Functional overdispersion and niche differentiation along the epigean–hypogean gradient: trait-based evidence from Telemidae and Ochyroceratidae in Brazil

The subterranean environment is traditionally considered an environmental filter, particularly for spiders, promoting functional convergence and reducing trait diversity within communities. However, recent evidence suggests that niche differentiation processes may also play a central role in structuring these communities. In this study, we assessed the functional trait diversity of epigean, troglophilic, and troglobitic spiders belonging to the families Telemidae and Ochyroceratidae (groups known for their edaphic and cryptobiotic habits) from the Brazilian states of Minas Gerais and Bahia, regions characterized by marked seasonality in temperature and precipitation. We analyzed a set of morphological traits associated with ecology, locomotion, and sensory perception. Functional diversity metrics and null model–based analyses were used to evaluate patterns of functional convergence or overdispersion. Contrary to the classical expectation of functional convergence in subterranean communities, troglobitic morphospecies exhibited greater functional trait variation and a tendency toward phenotypic overdispersion, suggesting niche differentitation and specialization. Epigean morphospecies, in contrast, showed functional clustering, suggesting a predominant role of environmental filtering associated with surface climatic conditions. Our results demonstrate that functional evolution in subterranean environments reflects a complex interplay among environmental filtering, exaptations, evolutionary history, and niche differentiation processes, contradicting the view that caves harbor exclusively functionally impoverished and homogeneous communities.