Climate, Not Soil, Drives the Distribution of Two Closely Related Worm Lizards

A central challenge in ecology is understanding how closely related species coexist, and sister species-with which they share a closely related evolutionary history-provide a powerful system for testing niche overlap and segregation. For fossorial organisms, the relative role of climate and soil in shaping distributions remains unclear, despite their potential to drive habitat suitability and species interactions underground. Here, we examine factors driving coexistence of two sister species of worm lizards, Amphisbaena bolivica and A. camura, which show distributions mostly parapatric but with partial overlap (sympatry). We used Maxent niche models to assess how climatic, edaphic, and relief variables influence their occurrences, and also evaluated their niche overlap in the environmental spaces defined by climate and soil. The projected habitat suitability for A. bolivica and A. camura closely aligns with their known occurrence records in Argentina, Bolivia, Brazil, and Paraguay. Climatic variables were more important than edaphic and relief variables for the distribution of both species. Isothermality was the most important variable (67% percentage contribution to the Maxent ecological niche model) for A. bolivica, followed by mean temperature of the wettest quarter (43%). For A. camura, mean diurnal range was the most important (64%) followed by mean temperature of the wettest quarter (27%). We found low niche overlap in the climate space and higher than expected similarity in the edaphic space. Our findings suggest conservatism of the edaphic space occupied by these sister species, with climatic factors underlying spatial segregation among fossorial organisms.