title: Sperm competition and the evolution of spermatogenesis.
abstract: Spermatogenesis is a long and complex process that, despite the shared overall goal of producing the male gamete, displays striking amounts of interspecific diversity. In this review, we argue that sperm competition has been an important selection pressure acting on multiple aspects of spermatogenesis, causing variation in the number and morphology of sperm produced, and in the molecular and cellular processes by which this happens. We begin by reviewing the basic biology of spermatogenesis in some of the main animal model systems to illustrate this diversity, and then ask to what extent this variation arises from the evolutionary forces acting on spermatogenesis, most notably sperm competition. We explore five specific aspects of spermatogenesis from an evolutionary perspective, namely: (i) interspecific diversity in the number and morphology of sperm produced; (ii) the testicular organizations and stem cell systems used to produce them; (iii) the large number and high evolutionary rate of genes underpinning spermatogenesis; (iv) the repression of transcription during spermiogenesis and its link to the potential for haploid selection; and (v) the phenomenon of selection acting at the level of the germline. Overall we conclude that adopting an evolutionary perspective can shed light on many otherwise opaque features of spermatogenesis, and help to explain the diversity of ways in which males of different species perform this fundamentally important process.
authors.affiliation: Evolutionary Biology, Bielefeld University, Morgenbreede 45, 33615 Bielefeld, Germany steven.ramm@uni-bielefeld.de.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Ramm
authors.affiliation: Evolutionary Biology, Zoological Institute, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Schärer
authors.affiliation: Central Animal Facility of the Faculty of Medicine, University of Münster, Albert-Schweitzer-Campus 1 (A8), 48149 Münster, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Ehmcke
authors.affiliation: Institute of Reproductive and Regenerative Biology, Centre of Reproductive Medicine and Andrology, University of Münster, Albert-Schweitzer-Campus 1 (D11), 48149 Münster, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Wistuba
mesh_terms: D000818:Animals; D005075:Biological Evolution; D048430:Cell Shape; D005260:Female; D005306:Fertilization; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D008297:Male; D012098:Reproduction; D012641:Selection, Genetic; D012726:Sexual Behavior, Animal; D013045:Species Specificity; D013076:Sperm Count; D013084:Sperm-Ovum Interactions; D013091:Spermatogenesis; D013094:Spermatozoa / Q000502:physiology*; D013737:Testis / Q000502:physiology*; D014158:Transcription, Genetic
keywords: evolution; sperm competition; spermatogenesis; spermatogonial stem cells; testicular function