Isolation by environment is more important than isolation by distance along a tropical gradient in direct developing frogs

Abstract

To identify which abiotic factors are most important for defining population structure, both spatiotemporal scales and species-specific life history attributes and ecology must be accounted for. Our study aim is to quantify the extent to which divergence is driven by abiotic factors such as temperature, precipitation and elevation. To do so, we used a direct-developing frog species, Craugastor loki that occurs along a steep elevation gradient. Using restriction-site associated DNA sequencing (RADseq) from individuals collected from 100 m to 2250 m of elevation at 13 localities at Sierra Madre de Chiapas in southern Mexico we described population structure using a variety of model-based clustering and landscape genomics approaches. We found that populations sampled at higher elevation correspond to an undescribed new species of Craugastor, and that populations from Craugastor loki between 120 m and 1500 m are clustered in two different genetic groups: a Pacific slope group and a Central Depression slope group. We found that a null model of isolation-by-distance was not supported and divergence is more likely influenced by the interaction between elevation and precipitation, but also temperature. Our results underscore the importance of isolation by environment and highlight that spatial analyses can illuminate fine scale population structure.