Oscar Flores-Villela

A general assessment of the conservation status and decline trends of Mexican amphibians

We present a review on the conservation status and population trends of the 372 amphibian species currently recognized for Mexico. We based our analyses on the information gathered by the International Union for the Conservation of Nature-the Global Amphibian Assessment (IUCN-GAA) as well as on available literature about imminent or potential threats to these organisms in Mexico. This country has the fifth largest amphibian fauna in the world and almost 58% of the species that inhabit this country are considered as threatened. We highlight the proportion of species per order, family, and genus that are currently under severe risk in Mexico. In addition, we prepared a detailed list of the main factors that are threatening amphibians in this country. Evidence is provided that the six main mechanisms that are globally leading amphibians to extinction (alien species, over-exploitation, land use change, global changes, pollution, and infectious diseases) are indeed currently operating in Mexico. We discuss the relative importance of each of these causes. We also highlight the paucity of quantitative studies that support the current conservation status of Mexican amphibian species.

Evolutionary relationships amongst polymorphic direct-developing frogs in the Craugastor rhodopis Species Group (Anura: Craugastoridae)

The Craugastor rhodopis Species Group includes two leaf-litter frog species (C. loki and C. rhodopis). These direct-developing frogs inhabit tropical regions of Mexico and northern Central America. Characterizing diversity within the group has been difficult due to high levels of phenotypic polymorphism within and between species. Because of these polymorphisms, each taxon has junior synonyms. Using a fragment of mitochondrial DNA (mtDNA), we investigated genetic diversity in the C. rhodopis Species Group. We then examined type specimens (including types of junior synonyms) to match nomenclature to geographically circumscribed genetic clusters. Our molecular analyses revealed four major lineages within the C. rhodopis Species Group: (1) a widely distributed clade in western Mexico, (2) a highland clade in eastern Mexico, (3) a widely distributed lowland clade occurring in eastern Mexico, Guatemala and El Salvador, and (4) a haplotype from Volcán San Martín in Veracruz, Mexico. We identified the first clade as C. occidentalis, a taxon currently placed in the ecologically similar but phylogenetically distant C. mexicanus Species Series. In light of this we place C. occidentalis in the C. rhodopis Species Group and designate a lectotype and paralectotype for the species. The second and third clades inhabiting eastern Mexico and northern Central America correspond to C. rhodopis and C. loki, respectively. Additionally, we examined the taxonomic distribution of certain colour pattern traits and compensatory mutations in Domain III of the mtDNA 12S ribosomal RNA gene. Our recovery of the divergent Veracruz haplotype and extensive mtDNA structure within species indicates that additional taxonomic revision will be necessary.

A New Long-Tailed Rattlesnake (Viperidae) From Guerrero, Mexico

A distinctive new species of rattlesnake is described from the western versant of the Sierra Madre del Sur of Guerrero, Mexico. This long-tailed rattlesnake cannot be confused with any other species of rattlesnake and is most similar to Crotalus stejnegeri and C. lannomi. The Guerrero species possesses a strikingly distinct color pattern and differs from all other rattlesnakes in aspects of lepidosis. Mexico continues to be the origin of newly discovered species that provide important insights into the evolution or ecology of particular groups. A few examples from recent decades include Exiliboa placata, a monotypic, relictual dwarf boa (Bogert, 1968), Rhadinophanes monticola, a monotypic, highland colubrid (Myers and Campbell, 1981), and Pseudoeurycea aquatica, the only aquatic bolitoglossine salamander (Wake and Campbell, 2001).

Limitations of Climatic Data for Inferring Species Boundaries: Insights from Speckled Rattlesnakes

Phenotypes, DNA, and measures of ecological differences are widely used in species delimitation. Although rarely defined in such studies, ecological divergence is almost always approximated using multivariate climatic data associated with sets of specimens (i.e., the “climatic niche”); the justification for this approach is that species-specific climatic envelopes act as surrogates for physiological tolerances. Using identical statistical procedures, we evaluated the usefulness and validity of the climate-as-proxy assumption by comparing performance of genetic (nDNA SNPs and mitochondrial DNA), phenotypic, and climatic data for objective species delimitation in the speckled rattlesnake (Crotalus mitchellii) complex. Ordination and clustering patterns were largely congruent among intrinsic (heritable) traits (nDNA, mtDNA, phenotype), and discordance is explained by biological processes (e.g., ontogeny, hybridization). In contrast, climatic data did not produce biologically meaningful clusters that were congruent with any intrinsic dataset, but rather corresponded to regional differences in atmospheric circulation and climate, indicating an absence of inherent taxonomic signal in these data. Surrogating climate for physiological tolerances adds artificial weight to evidence of species boundaries, as these data are irrelevant for that purpose. Based on the evidence from congruent clustering of intrinsic datasets, we recommend that three subspecies of C. mitchellii be recognized as species: C. angelensis, C. mitchellii, and C. Pyrrhus.

