher & Kendrick, 1974;[START_REF] Suberkropp | Fungi and bacteria associated with leaves during processing in a woodland stream[END_REF][START_REF] Charnier | Pectinases in leaf degradation by aquatic hyphomycetes. I. The field study. The colonization-pattem of aquatic hyphomycetes on leaf packs in a Surrey stream[END_REF][START_REF] Chergui | The dynamics of hyphomycetes on decaying leaves in the network of the River Rhone (France)[END_REF].

Foam sampling and membrane filtration of river water are inappropriate to assess the fungal assemblages associated with leaf litter, because these methods reflect the production of • Corresponding author, current address: Projektzentrum ôkosystem forschung, Christian-Albrechts-Vniversitat, Schauenburger Str. 112, 2300 Kiel 1, Gerrnany.

t Current address : Laboratoire de Biologie Appliquée, 34 rue Sainte Catherine, 54000 Nancy, France. conidia on various substrates and are also selective [START_REF] Shearer | Comparison of three techniques for the study of aquatic hyphomycete communities[END_REF][START_REF] Shearer | Aquatic hyphomycete communities in the River Teign. III. Comparison of sampling techniques[END_REF]. Analysing the mycoflora on leaves naturally deposited in the strearn channel is only a partial remedy for these shortcornings because the residence tirne of this material is not precisely known. Furthermore, due to the pulsed input of leaves to temperate streams and the marked differences in breakdown rates arnong leaf species [START_REF] Webster | Vascular plant breakdown in freshwater ecosystems[END_REF], plant rnaterial available Table 1. Water-chemical characteristics of the Touyre during field experiments (TOP = total dissolved phosphorus, DOC = dissolved organic carbon) Parameter pH Alkalînity (meq. )-') Spec. cond.

(µS cm-1 , 25 °) Ca'+ (mg I-1 ) Mg 2 -(mg 1-1 ) N0 3 --N (mg l-1 ) P0,3--P (µg 1-1 ) TOP (µg J-1 ) DOC (mg l-1 ) Oct. 1988to Feb. 1989Nov. 1989 for sampling at different periods of the year differs in age and quality. Seasonal differences in fungal community structure emerging from the examination of such samples are therefore either due to fungal succession as a result of changing substrate quality (internai factors) or to differences in general environmental conditions such as temperature, inoculum potential, and activity of detritivorous arthropods (external factors). The final outcome is probably the result of both processes, one superimposed on the other.

The discrimination of these factors is possible using an experimental approach. Consequently, [START_REF] Suberkropp | Effect of temperature on seasonal occurrence of aquatic hyphomycetes[END_REF] and Gônczôl (1989) analysed communities of aquatic hypho mycetes developing on standardized leaf packs exposed in streams at different periods of the year. However, decay rates and successional speed vary with season [START_REF] Suberkropp | Effect of temperature on seasonal occurrence of aquatic hyphomycetes[END_REF], so different successional stages can still be recorded even if identical exposure times are chosen. In the present study, standardized leaf packs were thus not only exposed at different seasons of the year but also retrieved at repeated intervals. The specific aims of the investigation were (1) to characterize the autumnal colonization pattern of aquatic hyphomycetes on aider leaves decomposing in a cold-water low-nutrient stream, (2) to check whether these patterns are stable within the period of natural leaf fa!!, (3) to document variations over the annual cycle, and (4) to elucidate differences between the colonization of naturally fallen fresh and air-dried leaves. As the spatial distribution of aquatic hyphomycetes on leaf litter is patch y [START_REF] Shearer | Comparison of three techniques for the study of aquatic hyphomycete communities[END_REF][START_REF] Charnier | The spatial distribution of fungi on decomposing alder leaves in a freshwater stream[END_REF], care was taken to base conclusions on an extensive set of data (Table 2).

STUDY SITE

The colonization of leaf litter by aquatic hyphomycetes was studied in the Touyre, a low-nutrient soft-water stream located in the French Pyrenees (42 ° 52' N, 1 ° 45' E). The study site chosen in 1988 was at 940 m elevation and corresponds to rhe one described in [START_REF] Gessner | Differences in processing dynan,;�: of fresh and dried leaf litter in a stream ecosystem[END_REF]. In the following year, a reach was chosen some 500 m downstream; it has generally similar characteristics but is situated downstream from a small reservoir from where water can be diverted to a hydroelectric power plant. It was thus hoped to protect the introduced leaf packs from major spates, but this turned out to be a fallacy. At the study sites the channel gradient is 5 %, average depth is 15-20 cm and stream width 6•5 m and 5 m, respectively. Bed sediments are primarily composed of cobble and boulders, and the riparian vegetation consists mainly of ash (Fraxinus excelsior L.), aider (A/nus glutinosa (L.) Gaertn.), and beech (Fagus sylvatica L.) with an understory of hazel ( Cary/us avellana L.). Further characteristics of the Touyre are given in Fig. 1 and Table 1.

MATERIAL AND METHODS

Standard leaf packs of about 5 g dry mass were constructed from autumn-shed leaves of A/nus glutinosa (L.) Gaertn., enclosed in nylon-mesh bags (9 mm openings) supported on a metal frame, attached to house bricks, and submerged in the Touyre [START_REF] Gessner | Differences in processing dynan,;�: of fresh and dried leaf litter in a stream ecosystem[END_REF]. Fresh leaves were immersed within 3 h after collection, while the leaves referred to as air-dried were kept at ambient temperature for at least 1 wk before • Leaves used in the autumn, winter, May, spring and summer series were collected simultaneously.

1 ' The remaining packs were lost during a flood. ,. After 8 wk, leaf packs were entirel y broken down.

submersion. From October 1988 to August 1990 a total of 99 packs, divided into 9 series, were placed in the sheam, and these were later retrieved at intervals of 4 wk or Jess (Table 2). At each sarnpling date, three replicate packs were removed, placed in plastic containers that were partially filled with stream water, and retumed to the laboratory on ice. On arrivai, individual leaves were carefully rinsed, and three leaves per pack were taken for the analysis of fungal community structure. When leaves occurred in distinct layers within the pack, one leaf each from the upper, middle and lower third was chosen so as to obtain a representative cross section of the fungal colonization of the entire pack.

From each leaf, ten (1988) or six (1989 and 1990) leaf dises were eut out with a cork borer (7 mm diam.) while avoiding major veins. Leaf dises were incubated in uncovered Petri dishes containing 10 ml of filtered stream water for 3 d at 10 °C, fixed in lactophenol [START_REF] Suberkropp | Fungi and bacteria associated with leaves during processing in a woodland stream[END_REF]Shearer & Webster, 1985 a), mounted on slides, stained with about 0•01 % t' rypan blue in lactic acid, and then one half of the dise surface was scanned at a magnification of 200 x . Loose conidia and those attached to conidiophores were recorded separately, but for statistical analyses ail data were lumped together. Except for the 1988 samples, the total number of spores produced per mm 2 of leaf surface was estimated by counting conidia in 5 microscopie fields (1•27 mm 2 each). Relative abundance of aquatic hyphomycete species was estimated in 8 classes: 0 (0%), I (0-1 %), 2 (1-5 %), 3 (5-20%), 4 (20-40%), 5 (40-60%), 6 (60-80%), 7 (80-100%). Results are either reported as mean abundance index according to the assignment to these categories or as relative frequency, which is the percentage of leaf dises per leaf pack on which a given species was recorded. Because Alatospora acuminata and Stenocladiella neg/ecta were not systematically distinguished, they are treated as a single species, and this is referred to as A. acuminata. Notice, however, that both species were quite common. Likewise, L aquatica and a form resembling L alabamensis were grouped as L aquatica.

Correspondence analysis (Greenacre,I 984;Chauvet,I 991) was used to detect regular structures in the data set and to display them graphically. The basic idea underlying this multivariate statistical method is to represent the complex information contained in the rows and columns of a data matrix in a set of simple graphical displays while losing a minimum of information. This is achieved by transforming the original variables to a set of abstract 'factors' such that the first few of these account for most of the information present in the original variables. These factors can be visualized as axes in a multidimensional space, and graphical representation of the original variables is then achieved by calculating their co-ordinates in this space and projecting the resulting set of points on a 'factorial' plane defined by two selected axes. T wo parameters are important for the interpretation of these displays: the cos 2 of a projected point is a measure of the quality of its representation, and a parameter termed 'inertia' provides information on how much of the variability in the 3.

data set is accounted for by a given axis. In contrast to related multivariate techniques such as principal component analysis, correspondence analysis treats the rows and the columns of the data matrix in the same way. These may therefore be depicted in the same display and thus be directly compared.

Ali statistical calculations were performed on the basis of the leaf pack as the elemental unit, because only these are both randomly distributed, independent samples [START_REF] Hurlbert | Pseudoreplication and the design of ecological field experiments[END_REF] and meaningful resource units (sensu [START_REF] Swift | Microbial succession during the decomposition of organic matter[END_REF]. Species occurring only sporadically were excluded from the analysis. The leaf material not used for the analysis of fungal community structure was frozen, lyophilized, weighed to the nearest O•Ol g, ground to pass a 1 mm-mesh screen, and extracted for ergosterol so as to determine leaf mass Joss and leaf-associated fungal biomass [START_REF] Newell | Estimating fungal biomass and productivity in decomposing litter. ln The Fungal Communily: ils Organizalion and Role in the Ecosys/em[END_REF][START_REF] Gessner | Fungal biomass associated with decaying leaf litter in a stream[END_REF]. Ergosterol was extracted by homogen ization in methanol and quantified using hplc with uv detection at 280 nm [START_REF] Gessner | Extraction and quantification of ergosterol as a measure of fungal biomass in leaf litter[END_REF].

RESULTS

Colonization patterns in autumn

A complete list of the aquatic hyphomycetes identified in the present study is given in Table 3; additional information on the fungal flora in the Touyre can be found in [START_REF] Chauvet | Dynamique saisonnière des spores d'hyphomycètes aquatiques de quatre rivières[END_REF] and [START_REF] Descals | Diversité des champignons Ingoldiens de quelques rivières du sud-ouest de la France[END_REF].

