title: Breeding system, shell size and age at sexual maturity affect sperm length in stylommatophoran gastropods.
abstract: BACKGROUND
  Sperm size and quality are key factors for fertilization success. There is increasing empirical evidence demonstrating that sperm form and function are influenced by selective pressures. Theoretical models predict that sperm competition could favour the evolution of longer sperm. In hermaphrodites, self-fertilizing species are expected to have shorter sperm than cross-fertilizing species, which use sperm stored from several mating partners for the fertilization of their eggs and thus are exposed to intense sperm competition. We tested this hypothesis by comparing original data on sperm length in 57 species of simultaneously hermaphroditic stylommatophoran gastropods from Europe and South America with respect to the species' breeding system. We used 28S rRNA nuclear and COI mitochondrial sequence data to construct a molecular phylogeny. Phylogenetic generalized linear models were applied to examine the potential influence of morphological and life-history characters.
  
  
  RESULTS
  The best-fit model revealed that the breeding system and age at sexual maturity influence sperm length in gastropods. In general, species with predominant cross-fertilization had longer sperm than species with predominant self-fertilization or a mixed breeding system. Across species with shells (snails), sperm length also increased with shell size.
  
  
  CONCLUSIONS
  Our study provides evidence that sperm length in stylommatophoran gastropods is influenced by the risk of sperm competition, as well as by age at sexual maturity and shell size. This finding extends present knowledge of sperm evolution to a group of so far poorly studied simultaneous hermaphrodites.
authors.affiliation: Department of Environmental Sciences, Section of Conservation Biology, University of Basel, St. Johanns-Vorstadt 10, 4056, Basel, Switzerland. schmera.denes@okologia.mta.hu.|MTA Centre for Ecological Research, Balaton Limnological Institute, Klebelsberg Kuno 3, 8237, Tihany, Hungary. schmera.denes@okologia.mta.hu.
authors.forename: Dénes
authors.initials: D
authors.lastname: Schmera
authors.affiliation: Departamento de Biología, Bioquímica y Farmacia, Laboratorio de Zoología de Invertebrados 1, Universidad Nacional del Sur, San Juan 670, 8000, Bahía Blanca, Argentina.
authors.forename: Julia
authors.initials: J
authors.lastname: Pizá
authors.affiliation: Department of Environmental Sciences, Section of Conservation Biology, University of Basel, St. Johanns-Vorstadt 10, 4056, Basel, Switzerland.
authors.forename: Ellen
authors.initials: E
authors.lastname: Reinartz
authors.affiliation: Department of Environmental Sciences, Section of Conservation Biology, University of Basel, St. Johanns-Vorstadt 10, 4056, Basel, Switzerland.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Ursenbacher
authors.affiliation: Department of Environmental Sciences, Section of Conservation Biology, University of Basel, St. Johanns-Vorstadt 10, 4056, Basel, Switzerland.
authors.forename: Bruno
authors.initials: B
authors.lastname: Baur
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology; D000818:Animals; D001947:Breeding; D019143:Evolution, Molecular; D057850:Hermaphroditic Organisms / Q000235:genetics; D008297:Male; D010802:Phylogeny; D012098:Reproduction; D012741:Sexual Maturation; D012908:Snails / Q000166:cytology* / Q000235:genetics; D013094:Spermatozoa / Q000166:cytology*
keywords: Comparative approach; Gastropods; Phylogeny; Sexual selection; Sperm competition; Sperm evolution