Reproductive Activity of Three Sympatric Viviparous Lizards at Omiltemi, Guerrero, Sierra Madre del Sur, Mexico

Abstract We studied the reproductive characteristics of sympatric populations of Sceloporus formosus scitulus, Sceloporus omiltemanus (Phrynosomatidae), and Mesaspis gadovii (Anguidae) at the Omiltemi forest reserve (Guerrero, Mexico). Males are larger and reach larger body sizes at reproductive maturity and are more colorful than females in both Sceloporus, whereas males are smaller than females and reach sexual maturity at similar body sizes in M. gadovii. These species are single brooded and follow a common pattern of annual reproductive activity. The reproductive activity of females and males of the three species is seasonal; vitellogenesis is initiated in late summer and continues in autumn/rainy season, gestation occurs throughout the winter/dry season, and parturition occurs in early spring. All three species have intersexual synchrony in reproductive activity. In spite of similar reproductive schedules, some subtle features related to the length of each of the reproductive stages could be observed. Sceloporus formosus scitulus has a more extended reproductive season, and large females start vitellogenesis earlier than do small ones. Males have a prolonged reproductive activity and a short nonreproductive season. In contrast, the reproductive cycle of the other two species is defined by shorter reproductive season and less intrasexual asynchrony for both sexes than found in S. f. scitulus. The seasonal pattern of reproduction shared by these three species is characteristic of other viviparous lizards at high elevations in tropical and subtropical latitudes of Central and South America, being convergent for different lizard families. This convergence in reproductive patterns suggests a common evolutionary response to environmental factors associated with montane habitats, whereas specific differences observed within species are attributed to the particular evolutionary history of each taxon.

Phylogeny, biogeography, and display evolution in the tree and brush lizard genus Urosaurus (Squamata:Phrynosomatidae)

The brush and tree lizards (Urosaurus) are a small clade of phrynosomatid lizards native to western North America. Though not as well known as their diverse sister clade, the spiny lizards (Sceloporus), some Urosaurus have nonetheless become model organisms in integrative biology. In particular, dramatic phenotypic and behavioral differences associated with specific mating strategies have been exploited to address a range of ecological and evolutionary questions. However, only two phylogenies have been proposed for the group, one of which is pre-cladistic and both based principally on morphological characters that might not provide robust support for relationships within the group. To help provide investigators working on Urosaurus with a robust phylogeny in which to frame ecological and evolutionary questions, we establish a molecular phylogeny for the group. We sampled three mitochondrial and three nuclear loci, and estimated phylogenetic relationships within Urosaurus using both maximum parsimony (MP) and Bayesian inference (BI), as well as a coalescent-based species tree approach. Finally, we used two methods of ancestral state reconstruction (ASR) to gain insight into the evolution of microhabitat preference and male display signals, traits that have been the focus of studies on Urosaurus. All reconstruction methods yield nearly the same ingroup topology that is concordant in most respects with the previous cladistic analysis of the group but with some significant differences; our data suggest the primary divergence in Urosaurus occurs between a clade endemic to the Pacific versant of Mexico and the lineages of Baja California and the southwestern US, rather than placing Urosaurus graciosus as the basal taxon and linking the Baja and Mexican endemics. We find support for a single transition to a saxicolous lifestyle within the group, and either the independent gain or loss of arboreality. The evolution of throat color patterns (i.e. dewlaps) appears complex, with multiple color morphs likely involving orange reconstructed as ancestral to the group and to most lineages, followed by a single transition to a fixed blue-throated morph in one clade. These results should provide a useful framework for additional comparative work with Urosaurus, and establish the phylogenetic context in which Urosaurus diversity arose.

Molecular systematics of the genus Sonora (Squamata: Colubridae) in central and western Mexico

Mexico possesses high levels of endemic biodiversity, especially for squamate reptiles. However, the evolutionary relationships among many reptiles in this region are not well known. The closely related genera of Sonora Baird and Girard 1853 and Procinura Cope 1879 are coralsnake mimics found from the central and western United States to southwestern Mexico and Baja California. Although species delimitation in this group has historically relied upon colour pattern and other morphological characters, many populations of these species display colour pattern polymorphism, which may confound taxonomy. We used molecular phylogenetics to assess the evolutionary relationships and delimit species within Sonora, focusing on the phylogenetic position of Procinura and the validity of S. mutabilis and aequalis. We sequenced two mitochondrial (ND4 and cytb) and two nuclear (c-mos and RAG-1) genes for the single species of Procinura and each of the four species of Sonora. We analysed these sequences using maximum parsimony, maximum likelihood and Bayesian phylogenetic analyses on separately concatenated mitochondrial and nuclear datasets. Additionally, we used Bayesian coalescent methods to build a species tree (Bayesian species tree analysis) and delimit species boundaries (Bayesian species delimitation). All methods indicated that Procinura is deeply nested within Sonora, and most individual species are well supported. However, we found that one taxon (S. aequalis) is paraphyletic with regard to another (S. mutabilis). We recommend that the genus Procinura be synonymised with Sonora and that S. aequalis be synonymised with S. mutabilis. Additionally, the phylogenetic patterns that we document are broadly congruent with a Miocene or Pliocene divergence between S. michoacanensis and S. mutabilis along the Trans-Mexican Volcanic Belt. Finally, our data are consistent with the early evolution of coralsnake mimicry and colour pattern polymorphism within the genus Sonora.

