Why anisogamy drives ancestral sex roles.
There is a clear tendency in nature for males to compete more strongly for fertilizations than females, yet the ultimate reasons for this are still unclear. Many researchers-dating back to Darwin and Bateman-have argued that the difference is ultimately driven by the fact that males (by definition) produce smaller and more numerous gametes than females. However, this view has recently been challenged, and a formal validation of the link between anisogamy and sex roles has been lacking. Here, we develop mathematical models that validate the intuition of Darwin and Bateman, showing that there is a very simple and general reason why unequal gamete numbers result in unequal investment in sexually competitive traits. This asymmetry does not require multiple mating by either sex, and covers traits such as mate searching, where the male bias has been difficult to explain. Furthermore, our models show males and females are predicted to diverge more strongly when the fertilization probability of each female gamete is high. Sex roles thus ultimately trace back to anisogamy and the resulting consequences for the fertilization process.
Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, 2052, Australia. jussi.lehtonen@iki.fi.|Evolutionary Biology, Zoological Institute, University of Basel, Vesalgasse 1, CH-4051, Basel, Switzerland. jussi.lehtonen@iki.fi.
Jussi
J
Lehtonen
Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, United Kingdom.
Geoff A
GA
Parker
Evolutionary Biology, Zoological Institute, University of Basel, Vesalgasse 1, CH-4051, Basel, Switzerland.
Lukas
L
Schärer
D000818:Animals; D019143:Evolution, Molecular; D005260:Female; D005306:Fertilization / Q000235:genetics*; D005854:Germ Cells / Q000166:cytology* / Q000502:physiology; D008297:Male; D008957:Models, Genetic; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal
Anisogamy; female; isogamy; male; sex roles; sexual selection