Sexual size dimorphism in mammals
2007 (English)In: Sex, size and gender roles: evolutionary studies of sexual size dimorphism / [ed] Daphne J. Fairbairn, Wolf U. Blanckenhorn, Tamás Székely, New York: Oxford University Press, 2007, 16-26 p.Chapter in book (Refereed)
This chapter explores the pattern of sexual size dimorphism in mammals and the processes that underly its evolution. We find that, on average, male mammals are the larger sex (average male/female mass ratio 1.184), with males being at least 10% larger than females in over 45% of species. Most mammalian orders are also have male-biased sexual dimorphism, although some orders do not show any bias or are significantly female-biased (Lagomorpha). Sexual size dimorphism increases with body size across mammals (Rensch’s rule), suggesting that there are parallel selection pressures on both male and female size. We found support for the hypothesis that male-biased dimorphism relates to sexual selection on males through male–male competition for females. We draw this conclusion from a positive correlation between the degree of sexual selection, as indicated by mating systems and the degree of male biased size dimorphism. The degree of sexual selection was also positively correlated with male and female size across mammals. Further, a parallel selection pressure on female mass is identified in that age at weaning is significantly higher in more polygynous species, even when correcting for body mass. We also explore the processes maintaining smaller female size in sexually dimorphic species and confirm that reproductive rate is lower for larger females, indicating that fecundity selection selects for smaller females in mammals. Although the patterns we discuss hold across mammals as a whole, there is considerable variation across orders and many of these relationships are not significant. Further work is still needed to more closely investigate the pattern of sexual dimorphism and processes driving sexual dimorphism in different clades.
Place, publisher, year, edition, pages
New York: Oxford University Press, 2007. 16-26 p.
IdentifiersURN: urn:nbn:se:su:diva-16290ISBN: 978-0-19-920878-4OAI: oai:DiVA.org:su-16290DiVA: diva2:182810