A taxonomic conundrum: Characterizing a cryptic radiation of Asian gracile skinks (Squamata: Scincidae: Riopa) in Myanmar.

Recognizing species-level diversity is important for studying evolutionary patterns across biological disciplines and is critical for conservation efforts. However, challenges remain in delimiting species-level diversity, especially in cryptic radiations where species are genetically divergent but show little morphological differentiation. Using multilocus molecular data, phylogenetic analyses, species delimitation analyses, and morphological data, we examine lineage diversification in a cryptic radiation of Riopa skinks in Myanmar. Four species of Riopa skinks are currently recognized from Myanmar based on morphological traits, but the boundaries between three of these species, R. anguina, R. lineolata, and R. popae, are not well-defined. We find high levels of genetic diversity within these three species. Our analyses suggest that they may comprise as many as 12 independently evolving lineages, highlighting the extent to which species diversity in the region is underestimated. However, quantitative trait data suggest that these lineages have not differentiated morphologically, possibly indicating that this cryptic radiation represents non-adaptive evolution, although additional data is needed to corroborate this.