Figure 2 shows the autumnal colonization pattern of the dominant species on fresh aider leaves. After 3 and 7 days of stream incubation, the production of conidia on leaf litter was only scarcely recorded. The early stage of colonization (2-wk exposure) was characterized by a dense sporulation of Flagellospora curvula and the regular occurrence of four other species, namely Lemonniera aquatica, L. centrosphaera, L. terrestris and Tetrachaetum elegans. These five fungi remained important components of the community in la ter stages of decay; however, by day 28 additional species had assumed significant importance, so that at this point in time the community included 13 abundant species (relative frequency > 10 %). About 50 % of the leaf material was broken cl own at this stage [START_REF] Gessner | Differences in processing dynan,;�: of fresh and dried leaf litter in a stream ecosystem[END_REF]. After 8 wk, when leaves were substantially degraded and sporulation markedly reduced (Tables 4 and5), some of these 13 species assumed greater importance while others declined in relative abundance (Fig. 2).

These dynamics of the aquatic hyphomycete community on leaf litter are confirmed by the display of correspondence analysis presented in Fig. 3. With a percentage of 71 % inertia ('variance') the principal factorial plane explains more than two-thirds of the total variability inherent in the data set, and the first axis (FI), which explains 57% of inertia alone, opposes the early (2 wk) and the late stages (6 and 8 wk) of colonization. Although the 4-wk samples are poorly repre sented on the first axis (cos 2 < 0•25), they lie systematically between the 2-wk and the 6-and 8-wk samples, with the 8wk sample in 1989 being a minor exception to this rule. Note, however, that this sample is not adequately represented either (cos 2 = 0•08). Thus the arrangement: of leaf packs along the first: axis can be interpreted as succession of the fungal community.

Among the well-represented species (cos 2 > 0•7), A.

acuminata and Clavatospora longibrachiata are associated with the late colonization stage, while F. curvula and T. elegans are relat:ed ta the early stage of colonization. Moreover, t:he t:hree Lemonniera species, which were identified as early colonizers (Fig. 2), are represented with positive values on the first axis, while the two species appearing only at a well-advanced stage of decay, H. stellata and G. monticola, are projected near t:he left margin of the display (Fig. 3). This pattern remains stable, when one or both of the two species contributing over proportionally to the calculation of axes (F. curvula and A. • Produced on one face of the leaf dises. 3.

HS GM FI: 57%

\ \ \ \ \ CQ CS \ \ F2: 14% LE GI Conidial production (no. mm -2 d-1 )• 68±23 38±2 5±3 8±3 38±18 24±13 56±13 44±22 55±27 11±1 0•2 >-------
acuminata) are excluded from the analysis. Owing to their inadequate representation (cos 2 � 0•3), other species such as

Articulospora tetracladia, Culicidospora aquatica, Geniculospora inflata, Heliscus lugdunensis, Tricladium splendens and T. patulum cannot be clearly assigned to a particular successional stage. 3. T. gracilis and C. subtilis are located outside the display ( -1•6 on FI and -1•7 on F2, respectively) and therefore appear in parentheses. 3.

The vertical axis (F2) accounts for 14 % of total inertia and resolves differences among the three series October 1988, November 1988 and November 1989 (Fig. 3). These differences are mainly brought about by the 4-wk samples of the November series in 1988, where C. subtilis and less so G. inf/ata assume rather great importance to the detriment of F. curvula, A. acuminata and C. longibrachiata (Fig. 2).

Seasonal colonization patterns

In contrast to the great constancy of successional patterns in autumn, there were differences in the colonization of leaf liHer among seasons, and these give rise to a cyclic pattern on the principal factorial plane of correspondence analysis (Fig. 4a). The first axis contrasts the early stage of colonization in winter (cos 2 = 0.54) and partly in autumn (cos 2 = 0•33) with later colonization stages in summer (cos 2 = 0•71), spring (cos 2 = 0•56), and also partly in autumn (cos 2 = 0•33), while the second axis (F2) is essentially defined by the mature (4-wk exposure) autumnal community (cos 2 = 0•61). As a result, the fungal assemblages on leaf packs are arranged in two annual cycles (in which the May series integrates perfectly) representing an early and an advanced successional stage, respedively. These cycles are shifted against each other along the first axis, and this shift may be interpreted as reflecting the succession of the fungal community, with the length of the displacement vedor being a measure of successional speed. Both the cyclic arrangement of leaf packs and the position of fungal species remain stable when the analysis is performed on the basis of relative frequencies rather than abundance indices.

The cyclic arrangement is not caused by a general replacement of dominant species, because the hyphomycetes classified as abundant in autumn (Fig. 2) were essentially the most frequent fungi ail year round (Fig. 5). The seasonal differences are rather due to (1) a shift in the relative abundance of a few dominant species such as C. aquatica, C. subtilis and L. centrosphaera (Figs 2 and5); (2) the concentration of some less abundant species (notably Tetracladium mar chalianum) in spring and summer (Fig. 4b); and (3) the changing successional speed over the year (summer > spring > autumn > winter). This latter fact resulted in a considerably reduced intensity of colonization in winter after 2 wk of exposure, to communities with similar degrees of maturity in spring after 2 wk, in autumn after 4 wk and in winter after 8 wk, and to an impoverished fungal assemblage in summer after 4 wk of exposure, which would correspond to a much later successional state ( > 8 wk) in autumn (Fig. 5).

These differences in the developmental velocity of fungal communities over the year are correlated with the dynamics of fungal biomass, conidial production, and leaf breakdown rates (Table 4).

Colonization of fresh and air-dried leaf litter

Figure 6 shows that aquatic hyphomycetes occupied air-dried leaf liHer more rapidly than fresh liHer. After one week of stream-exposure, four of the five early colonizers produced conidia on almost half of the air-dried dises, whereas sporulation pradically did not occur on fresh leaves. Note, however, that at this time the overall intensity of colonization was low, even on air-dried material. With progressing colonization, differences between the fungal assemblages on fresh and dried liHer diminished. After 2 wk, differences in relative frequencies of the early colonizers F. curvula, T. elegans, L. centrosphaera and L. aquatica were already small, so 3.

comrnunities differed primarily in the abundance of species occurring during later successional stages (Fig. 6 b,c). After 4 wk, then, the initial differences were completely levelled off (Fig. 6d,e), but subsequently the fungal communities grew apart again, and this occurred in opposite directions in I 988 and 1989 (Fig. 6f-h). This evolution of aquatic hyphomycete comrnunities on fresh and dried leaf litter apparent in Fig. 6 is in accordance with the dynamics of fungal biomass and conidial production (Table 5).

If the 1988 data are considered separately, correspondence analysis reveals differences between the fungal assemblages on fresh and dried leaves, since the vertical axis (F2) opposes leaf packs according to their pretreatment (Fig. 7 a). However, this axis only explains 8 % of the total variability inherent in the data set, while as much as 67% are accounted for by the first axis (FI) that, as in Fig. 3, represents fungal succession. For the I 989 data, the projection of data points on to the principal factorial plane produces three distinct clusters, and these correspond to the communities on leaf packs submerged for 2, 4 and 8 wk (Fig. 7 b). Therefore, in contrast to 1988, there was no evidence from the 1989 experiment indicating the development of distinctive fungal communities on fresh and air-dried leaves. This statement holds true also for any other axes of correspondence analysis.

DISCUSSION

Colonization patterns in autumn

The autumnal colonization patterns of aquatic hyphomycetes communities on leaf litter were stable both within the period of natural leaf fal] in 1988 (October v. November) and between two successive years (1988 v. 1989) (Figs 2 and3). (1984) and [START_REF] Suberkropp | Fungi and bacteria associated with leaves during processing in a woodland stream[END_REF], and occurred in spite of the marked decrease in water temperature immediately after exposure of the November series (Fig. 1), and despite the choice of different stream reaches for incubating leaf packs in the two years.

This stability corresponds with the results of Suberkropp

The rapid decomposition of aider leaves in the Touyre [START_REF] Gessner | Differences in processing dynan,;�: of fresh and dried leaf litter in a stream ecosystem[END_REF]Table 4) did not impede the development of fungal succession on this substrate. This succession was characterized by three stages: an assemblage of five pioneer species in the beginning, a mature community with more than 10 frequent species coinciding with about 50% loss in leaf mass, and an impoverished successional stage defined by a reduced species diversity (Figs 2 and 5), a slightly reduced fungal biomass and a greatly diminished rate of conidial production (Table 4). The tight coupling of community succession with the dynamics of leaf mass loss (Table 4) !ends support to the contention of [START_REF] Charnier | Pectinases in leaf degradation by aquatic hyphomycetes. I. The field study. The colonization-pattem of aquatic hyphomycetes on leaf packs in a Surrey stream[END_REF] that for a given habitat (stream reach) the state of leaf decay is defined by a characteristic fungal assemblage and vice versa. This does not preclude, however, that various stages of decay and succession co-occur on a particular leaf or even a leaf dise. The patterns observed in this and other studies rather reflect a 'mean succession' [START_REF] Frankland | Mechanisms in fungal successions[END_REF] or, better, average succession of the fungal comrnunity, because successional changes occur on small discrete leaf patches. Accordingly, the shift in community structure in the current study was not accompanied by species extinction, as is generally the case with successions of saprotrophic organisms [START_REF] Frankland | Mechanisms in fungal successions[END_REF][START_REF] Swift | Microbial succession during the decomposition of organic matter[END_REF]. In view of the physiological versatility of aquatic hyphomycetes (e.g. [START_REF] Suberkropp | Aquatic hyphomycete communities[END_REF], their small size and their mycelial growth form [START_REF] Frankland | Mechanisms in fungal successions[END_REF][START_REF] Swift | Microbial succession during the decomposition of organic matter[END_REF], the sampling grid was certainly too coarse, the changes in substrate quality too small (see [START_REF] Gessner | Differences in processing dynan,;�: of fresh and dried leaf litter in a stream ecosystem[END_REF], and the overall environmental conditions too stable. The obvious changes in the distribution of conidiophores on the leaf surface suggest, however, that a true replacement of species did indeed occur at the mm 2 scale.

In general accordance with literature accounts, L. centro sphaera, T. elegans (Barlocher, 1991; but see [START_REF] Charnier | Pectinases in leaf degradation by aquatic hyphomycetes. I. The field study. The colonization-pattem of aquatic hyphomycetes on leaf packs in a Surrey stream[END_REF], F. curvula and partly L. aquatica [START_REF] Suberkropp | Fungi and bacteria associated with leaves during processing in a woodland stream[END_REF][START_REF] Chauvet | Hyphomycètes aquatiques colonisant les feuilles de Salix a/ha L[END_REF][START_REF] Chergui | The dynamics of hyphomycetes on decaying leaves in the network of the River Rhone (France)[END_REF][START_REF] Suberkropp | Effect of sewage treatment plant effluents on the distribution of aquatic hypho mycetes in the River Errns, Schwabische Alb[END_REF]but see Barlocher & Kendrick, 1974;[START_REF] Biirlocher | Fungal colonization of fresh and dried leaves in the River Teign (Devon, England)[END_REF], were associated with short leaf incubation times in the Touyre and can thus be classified as early colonizers. Likewise, C. longibrachiata and H. ste/lata can be confidently referred to as late colonizers (Figs 2, 3;[START_REF] Chauvet | Hyphomycètes aquatiques colonisant les feuilles de Salix a/ha L[END_REF][START_REF] Biirlocher | Fungal colonization of fresh and dried leaves in the River Teign (Devon, England)[END_REF], which is consistent with the slow growth of these species in pure culture (unpublished data).

