Niche partitioning in small direct-developing frogs from the highlands of central Mexico

Background/Question/Methods

The Craugastor mexicanus species complex (Anura: Craugastoridae) is a group of direct-developing frogs that are endemic to central Mexico. These frogs inhabit the leaf litter and are often phenotypically polymorphic at the population level. We investigated genetic variation in 54 frogs from localities throughout their range in Mexico using mitochondrial DNA. Phylogenetic analyses revealed two major lineages and substantial genetic diversity. Within each of these lineages, there is evidence for a recent eastward expansion into parts of the Sierra Madre del Sur. These range expansions, while longitudinally parallel, appear to have occurred in separate elevational bands. Based on our sampling, there is a fairly distinctive break between the lineages at 2000 m with no evidence of genetic introgression on either side of this putative boundary. In the present study we investigated ecological factors that may be associated with this phenomenon by using an integrative dataset comprised of niche modeling, morphology, and molecules.

Results/Conclusions

Preliminary analyses indicate a fairly ancient origin in western Mexico for the C. mexicanus species complex. Additionally, we have observed adult body size and nucleotide substitution rate variation that corresponds to each of the two eastward expansions. While our sampling spans a large geographic area, including multiple localities in the states of Jalisco, Estado de México, Puebla, Hidalgo, Guerrero, and Oaxaca, we discuss localized microhabitat variation and the potential for bias in our analysis.