title: Population density and group size effects on reproductive behavior in a simultaneous hermaphrodite.
abstract: BACKGROUND
  Despite growing evidence that population dynamic processes can have substantial effects on mating system evolution, little is known about their effect on mating rates in simultaneous hermaphrodites. According to theory, mating rate is expected to increase with mate availability because mating activity is primarily controlled by the male sexual function. A different scenario appears plausible in the hermaphroditic opisthobranch Chelidonura sandrana. Here, field mating rates are close to the female fitness optimum, suggesting that mating activity remains unresponsive to variation in mate availability.
  
  
  RESULTS
  Applying an experimental design that aims at independent experimental manipulation of density and social group size, we find substantial increases in mate encounter rate with both factors, but no statistically detectable effects on mating rate in C. sandrana. Instead, mating rate remained close to the earlier determined female fitness optimum.
  
  
  CONCLUSIONS
  We demonstrate that mating rate in C. sandrana is largely unresponsive to variation in mate availability and is maintained close to the female fitness optimum. These findings challenge the prevailing notion of male driven mating rates in simultaneous hermaphrodites and call for complementary investigations of mating rate effects on fitness through the male sexual function.
authors.affiliation: Animal Evolutionary Ecology, Institute of Evolution and Ecology, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. dennis.sprenger@uni-tuebingen.de
authors.forename: Dennis
authors.initials: D
authors.lastname: Sprenger
authors.forename: Rolanda
authors.initials: R
authors.lastname: Lange
authors.forename: Nils
authors.initials: N
authors.lastname: Anthes
mesh_terms: D000818:Animals; D005260:Female; D049851:Gastropoda / Q000502:physiology*; D008297:Male; D011156:Population Density; D011157:Population Dynamics; D012098:Reproduction; D012726:Sexual Behavior, Animal