Kenzy I Peña-Carrillo
email: kenzy.p@gmail.com

Chantal Poteaux

Chloé Leroy

Rubí N Meza-Lázaro

Jean- Paul Lachaud

Alejandro Zaldívar-Riverón

Maria Cristina Lorenzi

Highly divergent cuticular hydrocarbon profiles in the cleptobiotic ants of the Ectatomma ruidum species complex

Keywords: biotic interactions, chemical divergence, nestmate recognition cues, species complex, thievery. Fig

In social insects, chemical communication is the main communication mode among colony members, which use the blends of cuticular hydrocarbons as recognition cues to discriminate between nestmates and non-nestmates and to prevent the exploitation of their nest resources by aliens. The aim of this study was to assess the variation of nestmate recognition cues in the ant Ectatomma ruidum, a species complex with a considerably conserved morphology and one of the few ant species where intraspecific thievery, a form of cleptoparasitism, has been reported. We analyzed the cuticular hydrocarbon profiles of ants collected from a number of geographically separated populations, and examined DNA sequence data to assess their species identity. We focused on one species of the complex, E. ruidum sp. 3-4, whose species delineation remains controversial. We documented that several quantitative and qualitative traits of the cuticular hydrocarbon profiles varied significantly between populations, indicating that this species harbors more cuticular chemical phenotypic diversity than expected within a single species. In particular, there was a striking divergence among populations in the proportion of methylalkanes, alkenes, alkadienes and odd-chain components, which likely play a major role in nestmate/non-nestmate discrimination, a process which might have been crucial in these cleptobiotic ants. Further investigations are needed to test the hypothesis that biotic pressures, such as the need to discriminate conspecific intruders and limit thievery, could have played an important role in promoting the evolutionary divergence between populations in this ant species complex.

Introduction

Recognition of group members has favored the evolution and maintenance of sociality [START_REF] Hamilton | Discrimination nepotism: expectable, common, overlooked[END_REF]d E and Lenoir 2010). Albeit social insects communicate in different forms, chemical communication is the main communication mode among colony members, allowing them to exchange different kinds of information [START_REF] Wyatt | Pheromones and Animal Behavior: Chemical Signals and Signatures[END_REF][START_REF] Leonhardt | Ecology and evolution of communication in social insects[END_REF]). Among the different contents that a chemical message can encode, social insects use the blend of hydrocarbons they bear on their cuticle as a chemical signature that conveys information about castes, task specialization and reproductive status [START_REF] Blomquist | Insect hydrocarbons: biology, biochemistry and chemical ecology[END_REF]. Cuticular hydrocarbons also allow social insects to discriminate between nestmates and non-nestmates, and prevent exploitation of nest resources by aliens (van Zweden and d E 2010; [START_REF] Leonhardt | Ecology and evolution of communication in social insects[END_REF]. Indeed, when social insects encounter another individual, the presence of sufficiently large differences between their cuticular hydrocarbon profiles can trigger aggressive behavioral responses and allows colony residents to reject intruders [START_REF] Dani | Deciphering the recognition signature within the cuticular chemical profile of paper wasps[END_REF][START_REF] Martin | Chemical basis of nest-mate discrimination in the ant Formica exsecta[END_REF][START_REF] Van Zweden | Nestmate recognition in social insects and the role of hydrocarbons[END_REF].

In insects, cuticular hydrocarbon mixtures are usually composed of different hydrocarbon classes, such as linear alkanes (n-alkanes), alkanes with one or more methyl branches (mono-, di-, tri-, tetra-methylalkanes) and hydrocarbons with one or two unsaturations, alkenes and alkadienes [START_REF] Blomquist | Insect hydrocarbons: biology, biochemistry and chemical ecology[END_REF]. Usually, quantitative variations of the same set of hydrocarbons discriminate between colonies (intraspecific differences), whereas different species have qualitatively different profiles, even among closely related taxa [START_REF] Hölldobler | Mechanisms of identification and discrimination in social Hymenoptera[END_REF][START_REF] Van Zweden | Nestmate recognition in social insects and the role of hydrocarbons[END_REF]. Cuticular hydrocarbons are typically species-specific and qualitatively stable across the entire species distribution range [START_REF] Lockey | Cuticular hydrocarbons of adult Himatismus species and a comparison with 21 other species of adult tenebrionid beetle using multivariate analysis[END_REF][START_REF] Drijfhout | The role of cuticular hydrocarbons in insects[END_REF][START_REF] Guillem | Species-specific cuticular hydrocarbon stability within European Myrmica ants[END_REF]. Consequently, they are considered as useful taxonomic tools for species delimitation [START_REF] Bagnères | Chemical taxonomy with hydrocarbons[END_REF][START_REF] Kather | Cuticular hydrocarbon profiles as a taxonomic tool: advantages, limitations and technical aspects[END_REF]. For instance, cuticular hydrocarbons allowed to separate Myrmica sabuleti from M. scabrinodis, two species that are morphologically extremely similar but differ chemically in the composition of their cuticular layers, in particular in the presence of specific methylalkanes, which thus can serve as accurate diagnostic characters [START_REF] Guillem | Using chemo-taxonomy of host ants to help conserve the large blue butterfly[END_REF]. Studies focused on species such as Formica japonica [START_REF] Akino | Intraspecific variation of cuticular hydrocarbon composition in Formica japonica Motschoulsky (Hymenoptera: Formicidae)[END_REF], Neoponera (=Pachycondyla) villosa [START_REF] Lucas | A multidisciplinary approach to discriminating different taxa in the species complex Pachycondyla villosa (Formicidae)[END_REF], Tetramorium caespitum/impurum complex [START_REF] Schlick-Steiner | A multidisciplinary approach reveals cryptic diversity in Western Paleartic Tetramorium ants (Hymenoptera: Formicidae)[END_REF], Crematogaster levior and Camponotus femoratus [START_REF] Hartke | Cuticular hydrocarbons as potential mediators of cryptic species divergence in a mutualistic ant association[END_REF] are other examples of ant taxa with confirmed cryptic diversity that was discovered after examining their cuticular hydrocarbon profiles. Cuticular hydrocarbon analyses have also recently highlighted that sympatric, cryptic species exist in Cr. levior and Ca. femoratus, two neotropical ant species that exhibit parabiotic association, a lifestyle which might have promoted chemical divergence [START_REF] Hartke | Cuticular hydrocarbons as potential mediators of cryptic species divergence in a mutualistic ant association[END_REF].

Ectatomma ruidum Roger is a mainly Neotropical, widely distributed ant taxon that is likely to include a cryptic species diversity, which only has been recently started to be unveiled. Two recent studies based on mitochondrial (mt) and nuclear DNA sequence data and morphological evidence revealed that this taxon actually represents a species complex [START_REF] Aguilar-Velasco | Uncovering species boundaries in the Neotropical ant complex Ectatomma ruidum (Ectatomminae) under the presence of nuclear mitochondrial paralogues[END_REF][START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF], though its species delineation still remains unclear. In the first of these studies, morphological data indicated the existence of four morphospecies, two of which apparently are widespread along the Neotropics (E. ruidum spp. 1 and 2), whereas the remaining two species (E. ruidum spp. 3 and 4) and a presumably hybrid population (E. ruidum sp. 2 x 3) are restricted to few localities in Oaxaca, southeast Mexico. These results became more complicated with the subsequent discovery of extensive heteroplasmy (i.e. presence of multiple mtDNA haplotypes in a single organism; [START_REF] Magnacca | Mitochondrial heteroplasmy and DNA barcoding in Hawaiian Hylaeus (Nesoprosopis) bees (Hymenoptera: Colletidae)[END_REF] in specimens of the morphospecies E. ruidum spp. 3, 4 and 2x3 which might represent a single species whose populations share heteroplasmy [START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF]).

E. ruidum, as currently known, is unique in a behavioral trait named intraspecific cleptobiosis. Besides the a a behavior, some colony members display an alternative, parasitic, foraging strategy that consists of visiting conspecific colonies to take food from inside the nest and bringing it back to their home colony [START_REF] Breed | Thievery, home ranges, and nestmate recognition in Ectatomma ruidum[END_REF][START_REF] Carli | Études en milieu naturel du comportement de cleptobiose chez la fourmi néotropicale Ectatomma ruidum (Hymenoptera, Ponerinae)[END_REF]. During foraging, thief ants exhibit a peculiar behavior: unlike other foragers, during their travel home they do not always follow a narrow path to their colony, and often hide [START_REF] Jandt | Intraspecific food-robbing and neighborhood competition: consequences for anti-robber vigilance and colony productivity[END_REF]. Thieves also differ from other foragers in their cuticular chemical profile, which is significantly poorer in hydrocarbons [START_REF] Jeral | Thief ants have reduced quantities of cuticular compounds in a ponerinae ant, Ectatomma ruidum[END_REF], and have been proposed as a distinct caste of foragers [START_REF] Mcglynn | Distinct types of foragers in the ant Ectatomma ruidum: typical foragers and furtive thieves[END_REF]. This behavior has been reported in different locations along the distribution range of E. ruidum [START_REF] Carli | Études en milieu naturel du comportement de cleptobiose chez la fourmi néotropicale Ectatomma ruidum (Hymenoptera, Ponerinae)[END_REF][START_REF] Breed | Thief workers and variation in nestmate recognition behavior in a ponerine ant, Ectatomma ruidum[END_REF]), but its relation with the taxonomic complexity of the species remains unclear.

