Amphibians and reptiles of the state of Coahuila, Mexico, with comparison with adjoining states

Abstract We compiled a checklist of the amphibians and reptiles of the state of Coahuila, Mexico. The list comprises 133 species (24 amphibians, 109 reptiles), representing 27 families (9 amphibians, 18 reptiles) and 65 genera (16 amphibians, 49 reptiles). Coahuila has a high richness of lizards in the genus Sceloporus. Coahuila has relatively few state endemics, but has several regional endemics. Overlap in the herpetofauna of Coahuila and bordering states is fairly extensive. Of the 132 species of native amphibians and reptiles, eight are listed as Vulnerable, six as Near Threatened, and six as Endangered in the IUCN Red List. In the SEMARNAT listing, 19 species are Subject to Special Protection, 26 are Threatened, and three are in Danger of Extinction. Coahuila is home to several species of conservation concern, especially lizards and turtles. Coahuila is an important state for the conservation of the native regional fauna.


Introduction
Coahuila is the third largest state of Mexico, encompassing 151,571 km 2 , between latitudes 24°32'S and 29°53'N and between longitudes 99°51'E and 103°58'W. It is bordered by the Rio Grande of Texas to the north, by the states of Durango, Zacatecas, and San Luis Potosí to the south, Chihuahua to the west, and Nuevo León to the east (Fig. 1). It represents 7.74% of the total area of Mexico.
Extensive sierras in the northern part of the state appear to form a single mountain mass, although they are actually composed of three ranges: Sierra El Carmen, the western third; Sierra El Burro, the eastern third; and Sierra de Santa Rosa, the southern third. The greatest altitude (2,120 m) is reached in the Sierra de Santa Rosa (28°18'N, 102°4'W). These sierras constitute about 40-50% of the northern part of the state; the rest of the northern part consists of plains whose average elevation is 1,000 m. In the extreme western part of the state, isolated, relatively small sierras, oriented north to south, arise abruptly from the arid/semiarid plains. The principal ones are Sierra Las Cruces, Sierra Mojada, Sierra El Pino and Sierra de Tlahualilo. The highest of these is Sierra Mojada (27°16'N, 103°42W), with a maximum altitude of 2,450 m. Around these mountains the plains, at an average altitude of 1,250 m, are dominated by areas of sand dunes. One set lies between Estación Sabaneta and an area east of Jaco (Chihuahua), a part of the Bolsón de Mapimí. Another is on the plains of Aguanaval east of the Sierra de Tlahualilo (Dunas Magnéticas), part of the Zona del Silencio. Still another is on the plains of the municipalities of Matamoros and Viesca, located in the extreme southwestern part of the area known as the Laguna de Mayrán. The extreme south central and southeastern parts of the state are characterized by a series of east-west crustal folds forming several sierras, notably the Sierra de Arteaga, Sierra La Concordia, and Sierra de Parras, contiguous to the east with the Sierra Madre Oriental. Cerro La Nopalera (25°8'N, 103°14'W), at 3,120 m, is the highest elevation in the area. Toward the southwest these ranges are continuous with those that form the southern limit of the Laguna de Mayrán. The eastern part of the state is mostly flat, broken by several isolated, low ranges extending N-S, notably the Sierra Pájaros Azules (27°0'N, 100°53'W), reaching an altitude of 1,930 m, and Sierra La Gloria. In the central part of the state is a small, low (~750 m) valley of 120 km 2 surrounded by mountain ranges with altitudes of up to 2,500 m. For tens of thousands of years this valley was of strictly internal drainage, fed by waters from several arroyos, creating a wide variety of aquatic habitats, including streams, wells, lakes and marshes. Its isolation and antiquity led to a high degree of endemism there (McCoy 1984). At present this valley is known as the Cuatro Ciénegas Basin.