Seasonal colonization patterns

Stable successional patterns, such as those described here for aider leaves colonized by aquatic hyphomycetes during the period of leaf fa!!, can be modulated by seasonal influences. [START_REF] Suberkropp | Effect of temperature on seasonal occurrence of aquatic hyphomycetes[END_REF], in particular, documented for a hard-water lowland stream (Augusta Creek in Michigan) the replacement of a distinct winter comrnunity by an equally well-defined summer assemblage. Sirnilarly, Biirlocher (1991) described differences in the community structure of aquatic hypho mycetes on leaf litter that was incubated either in September or in November in a southem English lowland stream (River Teign, Devon). In a series of laboratory and field experiments, these shifts in species composition were correlated with changes in water temperature [START_REF] Suberkropp | Fungi and bacteria associated with leaves during processing in a woodland stream[END_REF][START_REF] Suberkropp | Effect of temperature on seasonal occurrence of aquatic hyphomycetes[END_REF], leading to the formulation of the temperature-threshold hypothesis, according to which the summer assemblage with typical warm-water species such as Lunulospora curvula Ingold and Triscelophorus monosporus Ingold (Webster, Moran & Davey, 1976;[START_REF] Chauvet | Aquatic hyphomycete distribution in South-Western France[END_REF] appears when water temperature permanently exceeds 16-18 °. The bloom develops in mid-summer at temperatures of up to 26 °. Once established, the surnmer assemblage dominates until the temperature falls below 5 ° in late autumn. Strikingly, the differences observed by [START_REF] Biirlocher | Fungal colonization of fresh and dried leaves in the River Teign (Devon, England)[END_REF] between leaf packs submerged in September and November in the River Teign were mainly due to the dynamics of L. curvula, which co-dominated the fungal community in September but was no longer found among the abundant species when temperature had dropped below 5 ° in November.

In the Touyre, the annual temperature range was much smaller than in Augusta Creek and probably also smaller than in the River Teign. Even during the exceptionally hot summer in 1989, when the current experiments were carried out, water temperature hardly ever exceeded 15 ° during the measure ments made every 2 or 4 wk in the mornings (Fig. 1). Accordingly, none of the five warm-water species common to south-westem France (including L. curvula and T. monosporus; [START_REF] Chauvet | Aquatic hyphomycete distribution in South-Western France[END_REF] was recorded in the present investigation. Although the composition of fungal comrnunities depends on many factors, some of which rnay vary with season, it is ternpting to argue that the non-exceeding of the threshold temperature in the Touyre prevented the establishment of a typical summer assemblage in this stream, resulting in an aquatic hyphomycete community dominated by the winter species ail year round.

In spite of the striking Jack of species replacement in this sumrner cool mountain strearn, there was a tendency in the Touyre for seasonal changes, exhibiting a cyclic pattern on the principal plane of a correspondence analysis (Fig. 4). Three major reasons are probably responsible for this result. First, during the warmer months leaf litter decomposed more rapidly (Table 4). The mature fungal community hence developed faster in spring and summer and more slowly in winter, and as a consequence different successional stages were recorded in different seasons at equal exposure times (Fig. 5). This explanation is consistent with the dynamics of mycelial biomass and conidial production (Table 4), and probably holds particularly true for the projection of the winter series on the outer left margin of the display (Fig. 4). Second, some species of aquatic hyphomycetes that may be typical of cold water (e.g. L. centrosphaera, Taeniospora gracilis; [START_REF] Chauvet | Dynamique saisonnière des spores d'hyphomycètes aquatiques de quatre rivières[END_REF] and the rnycoparasite Crucella subtilis (Marvanova & [START_REF] Marvanovâ | Camplobasidium hydrophllum and its anamorph, Crucella subtilis: a new Heterobasidiomycete from streams[END_REF] were especially abundant in auturnn and winter, while in spring and surnmer other species such as T. marchalianum with a tendency for warmer temperatures [START_REF] Suberkropp | Effect of temperature on seasonal occurrence of aquatic hyphomycetes[END_REF][START_REF] Chauvet | Aquatic hyphomycete distribution in South-Western France[END_REF] assumed greater importance. Since correspondence analysis emphasizes 'shape' rather than the size of the data [START_REF] Greenacre | Theory and Applications of Correspondence Analysis[END_REF], T. marchalianum was clearly associated with the spring and summer samples (Fig. 4), although it never constituted an important component of the community. Third, the inoculum potential [START_REF] Frankland | Mechanisms in fungal successions[END_REF] may have varied sornewhat with season in the Touyre, and this could have accounted for the greater importance of C. aquatica during the warmer months.

Colonization of fresh and air-dried leaf litter

In accordance with the observations made by Barlocher (1991), the colonization of fresh leaf litter by aquatic hyphomycetes was delayed in the current study. This phenomenon is apparent from both the analysis of fungal cornmunity structure (Fig. 6a-c) and quantitative data on mycelial biomass dynamics and conidial production (Table 5), and may be related to inhibitory cornpounds that would be readily removed from dried leaves by leaching (Barlocher, 1990). However, with leaf decay progressing further, almost identical communities developed on fresh and dried litter (Fig. 6 d, e ), a finding that is consistent both between the two study years and with the results of Barlocher's (1991) investigation. The differences between fresh and dried leaves observed by this author in early autumn (September) were mainly due to the lower abundance of the surnrner species L. curvula on fresh leaves, obviously caused by the delay in fungal colonization of these leaves and the concurrent drop in water temperature below 5 °. Accordingly, no differences emerged when the experiment was repeated in Novernber (Barlocher, 1991). The equipment of aquatic hyphomycetes with plentiful hydrolytic enzymes [START_REF] Charnier | Cell-wall-degrading enzymes of aquatic hyphomycetes: a review[END_REF][START_REF] Suberkropp | Aquatic hyphomycete communities[END_REF] that would make thern independent of labile carbon sources and their low substrate specificity [START_REF] Suberkropp | Aquatic hyphomycete communities[END_REF] may have been the major grounds for the parallel developrnent of aquatic hyphomycete communities on fresh and air-dried leaf litter.

  04 mg 1-1 on 3Aug. 1990.

0

  Sep. Oct. Nov. Dec. Jan. Feb. Oct. Nov. Dec. Jan. Feb., Mar. Apr. May Jun. Jul. Aug. Sep. Air temperature at 5 km distance from the study sites (650 m elevation), water temperature and discharge of the Touyre. Discharge values are corrected daily means recorded at a gauging station 3 km downstream from the study sites. The arrow represents the exposure date of the November series and the horizontal bar the period of bulk leaf fa!!.

  Fig. 2. Autumnal colonization patterns of dominant aquatic hyphomycetes on fresh aider leaves submerged in the Touyre for 2, 4 or 8 wk. Species are ranked on the abscissa according to their importance in the whole data set. Vertical bars denote 1 s.o. For acronyms of species names see Table3.

Fi g . 3 .

 3 Projection of the fungal communities associated with leaf packs from October 1988 (■--■), November 1988 (e--e) and November 1989 (.Â. • • •• .Â,) on the principal factorial plane of correspondence analysis. Numbers denote the duration of leaf pack exposure in the stream in wk, and arrows indicate the succession of the fungal community. For acronyms of species names see Table

  Projection of aquatic hyphomycete communities on leaf packs (a) and leaf-associated hyphomycete species (b) of the autumn (.Â,), winter (♦), May (0), spring (■) and summer (e) series on the principal factorial plane of correspondence analysis. Numbers denote the duration of leaf pack exposure in the stream in wk and arrows indicate the cyclic pattern of seasonal changes. For acronyms of species names see Table

Fig. 5 .

 5 Fig. 5. Seasonal colonization patterns of dominant aquatic hyphomycetes associated with aider leaves in the Touyre. Species are ranked on the abscissa according to their importance in the whole data set. Vertical bars denote 1 s.o. For acronyms of species names see Table3.

Fig. 6 .

 6 Fig. 6. Differences in relative frequencies of dominant species of aquatic hyphomycetes on fresh and air-dried aider leaves during autumn 1988 and 1989. Positive values indicate higher frequencies on dried litter. For acronyms of species names see Table3.

Fig. 7 .

 7 Fig. 7. Projection of fungal communities on fresh (■) and air-dried (0) leaf packs on the principal factorial planes of two separate correspondence analyses perfonned with data from autumn 1988 (top panel) and autumn 1989 (bottom panel).

Table 2 .

 2 Overview of the series of leaf packs analysed for fungal community structure after exposure in the Touyre

	Date of	Pretreatment	Exposure	Leaf dises N ame
	submersion	of litter	time (wk)	examined of series
	17 Oct. 1988	None	0•4, 1, 2, 4, 6, 8	480	Oct. 1988
	17 Oct. 1988	Air-dried	0•4, 1, 2, 4, 6, 8	480	D ry 1988
	13 Nov. 1988	None	2, 4, 8	270	Nov. 1988
	3 Nov. 1989	None	2, 4, 8	162	Nov. 1989
	3 Nov. 1989	Air-dried•	2, 4, 8	162	Autumn
	26 Ja_ n. 1990	Air-dried•	2, 4, 8	162	Winter
	4 May 1990	Air-dried•	2"	54	May
	8 Jun. 1990	Air-dried•	2, 4 °	108	Spring
	27 Jul. 1990	Air-dried•	2, 4,•	108	Summer

Table 3 .