The intriguing complexity for species identification within the E. ruidum complex, coupled with its cleptobiotic behavior make it an ideal model system to study variation in recognition cues, as parasitic relationships have been identified as potential evolutionary drivers of polymorphism in these cues [START_REF] Crozier | Genetic clonal recognition abilities in marine invertebrates must be maintained by selection for something else[END_REF]). These results might also contribute to future integrative taxonomy approaches where data from multiple sources (i.e. morphology, genetic analyses, ecological niche modeling, chemical analyses, etc.) are useful to identify or define species boundaries [START_REF] Heethoff | Integrative taxonomy: combining morphological, molecular and chemical data for species delineation in the parthenogenetic Trhypochthonius tectorum complex (Acari, Oribatida, Trhypochthoniidae)[END_REF][START_REF] Fm | Turning one into five: Integrative taxonomy uncovers complex evolution of cryptic species in the harvester ant Messor "structor[END_REF]). Here we compared the cuticular hydrocarbon profiles within the E. ruidum complex. Specifically, we tested for the intraspecific variation of the cuticular hydrocarbon profiles between populations of E. ruidum sp. 3-4 from southeast Mexico, whose boundaries remain controversial [START_REF] Aguilar-Velasco | Uncovering species boundaries in the Neotropical ant complex Ectatomma ruidum (Ectatomminae) under the presence of nuclear mitochondrial paralogues[END_REF][START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF].

Material and methods

Study model

Ectatomma ruidum is an earth-dwelling ant that occurs in a wide range of habitats in Neotropics, including plantations and damp forests, from sea level up to 1600 m (McGlynn et al. 2015;[START_REF] Aguilar-Velasco | Uncovering species boundaries in the Neotropical ant complex Ectatomma ruidum (Ectatomminae) under the presence of nuclear mitochondrial paralogues[END_REF]. Typically, E. ruidum nests have a single entrance and contain between 50 and 200 individuals [START_REF] Lachaud | Recruitment by selective activation: an archaic type of mass recruitment in a ponerine ant (Ectatomma ruidum)[END_REF] and their densities can be very high (up to 11200 nests per hectare, [START_REF] Schatz | Effect of high nest density on spatial relationships in two dominant Ectatommine ants (Hymenoptera: Formicidae)[END_REF]. These ants have a very generalist diet and the foraging activity is mainly diurnal [START_REF] Lachaud | Foraging activity and diet in some neotropical ponerinae ants. I. Ectatomma ruidum Roger (Hymenoptera, Formicidae)[END_REF]). In general, colonies are monogynous but in some regions they are facultatively polygynous with size-dimorphic queens (macro and microgynes) [START_REF] Lachaud | Queen size dimorphism and reproductive capacity in the ponerine ant, Ectatomma ruidum Roger[END_REF].

Collection of ants

We collected E. ruidum colonies in the populations Cozoaltepec, Huaxpaltepec, Punto 3, Río Grande and Santo Domingo de Morelos along a transect of 150 km across the Pacific coastal zone in the state of Oaxaca, México, in order to increase the sampling area covered by Aguilar-Velasco et al. (2016) (populations Coyula, Mazunte, Piedras Negras, Puerto Escondido). We also collected ants in two additional populations, one 500 km far from Coyula, Oaxaca to the south Pacific coast in Cantón Leoncillos, Chiapas, Mexico, and the remaining one in Cali, Colombia (Fig. 1 and Table 1); the ants from Cali, Canton Leoncillos, Coyula, Mazunte, Piedras Negras and Puerto Escondido belong to the same sampling as that in [START_REF] Aguilar-Velasco | Uncovering species boundaries in the Neotropical ant complex Ectatomma ruidum (Ectatomminae) under the presence of nuclear mitochondrial paralogues[END_REF] and [START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF]. Colonies from the same population were at least 2 m distant from each other. In Oaxaca and Chiapas, Mexico, the climate is hot and semi-humid to semi-dry with tropical deciduous and semi-deciduous forests [START_REF] Rzedowski | Vegetación de México. 1ra edición digital[END_REF]. Ants in Mexico were collected in plantations or forest, whereas in Colombia, they were collected in the urban area.

Species identification

We identified the ants from Cozoaltepec, Huaxpaltepec, Punto 3, Río Grande, and Santo Domingo de Morelos based on the diagnostic morphological features of the species E. ruidum mentioned by [START_REF] Kugler | Revisionary & other studies on the ant genus Ectatomma, including the descriptions of two new species[END_REF] and [START_REF] Arias-Penna | Subfamilia Ectatomminae[END_REF] keys to species of Ectatomma. For their molecular characterization, we sequenced the barcoding region, which is a fragment of the cytochrome oxidase I (COI) mtDNA gene. We also included in the molecular analyses previously published sequences of ants from Cali, Cantón Leoncillos, Coyula, Mazunte, Puerto Escondido and Piedras Negras [START_REF] Aguilar-Velasco | Uncovering species boundaries in the Neotropical ant complex Ectatomma ruidum (Ectatomminae) under the presence of nuclear mitochondrial paralogues[END_REF][START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF]. All newly generated sequences were obtained following the laboratory procedures, primers and PCR programs mentioned by Aguilar-Velasco et al. ( 2016) (Table 1). The specimens that were sequenced in the current study were deposited in the National Collection of Insects (CNIN) at the National Autonomous University of Mexico (UNAM), Mexico, and the National Natural History Museum (MNHN) in Paris, France.

To confirm the taxonomical identification, we conducted a Maximum Likelihood (ML) analysis using the program RAxML version 8 [START_REF] Stamatakis | RAxML version 8: a tool for phylogenetic analysis and post-analysis of large phylogenies[END_REF] to reconstruct the phylogenetic relations among representative specimens (workers) of all the examined populations of the E. ruidum complex. We used the GTRCAT model of sequence evolution and partitions based on codon position, and bootstrap support values were generated with 1000 rapid bootstrap replicates. ML analyses were carried out in the CIPRES Science Gateway v. 3.3 [START_REF] Miller | Creating the CIPRES science gateway for inference of large phylogenetic trees[END_REF] portal. In case it was not possible to assign ants to any of the previously proposed morphospecies we used the putative species assignation of [START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF] based on mitogenome information. In [START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF], all the seven individuals of E. ruidum spp. 3 and 4 that were examined were heteroplasmic with highly divergent mitochondrial haplotypes (1.88 5.81 % polymorphic sites spread across their genomes).

Fig. 1 Map showing the examined populations of the E. ruidum species complex

Chemical analyses

A total of 130 foragers collected from the foraging area were used for the chemical analyses (five ants per colony, with the exception of Huaxpaltepec with nine ants per colony, and Santo Domingo de Morelos, with six ants in one of the colonies) (Table 1). Ants were killed by freezing them in individual tubes at -20 °C after their arrival to the laboratory. The extracts of their cuticular hydrocarbons were obtained by dipping each ant separately in 100 µl of pentane supplemented with an internal standard (C18 at 5ng/µl) for 20 min. The extracts were then dried and re-diluted in 20 µl of pentane before use.

We injected 2 µl of the extract in a 7890A Gas Chromatograph (Agilent Technologies, Santa Clara, CA, USA), equipped with an HP-5MS capillary column (30 m × 250 µm × 0.25 µm) and a splitless injector, coupled to a 5975C Mass Spectrometer (Agilent Technologies) with 70 eV electron impact ionization. The carrier gas was helium at a constant flow of 1 ml/min. The temperature program was as follows: an initial hold at 70°C for 1 min, then 70 200°C at 30°C/min, then 200 300°C at 3°C/min, then 300 320°C at 20°C/min, then hold at 320°C for 3 min. Peaks areas were integrated with the MSD ChemStation software E.02.01.1177 (Agilent Technologies).

Hydrocarbons were identified based on diagnostic ions and mass spectra and compared with entries of the mass spectral library in NIST 2014 to known standards. We calculated relative abundances of hydrocarbons as ion count proportions with respect to total ion-count in the chromatogram. Thirty-one peaks were not identified because at trace levels. These unknown hydrocarbons were used for the visual representation of proportions of different classes of cuticular hydrocarbons, but were excluded from the statistical analyses.

Statistical analyses

In general, the chemical profiles of the ants of the E. ruidum species complex consisted of large numbers of very small peaks between 23 and 37 carbon atoms. Individuals from each population had both shared and population-specific hydrocarbons, which were absent in individuals from the other populations. The high number of hydrocarbons (i.e., variables) and the high number of zeros in the whole dataset of the relative abundances (population-specific hydrocarbons absent from most populations) made most statistical analyses inappropriate. Moreover, both qualitative and quantitative data are relevant when comparing the chemical profiles of different species, especially if information (e.g., colony identity) is mainly encoded in quantitative traits (Menzel et al. 2017a). Therefore, we built a simplified chemical profile of each ant which on one side reduced the number of variables for the analyses, and on the other included quantitative compositional data. For this, we grouped the hydrocarbons with the same carbon-chain length (i.e., same number of carbon atoms) by class as described by [START_REF] Elmes | Interspecific differences in cuticular hydrocarbon profiles of Myrmica ants are sufficiently consistent to explain host specificity by Maculinea (large blue) butterflies[END_REF]. For each chain length between 23 and 37 carbon atoms, we calculated the total percentage of n-alkanes, alkenes, alkadienes, methylalkanes and dimethylalkanes. The simplified chemical profiles contained 53 variables with a maximum of 5 variables per chain length (e.g., for the chain length of 25 carbon atoms, we calculated the percentage of n-C25, C25:1, C25:2, methyl-C25, dimethyl-C25 and so on for any chain length). We used the simplified chemical profiles for all statistical and exploratory analyses.

We made detailed statistical analyses of the E. ruidum sp. 3-4 from Mazunte, Puerto Escondido and Piedras Negras (Oaxaca, n = 40 ants, with at least two colonies per population). In order to investigate the amount of chemical variation among these ants we analyzed nine different traits in their cuticular chemical profiles: 1-2) NMDS scores (axis 1 and 2); 3) median chain length; 4-8) proportion of hydrocarbon classes and 9) overall proportion of hydrocarbons with an odd number of carbon atoms.

