Variance in male reproductive success and sexual size dimorphism in pinnipeds: testing an assumption of sexual selection theory
Version of Record online: 24 JUL 2013
© 2013 The Mammal Society and John Wiley & Sons Ltd
Volume 44, Issue 2, pages 88–93, April 2014
How to Cite
González-Suárez, M. and Cassini, M. H. (2014), Variance in male reproductive success and sexual size dimorphism in pinnipeds: testing an assumption of sexual selection theory. Mammal Review, 44: 88–93. doi: 10.1111/mam.12012
- Issue online: 4 MAR 2014
- Version of Record online: 24 JUL 2013
- Manuscript Accepted: 12 JUN 2013
- Manuscript Revised: 18 APR 2013
- Manuscript Received: 22 FEB 2013
- Spanish Ministry of Science and Innovation. Grant Numbers: JCI-2011-09158, CGL2012-35931/BOS
- University of Luján (Fondos Finalidad 3.5), Argentina
- genetic paternity;
- habitat differentiation;
- marine mammals;
- mating behaviour
- The theory of evolution by sexual selection for sexual size dimorphism (SSD) postulates that SSD primarily reflects the adaptation of males and females to their different reproductive roles. For example, competition among males for access to females increases male body size because larger males are better able to maintain dominant status than smaller males. Larger dominant males sire most offspring while smaller subordinate males are unsuccessful, leading to skew in reproductive success. Therefore, species with male-biased SSD are predicted to have greater variance in male reproductive success than those in which both sexes are similar in size.
- We tested this prediction among the Pinnipedia, a mammalian group with a great variation in SSD. From a literature review, we identified genetic estimates of male reproductive success for 10 pinniped taxa (eight unique species and two subspecies of a ninth species) that range from seals with similarly sized males and females to species in which males are more than four times as large as females.
- We found no support for a positive relationship between variance in reproductive success and SSD among pinnipeds after excluding the elephant seals Mirounga leonina and Mirounga angustirostris, which we discuss as distinctive cases.
- Several explanations for these results are presented, including the revival of one of Darwin's original ideas. Darwin proposed that natural selection may explain SSD based on differences in energetic requirements between sexes and the potential for sexual niche segregation. Males may develop larger bodies to exploit resources that remain unavailable to females due to the energetic constraints imposed on female mammals by gestation and lactation. The importance of this alternative explanation remains to be tested.