Sex investment ratios in eusocial Hymenoptera support inclusive fitness theory

Bourke, Andrew F. G. ORCID: (2015) Sex investment ratios in eusocial Hymenoptera support inclusive fitness theory. Journal of Evolutionary Biology, 28 (11). pp. 2106-2111. ISSN 1010-061X

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Inclusive fitness theory predicts that sex investment ratios in eusocial Hymenoptera are a function of the relatedness asymmetry (relative relatedness to females and males) of the individuals controlling sex allocation. In monogynous ants (with one queen per colony), assuming worker control, the theory therefore predicts female-biased sex investment ratios, as found in natural populations. Recently, E.O. Wilson and M.A. Nowak criticized this explanation and presented an alternative hypothesis. The Wilson–Nowak sex ratio hypothesis proposes that, in monogynous ants, there is selection for a 1 : 1 numerical sex ratio to avoid males remaining unmated, which, given queens exceed males in size, results in a female-biased sex investment ratio. The hypothesis also asserts that, contrary to inclusive fitness theory, queens not workers control sex allocation and queen–worker conflict over sex allocation is absent. Here, I argue that the Wilson–Nowak sex ratio hypothesis is flawed because it contradicts Fisher’s sex ratio theory, which shows that selection on sex ratio does not maximize the number of mated offspring and that the sex ratio proposed by the hypothesis is not an equilibrium for the queen. In addition, the hypothesis is not supported by empirical evidence, as it fails to explain ‘split’ (bimodal) sex ratios or data showing queen and worker control and ongoing queen–worker conflict. By contrast, these phenomena match predictions of inclusive fitness theory. Hence, the Wilson–Nowak sex ratio hypothesis fails both as an alternative hypothesis for sex investment ratios in eusocial Hymenoptera and as a critique of inclusive fitness theory.

Item Type: Article
Additional Information: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Uncontrolled Keywords: kin selection,relatedness,sex ratio,social insect,split sex ratio,worker control
Faculty \ School: Faculty of Science > School of Biological Sciences
UEA Research Groups: Faculty of Science > Research Centres > Centre for Ecology, Evolution and Conservation
Faculty of Science > Research Groups > Organisms and the Environment
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Depositing User: Pure Connector
Date Deposited: 13 Nov 2015 15:00
Last Modified: 18 May 2023 00:23
DOI: 10.1111/jeb.12710


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