The nine traits were calculated as follows.

The NMDS scores were obtained by performing a non-parametric, descriptive analysis running Nonmetric Multidimensional Scaling (NMDS). We ran a NMDS whose scores were used to perform a further analysis (see below). In this analysis, we used the Bray-Curtis distance measures of the relative abundance of the (untransformed) simplified ant chemical profiles. We calculated the median chain length by computing the percentage of hydrocarbons for each chain length and we identified the median chain length as the lowest chain length where the cumulative sum of percentages was 50% [START_REF] Menzel | Tolerance requires the right smell: first evidence for interspecific selection on chemical recognition cues[END_REF]Menzel et al. 2017a;Menzel F. pers. comm.). We also determined the proportion of odd-chain (vs even) hydrocarbons in the chemical profile. Finally, we summarized the variation in the chemical profile of E. ruidum sp. 3-4 by entering the following traits in a Principal Component Analysis (PCA, variables standardized via correlation matrix, Varimax rotation): NMDS scores for axes 1 and 2, median chain length, proportion of the five hydrocarbon classes and overall proportion of odd-chain hydrocarbons.

We tested for differences in each chemical trait separately and in the PCs summarizing the E. ruidum sp. 3-4 ant chemical variation by running Generalized Linear Mixed Models (GLMMs) for normally distributed data (identity link), where traits were the response variables, population was the fixed factor and colony the random factor to account for the non-independence of data from ants of the same origin.

We performed a second NMDS on the complete dataset (n = 130 ants from the 11 populations) to explore the amount of chemical variation within the whole E. ruidum species complex (Bray-Curtis distance measures of the relative abundance of the simplified cuticular profiles). The small number of colonies sampled per population did not allow for statistical analyses on this data set.

All statistical analyses were conducted with the software IBM SPSS version 23. The NMDS was performed in PAST (Paleontological Statistics, version 3.25) [START_REF] Hammer | PAST: Paleontological statistics software package for education and data analysis[END_REF]. If not stated otherwise, descriptive values are given as mean ± standard errors.

Results

Species assignation

The phylogram derived from the ML analysis is given in Supplementary Material 1. Based on the clades that were recovered and on our morphological examination, we could not assign ant workers from Cozoaltepec, Punto 3 and Río Grande neither to E. ruidum sp. 3 nor sp.4. We therefore consider all populations from Oaxaca belonging to E. ruidum sp. 3-4 as a single putative species. Ants from Santo Domingo de Morelos were assigned to E. ruidum sp. 2. We could not assign the ants from Huaxpaltepec to any of the previously proposed putative species based on molecular data and thus we provisionally considered them as E. ruidum sp. 5. For the rest of populations, species identification is available in Table 1.

Chemical profile of the ants E. ruidum sp. 3-4 and median chain length

The chemical profiles of E. ruidum sp. 3-4 from Mazunte, Piedras Negras and Puerto Escondido comprised 75, 74 and 61 peaks, respectively, and they were separated in the NMDS plot (Fig. 2). Ants from Piedras Negras had variable and mainly negative values in NMDS axis 1, while those from Puerto Escondido only had positive values. While the ants from Mazunte had intermediate values in NMDS axis 1, they were fairly well differentiated from the others in the NMDS axis 2 (Fig. 2).

The median chain length of the cuticular hydrocarbons varied from 26 to 30 carbon atoms. The differences in the proportions of alkadienes, alkenes and methyl-branched alkanes were highly significant among the populations Mazunte, Puerto Escondido and Piedras Negras (alkadienes F2,37 = 3.798, P = 0.032; alkenes: F2,37 = 21.628, P < 0.0001; methyl-branched alkanes F2,37 = 18.960, P < 0.0001) (Fig. 3). In contrast, the proportions of linear alkanes and dimethyl branched alkanes did not differ significantly (linear alkanes F2,37 = 1.308, P = 0.283; dimethyl branched alkanes F2,37 = 1.810, P = 0.178).

All ants had chemical profiles extremely rich in odd-chain hydrocarbons (grand mean: 89.5% ± 0.3; Piedras Negras: 92.5 ± 0.5, Puerto Escondido: 89.5 ± 0.2, and Mazunte: 86.8 ± 0.6), but their proportions significantly differed by population (F2,37 = 30.166, P < 0.0001) (Fig. 3). There were significant differences between populations in the proportions of oddchain methylalkanes (F2,37 = 18.960, P < 0.000), alkenes (F2,37 = 21.628, P < 0.000), alkadienes (F2,37 = 3.798, P = 0.032). There were no significant differences in the proportions of odd-chain dimethylalkanes (F2,37 = 1.810, P = 0.178) and linear alkanes (F2,37 = 1.308, P =0.283).

Fig. 3 Mean proportions of: a) cuticular hydrocarbons and b) odd-chain hydrocarbons of ants E. ruidum sp. 3-4 by class

PCA on the chemical traits within E. ruidum sp. 3-4

The variation of the chemical profiles of the ants assigned to E. ruidum sp. 3-4 was summarized in two principal components that together explained 76.7% of the total variance. PC1 values (56.6 % variance explained) discriminated among the three populations (GLMM, F2,37 = 10.649, P < 0.0001). At one extreme of PC1 variation, the ants from Piedras Negras presented the highest proportions of alkenes and alkadienes (Table 2), whereas on the other extreme, ants from Puerto Escondido and Mazunte presented the highest values of NMDS axis 1 and the highest proportions of methylalkanes and dimethylalkanes (Table 2). With respect to PC2 (20.1 % variance explained), the ant profiles significantly differed by population (F2,37 = 29.032, P < 0.0001), with those from Mazunte having higher NMDS axis 2 scores and larger proportion of n-alkanes than those from Piedras Negras and Puerto Escondido (Table 2, Fig. 4).

Table. 2

Scores of the PCA factor loadings on the nine chemical traits (in bold only r > 0.700). The peaks are sorted by loading size. High loadings indicated that the trait was highly correlated with the PC.

Rotated Component Matrix

Principal Fig. 4 The PCA plot of the nine traits describing the cuticular hydrocarbon profiles of ants of E. ruidum sp. 3-4

Exploratory analysis of the chemical profiles in the E. ruidum species complex

The chemical profiles of the ants of E. ruidum sp. 3-4 had 64 peaks in Cozoaltepec and 58 in Punto 3 and Rio Grande. Ants of E. ruidum sp. 2 from Cali, Colombia, and Coyula and Santo Domingo de Morelos, Mexico, had 53, 50 and 42 hydrocarbon peaks, respectively, whereas the ones assigned to E. ruidum sp. 1 from Cantón Leoncillos, had 46 peaks. There were 55 peaks in the chemical profiles of the ants E. ruidum sp. 5 from Huaxpaltepec. Overall, we identified 12 alkadienes, 23 alkenes, 10 n-alkanes, 37 methylalkanes, 50 dimethylalkanes (Supplementary material 2). Including 31 peaks that could not be identified (unknown hydrocarbons), we had a total of 163 hydrocarbon peaks in the whole data set of E. ruidum.

The NMDS analysis performed on the simplified chemical profiles of the whole data set suggested that extensive variation might exist both within and between the putative species (E. ruidum sp. 1, sp. 2, sp. 3-4 and sp. 5) that have been proposed for the complex (Fig. 5), though no statistical analysis could be done due to the limited sample size. With respect to E. ruidum sp. 3-4, ants from Río Grande and Cozoaltepec appear as chemically distant from those of Mazunte, Puerto Escondido, Piedras Negras and Punto 3 (high negative values in NMDS axis 2). Within the E. ruidum sp. 2 samples, those from Santo Domingo de Morelos may differ from those from Coyula and Cali on the NMDS axis 1, while ants from Cali may differ from the ants of Santo Domingo de Morelos and Coyula on the NMDS axis 2.

Fig. 5 Two-dimensional Nonmetric Multidimensional Scaling ordination of the chemical profiles of the E. ruidum species complex

Discussion

The current results show striking divergences in quantitative and qualitative components in the chemical profiles of E. ruidum sp. 3-4 ant populations. Such chemical divergence largely exceeds the current taxonomic delimitation based on molecular data [START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF], indicates high intraspecific diversity within E. ruidum sp. 3-4 and highlights the need for integrative taxonomic studies. The chemical variation observed among populations of E. ruidum sp. 3-4 was particularly evident in traits involving branched and unsaturated hydrocarbons.

Within species, differences in chemical profiles are typically correlated to geographical distances. For example, distant populations (> 300 km) of the social wasp Polistes biglumis have more divergent chemical profiles than close ones (a few tens of km), although differences were typically quantitative [START_REF] Bonelli | Population diversity in cuticular hydrocarbons and mtDNA in a mountain social wasp[END_REF]. Our results, however, suggest that the divergence in the chemical profiles of E. ruidum sp. 3-4 might not be fully explained by geographical distance. The ants from Mazunte and Piedras Negras inhabit close geographic areas (< 10 km of distance), and were considered as a single species based on mtDNA genome data [START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF]), but differences in their chemical profiles exceeds the variation usually found at the intraspecific level. Therefore, factors other than geographical distance are likely to be the drivers of chemical divergence, although conclusive evidence will need extensive population sampling and focused experiments.