Much of Coahuila lies within the Chihuahuan Desert. The highlands in the extreme southeastern corner, including the Sierra de Arteaga, are an exception, and constitute the extreme northern end of the Sierra Madre Oriental. The vegetative cover of the state is made up of six types of vegetation (Chihuahuan Desert Scrub; Tamaulipan Thornscrub; Montane Forest; Sacatal Grassland; and Aquatic, Subaquatic and Riparian Vegetation) and 12 plant communities, that basically correspond to three floral provinces: The Mexican Plateau, the Coastal Plain of the Northeast and the Sierra Madre Oriental (Rzedowski 1978;Lemos-Espinal and Smith 2015b). Lemos-Espinal and Smith (2015b) reviewed herpetological studies previously done in the state of Coahuila, with the majority of herpetological collections in Coahuila focused in the central part of the state (Bolsón de Cuatro Ciénegas), the south-western part of the state (Laguna de Mayrán), and the extreme southeastern part of the state (Sierra de Arteaga). Other important regions of the state remain poorly studied, such as the extreme northwestern part of the state, due to lack of road access to these regions. However, in recent years, new highways has been constructed allowing access to previously unstudied areas, for example the highway from Múzquiz to Ojinaga, that traverses the northwestern part of Coahuila and connects this area with extreme northeastern Chihuahua. It is anticipated that this highway will increase herpetological studies of this region which is home of two important protected areas in Mexico: Área de Protección de Flora y Fauna Cañón de Santa Elena (Chihuahua) and Área de Protección de Flora y Fauna Maderas del Carmen (Coahuila).
Here, we report the list of amphibians and reptiles that have been recorded so far for the state of Coahuila. While checklists for Coahuila are available (e.g., Lemos-Espinal andSmith 2007, 2015b), we expand on these earlier efforts by also collecting and summarizing the conservation statuses of each documented species. We also compare the observed list to those available for the five adjoining states in the United States and Mexico for which recent checklists are available (Texas, Chihuahua, Durango, San Luis Potosí, and Nuevo León). Our goal is to place this checklist into a regional and conservation context not available in the previously published checklists.

Methods
We compiled the list of amphibians and reptiles of the state of Coahuila from the following sources: (1) our own field work; (2) specimens from the Laboratorio de Ecología -UBIPRO (LEUBIPRO) collections; (3) databases from the Comisión Nacional para el Conocimiento y Uso de la Biodiversidad (National Commission for the Understanding and Use of Biodiversity; CONABIO), including the 22 collections listed in Appendix I; and (4) a thorough examination of the available literature on amphibians and reptiles in the state. Species were included in the checklist only if we were able to confirm the record, either by direct observation or through documented museum records or vouchers in the state. In addition, we recorded the conservation status of each species based on three sources: 1) the IUCN Red List, 2) Environmental Viability Scores from Wilson et al. (2013a,b), and 3) listing in SEMARNAT (2010).
Scientific names used in this publication are based on the taxonomic list published in Lemos-Espinal (2015). The arrangement of the amphibian names follows Frost (2015) and arrangement of the reptile names follows Uetz and Hošek (2015). State lists used to compare the species composition between Coahuila and the adjoining states were: Lemos-Espinal and Smith  Dixon (2015: Texas). We modified the list provided by Valdez-Lares et al. (2013) to be able to compare it with the list of the rest of the states. These modifications were the following: we regarded the population of Barisia imbricata (Wiegmann) as Barisia ciliaris (Smith) (Baird & Girard). For these states we also determine the number of overlapping species.
The difficult access to large and important parts of the state assure us that the number of native amphibian and reptile species that inhabits Coahuila is larger than the one we are reporting here. Species such as the Texas Salamander (Eurycea neotenes Bishop & Wright) and the Plains Spadefoot (Spea bombifrons [Cope]) likely inhabit extreme northern Coahuila. Dixon (2000) indicated the occurrence of these species at several localities in Texas adjacent to the extreme northern border of the state. The Ornate Box Turtle Terrapene ornata (Agassiz) very likely inhabits the Chihuahuan Desert of Coahuila, although as yet there are no records of this species in the state. According to Lemos-Espinal andSmith (2007, 2015b) Smith (2007Smith ( , 2015b) also suggested that several species of snakes not recorded for Coahuila may inhabit the state, including Taylor´s Cantil (Agkistrodon taylori Burger & Robertson), the Tamaulipan Hook-nosed Snake (Ficimia streckeri Taylor), and the Red Black-headed Snake (Tantilla rubra Cope) in the southeastern portion of the