 3 Aquatic hyphomycete species identified on leaf litter of A/nus glufinosa decaying in the Touyre. Acronyms used in Figs 2--o are also

	given
	AA Alatospora acuminala lngold
	AF	Alatospora flagella/a (Gônczol) Marvanova
		Alatospora pulchella Marvanova
		Anguillospora crassa Ingold
	AL	Anguillospora longissima (Sacc. & Syd.) lngold
	AT Articulospora tetracladia lngold
		7Ca/carispora hiemalis Marvanova & Marvan
	CA	Clavariopsis aqualica de Wildeman
	CL	Clavafospora lo ng ibrachiata (lngold) Marvanova & S.
		Nilsson
	CS	Crucella subfi/is Marvanova
	CQ Culicidospora aquafica R. H. Petersen
		Culicidospora gravida R. H. Petersen
		Dendrospora erecla Ingold
		Dendrospora fusca Descals & Webster
	DF	Dimorphospora fo/iicola Tubaki
		Flabellospora acuminata Descals
	FC	Flagellospora curvula lngold

Gl

Geniculospora inflata (lngold) S. Nilsson ex Marvanova & S. Nilsson GM Goniopila monficola (Dyko) Marvanova & Descals HS Heliscella stellafa (lngold & Cox) Marvanova & S. Nilsson Heliscina antennata Marvanova Heliscina campanulata Marvanova HL Heliscus lugdunensis Saccardo & Thé rry 1Jaculispora submersa Hudson & lngold Lemonniera 7alabamensis Sinclair & Morgan-Jones LA Lemonniera aqualica de Wildeman LE Lemonniera cenfrosphaera Marvanova L T Lemonniera terres/ris T ubaki Slenocladiel/a neglecta (Marvanova & Descals) Marvanova & Descals Sympocladium frondosum Descals TG Taeniospora gracilis var. gracilis Marvanova TE Tefrachaelum elegans Ingold TM Tetracladium marchalianum de Wildeman Tetracladium maxilliforme (Rostrup) lngold Tetracladium setigerum (Grove) lngold 7Tricladium chaefocladium Ingold TP T ricladium patulum Marvanova & Marvan TL Tricladium splendens Ingold T ripospermum camelopardus lngold, Dann & McDougall T ripospermum myrti (Lind.) Hughes TU Tumularia aqualica (lngold) Descals & Marvanova Tumularia tuberculata (Gônczol) Descals & Marvanova Varicosporium elodeae Kegel

Table 4 .

 4 Mass loss of leaf litter of A/nus glutinosa, fungal biomass as ergosterol content, and conidial production at different seasons of the year. Values are means ± s.D. of three replicate leaf packs

		Exposure D ry mass	Ergosterol
		time	remaining	content (µg g-1
	Season	(wk)	(%)	leaf mass)
	Autumn	2	65•9±2•3	370 ± Il
		4	54•9±5•6	573±28
		8	22•0±9•1	424±33
	Winter	2	75•8±0•5	77±5
		4	55•4±3•4	301 ±31
		8	24•1 ±20•6	403±99
	Spring	2	52•6±12•9	241 ±29
		4	19•9±8•1	508±54
	Summer	2	48•1 ±8•0	305±30
		4	20•4±14•0	271±26

Table 5 .

 5 Fungal biomass as ergosterol content and conidial production of fresh and air-dried leaf litter of Alnus glulinosa during decomposition in the Touyre

		Exposure time (wk)
	Pretreatment
	of leaf litter	0			2	4	6	8
	Ergosterol content (µg g-1
	detrital d ry mass)
	None•	4•4	7•9±1-5	14±1	148±1	422±1	462±5	378±9
	Air-dried• None 1 •	3•2 0	14•5 ±0•4	53 ± 1	229±21 271 ±26	396±32 579 ± 20	402±7	366± 15 559±22
	Air-dried"	0			370 ± 11	573±28		424±33
	Conidial production
	(no. mm-2 d-1 )
	None h	0			41±13	54±9		11±1
	Air-dried"	0			68±23	38±2		5±3

• Exposure on 17 Oct. 1988, mean ± range (pooled samples). " Exposure on 3 Nov. 1989, mean±s.o. (n = 3).

We are grateful to Drs Enrique Descals for taxonomie and André Fabre for statistical advice. Professer John Webster kindly commented on the manuscript. This work was supported by a grant to M. O. Gessner from the Commission of the European Communities.


Emmanuel Baudouin
email: emmanuel.baudouin1@gmail.com

Chapter 2 Spread and Independent Technical Invention of the Earthen Material in the Southern Caucasus and Northern Mesopotamia during the sixth Millennium BCE

Keywords: NEOLITHIC, EARTHEN ARCHITECTURE, SUN-DRIED MUD-BRICK, COB NÉOLITHIQUE, ARCHITECTURE EN TERRE, BRIQUE CRUE, BAUGE

The existence of relationships between Southern Caucasus and Northern Mesopotamian communities was inferred since the 1960's. Since 2008, international archaeological teams have focused on the Southern Caucasus in order to verify these hypotheses and understand the "neolithisation process" on the periphery of the Near East. Here I will focus on the evolution of cob and mud-brick. An evolution of these earthen material techniques during the sixth millennium BCE is proposed by means of a re-examination of stratigraphic contexts, bibliographical data and also by recent discoveries in these regions. The spread of cob could be traced across Northern Mesopotamia since the end of the seventh millennium BCE, and then towards Eastern Anatolia and Southern Caucasus during the sixth millennium BCE. Simultaneously, the molded plano-convex mud-brick appeared in the Shulaveri-Shomu culture in the sixth millennium BCE. This special technique seems to be a local and independent innovation, according to other architectural characteristics.

Introduction

At the end of the seventh millennium BCE, the syro-mesopotamian were in an advanced stage of the Neolithic "way of life" and three main cultural horizons can be identified in this period. The first is the Hassuna culture that appeared at the middle of the seventh millennium BCE in Iraqi Jezirah. Proto-Hassuna sites have been identified in the Upper Khabur (Le Mière 2000), but no proper "Hassuna" sites have been discovered, while Hassuna-Samarra sites are attested in Upper Tigris at Hakemi Use [START_REF] Tekin | Hakemi Use: A Newly Discovered Late Neolithic Site in Southeastern Anatolia[END_REF], and lasted until the end of the seventh millennium BCE. The second is the Samarra culture (6300-5800 cal. BCE), which is known in Eastern Jezirah and Central Mesopotamia. Based on ceramic data, research shows that Samarra represents a geographical extension of Hassuna in the Jezirah (Forest, 1996, p. 36;Hole, 1977, p. 12). This expansion could be explained by a movement of the Hassuna population to the south, in Central Mesopotamia, result of a demographic pressure applied by the arrival of the Halaf communities (Sauvage, 2001, pp. 426). This opinion must be qualified (Butterlin, 2018, p. 107) because of the unreliability of the stratigraphic contexts, especially for the Zagros foothills as at Choga Sefid (Oates, 1987, p. 166).

The third is the Halaf culture that spread over a large area stretching from Cilicia to the east, as far as the Zagros foothills and occupying essentially all the High Jezirah. Some archaeologists suggested that Halafian communities originated from the mountains located between the Van Lake and the north Iraqi steppe [START_REF] Mallowan | The Excavations at Tell Chagar Bazar[END_REF][START_REF] Mallowan | Excavations at Tall Arpachiyah[END_REF][START_REF] Mellaart | Excavations at Hacilar[END_REF]. However, other archaeologists trace the birth of Halaf around 5600 cal. BCE in High Jezirah, in the Balikh and Khabur region. Two main assumptions contrast about Halaf´s origin and development: 1) the appearance of Halaf populations from Van Lake and Eastern Jezirah areas; 2) a local origin replacing previous cultures (Proto-Halaf, Proto-Hassuna, Hassuna, Samarra). Recent research [START_REF] Campbell | Rethinking Halaf Chronologies[END_REF] enabled to place the beginning of Halaf at the end of the seventh millennium BCE (Molist et al., 2007, p. 4;Akkermans et al., 2014, p. 30). But the origin of this culture still remains controversial [START_REF] Akkermans | Late Neolithic Architectural Renewal: The Emergence of Round Houses in the Northern Levant, c. 6500-6000 BC[END_REF][START_REF] Akkermans | Old and New Perspectives on the Origins of the Halaf Culture[END_REF]Breniquet, 1996, pp. 63-64) just as its disappearance at the end of the sixth millennium BCE.

Outside of Mesopotamia, the Hajji Firuz culture, that developed in Northern Zagros, close to the Urmiah Lake, is still poorly known and it is mainly documented by the eponymous site dated around 6300-5600 cal. BCE (Lawn, 1974, p. 222;Stuckenrath, 1963, p.90).

On the other hand, the first studies on the sedentary communities of the sixth millennium BCE in the Southern Caucasus began in the middle of the XXth century. Excavations were carried out almost simultaneously in the Middle Kura Valley, Azerbaijan, and in the Kvemo-Kartli Plain, Georgia, where archaeologists identified a unique culture, so-called Shomu-Shulaveri or Shulaveri-Shomu [START_REF] Dzhavakhishvili | Otchet Kvemo-Kartlijskoj arkheologicheskoj ekspeditsii (1965-1971 gg[END_REF][START_REF] Kiguradze | Neolithische Siedlungen von Kvemo-Kartili, Georgien[END_REF][START_REF] Kushnareva | The Southern Caucasus in Prehistory: Stages of Cultural and Socioeconomic Development from the Eighth to the Second Millennium BC[END_REF][START_REF] Narimanov | Arkheologischeskie issledovanija poselenija Shomu Tepe v 1963 G. [The archeological investigations of Shomu Tepe settlement in 1963[END_REF][START_REF] Narimanov | Kul'tura Drevneyshego Zemledel'chesko-Skotovocheskogo Naseleniya Azerbadzhana, Epokho Eneolita VI-IV tys[END_REF]. At the same time, excavations were undertaken in the Ararat Plain, on the Araxes Valley, which revealed the archaeological remains of a contemporary occupation to the south of the Lesser Caucasus, a regional variant of Shulaveri-Shomu [START_REF] Kiguradze | Aghmosavlet Amierkavkasiis Adresamitsatmokmedo Lulturis Periodiatsia[END_REF][START_REF] Badalyan | Aknashen -The Late Neolithic Settlement of the Ararat Valley: Main Results and Prospects for the Research[END_REF].

Previously, other research had been undertaken at Kültepe, Nakhichevan [START_REF] Abibullaev | Eneolit i Bronza Na Territorii Nakhichevanskoj ASSR [Eneolithic and Bronze Age in the Territory of Nakhichevan ASSR[END_REF][START_REF] Abibullaev | Arkheeologicheskie Rakopki v Kyultepe [Archaeological Excavations at Kültepe[END_REF], where the discovery of Halaf ceramics has enabled archaeologists to hypothesise relationships with contemporary cultures in Mesopotamia [START_REF] Abibullaev | Arkheeologicheskie Rakopki v Kyultepe [Archaeological Excavations at Kültepe[END_REF][START_REF] Narimanov | Kul'tura Drevneyshego Zemledel'chesko-Skotovocheskogo Naseleniya Azerbadzhana, Epokho Eneolita VI-IV tys[END_REF].

