Male phenotypic quality influences offspring sex ratio in a polygynous ungulate.
Evolutionary models of sex ratio adjustment applied to mammals have ignored that females may gain indirect genetic benefits from their mates. The differential allocation hypothesis (DAH) predicts that females bias the sex ratio of their offspring towards (more costly) males when breeding with an attractive male. We manipulated the number of available males during rut in a polygynous ungulate species, the reindeer (Rangifer tarandus), and found that a doubling of average male mass (and thus male attractiveness) in the breeding herd increased the proportion of male offspring from approximately 40 to 60%. Paternity analysis revealed indeed that males of high phenotypic quality sired more males, consistent with the DAH. This insight has consequences for proper management of large mammal populations. Our study suggests that harvesting, by generating a high proportion of young, small and unattractive mates, affects the secondary sex ratio due to differential allocation effects in females. Sustainable management needs to consider not only the direct demographic changes due to harvest mortality and selection, but also the components related to behavioural ecology and opportunities for female choice.
Røed
Knut H
KH
Department of Basic Sciences and Aquatic Medicine, Norwegian School of Veterinary Science, PO Box 8146, Departmental Division, 0033 Oslo, Norway.
Holand
Øystein
Ø
Mysterud
Atle
A
Tverdal
Aage
A
Kumpula
Jouko
J
Nieminen
Mauri
M
D000818:Animals; D005075:Biological Evolution; D003247:Conservation of Natural Resources / Q000379:methods*; D005387:Finland; D016015:Logistic Models; D008297:Male; D008962:Models, Theoretical; D010641:Phenotype; D012053:Reindeer / Q000502:physiology*; D012737:Sex Factors; D012744:Sex Ratio; D012726:Sexual Behavior, Animal / Q000502:physiology*