state; the Tampico Threadsnake (Rena myopica [Garman]) and the Nuevo León Graceful Brownsnake (Rhadinaea montana Smith) in the extreme eastern portion; Dekay´s Brownsnake (Storeria dekayi [Holbrook]) and the Trans-Pecos Black-headed Snake (Tantilla cucullata Minton) in the extreme northeastern part; and Table 1. Checklist of amphibians and reptiles of Coahuila. We also provide the Habitat type (CD = Chihuahuan Desert, SM = Sierra Madre Oriental, TS = Tamaulipan Thornscrub), IUCN Status (DD = Data Deficient; LC = Least Concern, V = Vulnerable, NT = Neat Threatened; E = Endangered; CE = Critically Endangered) according to the IUCN Red List (The IUCN Red List of Threatened Species, Version 2014.2; www.iucnredlist.org; accessed 2 December 2015), Environmental Vulnerability Score (EVS; the higher the score the greater the vulnerability) from Wilson et al. (2013a,b), and conservation status in Mexico according to SEMARNAT (2010) (P = in danger of extinction, A = threatened; Pr = subject to special protection, NL -not listed). Source denotes whether the species was observed in the field by the authors (A), documented in the CONABIO data base and/or museum collections (C/M), or found in the literature (citation of source).  (1996) indicated the presence of the Mexican Gartersnake (Thamnophis eques (Reuss)), the Mexican Black-bellied Gartersnake (Thamnophis melanogaster [Peters]), and the Madrean Narrow-headed Gartersnake (Thamnophis unilabialis Tanner) in extreme southwestern Coahuila; however, no records for these species exist for Coahuila and we did not include them in the species list for this state. Thirty five of the 132 species of amphibians and reptiles that inhabit Coahuila are endemic to Mexico, 20 of them are limited to areas of the Chihuahua Desert, including six endemic to Coahuila: Terrapene coahuila (Fig. 2), Trachemys taylori (Fig.  3), Gerrhonotus lugoi (Fig. 4), Crotaphytus antiquus (Fig. 5), Uma exsul (Fig. 6) Table 1 for abbreviations; in some cases species have not been assigned a status by the IUCN and therefore these may not add up to the total number of species in a taxon). Mean EVS is the mean Environmental Vulnerability Score, scores ≥ 14 are considered high vulnerability (Wilson et al. 2013a,b) and conservation status in Mexico according to SEMARNAT (2010) in the Order NL, Pr, A, P (see Table 1 for abbreviations).

Discussion
Like many other states in Mexico, Coahuila has a rich herpetofauna, but especially a rich reptile fauna. In particular, Coahuila has a high diversity of lizards in the genus Sceloporus (19 species). The richness of reptiles is consistent with the importance of desert habitats in Coahuila. Despite its richness in reptiles and amphibians, Coahuila has a relatively small number of endemics to the state. However, several regional endemics are present in Coahuila, and thus the state serves as a reservoir for regional endemism.
In addition, Coahuila is home to several species of conservation concern, especially lizards and turtles. Coahuila thus may be an important state for the conservation of the native regional fauna. Given the relatively unstudied nature of some regions of Coahuila, including the northwestern part of the state that houses two protected areas, the importance of Coahuila may be greater than we currently understand. Indeed, parts of Coahuila have been identified as "species richness hotspots" for lizards (Barrows et al. 2013). In addition, as with the relatively few endemic species, the relative number of species listed as being of conservation concern (i.e., endangered, near threatened, or vulnerable) is also low (22 total in these categories out of 132 native species; 16.7%). We therefore encourage more surveys and more studies on the conservation statuses of the state's herpetofauna, especially the regions that are now becoming more accessible. This is especially important because as these regions become more accessible to herpetologists, they are also likely to become more susceptible to anthropogenic impacts which could affect the flora and fauna. Coahuila shares several species with the neighboring states, with the greatest overlap with Nuevo León and Texas. In an analysis of the herpetofauna of the border states of the United States and Mexico, Coahuila frequently clustered with Nuevo León, but was less related to Texas (Smith and Lemos-Espinal 2015). Such overlap is not unexpected, especially given the shared habitats among these states. In particular, the sharing of habitats is likely to be important in explaining the overlap in species composition among states. Indeed, in a comparison of herpetofaunas among the United States-Mexico border states, Smith and Lemos-Espinal (2015) found that the sharing of herpetofaunas paralleled sharing of habitat types. For example, Coahuila shares much of its habitat types with Nuevo León and Tamaulipas, and to a lesser extent with Texas (Smith and Lemos-Espinal 2015). The patterns of shared species are also likely attributed in part to the geological history of the region (Riddle and Hafner 2006).