Geographical and seasonal evidence of cryptic diversity in the Baetis rhodani complex (Ephemeroptera, Baetidae) revealed by means of DNA taxonomy

Previous phylogenetic investigations on the mayfly Baetis rhodani Pictet from several European countries, excluding Italy, strongly suggested the presence of cryptic species. Our paper reports a DNA-taxonomy phylogenetic analysis of B. rhodani with additional populations coming from Italian and UK sites, and aims to identify potential cryptic species with a coalescent-based method (GMYC model) and to understand the mechanisms of local coexistence of cryptic species. Twenty-five haplotypes of Italian samples and five haplotypes of UK samples were identified and added to a large European dataset. A total of 11 potential cryptic species have been recognised, and three of them co-occured in one Italian area. Such cryptic species seem to be phylogenetically over-dispersed on the tree and temporally segregated, and the seasonal substitution pattern of cryptic species could explain the apparently widespread distribution of the B. rhodani complex and its ability to adapt to different temperatures and food resources, justifying some of the differences observed in the relationship between water temperature, growth rates and phenology documented from field studies.