Cuticular hydrocarbons are typically species-specific [START_REF] Lockey | Cuticular hydrocarbons of adult Himatismus species and a comparison with 21 other species of adult tenebrionid beetle using multivariate analysis[END_REF][START_REF] Drijfhout | The role of cuticular hydrocarbons in insects[END_REF][START_REF] Guillem | Species-specific cuticular hydrocarbon stability within European Myrmica ants[END_REF]. The statistically different chemical profiles within the ants from the three populations of E. ruidum sp. 3-4 therefore support the existence of cryptic diversity in the complex. Similar examples of several chemotypes identified within single putative species were found in eusocial insects as the orchid bees of the genus Euglossa [START_REF] Pokorny | Cuticular hydrocarbons distinguish cryptic sibling species in Euglossa orchid bees[END_REF], as well as the Formica japonica [START_REF] Akino | Intraspecific variation of cuticular hydrocarbon composition in Formica japonica Motschoulsky (Hymenoptera: Formicidae)[END_REF] and Crematogaster levior and Camponotus femoratus [START_REF] Hartke | Cuticular hydrocarbons as potential mediators of cryptic species divergence in a mutualistic ant association[END_REF] ants, where variation in the quantities of branched hydrocarbons and unsaturated compounds unveiled hidden cryptic diversity. High intraspecific diversity was also found in the ant Formica archboldi, where different populations from Florida, USA, varied considerably in the abundance of methyl-branched cuticular compounds, matching the chemical profiles of different, sympatric species of Odontomachus ants more closely than those of conspecific populations [START_REF] Smith | Prey specialization and chemical mimicry between Formica archboldi and Odontomachus ants[END_REF], but genetic distance among F. archboldi ant populations is unknown.

Overall, the cuticular traits related to branched alkanes, alkenes and alkadienes were the most variable in E. ruidum sp. 3-4 ants. These classes of compounds likely play a major role in the recognition processes in social insects, and especially in nestmate-non-nestmate discrimination [START_REF] Dani | Deciphering the recognition signature within the cuticular chemical profile of paper wasps[END_REF][START_REF] Châline | Learning and discrimination of individual cuticular hydrocarbons by honeybees (Apis mellifera)[END_REF][START_REF] Lorenzi | Facultative social parasites mark host nests with branched hydrocarbons[END_REF]. For instance, [START_REF] Dani | Deciphering the recognition signature within the cuticular chemical profile of paper wasps[END_REF] showed that the supplementation of linear alkanes on alive social wasps of Polistes dominulus did not have aggression-eliciting effects on nestmates, whereas alkenes and methyl-branched alkanes did. Linear alkanes and alkenes had similar effects in Formica exsecta ants [START_REF] Martin | Chemical basis of nest-mate discrimination in the ant Formica exsecta[END_REF], where C25:1-supplemented ants were attacked by nestmates more than n-C25-supplemented ones. Linear alkanes are likely to serve mainly as waterproofing functions [START_REF] Wagner | Task-related environment alters the cuticular hydrocarbon composition of harvester ants[END_REF]d E and Lenoir 2010;[START_REF] Van Zweden | Nestmate recognition in social insects and the role of hydrocarbons[END_REF], even if not exclusively (e.g. [START_REF] Lorenzi | Cuticular hydrocarbon dynamics in young adult Polistes dominulus (Hymenoptera: Vespidae) and the role of linear hydrocarbons in nestmate recognition systems[END_REF]. Although sampling from a larger number of colonies would have increased the statistical power of our analyses, our current results on E. ruidum sp. 3-4 show that traits related to branched alkanes, alkenes and alkadienes distinguish the three different populations, whereas linear alkanes play a minor role. While E. ruidum sp. 3-4 ants have relatively similar external morphologies, they have highly diversified chemical recognition cues, and our preliminary analyses suggest that the same might be true for other taxa within the E. ruidum complex.

Environmental factors are known to affect the expression of cuticular hydrocarbons. For instance, diet changes in Linepithema humile and Acromyrmex subterraneus subterraneus ants altered chemical profiles and affected nestmate recognition [START_REF] Buczkowski | Diet-related modification of cuticular hydrocarbon profiles of the Argentine ant, Linepithema humile, diminishes intercolony aggression[END_REF][START_REF] Richard | Food influence on colonial recognition and chemical signature between nestmates in the fungus-growing ant Acromyrmex subterraneus subterraneus[END_REF]). On the other hand, in burying beetles (Nicrophorus vespilloides), differences in diet highlighted the importance of cuticular hydrocarbons as encoders of nutritional condition and other physiological states [START_REF] Steiger | The smell of parents: breeding status influences cuticular hydrocarbon pattern in the burying beetle Nicrophorus vespilloides[END_REF]). Also, abiotic factors such as air temperature and humidity affected the cuticular lipid layer of the fly Drosophila melanogaster (Rajpurohit et al. 2016). Although focused studies would be necessary to test the effect of abiotic factors on the cuticular chemical variation of E. ruidum sp. 3-4 ants, at present, there is no indication that the diet varies significantly among the populations under scrutiny. With respect to physical climatic parameters, our data suggest that linear alkanes (the likely most important waterproofing component of cuticular hydrocarbons) do not contribute significantly to the variation between populations. However, proportion of alkenes and methyl branched alkanes can also be affected by physical environmental conditions (Menzel et al. 2017b;[START_REF] Sprenger | Cuticular hydrocarbons in ants (Hymenoptera: Formicidae) and other insects: how and why they differ among individuals, colonies, and species[END_REF] making the link between function and hydrocarbon class less clear-cut.

Interspecific interactions have also been addressed as potentially relevant forces in the evolutionary change of cuticular hydrocarbons, both in quantitative and qualitative aspects. For example, living in association with other species (parabiosis) and not climatic factors may have promoted the evolution of chemical profiles characterized by longer hydrocarbons and higher proportions of branched alkenes and alkadienes among the ants of the genus Camponotus and Crematogaster (Menzel and Schmitt 2012; but see [START_REF] Sprenger | Influence of mutualistic lifestyle, mutualistic partner, and climate on cuticular hydrocarbon profiles in parabiotic ants[END_REF]. Similarly, the proportion of branched hydrocarbons was larger in two populations of Polistes biglumis social wasps that were infested by Polistes atrimandibularis social parasites than in a parasite-free population, while local climatic factors did not explain this divergence [START_REF] Lorenzi | Evolutionary consequences of deception: Complexity and informational content of colony signature are favored by social parasitism[END_REF]). On a qualitative perspective, Formica fusca and Temnothorax longispinosus ant colonies from parasitized populations had higher cue diversity than non-parasitized ones [START_REF] Martin | Is parasite pressure a driver of chemical cue diversity in ants?[END_REF][START_REF] Jongepier | Ant recognition cue diversity is higher in the presence of slavemaker ants[END_REF].

Ants of the E. ruidum complex discriminate nestmates from non-nestmates, although at different extents depending on geographic location [START_REF] Breed | Thief workers and variation in nestmate recognition behavior in a ponerine ant, Ectatomma ruidum[END_REF]. However, to our knowledge no study has tested which hydrocarbons (or which hydrocarbon classes) act as recognition cues. If branched alkanes, alkenes and alkadienes are the most important recognition cues in this ant complex, as it occurs in other social insects [START_REF] Van Zweden | Nestmate recognition in social insects and the role of hydrocarbons[END_REF], the need to distinguish between nestmates and non-nestmates may have been one of the most important pressures for the divergence of chemical cues among its species. Further studies and extended sampling are needed to test the link between local biotic and abiotic factors and CHC variation in this group.

The colonies of E. ruidum reach extremely high densities [START_REF] Pratt | Recruitment and other communication behavior in the ponerine ant Ectatomma ruidum[END_REF][START_REF] Schatz | Effect of high nest density on spatial relationships in two dominant Ectatommine ants (Hymenoptera: Formicidae)[END_REF]) and these ants exhibit intraspecific thievery, where specialized individuals consistently a b a d b c [START_REF] Breed | Thievery, home ranges, and nestmate recognition in Ectatomma ruidum[END_REF][START_REF] Carli | Études en milieu naturel du comportement de cleptobiose chez la fourmi néotropicale Ectatomma ruidum (Hymenoptera, Ponerinae)[END_REF][START_REF] Mcglynn | Distinct types of foragers in the ant Ectatomma ruidum: typical foragers and furtive thieves[END_REF]. Although in some populations these ants have a relatively permissive non-nestmate acceptance threshold [START_REF] Breed | Thievery, home ranges, and nestmate recognition in Ectatomma ruidum[END_REF][START_REF] Carli | Études en milieu naturel du comportement de cleptobiose chez la fourmi néotropicale Ectatomma ruidum (Hymenoptera, Ponerinae)[END_REF][START_REF] Jandt | Intraspecific food-robbing and neighborhood competition: consequences for anti-robber vigilance and colony productivity[END_REF], high nest density and thievery might have promoted stricter acceptance thresholds in other populations. Intruder acceptance thresholds are usually plastic and are adjusted to local food availability (d E et al. 2004;[START_REF] Jandt | Intraspecific food-robbing and neighborhood competition: consequences for anti-robber vigilance and colony productivity[END_REF], as well as thievery frequency in E. ruidum ants [START_REF] Guénard | Intraspecific thievery in the ant Ectatomma ruidum is mediated by food availability[END_REF]).

