Evidencia genetica y morfologica pone en duda la validez de las especies mexicanas troglobias del bagre neotropical del genero Rhamdia (Siluriformes: Heptapteridae)

Four of the 7 species of Rhamdia present in Mexico stand out for being microendemic and also troglobitic, that is, for being restricted to their type-locality caves and for exhibiting a distinctive phenotype characterized by ocular reduction/loss and body depigmentation. Diagnosis and recognition of Mexican troglobitic forms as distinct species, however, appears to be primarily based on their regressive troglomorphic phenotype and highly localized geographic distributions. To test the adequacy of its current taxonomy, we investigated patterns of genetic and phenotypic variation in Mexican troglobitic Rhamdia in a phylogenetic context. Our results indicate that external morphology does not allow for unambiguous differential diagnoses and robust distinction among troglobitic species. Similarly, beyond typical regressive troglomorphic traits, troglobitic species do not differ greatly in external morphology from their most closely related congener, the epigean species Rhamdia laticauda. From a phylogenetic perspective, continued recognition of troglobitic species implies a deep and generalized paraphyly in R. laticauda. Despite the evidence presented herein, we refrain from making nomenclatural decisions until we can unambiguously ascertain that our findings are indeed explained by phylogeographic structure in R. laticauda, instead of by recent divergence and subsequent speciation of cave-dwelling lineages from this widespread epigean species.

Automated summary

The recognition and classification of Mexican troglobitic Rhamdia species are primarily based on morphological characteristics and geographic distribution, but external morphology and regressive troglomorphic traits do not provide clear differential diagnoses among these species. The continued recognition of troglobitic species implies a deep and generalized paraphyly in R. laticauda.