title: Evolution of sperm morphology in anurans: insights into the roles of mating system and spawning location.
abstract: BACKGROUND
  The degree of postcopulatory sexual selection, comprising variable degrees of sperm competition and cryptic female choice, is an important evolutionary force to influence sperm form and function. Here we investigated the effects of mating system and spawning location on the evolution of sperm morphology in 67 species of Chinese anurans. We also examined how relative testes size as an indicator of the level of sperm competition affected variation in sperm morphology across a subset of 29 species.
  
  
  RESULTS
  We found a significant association of mating system and spawning location with sperm morphology. However, when removing the effects of body mass or absolute testes mass for species for which such data were available, this effect became non-significant. Consistent with predictions from sperm competition theory, we found a positive correlation between sperm morphology and relative testes size after taking phylogeny into account.
  
  
  CONCLUSIONS
  Our findings suggest that sexual selection in Chinese anurans favors longer sperm when the level of sperm competition is high. Pre-copulatory male-male competition and spawning location, on the other hand, do not affect the evolution of sperm morphology after taking body mass and absolute testes mass into account.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zeng
authors.forename: Shang Ling
authors.initials: SL
authors.lastname: Lou
authors.affiliation: Key Laboratory of Southwest China Wildlife Resources Conservation (Ministry of Education), China West Normal University, Nanchong 637009, P, R, China. Liaobo_0_0@126.com.
authors.forename: Wen Bo
authors.initials: WB
authors.lastname: Liao
authors.forename: Robert
authors.initials: R
authors.lastname: Jehle
mesh_terms: D000818:Animals; D001001:Anura / Q000033:anatomy & histology / Q000145:classification* / Q000502:physiology*; D005075:Biological Evolution; D005260:Female; D008297:Male; D012098:Reproduction; D013094:Spermatozoa / Q000166:cytology* / Q000502:physiology; D013737:Testis / Q000033:anatomy & histology