E. ruidum species complex has a broad Neotropical distribution range but to our knowledge E. ruidum sp. 3-4 ants are found only in a relatively small geographic area in the state of Oaxaca. The distribution of the E. ruidum complex of closely related species [START_REF] Aguilar-Velasco | Uncovering species boundaries in the Neotropical ant complex Ectatomma ruidum (Ectatomminae) under the presence of nuclear mitochondrial paralogues[END_REF]Meza-Lazaro et al. 2018) might reflect a mosaic sympatry (sensu [START_REF] Mallet | Space, sympatry and speciation[END_REF]) and be the result of non-allopatric speciation events originating from polymorphism in recognition cues. Intraspecific parasitic interactions favor genetic divergence (e.g. [START_REF] Savolainen | Sympatric speciation through intraspecific social parasitism[END_REF] and the maintenance of variation in recognition cues [START_REF] Crozier | Genetic clonal recognition abilities in marine invertebrates must be maintained by selection for something else[END_REF]). E. ruidum ants exhibit cleptobiosis [START_REF] Breed | Thievery, home ranges, and nestmate recognition in Ectatomma ruidum[END_REF][START_REF] Carli | Études en milieu naturel du comportement de cleptobiose chez la fourmi néotropicale Ectatomma ruidum (Hymenoptera, Ponerinae)[END_REF], which is a form of parasitic interactions [START_REF] Breed | Cleptobiosis in social insects[END_REF][START_REF] Guénard | Intraspecific thievery in the ant Ectatomma ruidum is mediated by food availability[END_REF]. For the foregoing reasons, it is suggestive to draw an evolutionary scenario where high colony density and high risk of colony intrusion by intraspecific thief ants (cleptobiosis) may have promoted polymorphism in recognition cues (via disruptive selection) and this in turn may have favored genetic divergence within the species complex. This hypothesis needs to be tested in future studies exploring the association between thievery, intruder acceptance threshold and variation in cuticular hydrocarbons in different populations to explore the role of recognition cues in the speciation process.

Fig. 2

 2 Fig. 2 Two-dimensional Nonmetric Multidimensional Scaling ordination of the chemical profiles of E. ruidum sp. 3-4 Variation in the classes of hydrocarbons within E. ruidum sp. 3-4

  Fig e

Table 1 Collection sites of the Ectatomma ruidum ants.

 1 *Sampling: original sampling means that the ants used for the analyses of the cuticular hydrocarbons were studied by[START_REF] Aguilar-Velasco | Uncovering species boundaries in the Neotropical ant complex Ectatomma ruidum (Ectatomminae) under the presence of nuclear mitochondrial paralogues[END_REF][START_REF] Meza-Lázaro | Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)[END_REF]; new sampling refers to the newly collected ants.

						Number of workers
	Species		Locality	State, Country	Coordinates	used in chemical analysis	Gen Bank accession number	References
						(number of colonies,
						sampling**)
	1		Cantón Leoncillos	Chiapas, Mexico	14°45'59.00"N/ 92°24'12.00"W	20 (4, original sampling )	KU570636-39	Aguilar-Velasco et al. 2016
			Cali	Cali, Colombia	3 22 39"N/ 76 31 52 W	10 (2, original sampling)	MG870224	Meza-Lázaro et al. 2018
	2		Coyula	Oaxaca, Mexico	15°45'2.85"N/ 96°17'51.05"W	10 (2, original sampling)	MN957982-85	Aguilar-Velasco et al. 2016
			Santo Domingo de Morelos	Oaxaca, Mexico	15°50'34.00"N/ 96°40'11.00"W	11 (2, new sampling)	MN848418-19	This paper
		3*	Puerto Escondido	Oaxaca, Mexico	15°56'24.00"N / 97° 4'15.60"W	20 (4, original sampling)	KU570668	Meza-Lázaro et al. 2018/ *Aguilar-Velasco et al. 2016
	3-4	4*	Mazunte Piedras Negras	Oaxaca, Mexico Oaxaca, Mexico	15°41'7.44"N/ 96°33'42.48"W 15°43'30.00"N/ 96°39'36.00"W	10 (2, original sampling) 10 (2, original sampling)	KU570662-64 MG870246	Meza-Lázaro et al. 2018/ *Aguilar-Velasco et al. 2016
			Cozoaltepec	Oaxaca, Mexico	15°45'44.80"N/ 96°42'41.01"W	10 (1, new sampling)	MN848420-21	This paper
			Punto 3	Oaxaca, Mexico	15°57'24.84"N/ 97°11'46.32"W	10 (1, new sampling)	MN848417	This paper
			Río Grande	Oaxaca, Mexico	16° 1'8.76"N/ 97°26'26.16"W	10 (1, new sampling)	MN848415-16	This paper
	5		Huaxpaltepec	Oaxaca, Mexico	16°20'26.00"N/ 97°57'34.00"W	9 (1, new sampling)	MN848413-14	This paper

*

Centre de Recherches sur la Cognition Animale, Centre de Biologie Intégrative, Université de Toulouse CNRS, UPS, 118 route de Narbonne, 31062 Toulouse Cedex 09, France.

Acknowledgments

This study is part of the PhD project of KIPC supported by a CONACyT-French government scholarship and partially funded by a grant given by DGAPA UNAM (Proyecto PAPIIT no. IN201119) and CONACyT (Programa Ciencia de Frontera convocatoria 2019, project No. 58548) to AZR and by a grant given by the Ecos-Nord-CONACYT Program (proyecto no.M12A01) to AZR and CP. Thanks to Jovanna Jasso, Sian Gadelha, Jorge Guitérrez, Carlos Santamaria and Gabriela Pérez-Lachaud for their help during the field trips in Oaxaca, México. We also thank two anonymous referees for valuable feedback on previous versions of the manuscript.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.


Wesley D Attilo
email: wdattilo@hotmail.com

Miguel V Asquez-Bola

Diana A Ños

Reuber Ahuatzin

Edgar Antoniazzi

Avez-Gonz Ch

Erick Alez

Pedro Corro

Roger Luna

Fabricio Guevara

Ricardo Villalobos

J Madrigal-Chavero

C Essica

Falc De Faria

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A N Adri

AGUST IN Rafael Bonilla-Ram Irez

I A Garc

Aldo Romero

L A De

Alfredo Mora

Irez-Hern Ram

Ana Andez

Escalante-Jim Leticia

Ana P Enez

Inez-Falc Mart

ANDR Es I On

Ashley Villarreal

O N Col

BOL Ivar Sandoval

Brenda Aponte

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Citlalli Arez

Claudia E Castillo-Guevara

Cristopher Moreno

Dora Albor

Mart Luz

Elisabeth Inez-Tlapa

Federico Huber-Sannwald

Fernando J Escobar

Fernando Montiel-Reyes

Varela-Hern

Gabriela Andez

Gabriela P Casta Ño-Meneses

GIBR A N Erez-Lachaud

P Renoy

Irene Erez-Toledo

A-Mart Alcal

Iris Inez

Rivera-Salinas Saraeny

Isa Ias

Chairez-Hern Andez

Ivette A Chamorro-Florescano

Jaime Hern

Javier Mart

Inez Toledo

JES US LUMAR Jean-Paul Lachaud

Reyes-Mu Ñoz

Jorge E Valenzuela-Gonz

Jorge Alez

Ictor Horta-Vega

Domingo Cruz-Labana

Javier Reynoso-Campos

L Navarrete-Heredia

Juan Antonio

Rodr Iguez-Garza

Juan Francisco

P Erez-Dom Inguez

Julieta Ben Itez-Malvido

Katherine K Ennis

Laura S Aenz

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Luis Antonio

Tarango-Ar Ambula

Luis N Quiroz-Robedo

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MAR IA Margarita Villalvazo-Palacios

G Omez-Lazaga

Mariana Cuautle

Mario J Aguilar-M Endez

Martha L Baena

Martha Madora-Astudillo

Maya Rocha-Ortega

Michel Pale

Miguel A Garc

Ia-Mart Inez

Miguel Angel Soto-C Ardenas

Miguel Mauricio Correa-Ram Irez

Milan Janda

REN Patricia Rojas

E Torres-Ricario

Robert W Jones

Rosamond Coates

Sandra Luz

SA G Omez-Acevedo

U L Ugalde-Lezama

Stacy M Philpott

Tatiana Joaqui

Tatianne Marques

Veronica Zamora-Gutierrez

Viviana Mart

Inez Mandujano

Mauricio Correa-Ramírez

René Torres-Ricario

Sandra Luz Gómez-Acevedo

Saúl Ugalde- Lezama

Veronica Zamora- Gutierrez

Viviana Martínez Mandujano

Zachary Hajian-Forooshani

Ian Macgregor-Fors

Mexico ants: incidence and abundance along the Nearctic-Neotropical interface

Keywords: biodiversity hotspot, Formicidae, geographic range, Hymenoptera, inventory, Mexican fauna, sampling methods, species abundance, species incidence

Mexico is one of the most biodiverse countries in the world, with an important proportion of endemism mainly because of the convergence of the Nearctic and Neotropical biogeographic regions, which generate great diversity and species turnover at different spatial scales. However, most of our knowledge of the Mexican ant biota is limited to a few well-studied taxa, and we lack a comprehensive synthesis of ant biodiversity information. For instance, most of the knowledge available in the literature on Mexican ant fauna refers only to species lists by states, or is focused on only a few regions of the country, which prevents the study of several basic and applied aspects of ants, from diversity and distribution to conservation. Our aims in this data paper are therefore (1) to compile all the information available regarding ants across the Mexican territory, and (2) to identify major patterns in the gathered data set and geographic gaps in order to direct future sampling efforts. All records were obtained from raw data, including both unpublished and published information. After exhaustive filtering and updating information and synonyms, we compiled a total of 21,731 records for 887 ant species distributed throughout Mexico from 1894 to 2018. These records were concentrated mainly in the states of Chiapas (n = 6,902, 32.76%) and Veracruz de Ignacio de la Llave (n = 4,329, 19.92%), which together comprise half the records. The subfamily with the highest number of records was Myrmicinae (n = 10,458 records, 48.12%), followed by Formicinae (n = 3,284, 15.11%) and Ponerinae (n = 1,914, 8.8%). Most ant records were collected in the Neotropical region of the country (n = 12,646, 58.19%), followed by the Mexican transition zone (n = 5,237, 24.09%) and the Nearctic region (n = 3,848, 17.72%). Native species comprised 95.46% of the records (n = 20,745). To the best of our knowledge, this is the most complete data set available to date in the literature for the country. We hope that this compilation will encourage researchers

INTRODUCTION

Ants (Hymenoptera: Formicidae) are one of the most diverse, abundant and ecologically important taxa in most terrestrial environments (Hölldobler andWilson 1990, Lach et al. 2010), with most species diversity currently found in the New World tropics and subtropics [START_REF] Moreau | Testing the museum versus cradle tropical biological diversity hypothesis: phylogeny, diversification, and ancestral biogeographic range evolution of the ants[END_REF]. The main characteristics that lead ants to be successful and notably ecologically important in the most diverse habitats and environmental conditions across the globe are the great variety of food resources that they use, together with their social and nesting behaviors (Hölldobler andWilson 2009, Andersen 2019). Moreover, ants are critical participants in multiple ecosystem services and regulate fundamental ecological processes, such as the improvement of soil aeration, plant pollination, and nutrient cycling [START_REF] Schultz | The interactions of ants with other organisms[END_REF][START_REF] Rico-Gray | The ecology and evolution of ant-plant interactions[END_REF][START_REF] Hölldobler | The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies[END_REF].