From the second half of the XXth century, the issues focused on the origin of Shulaveri-Shomu and especially on the neolithisation process in the region and three main hypotheses were made: a)-A "colonization" by communities from Mesopotamia [START_REF] Munchaev | Kavkazna Zare Bronzovogo Veke [The Caucasus at the Dawn of the Bronze Age[END_REF]; b)-Relationships and exchanges between syro-mesopotamian communities (Hassuna, Samarra, Halaf) and those of Southern Caucasus [START_REF] Kiguradze | Neolithische Siedlungen von Kvemo-Kartili, Georgien[END_REF][START_REF] Kushnareva | The Southern Caucasus in Prehistory: Stages of Cultural and Socioeconomic Development from the Eighth to the Second Millennium BC[END_REF]; c)-An independent and local development [START_REF] Lisitsyna | Paleoetnobotanicheskie Nakhodki Kavkaa i Blizhnego Vostoka [Paleobotanical Data from the Caucasus and the Near East[END_REF][START_REF] Niebieridze | Arkheologischeskie Issledovanija v Tverdzhol'skom Rajone [The Archaeological Investigations in the Tverdzhol Province[END_REF].

The resumption of research since 2008 in the Middle Kura Valley, at Mentesh Tepe [START_REF] Lyonnet | Recent Research on the Chalcolithic Period in Western Azerbaijan[END_REF][START_REF] Lyonnet | Mentesh Tepe, an Early Settlement of the Shomu-Shulaveri Culture in Azerbaijan[END_REF][START_REF] Lyonnet | Mentesh Tepe (Azerbaijan), a Preliminary Report on the 2012-2014 Excavations[END_REF][START_REF] Lyonnet | Recent Research on the Chalcolithic Period in Western Azerbaijan[END_REF], Göy Tepe [START_REF] Guliyev | Göytepe Neolit Yaşayiş Yerinde Arkeoloji Qazintilar (Tovuz Rayonu)[END_REF](Guliyev et al., , 2012[START_REF] Guliyev | Excavations at the Neolithic Settlement of Göytepe, West Azerbajan 2010-2011[END_REF]Nishiaki et al., 2015a), Haci Elamxanlı Tepe (Nishiaki et al., 2015b) and Kiçik Tepe, in the Kvemo-Kartli Plain, at Aruchlo [START_REF] Hansen | Aruchlo 2005-2006 Bericht Über Die Ausgrabungen in Einem Neolithischen Siedlungshügel[END_REF][START_REF] Hansen | Aruchlo 2007 Bericht Über Die Ausgrabungen in Einem Neolithischen Siedlungsügel[END_REF][START_REF] Hansen | Ancient Kura 2010-2011: The First Two Seasons of Joint Field Work in the Southern Caucasus[END_REF] and Gadachrili Gora [START_REF] Hamon | Gadachrili Gora: A New Neolithic Excavation within the Shulaveri Group (Chramis Valley, Georgia)[END_REF] and in the Ararat Plain, at Aratashen [START_REF] Arimura | Current Neolithic Research in Armenia[END_REF][START_REF] Badalyan | New Data on the Late Prehistory of the Southern Caucasus. The Excavations at Aratashen (Armenia): Preliminary Report[END_REF], Akhnashen-Katunarkh [START_REF] Badalyan | Aknashen -The Late Neolithic Settlement of the Ararat Valley: Main Results and Prospects for the Research[END_REF][START_REF] Badalyan | New Data on the Late Prehistory of the Southern Caucasus. The Excavations at Aratashen (Armenia): Preliminary Report[END_REF] and Masis Blur [START_REF] Martyrosyan-Olshansky | Masis Blur: A Late Neolithic Settlement in the Plain of Ararat, Armenia[END_REF], has set as an objective questioning these assumptions.

Simultaneously, the identification of contemporary sites in the Mil Plain has enabled to identify another cultural horizon, known as the Kamiltepe culture [START_REF] Lyonnet | Recent Research on the Chalcolithic Period in Western Azerbaijan[END_REF]. In spite of the regional variants, it is customary to define a unique Neolithic culture, that of Shulaveri-Shomu. However, even if these communities homogeneously adopted a sedentary way of life based on agriculture and animal herding [START_REF] Benecke | Exploitation of Animal Resources in Neolithic Settlements of the Kura Region (South Caucasia)[END_REF] from the beginning of the sixth millennium BCE, one of the main regionalised traits of these communities is represented by architecture.

Technological differences conduct us to distinguish four "cultural" entities: Shulaveri-Shomu, in the Kvemo-Kartli Plain, the Middle Kura Valley and the Karabagh Plain; Aratashen, in the Ararat Plain; Kültepe, in the Nakhichevan; and Kamiltepe, in the Mil Plain.

The purpose of this article is to define exchanges of know-how and techniques between communities of the Syro-Mesopotamian Basin and Southern Caucasus throughout the sixth millennium BCE. I will focus on the development of sun-dried mud-brick and cob. We posit two main hypotheses: technical transfer or autonomous inventions [START_REF] Leroi-Gourhan | Evolution et techniques[END_REF]). We will see whether it is conceivable and relevant to define a "center" and a "periphery" or rather propose more diffuse relationships between the communities of these regions (Breniquet, 2016, p. 208;[START_REF] Lombard | Le Néolithique et le Chalcolithique en Transcaucasie: l'exemple des bassins de la Kura et de l'Araxe[END_REF]. This study is based on the examination of 56 sites and more than 200 instances of mudbrick or cob inventoried and individually numbered in table 1 (inserted at the end of the chapter), intending to keep these records as objective as possible due to the ambiguity and variety of terms used in earthen architecture [START_REF] Aurenche | Essai de classification des modalités de mise en oeuvre de la terre crue en parois verticales et de leur nomenclature[END_REF].

Methodology, chaîne opératoire, identification

The study of building materials provides a better understanding of the mechanisms associated with technological changes and emphasises the choices made by certain populations, thus making it possible to identify "cultural" entities (Sauvage, 2001, p. 428). Over the last three decades, specialized studies have clarified the archaeological study of mud-brick, pisé or rammed earth, and cob [START_REF] Aurenche | Essai de classification des modalités de mise en oeuvre de la terre crue en parois verticales et de leur nomenclature[END_REF]Chazelles et al., 2003[START_REF] Aurenche | Essai de classification des modalités de mise en oeuvre de la terre crue en parois verticales et de leur nomenclature[END_REF]Guillaud et al., 2007;[START_REF] Roux | Les techniques constructives en bauge dans l'architecture protohistorique de Latarra (milieu du Ve -milieu du IVe s. av. n. è.)[END_REF]; each represents a different type of earthen construction, featuring different chaînes opératoires.

"Terre massive": pisé vs cob

The notion "terre massive" (stacked mud) has been introduced by C.A. de Chazelles indicating an building technique which consists of setting the earth directly where the wall is planned to stand. The two main techniques are cob and pisé. In pisé, earth is compacted in a wooden formwork with a rammer (Doat et al., 1979, p. 13-92). This technique is not attested historically before the Roman period (Aurenche et al., 2011, p. 22;Chazelles, 1997, p. 95).

Like pisé, cob is shaped directly on the location of the wall. As it's made of mud, a drying time is necessary between each layer, in order to avoid any defect. J.C. Roux and C. Cammas (2010, pp. 222-23) identify five implementation techniques. Two of them seem to be used frequently in Near Eastern and Southern Caucasus: cob in lumps and in layers. In the Near Eastern, the earliest instances are from the ninth millennium BCE and appear simultaneously in the Levant, at Gilgal [START_REF] Noy | Ten Years of Research in the Area of Gilgal, Lower Jordan Valley[END_REF][START_REF] Noy | Gilgal I, a Pre-Pottery Neolithic A Site in the Lower Jordan Valley[END_REF], in Eastern Jezirah, at Nemrik 9 (Kozlowski et al.,1990, p. 352), in the Zagros foothills, at Tepe Guran (Melgaard et al., 1963, p. 110) and in the Middle Euphrates and Mureybet [START_REF] Aurenche | Dictionnaire illustré multilingue de l'architecture du Proche-Orient ancien[END_REF].

Prefabricated components (mud-bricks)

Unlike stacked mud, prefabricated components are made in series and in advance. After drying, they are bonded with mortar in superimposed courses to make the wall; this technique is much faster than cob. Mud-bricks can be shaped by hands or made in a wooden mold. This second technique allows to standardize both shape and size of the mud-bricks and to increase the production rate (Aurenche, 1981, p. 66). It should be noted that duly documented examples of molded mud-bricks are rare and it is often only in terms of the regularity of the modules and the length/width ratio that it can be deduced that they are mold-made (Baudouin, sous presse).

For the molded mud-bricks, a thorough dismantling of the wall during the excavation enables to observe two features of the chaîne opératoire: 1) the removal of the excess of mud by scraping leaves circular or longitudinal marks on the surface (Baudouin, 2017: pp. 11-12, 159-160); 2) the removal of the mold leaves often a tiny ridge clearly visible at the top edges of the mud-bricks (Aurenche 1981, p. 18, 64;Baudouin 2017, pp.159-160, fig. 13).

At the current state of knowledge, the first mud-bricks shaped by hand appear in different places in the Near East at the beginning of the ninth millennium BCE (Aurenche, 1993, p. 84;Sauvage, 1998, p. 192). Their shapes are diversified: plano-convex at Nemrik 9 (Kozlowski, 1989, p. 27;Kozlowski et al., 1990, p. 11, pl.1, 355) or also cigar-shaped at Jericho (Kenyon, 1957, pl. 11B, 33A) and Choga Bonut (Kantor, 1978, p. 191, pl. IIa). On the other hand, the first molded mud-bricks appeared in the second half of the eighth millennium BCE in the Middle Euphrates Valley at Cafer Hüyük (Aurenche et al., 1985, pp. 13-15), at Gritille (Aurenche, et al., 1988, p. 5), at El-Kowm 2 (Stordeur, 2000, pp. 37-38), at Qdeir (Contenson, 1985, pp. 338, 340) and at Tell Halula (Molist et al., 2014, p. 108).

