Revision of the genus Bosmina Baird, 1845 (Cladocera: Bosminidae), based on evidence from male morphological characters and molecular phylogenies

The systematics of the freshwater crustacean genus Bosmina Baird, 1845 (Anomopoda: Bosminidae) is notoriously confused. Part of the problem stems from a lack of characters in this cyclic parthenogen. We aimed to remedy this problem by scoring male morphological characters (previously described in just a few species), and by estimating molecular phylogenies. More specifically, the goals of this investigation are: (1) a detailed description of the adult males of Bosmina species; (2) a study of the changes of male characters during the postembryonic development in different subgenera; (3) an analysis of the taxonomical value of male characters; and (4) the estimation of a phylogenetic tree based on male characters and genetic characters from mitochondrial 16S rDNA and nuclear rDNA-internal transcribed spacers (ITS) gene sequences. We redescribed males of ten species: Bosmina (Bosmina) longirostris (O. F. Müller, 1785); Bosmina (Bosmina) liederi De Melo & Hebert, 1994; Bosmina (Sinobosmina) fatalis Burckhardt, 1924; Bosmina (Sinobosmina) cf. fatalis cyanopotamia Burckhardt, 1924; Bosmina (Liederobosmina) meridionalis Sars, 1904; Bosmina (Liederobosmina) cf. hagmanni Stingelin, 1904; Bosmina (Lunobosmina) oriens (De Melo & Hebert, 1994); palaearctic Bosmina (Eubosmina) cf. coregoni Baird, 1857 (including the morphs ‘coregoni s.s.’, ‘coregoni kessleri’, ‘longispina’, and ‘crassicornis’); Beringian ‘Bosmina (Eubosmina) cf. longispina Leydig, 1860’; and Bosmina (Eubosmina) tanakai sp. nov. In addition, we fully redescribe B. (Lunobosmina) oriens and describe B. (E.) tanakai sp. nov. (an endemic Japanese lineage of the subgenus Eubosmina). A cladistic analysis of 24 morphological characters of males led to a single most parsimonious tree that agreed with phylogenies based on 16S mtDNA and nuclear genes. Both the male morphological and the genetic analyses indicated that the Japanese lineage containing B. (E.) tanakai sp. nov. is divergent and unique. Thus, these approaches resolved relationships that were unresolved with female morphology. Divergent life history evolution appears to have rendered male morphology more informative than female morphology for systematic biology. We provide a key for Bosmina species with adequately described males. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 156, 1–51.