A total of 13,594 described valid ant species are known globally (including synonyms and excluding subgenera, subspecies, and fossil taxa), and are distributed within 17 subfamilies and 334 genera [START_REF] Bolton | An online catalog of the ants of the world[END_REF]. Despite the high number of synonyms made every year, based on the yearly rate of descriptions of new species and the estimated number of species still not scientifically named, the total number of existing ant species is estimated to be about 30,000 [START_REF] Fisher | Biogeography[END_REF]. Regardless of the high diversity and great ecological importance of ants, there are gaps in our information about their diversity and distribution, and the lack of a synthesis limits knowledge of these organisms in some regions of the world [START_REF] Alonso | Ant conservation: current status and a call to action[END_REF][START_REF] Guénard | The Global Ant Biodiversity Informatics (GABI) database: synthesizing data on the geographic distribution of ant species (Hymenoptera: Formicidae)[END_REF].

Mexico is one of the top five richest countries in terms of biodiversity and endemism [START_REF] Mittermeier | Megadiversity. Earth's Biologically Wealthiest Nations[END_REF]. The great diversity and turnover of species throughout the Mexican territory have been associated with its large variety of ecosystems (from deserts to tropical rainforests) and the topographic complexity of the territory, with elevations ranging from 0 up to almost 6000 m above sea level [START_REF] Sarukhán | Biological conservation in a high beta-diversity country[END_REF][START_REF] Arita | The non-volant mammal fauna of Mexico: species richness in a megadiverse country[END_REF][START_REF] Campbell | Distribution patterns of amphibians in Middle America[END_REF]. Moreover, in central Mexico, the southern and northern limits of the Nearctic and Neotropical biogeographic regions, respectively, converge, bringing into contact biotas with marked evolutionary histories that, together with endemism, increase biodiversity in the country [START_REF] Halffter | Biogeography of the montane entomofauna of Mexico and Central America[END_REF]Morrone 2017). Although Mexico is an important biodiversity hotspot and an interesting biogeographic area, most of the knowledge about its biota has been historically focused on the study of plants (Rzedowski and Huerta 1994[START_REF] Llorente-Bousquets | Estado del conocimiento de la biota[END_REF][START_REF] Villaseñor | Checklist of the native vascular plants of Mexico[END_REF]) and vertebrates [START_REF] Rodríguez | El componente beta de la diversidad de mamíferos de México[END_REF][START_REF] Rojas-Soto | Forecasting cloud forest in eastern and southern Mexico: conservation insights under future climate change scenarios[END_REF][START_REF] Álvarez-Castañeda | DNA barcoding of mammals in Mexico: implications for biodiversity[END_REF], with other groups such as arthropods, including ants, inevitably often neglected.

A total of 973 ant species are currently known from Mexico (ca. 6% of the world's total) (AntWeb 2019). The first zoological study that attempted to synthesize information about the ant fauna in the country dates back only to the mid-1990s and reported 501 ant species [START_REF] Rojas-Fernández | Formicidae (Hymenoptera)[END_REF]. There has been no comprehensive effort to synthesize knowledge on the diversity of Mexican ants since then and knowledge of the geographic distribution of ants across Mexico has been particularly scarce. Because little is known about the geographic distribution of ant species across Mexico, the available databases with a global focus fail to accurately represent Mexican ant distribution (e.g., [START_REF] Gibb | A global database of ant species abundances[END_REF][START_REF] Guénard | The Global Ant Biodiversity Informatics (GABI) database: synthesizing data on the geographic distribution of ant species (Hymenoptera: Formicidae)[END_REF], Parr et al. 2017). Most of the available knowledge on Mexican ants in the literature refers to information such as species lists within broad political divisions in the country, such as states [START_REF] Vásquez-Bolaños | Lista de especies de hormigas (Hymenoptera: Formicidae) para México[END_REF][START_REF] Vásquez-Bolaños | Taxonomía de Formicidae (Hymenoptera) para México[END_REF] or focuses on only a few habitat types (e.g., tropical dry and rain forests) (Ríos-Casanova 2014, [START_REF] Ahuatzin | Forest cover drives leaf litter ant diversity in primary rainforest remnants within human-modified tropical landscapes[END_REF]. The current lack of systematic records on ant species diversity and distribution limits research on a large spatial scale, and, therefore our ability to answer key questions, such as about the threats to ants from landscape modification, climate change and invasive species. Based on all the above, we believe that compiling the information currently available for Mexican ants could allow the use of spatially explicit information regarding distributions of this insect group in a megadiverse country.

In this data paper, we compiled all the available published and unpublished geographic information (including both incidence and abundance records) about native and exotic ant species recorded within Mexico over 124 years (from 1894-2018). After exhaustive filtering, the updating of information and the curation of synonyms, our data set contains 21,731 records of 887 ant species distributed throughout Mexico. To the best of our knowledge, this is the most complete data set available in the literature for the country at the moment. We hope that this compilation of the MEXICO ANTS data set will encourage researchers to explore different aspects of the population and community ecology of ants, and will provide useful information for establishing conservation policies and actions. Just as we were encouraged by the incredible work of the ATLANTIC SERIES initiative, whose objective is to compile all sorts of information from this biodiversity hotspot, we hope that our data set stimulates other Mexican research groups to organize their collections and data and make them publicly available.

ABSTRACT

Mexico is one of the most biodiverse countries in the world, with an important proportion of endemism mainly due to the convergence of the Nearctic and Neotropical biogeographic regions, which generate great diversity and species turnover at different spatial scales. However, most of our knowledge of the Mexican ant biota is limited to a few well-studied taxa, and we lack a comprehensive synthesis of ant biodiversity information. For instance, most of the knowledge available in the literature on Mexican ant fauna refers only to species lists by states, or is focused on only a few regions of the country, which prevents the study of several basic and applied aspects of ants, from diversity and distribution to conservation. Our aims in this data paper are therefore to (i) compile all the information available regarding ants across the Mexican territory, and (ii) identify major patterns in the gathered dataset and geographic gaps in order to direct future sampling efforts. All records were obtained from raw data, including both unpublished and published information. After exhaustive filtering and updating information and synonyms, we compiled a total of 21,731 records for 887 ant species distributed throughout Mexico from 1894 to 2018. These records were concentrated mainly in the states of Chiapas (n= 6,902, 32.76%) and Veracruz de Ignacio de la Llave (n= 4,329, 19.92%), which together comprise half the records. The subfamily with the highest number of records was Myrmicinae (n=10,458 records, 48.12%), followed by Formicinae (n= 3,284, 15.11%) and Ponerinae (n= 1,914, 8.8%). Most ant records were collected in the Neotropical region of the country (n= 12,646, 58.19%), followed by the Mexican transition zone (n= 5,237, 24.09%) and the Nearctic region (n= 3,848, 17.72%).

Native species comprised 95.46% of the records (n= 20,745). To the best of our knowledge, this is the most complete data set available to date in the literature for the country. We hope that this compilation will encourage researchers to explore different aspects of the population and community research of ants at different spatial scales, and to aid in the establishment of conservation policies and actions. There are no copyright restrictions. Please cite this data paper when using its data for publications or teaching events. D. Keywords: biodiversity hotspot, Formicidae, geographic range, Hymenoptera, inventory, Mexican fauna, sampling methods, species abundance, species incidence.

