title: How sexual selection can drive the evolution of costly sperm ornamentation.
abstract: Post-copulatory sexual selection (PSS), fuelled by female promiscuity, is credited with the rapid evolution of sperm quality traits across diverse taxa. Yet, our understanding of the adaptive significance of sperm ornaments and the cryptic female preferences driving their evolution is extremely limited. Here we review the evolutionary allometry of exaggerated sexual traits (for example, antlers, horns, tail feathers, mandibles and dewlaps), show that the giant sperm of some Drosophila species are possibly the most extreme ornaments in all of nature and demonstrate how their existence challenges theories explaining the intensity of sexual selection, mating-system evolution and the fundamental nature of sex differences. We also combine quantitative genetic analyses of interacting sex-specific traits in D. melanogaster with comparative analyses of the condition dependence of male and female reproductive potential across species with varying ornament size to reveal complex dynamics that may underlie sperm-length evolution. Our results suggest that producing few gigantic sperm evolved by (1) Fisherian runaway selection mediated by genetic correlations between sperm length, the female preference for long sperm and female mating frequency, and (2) longer sperm increasing the indirect benefits to females. Our results also suggest that the developmental integration of sperm quality and quantity renders post-copulatory sexual selection on ejaculates unlikely to treat male-male competition and female choice as discrete processes.
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.|Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Lüpold
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.|Department of Biological Sciences, The George Washington University, 800 22nd St. NW, Suite 6000, Washington DC 20052, USA.
authors.forename: Mollie K
authors.initials: MK
authors.lastname: Manier
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.|Department of Biological Sciences, National University of Singapore, 14 Science Drive, SG 117543, Singapore.
authors.forename: Nalini
authors.initials: N
authors.lastname: Puniamoorthy
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Schoff
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.
authors.forename: William T
authors.initials: WT
authors.lastname: Starmer
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.
authors.forename: Shannon H Buckley
authors.initials: SH
authors.lastname: Luepold
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Belote
authors.affiliation: Center for Reproductive Evolution, Department of Biology, Syracuse University, 107 College Place, Syracuse, New York 13244-1270, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Pitnick
mesh_terms: D000818:Animals; D005075:Biological Evolution; D048429:Cell Size; D003163:Competitive Behavior / Q000502:physiology; D003307:Copulation / Q000502:physiology; D004331:Drosophila melanogaster / Q000033:anatomy & histology* / Q000145:classification / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D005260:Female; D008297:Male; D052586:Mating Preference, Animal / Q000502:physiology*; D010063:Ovum / Q000166:cytology / Q000502:physiology; D010641:Phenotype; D012727:Sex Characteristics; D013094:Spermatozoa / Q000166:cytology* / Q000502:physiology*