Niche Divergence in the South American Freshwater Crustacean Aegla Provides Insights Into Its Diversification.

Understanding how taxa diverge within their ecological niches is essential for revealing mechanisms driving biodiversity and biogeographic patterns, particularly in regions with complex environmental gradients. Ecological niche dynamics have profound implications for speciation and species distributions, yet remain underexplored in freshwater organisms. Here, we investigated ecological niche variation among clades of Aegla (Aeglidae), a diverse freshwater crustacean genus endemic to southern South America, to uncover links between niche differentiation and lineage diversification. Using MaxEnt to build niche models with climatic and elevation variables, we assessed niche overlap and similarity in environmental space via PCA-env, Hellinger's I, and Schoener's D metrics, complemented by equivalence and similarity tests. We found pronounced niche divergence among Aegla clades, characterized by distinct climatic preferences and low-to-moderate pairwise overlap. Niche equivalence tests rejected conservatism in all comparisons. This divergence is consistent with the combined effects of geographical isolation among drainage basins and regional climatic heterogeneity, which may have restricted dispersal and promoted the independent occupation of contrasting environmental conditions. These patterns suggest that ecological differentiation, together with historical geographic isolation, is closely associated with diversification within the group. Our results demonstrate that ecological adaptation has likely contributed to diversification in Aegla, highlighting niche divergence as an important component of freshwater biodiversity. These insights emphasize the sensitivity of such taxa to ongoing environmental changes and advance our understanding of ecological processes in shaping evolutionary patterns in South American aquatic systems.