The Baetis vernus group (Ephemeroptera: Baetidae) of northernmost Europe: An evidently diverse but poorly understood group of mayflies

Abstract

The Baetis vernus group is known to be a taxonomically difficult group of mayflies. Morphological characters such as the mandibles or gills of nymphs overlap widely. We report here that enzyme electromorph frequencies also fail to show reproductive isolation in many cases. Baetis macani has been divided in the literature into two forms, a lentic one with broader gills living in stagnant waters, while the lotic one with narrower gills lives in flowing water. We show that the two evidently represent reproductively isolated taxa, B. macani Kimmins = B. bundyae auct. nec, while the one with broader gills appears to be a new species. Baetis macani, B. subalpinus, B. liebenauae and B. vernus form a cluster that is genetically not divisible according to the recognized species boundaries. Nymph gill length differentiates, however, B. macani from B. subalpinus and B. vernus. We call for studies on population structuring and molecular taxonomy to resolve the taxonomy and ecology of this important group of mayflies. © Entomologica Fennica. 2007.