Macroevolutionary patterns of habitat transitions in aquatic Coleoptera

Resumen

Understanding the evolutionary processes underlying extant biodiversity may help us to comprehend why species richness is not equally distributed between clades. One of the main causes to explain the disparity of species richness is the development of key innovations in particular clades, increasing or decreasing their capabilities to occupy new environments, to exploit novel resources or to cope with competition. The present thesis focuses on explaining the macroevolutionary consequences of two of the most common habitat transitions in aquatic environments: between environments with different degree of salinity, and between running and standing waters. Among inhabitants of aquatic environments aquatic Coleoptera are one of the most diverse, with representatives living in all kind of environments, including both running and standing waters and, not infrequently, saline environments. The most speciose aquatic Coleoptera families living in aquatic habitats are Hydrophilidae, Dytiscidae and Hydraenidae, but only the evolution of the ecological transitions of the former have been previously studied under a phylogenetic perspective. In this thesis, we assessed the evolutionary patterns of selected tribes belonging to the other two families. Despite aquatic Coleoptera being a relatively well-studied fauna, we needed to address several systematic modifications that revealed the true evolutionary history of the studied groups, describing a genus and three subgenera of Hygrotini, plus other modifications of both Hygrotini and Ochthebiini taxonomy (Chapters 1 and 3), setting the basis of this thesis. Transitions between environments with different degree of saline waters was addressed for Hygrotini (Dytiscidae family, Chapter 2) and Ochthebiini (Hydraenidae family, Chapter 5). We detected multiple origins of tolerance to saline waters, with a gradual acquisition in almost all cases and only direct transitions to hypersaline waters in fairly isolated clades, mostly associated with coastal rockpools. Moreover, tolerance to hypersaline waters was found to be irreversible, but it did not follow an evolutionary dead-end pattern as lineages exhibiting this trait still maintain their diversification capabilities (as seen in Cobalius subgenus, Chapter 5). Additionally, our results seem to link the origin of lineages exhibiting tolerance to saline waters to periods of global aridification, in accordance with previous studies in Hydrophilidae. Transitions between running and standing waters were studied in Hydroporini (Dytiscidae family, Chapter 6). We unveiled that species living in lotic and lentic habitats display similar diversification patterns, but the habitat preference is affecting the body size of the species, with reduced body sizes in specialized environments (i.e. smaller species in running waters). Finally, the field sampling in saline habitats led to the discovery of a new species for science, described as Ochthebius (Micragasma) minoicus (Chapter 4).