Results

Mesopotamian and Northern Zagros communities

Cob

In Jezirah, at Telul eth-Thalathat n°197 (Proto-Hassuna, level XV), Japanese scholars identified elongated and irregular lumps, piled up without mortar (Fukai et al., 1970, pp. 7, 22) My recent study1 of the photographic archives of this level shows the regularity of courses (around 8-9cm) for some walls and the irregularity of lumps on each course. At Tell Hassuna n°87 (Hassuna, levels I-II), "lumps of mud of various size" (Lloyd et al., 1945, p. 273) are arranged in a wet state on the location of the wall. After drying, both sides of the wall were smoothed to homogenize the surface. At Tell Sabi Abyad n°124,126, lumps seem used from level 8 (Op. I, Pre-Halaf, 6125-6075 cal. BCE), excavators recognized "layers of slabs" (Akkermans et al., 2014, p. 36), as at Tell Arpachiyah n°7 (Halaf, 6400-5400 BCE) where it is used for the construction of tholoi (Mallowan et al., 1935, p. 25). Layers of cob are attested at Tell Sabi Abyad n°132-133 (Op. I, Early Halaf, level 6) and namely a wall made of different layers of mud with different colours and textures; this technique continues at least up to level 3B, where excavators describe a similar alternation of layers (Verhoeven et al., 1996, pp. 44, 94). At Yarim Tepe II (Halaf IA, level VI), the wall of tholos 41 n°201 consists of "clay layers", joined with a yellowish mortar (Merpert et al., 1976, p. 45), close to the technique used for the circular buildings 44A and 44B n°202 (Merpert et al., 1977, p. 89). In the Northern Zagros, at Hajji Firuz n°76-80 (Hajji Firuz, levels J to A2), earthen beds are arranged in successive layers along the entire length of the wall (Voigt, 1983, p. 33). This technique seems to persist in the region during the Dalma period where layers of cob have been identified at Dalma Tepe n°52 in levels 5-4 (Hamlin 1975: 113). Nevertheless, many architectural features remain unspecified. At Tell Sabi Abyad n°125,128 (Op. I, Pre-Halaf, level 7B), the architectural elements appear as homogeneous "mud blocks", maybe similar to the "slabs" described in levels 8 and 7B (Akkermans et al., 2014, pp. 37, 45, 52). At Mattarah n°109 (Hassuna, levels I-II), the walls are reported as packed mud (tauf), without additional precisions (Braidwood et al., 1952, p. 6). At Tell Boueid II n°39 (Proto-Hassuna/Pre-Halaf), at Tell Arpachiyah n°8 (Halaf II, TT7 to TT10), at Tilki Tepe n°198 (Halaf II), at Salat Cami Yani n°141 (level 2) and at Hakemi Use n°89 (Hassuna or Samarra, level III) buildings are made of cob, though incorrectly called pisé by the authors (Suleiman et al., 2002, p. 6;Mallowan et al., 1935, p. 25;Chataigner, 1995, p. 59;Tekin, 2011, p. 152-53;Miyake, 2011, p. 131), or called tauf, as at Fıstıklı Höyükn°53 (Halaf I, level II) and at Tell Hassan n°92 (Halaf II) (Bernbeck et al., 2003, p. 164;Jasim 1985, p. 164). At Tell Turlu n°199 (Halaf), a similar material may be used though no precisions are available (Breniquet, 1987, p. 113). Finally, data at Tell Sungur n°189-194 shows the use of cob in Halaf-Ubaid Transitional (HUT) and in Ubaid 2-3. At Tell Sungur B (HUT, levels I to III), the walls of buildings B1 and B2 are built with "tauf" (Fuji, 1981, pp. 184, 190), just like at Tell Sungur C (Ubaid 2-3, level I) (Fuji, 1981, pp. 188, 190, 191;Jasim, 1985, p. 156).

In addition, the recent recovery of the archives of the sites of Telul eth-Thalathat and of Tell Kashkashok shows that cob initially identified by the excavators in the Proto-Hassuna levels has to be questioned. Indeed, at Telul eth-Thalathat, some walls of level XVb (squares NVIII-NIX) seem built with mud-bricks, the courses being apparently regular (around 8-10cm) with some modules being visible, as well as the mortar between these bricks and the interior plaster still preserved.

At Tell Kashkashok (level 3, square G7), walls preserved on at least one course seem made of mudbricks (possibly 30x25cm) and not in tauf (Matsutani, 1991, pp. 11, 13) (fig. 5 c-d, fig. 6).

Mud-bricks

Around 6000 BCE, in Eastern Anatolia, at Hakemi Use n°90-91 (Hassuna or Samarra, period III), the size of mud-bricks is not standardized (Tekin, 2011: 152), their length/width ratio varying between 1 and 2:1 Between 6400 and 5800 BCE, in Western Jezirah, hand-shaped mud-bricks and cob are used concurrently at Tell Sabi Abyad (see above). During the Pre-Halaf phase n°129-131 (level 7), the mudbricks used in buildings 7.5 (Akkermans et al., 2014, p. 57) and 7.11 (Akkermans et al., 2014, p. 61) are close to square (ratio: 0.9-1.4:1). This type of mud-brick is used until level 3B n°137-140 where it becomes smaller as in tholos I (Verhoeven et al., 1996, p. 96) and tholos N/AE (Verhoeven et al., 1996, p. 97). Within a century (between 6020 and 5905 cal. BCE), there is a gradual decrease in the size while the length/width ratio is constant.

At Tell Boueid II n°40 (Proto-Hassuna or Pre-Halaf), rectangular mud-bricks are used occasionally and are not standardized (Suleiman et al., 2002, p. 6). At Yarim Tepe I n°200 (Halaf), the large size of the elongated "mud-bricks", 90x15x6cm (Munchaev et al., 1973, p. 6), suggest that it is rather cob.

In Eastern Jezirah, at Tell Arpachiyah n°9-12 (Halaf II, levels TT4-5), the mud-bricks are irregular (Mallowan et al., 1935, p. 16) and the production is divided into two categories (Aurenche, 1981, tab. 6): large and almost square mud-bricks, with a ratio around 1:1, representatives of Halaf (Tell Sabi Abyad), and smaller mud-bricks, with a ratio around 2:1, conforming to the standardized molded mud-bricks of the same period.

In Central Mesopotamia, while the use of molded mud-bricks is becoming widespread in Samarra (5800-5400 cal. BCE), some mud-bricks are still shaped by hand: at Tell es-Sawwan n°151-152 (PN(?), level II), the length varying between 60 and 100cm, for a ratio between 1.8 and 3.3:1 (Wahida, 1967, p. 172). The weight of these bricks is estimated around 47kg for the largest ones. Such bricks, difficult to transport (Wahida, 1967, p. 172), may have been misidentified during the excavation according to J.D. Forest who identified half-bricks (Forest, 1983, p. 13).

In the Hamrin Basin, mud-bricks at Choga Mami n°45-46 (Late Samarra, level III), are elongated (ratio: 3,3 to 7,5:1) and cigar-shaped like in the Halaf levels (level II), with fingerprints visible on the upper side (Oates, 1969, pp. 116, 117) and at Tell Sungur A n°187-188 during Late Samarra (Matsumoto,1987, p. 189;1984, p. 37). In the Zagros foothills, similar mud-bricks with fingerprints are produced at Choga Mish n°47-48 during Archaic Susiana 3 (Delougaz et al., 1972, p. 93) and at Choga Sefid n°49-51 (CMT) where the length reaches 160 to 260cm (Hole, 1977, p. 78). The maximum ratio of 1:7.3 by far exceeds the usual data, for an estimated weight of 93.6kg: such prefabricated elements are inconceivable to achieve because they would be difficult to transport without the risk of breaking the elements; it is more reasonable to interpret these "bricks" as cob (Aurenche, 1981, p.195-199, but for an opposite argument, see Butterlin, 2018, p. 124.). [START_REF] Akkermans | Excavations at Late Neolithic Tell Sabi Abyad, Syria: The 1994-1999 Field Seasons[END_REF](after Baudouin et al., 2018, p. 66, fig. 16).

The molded mud-bricks are attested before the middle of the seventh millennium BCE, in South-Eastern Anatolia, at Akarçay Tepe n°1-2 (Pottery Neolithic Phase, level F), where the excavators identified two different sizes with a ratio of 1.3 and 1.6:1 (Özbaşaran et al., 2011, p. 173).

After this period, in Northern Zagros, at Hajji Firuz n°81-88 (levels A to G), M. Voigt (1983, p. 19) identified molded mud-bricks based on the steady of size and the regular shape close to square. In the Jezirah, at Chagar Bazar n°44 (Proto-Halaf, phase 10), the mud-bricks used for circular buildings are shaped by hands or molded (Cruells et al., 2013, p. 471). At Yarim Tepe II n°203 (Halaf II, level VI), the wall of tholos 37 is made with molded mud-bricks without, however, more precise information on their identification (Breniquet, 1996, p. 84). At Tepe Gawra n°69 (Halaf, level XX), the regularity of size suggests that they are molded (Tobler, 1950, p. 48).

In Central Mesopotamia, at Tell Baghouz n°36-38 (Late Samarra), R. Du Mesnil du Buisson (1948, p. 15; pl. XV-3) distinguished three different size and photographs enable to suppose that they are molded. At Tell es-Sawwan n°142-150, 153-164 (PN(?)/levels I-II), large oblong and molded mud-bricks (El-Wailly et al., 1965, p. 21) are produced with a ratio between 2 and 3:1, while in level IV (Samarra) n°165-166, the molded mud-bricks tend towards a ratio of 2:1 (Breniquet, 1992, p. 9;El-Wailly et al., 1965, p. 21). The mud-bricks at Tell es-Sawwan are considered by default as molded (Sauvage, 1998, pp. 101,214). However, the weight of some bricks, reaching around 40kg, makes them difficult both to make and transport.

Southern Caucasus communities

Cob

In Southern Caucasus, recent discoveries record the use of lumps (figs. 4 and 11) in the Kvemo-Kartli (Georgia) and in the Ararat (Armenia) plains. At Gadachrili Gora n°54 (Shulaveri-Shomu, horizon II), wall 217 is built with lumps (fig. 12) [START_REF] Baudouin | Architectural Techniques and Cultural Relationships between the Caucasus and Mesopotamia at the Beginning of the Sixth Millennium B.C[END_REF]Hamon et al., 2016, p. 165, fig. 23), like in walls 139 and 164 (Hamon et al., 2016, p. 164) and at Masis Blur n°113 (Aratashen, level I) (Hayrapetyan et al., 2014, p. 180).

