Genetic Variation in a Dwarfed Lineage, the Mexican Salamander Genus Thorius (Amphibia: Plethodontidae): Taxonomic, Ecologic and Evolutionary Implications

• Published in: Copeia 1983-12, Vol.1983 (4), p.1051-1073
• Main Author: Hanken, James
• Format: Article
• Language: English
• Subjects: Alleles; Amphibia. Reptilia; Biological and medical sciences; Biological taxonomies; Body size; Cloud forests; Fundamental and applied biological sciences. Psychology; Genetic loci; Genetic variation; Population genetics; Population mean; Salamanders; Sympatric species; Thorius; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0045-8511; 1938-5110
• DOI: 10.2307/1445108

Patterns of genetic relationship and taxonomic identity are examined in Thorius, an enigmatic genus of minute neotropical salamanders that represent the smallest tailed tetrapods. Data comprise an electrophoretic analysis of 16 protein loci in 69 population samples from 55 localities throughout the range of the genus in southern México. Eight of the nine described species are genetically distinct: Nei's D commonly exceeds 0.9. There is no biochemical evidence of more than a single species at Zoquitlán, Pue., type locality of T. schmidti and T. maxillabrochus. Genetic differentiation between disjunct subspecies of T. pennatulus is less than the mean pairwise value between described species, but exceeds that observed between some sympatric species pairs. Seven additional as yet undescribed species are identified, based either on their sympatric occurrence with, or great genetic differentiation from, described species. Most species initially identified by electrophoresis are morphologically distinct. Electrophoretic data fail to resolve the taxonomic affinity of a few remaining populations, although they do provide clearcut and distinguishable hypotheses of relationship that can be tested using other sources, such as morphology. The 15 species constitute three faunal units: Veracruz and eastern Puebla; Sierra de Juárez, Oaxaca; southern and western Oaxaca, and Guerrero. Local endemism is observed within each region, in which sympatry involving two or three species is common. Species frequently demonstrate narrow elevational zonation and distinct habitat and microhabitat preference (e.g., arboreal vs terrestrial). The distribution of four species on Cerro Pelón, Oax., is examined in detail.