Genetic Variation, Species Status, and Phylogenetic Relationships in Rose-Bellied Lizards (Variabilis Group) of the Genus Sceloporus (Squamata: Phrynosomatidae)

We investigated species boundaries and phylogenetic relationships in the Sceloporus variabilis group, using multilocus isozyme characters. Forty-one genetic markers were screened in a sample of 238 lizards from 47 localities, representing eight ingroup species. Thirty-four loci were variable within or between taxa. Morphologically well-defined species (S. chrysostictus, S. cozumelae, and S. parvus) were strongly and unambiguously differentiated genetically. Within S. variabilis, S. v. marmoratus, highelevation populations of S. v. variabilis (from Hidalgo, Queretaro and San Luis Potosi), low-elevation populations of S. v. variabilis, and S. v. olloporus, were each recognized as full species. Low-elevation populations of S. v. variabilis were only slightly divergent from S. v. teapensis and were retained as conspecific. Two different methods of parsimony analysis recovered trees with the following structure: (S. parvus (S. chrysostictus (S. cozumelae + S. variabilis species-group))). A FREQPARS analysis recovered a different topology. Investigamos el limite entre especies y las relaciones filogeneticas en el grupo Sceloporus variabilis, utilizando isoenzimas con multiples loci. Se revisaron 41 marcadores geneticos en una muestra de 238 lagartijas de 47 localidades, las cuales representaban 8 especies. Treinta y cuatro loci fueron variables inter e intra especificamente. Las especies distinguibles morfologicamente, tambien resultaron estar fuertemente diferenciadas geneticamente (S. chrysostictus, S. cozumelae y S. parvus). Entre las subespecies de S. variabilis, S. v. marmoratus, poblaciones de S. v. variabilis de tierras altas (en Hidalgo, Queretaro y San Luis Potosi), poblaciones de S. v. variabilis de tierras bajas, y S. v. olloporus, se reconocen como especies diferentes. Las poblaciones de tierras bajas de S. v. variabilis fueron solo ligeramente divergentes de S. v. teapensis, por lo que se retuvieron como entidades conespecificas. Dos analisis diferentes de parsimonia resultan en arboles con la siguiente topologia: (S. parvus (S. chrysostictus (S. cozumelae + especies del grupo S. variabilis))). Un anilisis con FREQPARS, arroja una topologia diferente.

Cryptic Population Structuring and the Role of the Isthmus of Tehuantepec as a Gene Flow Barrier in the Critically Endangered Central American River Turtle

The critically endangered Central American River Turtle (Dermatemys mawii) is the only remaining member of the Dermatemydidae family, yet little is known about its population structuring. In a previous study of mitochondrial (mt) DNA in the species, three main lineages were described. One lineage (Central) was dominant across most of the range, while two other lineages were restricted to Papaloapan (PAP; isolated by the Isthmus of Tehuantepec and the Sierra de Santa Marta) or the south-eastern part of the range (1D). Here we provide data from seven polymorphic microsatellite loci and the R35 intron to re-evaluate these findings using DNA from the nuclear genome. Based on a slightly expanded data set of a total of 253 samples from the same localities, we find that mtDNA and nuclear DNA markers yield a highly congruent picture of the evolutionary history and population structuring of D. mawii. While resolution provided by the R35 intron (sequenced for a subset of the samples) was very limited, the microsatellite data revealed pronounced population structuring. Within the Grijalva-Usumacinta drainage basin, however, many populations separated by more than 300 kilometers showed signals of high gene flow. Across the entire range, neither mitochondrial nor nuclear DNA show a significant isolation-by-distance pattern, but both genomes highlight that the D. mawii population in the Papaloapan basin is genetically distinctive. Further, both marker systems detect unique genomic signals in four individuals with mtDNA clade 1D sampled on the southeast edge of the Grijalva-Usumacinta basin. These individuals may represent a separate cryptic taxon that is likely impacted by recent admixture.

A new species of Tantilla (Squamata: Colubridae) of the calamarina group from Volcán Ceboruco, Nayarit, Mexico

Abstract A new species of Tantilla is described from a single specimen obtained from Volcán Ceboruco, southern Nayarit, Mexico. The new species closely resembles other species of the Tantilla calamarina group. With the addition of the taxon described herein, the calamarina group now contains seven species, T. calamarina, Tantilla cascadae, Tantilla coronadoi, Tantilla deppei, Tantilla sertula, Tantilla vermiformis, and the new species described herein. Collectively, members of the group are distributed along the Pacific versant of Middle America in three disjunct regions: (1) from northern Sinaloa to Guerrero, including the Tres Marías Islands; (2) the Balsas Basin of Morelos, Puebla, Distrito Federal, and the State of Mexico; and (3) from El Salvador to northwestern Costa Rica. We provide a small list of specimens collected in the highlands of Nayarit, and report Lithobates psilonota, Ambystoma rosaceum, Elgaria kingi, Plestiodon lynxe and Rhadinaea hesperia for the first time from the state. We report the second specimen of T. sertula, known previously only from the holotype.