In the Ararat Plain, layers of cob seem used at Aknashen-Katunarkh (Aratashen, level IV) for wall T5W4 where strips of yellow clay divided horizontally by strips of darker clay have been identified (C. Chataigner, personal communication). At Masis Blur n°114 (Aratashen, level I), wall S011 is made with "straight row of alternating dark and light clay rectangles" (Hayrapetyan et al., 2014, p. 180).

Several occurrences of cob could not be defined in detail. In the Kvemo-Kartli Plain, at Aruchlon°13-14 (Shulaveri-Shomu, level I), cob, which is there called pisé (Chataigner, 1995, p. 59;Kushnareva et al., 1970, p. 22), has been used for buildings 4 to 9. At Shulaveris Gora n°188 (Shulaveri-Shomu), A. Sagona (1993, p. 456) described this technique as "wattle-and-daub", while the excavators as pisé ( Dzhavakhishvili et al., 1975, p. 203). In these two cases, stacked mud and plano-convex mud-bricks are used simultaneously (see below). In Nakhichevan, at Kültepe n°112 (Kültepe), Abibullaev (1963, p. 157-58) mentioned pisé, without specifics.

Mud-bricks

In Southern Caucasus, two morphological types of sun-dried mud-bricks have been identified: plano-convex mud-bricks, flat on the inside and curved on the outside, characteristic of Shulaveri-Shomu in the Kura Valley, and elongated and flat mud-bricks, characteristic of Aratashen in the Araxes Valley (Chataigner, 1995, p. 64) but also used in the Middle Kura Valley and the Kvemo-Kartli Plain. The publications usually describe the shape without specifying the manufacturing technique. C. Chataigner is the only one to identify plano-convex bricks as mud-bricks shaped by hands, similar to the curved bricks produced during the PPNA (9500-8700 BCE) in the Near East (Chataigner, 1995, p. 57).

Plano-convex mud-bricks seem to be used from the beginning of the sixth millennium BCE in Shulaveri-Shomu. At Shomu Tepe n°167-175 (Narimanov, 1987, p. 86), they have a length/width ratio always between 2:1 and 3:1, and two sizes: small and large (figs. 7 and 8). At Mentesh Tepe n°118-123 (level I), sizes is relatively homogeneous, with a ratio between 2.7:1 and 3.6:1. While the mud-bricks of structure ST346 are certainly shaped by hands, other could be mold-made (see below). At Göy Tepe n°70-72 (levels 1 to 14), plano-convex mud-bricks in level 13 are replaced by flat mud-bricks in the other levels (Guliyev et al., 2014, p. 5, Y. Nishiaki, personal communication); medium mudbricks have a length of 30 to 40cm, and large mud-bricks are 40-60cm (Guliyev et al., 2009, p. 47;2012, p. 74;2014, p. 5). At Gargalar Tepesi n°61-68, there is a clear decrease in size from levels 1 to 3 (Narimanov, 1992, pp. 20-21).

In the Kvemo-Kartli Plain, at Aruchlo n°15-23, scholars insisted on the irregularity of the size, with length varying between 18 and 50cm (Hansen et al., 2013, p. 390). In addition, the stratigraphic data enable to associate the largest mud-bricks to the oldest levels (Hansen et al., 2017, p. 209, fig. 22;p. 210, fig. 23). At Shulaveris Gora n°176-186 (Dzhavakhishvili, 1973, p. 19), the same irregularity is attested, length varying between 25 and 50cm (Kushnareva et al., 1970, p. 28), but no stratigraphic data enable to assume an evolution of the size. At Gadachrili Gora n°54-60 (level I), mud-bricks of building 2004 are elongated and flat with a ratio of 2:1 [START_REF] Baudouin | Architectural Techniques and Cultural Relationships between the Caucasus and Mesopotamia at the Beginning of the Sixth Millennium B.C[END_REF]. In building 2003, mud-bricks of the peripheral wall have a plano-convex shape, with a ratio of 2:1, and those of the dividing wall are square and flat (Hamon et al., 2016, p. 161-62). At Khramis Didi Gora n°104-111, plano-convex mud-bricks have a ratio between 1.9 and 2.7:1. At Imiris Gora n°88-94, such mud-bricks are of different size (Dzhaparidze et al., 1971, p. 28;Dzhavakhishvili, 1973, p. 48), varying between 32 and 50cm, but the lack of stratigraphic data does not enable to interpret an evolution.

In the Ararat Plain (Aratashen), flat and elongated mud-bricks are attested at Aratashen n°6 in level I (Badalyan et al., 2004, p. 402) and at Akhnashen-Katunarkh n°3-5 where small and large mud-bricks are identified in level VII (Badalyan et al., 2014, p. 165). At Tekhut n°196 (levels II and XII), mudbricks are also flat with a ratio of 1.3:1 (Torosjan, 1976, pp. 23-27).

In the Mil Plain, at Kamiltepe n°101-103 (Kamiltepe, phase Kamiltepe I), if Narimanov (1992, p. 35) identified rectangular mud-bricks, those used for the terrace, shaped by hand, are smaller and square (Helwing et al., 2017, p. 17).

Recent research at Aruchlo [START_REF] Ioseliani | Architecture Debris from the Burnt Layers[END_REF] and Mentesh Tepe [START_REF] Baudouin | Architectural Techniques and Cultural Relationships between the Caucasus and Mesopotamia at the Beginning of the Sixth Millennium B.C[END_REF] confirmed the use of molded plano-convex mud-bricks during the first third of the sixth millennium BCE in Baudouin,in press). At Mentesh Tepe n°110-111, mud-bricks are clearly molded (fig. 13): the edges are perfectly straight and marks of clipping are visible at the top of these mud-bricks (Baudouin, 2018a, p. 150-51;Baudouin et al., 2017, pp. 44-45, fig. 4). In addition, slight longitudinal ridges on the convex face of several mud-bricks indicate a flattening of the surface before the removal of the frame. At Aruchlo n°24-35, molded plano-convex mud-bricks have been identified in a burned collapse attributable to the oldest occupation. These mud-bricks have a standard size and have specific stigmas (Ioseliani 2017, p. 282) similar of those observed at Mentesh Tepe.

Discussion

Technical evolution: the gradual replacement of cob by mud-bricks

Stacked mud is used from the end of the seventh to the end of the seventh to the middle of the sixth millennium BCE. Lumps seems to be older, attested from Hassuna (Proto-Hassuna), but we observe the recurrence of cob in layers in the Jezirah, Northern Zagros and Southern Caucasus since 6200-6000 BCE: its use could be simultaneous during Early Halaf/Halaf I (ca. 6010-5800 BCE), Hajji Firuz (ca.6200-6000 BCE), Aratashen (ca. 6000-5750 BCE) and Shulaveri-Shomu (from 5900 BCE). The use of cob seems significant from the end of the seventh millennium to the first third of the sixth millennium BCE. but it gradually disappears during the end of Hassuna and Halaf in the Syro-Mesopotamian Basin, replaced by mud-brick.

Until the middle of the sixth millennium BCE, and whatever the manufacturing technique, the production of mud-bricks testifies to extremely marked regional facies throughout the region considered, identifiable by differences in shapes or sizes. The reason of this heterogeneity is probably related to cultural particularisms. Both in the Syro-Mesopotamian Basin (Halaf) and in the Southern Caucasus, the appearance of molded mud-bricks is not well defined. In the first area, they seem to appear late and perhaps as a result of an Ubaid impulse (Breniquet, 1996, p. 84), during Baudouin et al., 2018, p. 58, fig. 8).

the Halaf II period (ca. 5800-5400 BCE). Their discovery in the Proto-Halaf levels at Chagar Bazar and in the Hajji Firuz levels on the eponymous site suggests that the East of the Euphrates was able to benefit from a technical spread from the Middle Euphrates at the end of the seventh millennium (Sauvage, 2009, p. 195). Indeed, the use of the molded mud-brick on several sites (Cafer Hoyük, Tell Halula, Bouqras, Gritille) of Late PPNB (ca. 7000 BCE) in this region encourages to follow this assumption. In Southern Caucasus, mud-bricks are duly molded since the beginning of the sixth millennium BCE.

Cob development: technical transfer or convergence?

The process of the spread of a technique can be considered through time and space. This process involves an imbalance between two (or more) communities (Leroi-Gourhan, 1945, p. 460). However, other factors need to be considered, such as the technical degree of the communities and the natural setting. The former presence of cob in Jezirah and the large amount of archaeological evidence enable us to precisely track the technical evolution and its origin in Northern Zagros and in the Southern Caucasus communities.

The development of Halaf architecture

The assumption of the spread of cob in Halaf is conceivable. It was adopted gradually during the Halaf expansion, between 5900 and 5300 BCE, towards Central Mesopotamia, Western Jezirah and near the Van Lake in Northern Zagros (fig. 14): there would be a convergence between spatial organization and chronology, that can confirm the assumption of a slow spread, phenomenon already emphasized for ceramics (Breniquet, 1996, p. 65). An analysis of the stratigraphic sequence at Hajji Firuz brings new informations. Firstly, cob is used alone until levels G-F (fig. 15). Furthermore, this technique has been used in "competition" with molded mud-brick from levels D to B. In this case, the molded mud-brick may be interpreted as a technical invention which will totally replace cob from levels C-B.

The development of cob in Northern Zagros and Southern Caucasus

In the current state of knowledge, it is likely that cob appeared from the beginning of the Hajji Firuz (ca. 6300 cal. BCE), perhaps as result of the stimuli of the Eastern Jezirah or High Tigris communities during Early Hassuna or Samarra, especially because these cultures share extraarchitectural affinities, as in decorations and ceramic forms (Voigt, 1983, p. 163).

In the Southern Caucasus, the issue is different. Halaf reaches the shore of the Van Lake ca. 5700/5300 BCE, at least two hundred years after first settlement in Southern Caucasus. Therefore it seems unlikely that this technique was older than the Halaf expansion to the northeast, although there could have been relations between these different communities at the beginning of the sixth millennium BCE, as represented by the discovery of sherds of "Mesopotamian" style at several sites. On the other hand, the possibility of a spread from the Urmiah Lake (Hajji Firuz) and High Tigris (Hassuna or Samarra) regions is weak because, except cob, technical affinities seem extremely thin with Caucasian architecture (Baudouin, in progress, 2019(Baudouin, in progress, , 2018a(Baudouin, in progress, , 2018b)). It would be unusual that the technical input only affected one specific material without changing other material components. Thus, in our current state of knowledge, a local and autonomous origin of cob in the Araxes Valley is likely. Nevertheless, an "internal" spread in the Southern Caucasus from the Araxes to the Kura Valley is possible. However, lack of precise stratigraphic and chronological data does not enable for sure to support this assumption.

