title: Coexisting cyclic parthenogens comprise a holocene species flock in Eubosmina.
abstract: BACKGROUND
  Mixed breeding systems with extended clonal phases and weak sexual recruitment are widespread in nature but often thought to impede the formation of discrete evolutionary clusters. Thus, cyclic parthenogens, such as cladocerans and rotifers, could be predisposed to "species problems" and a lack of discrete species. However, species flocks have been proposed for one cladoceran group, Eubosmina, where putative species are sympatric, and there is a detailed paleolimnological record indicating a Holocene age. These factors make the Eubosmina system suitable for testing the hypotheses that extended clonal phases and weak sexual recruitment inhibit speciation. Although common garden experiments have revealed a genetic component to the morphotypic variation, the evolutionary significance of the morphotypes remains controversial.
  
  
  RESULTS
  In the present study, we tested the hypothesis of a single polymorphic species (i.e., mixing occurs but selection maintains genes for morphology) in four northern European lakes where the morphotypes coexist. Our evidence is based on nuclear DNA sequence, mitochondrial DNA sequence, and morphometric analysis of coexisting morphotypes. We found significant genetic differentiation, genealogical exclusivity, and morphometric differentiation for coexisting morphotypes.
  
  
  CONCLUSIONS
  We conclude that the studied morphotypes represent a group of young species undergoing speciation with apparent reproductive barriers despite coexistence in the freshwater pelagic zone.
authors.affiliation: Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York, United States of America. marfaustova@hotmail.com
authors.forename: Markéta
authors.initials: M
authors.lastname: Faustová
authors.forename: Veronika
authors.initials: V
authors.lastname: Sacherová
authors.forename: H David
authors.initials: HD
authors.lastname: Sheets
authors.forename: Jan-Erik
authors.initials: JE
authors.lastname: Svensson
authors.forename: Derek J
authors.initials: DJ
authors.lastname: Taylor
mesh_terms: D000818:Animals; D001947:Breeding; D003445:Crustacea / Q000145:classification / Q000235:genetics* / Q000502:physiology; D004272:DNA, Mitochondrial / Q000235:genetics; D005060:Europe; D005618:Fresh Water
chemical_list: D004272:DNA, Mitochondrial