Dispersal capacity rather than shared environmental constraints determines taxon-specific demographic dynamics in an alpine lake network

Networks of alpine lakes and ponds support unique assemblages of aquatic organisms and provide an ideal biogeographical setting for studying the evolutionary, ecological, and demographic outcomes of population fragmentation. In this study, we integrate genomic, morphological, and community-level data within a comparative multi-taxon framework to investigate genetic connectivity, demographic trajectories, and eco-evolutionary dynamics in four diving beetles (Coleoptera: Dytiscidae) representative of the macroinvertebrate assemblages inhabiting high altitude lakes in Sierra Nevada massif, southeastern Iberia. Although the focal taxa share similar ecological requirements, primarily occupy lentic habitats, and disperse by flight, our results reveal substantial heterogeneity in their demographic responses to the naturally fragmented distribution of alpine lakes. Taxa with higher wing loading exhibited stronger genetic differentiation among populations, probably due to their reduced capacity to disperse across the direct geographic distances separating lakes. Populations located at the range periphery tended to exhibit lower genetic diversity than central populations in all taxa. Demographic reconstructions showed a general decline in effective population size from the last glacial maximum (LGM) to the present. However, some populations of genetically more structured taxa went through brief bottlenecks that coincided with periods of warmer climate and lower lake levels, as inferred from local paleoclimatic reconstructions. Finally, the composition of macroinvertebrate assemblages (α-diversity and β-diversity) was not associated with intraspecific genetic diversity or differentiation, suggesting that species-level demographic trajectories and community-level dynamics are decoupled. Our findings indicate that interspecific differences in dispersal capacity outweigh shared environmental constraints in determining the contrasting demographic trajectories of the studied taxa. Collectively, these results emphasize the importance of multi-taxon approaches for understanding the dynamics of species assemblages in alpine ecosystems that are highly vulnerable to climate warming.