The mud-brick technology: a medium for a technical transfer?

The interpretation of an autonomous invention of the molded mud-brick during Late PPNB (ca. 7500-7000 BCE) in the Middle Euphrates and a spread to Samarra in Central Mesopotamia (ca. 6500 BCE) is argued by Sauvage (2009, p. 195). In the Jezirah, the molded mud-brick would have been adopted late (Halaf II) and gradually at the impulse of Ubaid communities (Breniquet, 1996, p. 95). Such a technical change would correlate with the social transformations within Halaf communities. Chronologically, the assumption of a spread of the molded mud-brick from the Middle Euphrates to Central Mesopotamia is conceivable (Sauvage, 2009, p. 195). It is explained by a "late" occupation in the Syrian desert at El-Kowm 2, ca. 7900-5600 cal. BCE (Stordeur, 2000, p. 305, tab.1), and Qdeir, ca. 7290-5730 cal. BCE (Hours et al., 1994, p. 408), or in the Euphrates Valley at Bouqras, ca. 7100-6200 cal. BCE (Hours et al., 1994, pp. 388-89), which thus extends Late PPNB and reduces the gap with the beginning of Samarra, ca. 6400-5700 cal. BCE (El-Wailly et al., 1965, p. 19;Burleigh et al., 1982, p. 247;[START_REF] Helwing | Reconsidering the Neolithic Graveyard at Tell es-Sawwan, Iraq[END_REF]. The similarity of the size of mud-bricks in Late PPNB (Bouqras n°41-43, Gritille n°73-75) and Samarra (fig. 16) corroborates relationships between these two chrono-cultural areas and confirms the assumption of a spread of the molded mud-brick technique from the Middle Euphrates to Central Mesopotamia at the beginning of the sixth millennium BCE. In addition, this spread can be corroborated by other technical elements adopted in Central Mesopotamia like buttresses, attested for the first time at Cafer Höyük, during Late PPNB, ca. 8500-6500 cal. BCE (Molist et al., 1991, p. 7), or the standardized plan (Aurenche, 1981, p. 200;[START_REF] Breniquet | De Bouqras à Tell es-Sawwan. Les premiers avatars des plans tripartites du nord mésopotamien[END_REF][START_REF] Stordeur | El Kowm 2 : une île dans le désert[END_REF]Aurenche et al., 2009, p. 156;Baudouin, 2018a, pp. 497-508) attested at Tell Bouqras and at El-Kowm 2.

The development of mud-brick in Mesopotamia

A technical improvement in Northern Zagros and Jezirah

In Northern Zagros (Hajji Firuz), the typical mud-brick size at Hajji Firuz (fig. 16; in blue), with a ratio of 1:1, overlap very little with the production of Late PPNB (in grey) and Samarra (in yellow).

The assumption of an autonomous technical evolution in Northern Zagros seems thus more viable and could explain the gradual disappearance of cob at the benefit of mud-brick (fig. 15). A similar assumption could be proposed in western Jezirah for hand-shaped mud-bricks at Tell Sabi Abyad (Op. I) where we observed the same gradual displacement from level 8 to level 3B (6125-5905 cal. BCE), cob nearly totally disappearing ca. 6000 BCE (fig. 17).

How to interpret the original shape of the Caucasian mud-bricks?

Lastly, mud-bricks made in the Kura Valley during the Shulaveri-Shomu are characteristic by their size and their shape (fig. 16). The hypothesis of a local invention would justify and corroborate the interpretation of an autonomous settling of communities in the Kura Valley. This assumption is strengthened by the presence of circular subterranean architecture in the Kura Valley, Mil Plain and in the Karabagh Plain at where in few sites these structures were built on the virgin soil and are the first settlement phases during the first third of the sixth millennium BCE This "first" architecture, compared with ethnographic examples, can be considered as the original settlement of former nomadic communities (Baudouin, 2019, pp. 145-146). Finally, the exclusive use of the circular plan throughout more than 700 years in the entire Southern Caucasus enables us to interpret a technical inertia in the region and confirms the assumption of an autonomous settlement of communities of this region.

Conclusion

The spread of cob in the entire area of the Halaf cultural expansion is most likely. However, in Northern Zagros and Southern Caucasus, such a hypothesis is unlikely because no other technologies were adopted. The search the "way" of spread of one single technique is constrained by chronological imprecisions and a lack of diagnostic markers. In addition, cob is often considered like a "basic" technique characterising communities who did not reach a high degree of technicality. Therefore, a local development in Northern Zagros and the Southern Caucasus, where the first settlement appeared at the beginning of the sixth millennium BCE, cannot be excluded. Later, the gradual disappearance of cob and its replacement by mud-brick is a phenomenon clearly visible at a local scale (Hajji Firuz, Tell Sabi Abyad), but it is not possible to generalize in the current state of data.

On the other hand, the appearance of molded mud-brick represents an undeniable technical development, the spread of which is clearly visible from Late PPNB to Samarra, and can only be approached by a general study of the "complex" architecture in the Syro-Mesopotamian Basin. Therefore, the development of the Ubaid tripartite architecture represents a new stage of progress at the end of the fifth millennium BCE (Baudouin, 2018a(Baudouin, , 2018b, p. 407), p. 407). This brief overview of the development of cob and mud-brick techniques glimpses the potential of this research and confirms the importance of systematizing such an approach in order to better define the contents of technical exchanges and cultural relationships between communities. et al., 2014et al., (after Baudouin et al., 2018, p. 67, fig. 17), p. 67, fig. 17).

Table 1

Data are arranged in alphabetical order of the site names. The call number in column one of the table corresponds to the return of the text. Columns three to five specify the cultural attribution, the level, the dating and the building or wall concerned according to the name given by the excavator. Columns eight to ten specify the size of mud-bricks (length, width, height), as well as the length/width ratio and the estimated weight according to these size: the underlined weights correspond to the values greater than 28kg whose manufacture or transport are considered difficult. Columns eleven and twelve specify material used (cob or mud-bricks), layout and form (abbreviations below). Finally, the authors' citations as well as the associated bibliographic references are listed in columns thirteen and fourteen. The references preceded by the sign "*" are those of the radiocarbon dates.

Fig 1 .

 1 Fig 1. Map and chronology of the Northern Mesopotamia and Southern Caucasus communities from the end of the seventh millennium to the middle of the fifth millennium BCE.

Fig 2 .

 2 Fig 2. Summary diagram of implementation using earthen material (afterBaudouin et al., 2018, p. 60, fig. 11).

Fig 3 .

 3 Fig 3. General map of Northern Mesopotamia with the sites mentioned in the text. Fig 4. Summary diagram of the attestations of the stacked mud technique (seventh-sixth millennium BCE)

Fig 5 .

 5 Fig 5. Telul eth-Thalathat II (level XVb): a-b.) Wall in cob in squares O-VIII, view from the west; c-d.) Walls in mud-bricks in squares N-VIII, N-IX, view from the south-west. Japanese archaeological excavations at Telul eth-Thalathat (campaign 1976), unpublished archives of the University Museum, The University of Tokyo.

Fig 6 .

 6 Fig 6. Tell Kashkashok (level 3): a-b.) Wall in mud-bricks in square G7, view from the south-west; c-d.) The same wall, view from the south-east. Japanese archaeological excavations at Tell Kashkashok (campaign 1988), unpublished archives of the University Museum, The University of Tokyo.

Fig 7 .

 7 Fig 7. Summary diagram of the attestations of the mud-bricks shaped by hands and moulded mud-bricks in Northern Mesopotamia and Caucasus (seventh-sixth millennium B.C.)

Fig 9 .

 9 Fig 9. Summary table of the evolution of mud-bricks sizes at Tell Sabi Abyad (Syria) (Op. I) between levels 8 and 3B (6125-5905 BCE),based on[START_REF] Akkermans | Excavations at Late Neolithic Tell Sabi Abyad, Syria: The 1994-1999 Field Seasons[END_REF] (after Baudouin et al., 2018, p. 66, fig. 16).

Fig 10 .

 10 Fig 10. Summary diagram of the attestations of the molded mud-brick in Northern Mesopotamia and Caucasus (seventh-sixth millennium BCE)

Fig 11 .

 11 Fig 11. General map of Southern Caucasus with the sites mentioned in the text.

Fig 12 .

 12 Fig 12. Gadachrili Gora, example of the wall 217 made lump (after Baudouin et al., 2018, p. 60, fig. 12).

Figure 13 .

 13 Figure 13. Molded plano-convex mud-bricks from Mentesh Tepe. a.: Detail of the four courses of mud-bricks, wall 293 (Sector 10) -View from the West; b.: Detail of the mortar between the mud-bricks, the wall 293 -View from the West; c.: Detail of the first course of mud-brick, wall 285 (Sector 15) -View from the North-East (afterBaudouin et al., 2018, p. 58, fig. 8).

Fig 14 .

 14 Fig 14. Use of cob and spread of the technique in the syro-mesopotamian basin, Eastern Anatolia, Northern Zagros and SouthernCaucasus from the second half of the seventh millennium to the middle of the fifth millennium BCE.

Fig 15 .

 15 Fig 15. Summary table of the evolution of cob and mud-bricks sizes at Hajji Firuz between levels L and A2, based on[START_REF] Voigt | Hajji Firuz Tepe, Iran: The Neolithic Settlement[END_REF]

Fig 16 .

 16 Fig 16. Sizes of molded mud-bricks from the seventh millennium and the middle of the sixth millennium BCE in the Syromesopotamian basin, Northern Zagros and Southern Caucasus.

Fig 17 .

 17 Fig 17. Summary table of the architectural techniques at Tell Sabi Abyad (Syria) with a gradual disappearance of the cob techniqueand its replacement by mud-bricks, based on[START_REF] Akkermans | Excavations at Late Neolithic Tell Sabi Abyad, Syria: The 1994-1999 Field Seasons[END_REF] (after Baudouin et al., 2018, p. 67, fig. 17).

  Abbreviations:

I thank Professor Y.Nishiaki (The University Museum, The University of Tokyo) for giving me access to these archives. This research was made thanks to the Japan Society for the Promotion of Science (JSPS) as part of a postdoctoral fellowship at the University of ToKyo.