E. Description

We selected all continental land and islands and merged all polygons into a single shapefile to organize the data set of ant records within the Mexican territory (Fig. 1). Our data set is comprised of 21,731 records of ants with taxonomic certainty to species-level identification. Our ant records were obtained from 242 different data collectors who were individually responsible for 4,683 records (21.55%), and 3,149 records (14.49%) that were the joint efforts between two and four collectors. This information was not available for the remaining 14,569 records (63.96%). Only 23 collectors contributed more than 50 ant records (Fig. 2). It is important to note that, in our data set, 'collectors' are defined as people who personally retrieve the specimens from the field. We extracted the state and municipality names from the latitudinal and longitudinal information of our ant records using the current and official shapefile from the National Institute of Statistics and Geography of Mexico (INEGI) in a WGS84 projection and with a spatial resolution of 250 m (Available at: http://www.conabio.gob.mx/informacion/metadata/gis/muni_2018gw.xml?httpcache=yes &_xsl=/db/metadata/xsl/fgdc_html.xsl&_indent=no). We obtained records from 32 Mexican states, however, these records are mainly concentrated in a few states (Fig. 1 and 3). The states of Chiapas (n = 6,902, 31.76%), and Veracruz de Ignacio de la Llave (n = 4,329, 19.92%) hold just over half the records, and Colima (n = 50, 0.23%), Ciudad de México (n = 40, 0.18%), and Aguascalientes (n = 39, 0.18%) each have only a handful of records. There are ant records for 829 different municipalities, with Ocosingo (state of Chiapas) and San Andrés Tuxtla (state of Veracruz de Ignacio de la Llave) holding the highest number of records, 2,703 (12.44%) and 1,211 (5.57%) respectively (Fig. 4). We obtained 15,916 ant records (73.24%) made within 96 different plant associations and land cover types. Note that the collectors made these classifications directly in the field, and most were made in tropical rainforest (n = 5,811, 26.74%), secondary forest (n = 1,299, 5.98%) and cloud forest (n = 1,247, 5.73%) (Fig. 5). We characterized the environmental conditions and elevation at the sampling points for all records from the geographical coordinates (i.e., latitude and longitude information) of the sampling sites. To do this, we first overlapped all geographical coordinates with the climate layers, using the "extract" function of the raster package [START_REF] Hijmans | Raster: geographic analysis and modelling with raster data[END_REF] in the R program (R Core Team 2017). The raster files corresponding to the annual mean temperature and precipitation values were obtained from the WorldClim database version 2 (http://www.worldclim.org/version2) with a spatial resolution of 30 seconds/~1 km 2 ). We used the SRTM Digital Elevation database version 4.1 to obtain elevation data, (https://cgiarcsi.community/data/srtm-90m-digital-elevation-database-v4-1/) with a spatial resolution of 250 m. The elevation of our sampling sites ranged from 0 to 3,685 m (mean ± SD: 763 ± 715 m a.s.l.), and most sites (n = 14,126, 65,00%) are below 1,000 m in elevation, followed by the categories: (i) from 1,000 m up to the limit of the 2,000 m mark with 5,628 records (25.90%); (ii) from 2,000 m up to the limit of the 3,000 m mark with 1,599 records (7.36%); and (iii) those above 3000 m with only 15 records (0.07%) (Fig. 6). The mean annual temperature of the sampling sites ranged from 5.74 to 28.55 °C (mean ± SD: 21.72 ± 3.56 °C) and was concentrated mainly between 20 and 28.55° C (n = 15,489 records, 71.28%) (Fig. 6). The mean annual precipitation of the sampling sites ranged from 53.59 to 4557 mm (mean ± SD: 1645.8 ± 1020.45 mm), although most of the sampling sites were concentrated between 1,000 and 3,000 mm of rainfall (n = 11,304 records, 52.02%) (Fig. 6). transported to Mexico beyond their natural geographic dispersal barriers) (n = 614, 2.83%), and those classified as exotic and invasive (i.e., those ant species which are naturally or transported by humans to Mexico, and that decrease the local diversity of native species mainly through competitive displacement) (n = 372, 1.71%) (Fig. 12). We were able to determine whether the sampling records were inside (n = 2,849, 39.97%) or outside (n = 4,279, 60.03%) protected areas for 32.80% (n = 7,128) of records (Fig. 13). When fragment sizes could be obtained directly by the authors or through the information available for protected areas (SEMARNAT-CONANP 2017) (n=4122, 18.96 %), they ranged from 0.14 to 723.185 ha, in which 25.16% of the fragments were less than 100 ha in size (Fig. 14). Of the ant records recorded inside protected areas, 33.45% (n = 953) were from the Estación de Biología Tropical Los Tuxtlas, followed by Reserva de la Biósfera Los Tuxtlas (n = 590, 20.71%), and Centro de Investigaciones Costeras La Mancha (n = 273, 9.58%) (Fig. 15). Fragment size was obtained either directly from the authors or through the information available for protected areas. Of the sample methods used to obtain all records (n= 10,828), 41.51% of records were collected by hand (n = 2,932) or with pitfall traps (n = 1,563) (Fig. 16). Most of our records (n = 16,001, 73.63%) are of species incidence rather than ant abundance (n = 5,130, 23.61%) (Fig. 17). Of the 50 different scientific collections where the ants are deposited, the CAS-ENT Entomology Collection (California Academy of Sciences, United States of America), IEXA Entomological Collection (Instituto de Ecología A.C., Mexico), and CZUG Entomological Collection (Universidad de Guadalajara, Mexico) have the highest number of records, with 5,414 (38.88%), 3,315 (23.81%) and1,387 (9.96%) records respectively (Fig. 18). Although we compiled information on records for 124 years (1894 to 2018), more than 90% of the records were from between 2000 and 2018 (Fig. 19). 33.88% of the ant records were obtained from databases (i.e., those records available within official online repositories such as collections, GBIF and SNIB-CONABIO), only (n = 7,363), 32.25% were obtained from scientific papers (n = 7,009), and 24.16% were from unpublished data (i.e., records that are not available publicly, but were sent directly by the authors) (n = 5,251). Another 9.71% were obtained from various other sources, such as records from iNaturalist observations, records from abstracts of scientific meetings, non-digitized records of collections and personal websites), as well as book chapters, thesis, and books (n = 2,188) (Fig. 20). We separated published records (n = 16,480, 75.83%) into study categories. We found that most studies were diversity studies (i.e., inventories, checklists, surveys) (n= 12,972 records, 78.71%), followed by taxonomy and systematics studies (i.e., taxa descriptions, revisions, morphology, genetics, phylogenies and evolution) (n= 1,782 records, 10.81%), ecological studies (i.e., population, community and other hypothesis-based ecological studies) (n= 1,460 records, 8.85%), and studies on ant control and management (i.e., economical and sanitary impact of ants) (n= 266 records, 1.61%) (Fig. 21).

B. Specific subproject description

Site description: We adopted a broad delimitation of the Mexican territory according to the National Institute of Statistics and Geography of Mexico (INEGI 2018) (Fig. 1), which encompasses several biomes and biogeographical regions, thus ensuring a more comprehensive inclusion of ant inventories in the country.

Data compilation: Data was obtained from raw unpublished data (records, reports, databases) and published information (including books, book chapters, scientific papers, and thesis). We searched for potential information in the following sources: (i) online academic databases (e.g., Scielo, Scopus, ISI Web of Knowledge, Google Academic, GBIF, EncicloVida/CONABIO, iNaturalist); (ii) references cited in literature, and (iii) by formal petition through direct contact with authors and other experts to request the contribution of their raw data. The searches were performed with the following keywords: ant(s), inventory(ies), and Mexico. Search terms in the academic databases were used in English, Spanish, and Portuguese. Ant records were compiled from 282 studies (for more detailed information, please see our data set) and our own observations. Our basic criteria included information on the geographical coordinates of the records (i.e., latitude and longitude) and the identification of specimens to species level. Missing information was labeled "NA" in the data set. We used the following filters for records extracted from iNaturalist (https://www.inaturalist.org): (i) quality rating: "Research", (ii) revised: "Yes", (iii) identification: "Most users agree", (iv) country: "Mexico", (v) species or group: "Formicidae", and (vi) exact range: "Species".

Taxonomic data: We used the taxonomic names provided by the AntWeb/California Academy of Sciences (2019), which is derived from three sources: The Bolton Catalog of ant names (https://www.antweb.org/world.jsp), specimen records, and user-created species lists (e.g., regions and projects). We therefore updated the identity of some ant species to the most recent nomenclature.

Validation: Specialists (Dr. Miguel Vásquez Bolaños and Dr. Wesley Dáttilo) verified all information compiled and excluded records that were erroneous (i.e., names for each ant species, synonyms, and duplicate data). Sampling coordinates were verified using the World Geodetic System (WGS84) as the spatial reference system gathering all records within the extent of the Mexican territory. Specifically, we searched for extreme values, corrected any transcription errors and homogenized taxonomic information.

C. Data limitations and potential enhancements

Ants are an extremely diverse group in terms of species richness, habitat use and behavior, however, many taxonomic groups are represented by cryptic species, mainly leaf litter ants. For this reason, we did not compile information on ant morphotype records, since these morphotypes from different research groups and scientific papers are not comparable. In this sense, we prefer to be conservative in using only species identified to the species level and validating the species name to the most recent taxonomy and adjoining synonyms.

Despite the large number of records that we were able to compile (21,731 records involving 887 ant species), this represents only a subset of one of the planet's most diverse terrestrial organisms. In fact most of the states of Mexico (n = 21, 65.63%) had fewer than 300 ant records, indicating that most of the country is under-sampled and this fauna is underestimated. Many records come from indirect sampling, or samples resulting from studies that were not directly intended to study ants, such as studies of the diets of other animals (birds and lizards), fossils, culinary practices, and funerary bundles. This type of data is extremely important for ant records, as it complements traditional sampling methods. We also used 670 records (3.08%) from the citizen science website iNaturalist (https://www.inaturalist.org), a website that allows naturalists to map and share photographic observations of biodiversity across the globe. The identification of those records may not always be reliable, however, and, therefore we left the source information of the record, allowing the potential users of this data paper to choose whether or not to use such records. One major limitation of our database is the difference in the standardization of sampling methods and efforts, which means that the ant communities in many regions cannot be compared with each other. Another limitation in our dataset is the classification of vegetation and land cover types. Although this classification was made directly in the field by collectors, which makes the records reliable, there could be limitations to the standardization of categories between different records. Accordingly, we suggest caution in using this information to avoid inappropriate inferences. It is also important to note that in some of the compiled studies, the authors do

Fig. 1 .

 1 Fig. 1. Distribution of the 21,731 records in the MEXICO ANTS data set throughout the

Fig. 2 .

 2 Fig. 2. Number of records per collector (only those people with more than 50 records are

Fig. 3 .

 3 Fig. 3. Number of records per state within the MEXICO ANTS data set.

Fig. 4 .

 4 Fig. 4. Number of records per municipality (only those with more than 100 records are

Fig. 5 .

 5 Fig. 5. Number of records per vegetation or land cover type (only those with more than

Fig. 6 .

 6 Fig. 6. Variation of elevation, mean annual temperature, and mean annual precipitation

Fig. 7 .

 7 Fig. 7. Number of records per ant subfamily within the MEXICO ANTS data set.

Fig. 8 .

