Turnover, Uniqueness, and Environmental Filtering Shape Helminth Parasite Metacommunities in Freshwater Fish Pseudoxiphophorus bimaculatus (Cyprinodontiformes: Poeciliidae)

Understanding the processes that shape parasite community structure across spatial scales is essential for linking ecological theory with host–parasite dynamics. Using a metacommunity framework, we examined the metacommunity of helminth parasites infecting the freshwater fish Pseudoxiphophorus bimaculatus across 11 sites along the La Antigua River basin (Veracruz, Mexico). We combined β-diversity partitioning, local and species contributions to diversity, elements of metacommunity structure (EMS), and variance partitioning to identify the mechanisms underlying spatial variation in parasite composition. Helminth metacommunity was dominated by a few widespread taxa, with balanced variation in species abundances—indicative of turnover—emerging as the main driver of β-diversity at both host and site levels. Both rare and common species contributed disproportionately to regional diversity. EMS analyses revealed coherent, non-random community structures that varied from nested to quasi-Gleasonian and quasi-Clementsian types among sites and guilds, suggesting that species respond individually to shared environmental gradients. Variance partitioning indicated that environmental filtering, particularly through habitat structure, explained most of the variation in community composition, exceeding the effects of water quality and host size. Overall, our results demonstrate that turnover, species uniqueness, and environmental filtering interact to shape helminth parasite metacommunities in tropical freshwater systems, highlighting the integrative role of environmental heterogeneity and dispersal limitation in parasite community assembly.