 8 Fig. 8. Number of records per ant genus (only those with more than 250 records are

Fig. 9 .

 9 Fig. 9. Number of records per ant species (only those with more than 150 records are

Fig. 10 .

 10 Fig. 10. Number of records per specialist who identified the ants (only those with more

Fig. 11 .

 11 Fig. 11. Number of records in each biogeographical region (i.e., Neotropical, Nearctic or

Fig. 12 .

 12 Fig. 12. Number of records of native, exotic, and both exotic and invasive ant species

Fig. 13 .

 13 Fig. 13. Number of records outside (No) or inside (Yes) protected areas within the

Fig. 14 .

 14 Fig. 14. Rank of the fragment size distributions within the MEXICO ANTS data set.

Fig. 15 .

 15 Fig. 15. Number of ant records per protected area within the MEXICO ANTS data set.

Fig. 16 .

 16 Fig. 16. Number of records per sampling method within the MEXICO ANTS data set.

Fig. 17 .

 17 Fig. 17. Number of records by data category (incidence or abundance) within the

Fig. 18 .

 18 Fig. 18. Number of records per scientific collection within the MEXICO ANTS data set.

Fig. 19 .

 19 Fig. 19. Distribution of the number of records from 1894 to 2018 within the MEXICO

Fig. 20 .

 20 Fig. 20. Number of records per reference type within the MEXICO ANTS data set.

Fig. 21 .

 21 Fig. 21. Number of records per category of study within the MEXICO ANTS data set.

Table 1 . Description of the fields related to the data set linked to the file MEXICO_ANTS_DATASET.csv.

 1

	Variables	Description	Levels	Example
		Person or
		people
	Collector	responsible for	355	Dáttilo, W.
		collecting the
		record
		Corrected and
		transformed
	Longitude	coordinates of longitude in decimal	decimal degree	-92.33593
		degrees (Datum
		WGS84)
		Corrected and
		transformed
	Latitude	coordinates of latitude in decimal	decimal degree	15.17067
		degrees (Datum
		WGS84)
	Country	English name of the country	Mexico	Mexico

Centro de Investigación en Biodiversidad y Conservación, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, Mexico. Unidad de Morfología y Función, Facultad de Estudios Superiores Iztacala, Tlalnepantla, Estado de México, Mexico Centre de Recherches sur la Cognition Animale, Centre de Biologie Intégrative, Université de Toulouse UPS, Toulouse, Cedex, France. Facultad de Ciencias Biológicas, Universidad Juárez del Estado de Durango, Gómez Palacio, Durango, Mexico. Instituto Tecnológico de Cd. Victoria, Cd. Victoria, Tamaulipas, Mexico. Posgrado en Recursos Genéticos y Productividad-Ganadería, Colegio de Postgraduados Campus Montecillo, Texcoco, Estado de México, Mexico. División de Ciencias e Ingeniería, Universidad de Quintana Roo, Chetumal, Quintana Roo, Mexico. Campo Experimental Centro Altos de Jalisco, Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, Tepatitlán de Morelos, Jalisco, Mexico. Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico. Environmental Studies Department, University of California, Santa Cruz, California, United States of America. Escuela de Biología, Universidad de San Carlos de Guatemala, Ciudad de Guatemala, Guatemala. Posgrado de Innovación en Manejo de Recursos Naturales, Colegio de Postgraduados Campus San Luis Potosí, Salinas de Hidalgo, San Luis Potosí, Mexico

ACKNOWLEDGMENTS:

The authors W. Dáttilo and J.C.F. Falcão dedicate this work to Cauê Dáttilo de Faria (our first child who was born while we were compiling the metadata for this manuscript). We thank the MEXICO ANTS team, who made this work possible. We would like to thank A. Angeles, A.B. Viana-Jr, A. A. García-Ballinas, Carta, A.C. Velázquez-Narváez, A. Larsen, B. Bautista, B. Chilel, C. Leal, C. Murnen, C. Rivera, C. Salazar, D. Garcia-Moreno, D. Gloede, D. Gonthier, D. Villafranca, F.H. Rocha, F. Luna-Castellanos, G. Dominguez-Martínez, G. Lopez-Bautista, I. Astorga, I. Mendoza, J.M. Mora (El General), J. Hernández, J. Pelayo, J. Vadillo-Hernández, Jamangape family, K. Andalco, L.E. Cavanzón-Medrano, L. Hernández, M. Alfaro, M.E. Cruz, M. Harris, M. Rocha-Ortega, N. López, N.M.Tagüeña, O. Trujillo, P. Bichier, P. Gillette, P. Nava, P. Sinaca-Colín, R. Mateo, R. Sotelo, S. Jiménez, S. Sinaca-Colín, V.R. Gómez, V.V. Catzim for their field work assistance. We are indebted to R. Coates and A. Campos for their support at Los Tuxtlas Biological Station; Familia Ávila for their support in Pinotepa Nacional. P.S. Ward and R. Johnson for providing the data set for the ants of Baja California. J. Vandermeer, I. Perfecto, P. Foster, Z. Serber, R. Rice, and R. Greenberg provided support with study design and to the farm owners W. Peters, I. Hoffmann, B. Gisemann in Chiapas. The authors thank D.L.M. Tlapa, J.M. Lobato, J.M. Trejo, and R.L. Estrada for their technical assistance. Special thanks to J.H.C. Delabie. J.

Longino, M. Rocha-Ortega, M. Vásquez Bolaños, V. Meléndez-Ramírez for ant identification. Some of the records were kindly made available by the Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (CONABIO). EncicloVida2016 (Online database: http://www.enciclovida.mx). We thank the researchers cited in this data paper for all their scientific efforts. This data paper was motivated and inspired by the data

The subfamily with the most records was Myrmicinae (n = 10,458, 48.12%), followed by Formicinae (n = 3,284, 15.11%), Ponerinae (n = 1,914, 8.81%), Pseudomyrmecinae (n = 1,863, 8.57%), Dolichoderinae (n = 1,802, 8.29%), Dorylinae (n = 1,077, 4.96%), Ectatomminae (n = 788, 3.63%), Proceratiinae (n = 293, 1.35%), Amblyoponinae (n = 222, 1.02%) Agroecomyrmecinae (n = 19, 0.09%) Heteroponerinae (n = 11, 0.05%) (Fig. 7). Our records are distributed among 96 genera of ants, where Camponotus (n = 2,122, 9.76%), Pseudomyrmex (n = 1,863, 8.57%), and Pheidole (n = 1,536, 7.07%) were the genera with the largest number of records, accounting for 25.41% of all records. The genera Discothyrea, Mycetophylax, Myrmicocrypta, and Probolomyrmex had the fewest records in the data set (only one record each) (Fig. 8). Of the 887 ant species recorded, 28 species represent 33.76% of the records (Fig. 9). The five most recorded species were Solenopsis geminata (n = 501 records), followed by Octostruma balzani (n = 435), Atta mexicana (n = 430), Cyphomyrmex rimosus (n = 427), and Liometopum apiculatum (n = 398). All ant species were identified by 72 independent people, of whom 15 identified 25.68% of all records (n = 5,580) (Fig. 10).

We extracted the biogeographical region at which the records were obtained from the latitude and longitude information of our ant records, using the shapefile proposed by [START_REF] Morrone | Mexican biogeographic provinces: map and shapefiles[END_REF]. The majority of the ant records were registered in the Neotropical region of the country (n = 12,646, 58.19%), followed by the Mexican Transition Zone (n = 5,237, 24.10%) and the Nearctic region (n = 3,848, 17.71%) (Fig. 11). The native species (i.e., those species that historically occur in Mexico) comprised 95.46% of the records (n = 20,745), followed by exotic species (i.e., those species that have been the other authors.

Period of Study:

Data sampling ranged from 1894 to 2018.

Objectives:

The aims of this data paper were to i) compile the information available in the English, Spanish, and Portuguese literature on sampling sites of ant communities throughout Mexico, and to (ii) identify major patterns in the ant records and identify knowledge gaps to guide future sampling efforts. Our data set is a first attempt to obtain a large-scale catalog of ant communities in Mexico for use on a wide variety of scalesfrom local to landscape, regional, and macroecological perspectives.

Abstract:

As above.

Sources of funding:

The compilation of this data set was supported by grants, Ground Biodiversity), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior not explicitly separate maxi-Winkler from mini-Winkler records. We therefore cannot assume exactly which technique was employed for extracting ants from leaf-litter since in some cases the paper or label only noted the Winkler method. Finally, the geographical accuracy of data is another important topic that deserves attention. In this case, geographical coordinates were provided by the authors and we extracted them from scientific papers with different levels of precision (in meters). This difference in the accuracy of the data could represent a bias (in the extraction of the name of the municipalities, precipitation, temperature, elevation and sampling point) in our data set when information is required on a finer scale. Despite all these limitations, we were able to compile the largest and most complete data set of ant species for Mexico. After viewing the information compiled in this data set, we suggest that upcoming studies on Mexican ants should attempt (i) to standardize sampling methods and efforts, (ii) to perform long-term inventories, (iii) to deposit sample specimens in scientific collections, and (iv) to provide the record information in online repositories (preferably free of charge to users). We expect that the users of this data set will be able to determine priority areas for ant conservation and conduct research into macroecological and biogeographical patterns, as well as fulfilling many other ecological and conservation-related knowledge gaps.

Class III -Data set Status and Accessibility

A. Status

Latest update

December 2018.

Please cite this data paper when using its data for publications or teaching events.

Costs

Format and storage mode:

Comma-separated values (.csv)

Header Information:

See column descriptors in Section B.

Alphanumeric attributes:

Mixed.

Data anomalies:

If no information is available for a given record, this is indicated as 'NA'.

B. Variable information

State