Abstract
The median proportion of investment in females among 11 populations of seven bumble bee (Bombus) species was 0.32 (range 0.07 to 0.64). By contrast, two species of workerless social parasites in the related genus Psithyrus had female-biased sex allocation, the reasons for which remain unclear. Male-biased sex allocation in Bombus contradicts the predictions of Trivers and Hare's sex ratio model for the social Hymenoptera, which are that the population sex investment ratio should be 0.5 (1:1) under queen control and 0.75 (3:1 females:males) under worker control (assuming single, once-mated, outbred queens and non-reproductive workers). Male bias in Bombus does not appear to be either an artefact, or purely the result of symbiotic sex ratio distorters. According to modifications of the Trivers–Hare model, the level of worker male-production in Bombus is insufficient to account for observed levels of male bias. There is also no evidence that male bias arises from either local resource competition (related females compete for resources) or local mate enhancement (related males cooperate in securing mates). Bulmer presented models predicting sexual selection for protandry (males are produced before females) in annual social Hymenoptera and, as a consequence (given some parameter values), male-biased sex allocation. Bumble bees fit the assumptions of Bulmer's models and are protandrous. These models therefore represent the best current explanation for the bees' male-biased sex investment ratios. This conclusion suggests that the relative timing of the production of the sexes strongly influences sex allocation in the social Hymenoptera.
Keywords: Social Insect Bombus Psithyrus Sex Allocation Mating System Protandry
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Selected References
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- Benford F. A. Fisher's theory of the sex ratio applied to the social hymenoptera. J Theor Biol. 1978 Jun 20;72(4):701–727. doi: 10.1016/0022-5193(78)90279-5. [DOI] [PubMed] [Google Scholar]
- Clark A. B. Sex ratio and local resource competition in a prosimian primate. Science. 1978 Jul 14;201(4351):163–165. doi: 10.1126/science.201.4351.163. [DOI] [PubMed] [Google Scholar]
- Estoup A., Scholl A., Pouvreau A., Solignac M. Monoandry and polyandry in bumble bees (Hymenoptera; Bombinae) as evidenced by highly variable microsatellites. Mol Ecol. 1995 Feb;4(1):89–93. doi: 10.1111/j.1365-294x.1995.tb00195.x. [DOI] [PubMed] [Google Scholar]
- Estoup A., Solignac M., Cornuet J. M., Goudet J., Scholl A. Genetic differentiation of continental and island populations of Bombus terrestris (Hymenoptera: Apidae) in Europe. Mol Ecol. 1996 Feb;5(1):19–31. doi: 10.1111/j.1365-294x.1996.tb00288.x. [DOI] [PubMed] [Google Scholar]
- Hamilton W. D. Extraordinary sex ratios. A sex-ratio theory for sex linkage and inbreeding has new implications in cytogenetics and entomology. Science. 1967 Apr 28;156(3774):477–488. doi: 10.1126/science.156.3774.477. [DOI] [PubMed] [Google Scholar]
- Hamilton W. D. The genetical evolution of social behaviour. II. J Theor Biol. 1964 Jul;7(1):17–52. doi: 10.1016/0022-5193(64)90039-6. [DOI] [PubMed] [Google Scholar]
- Sundstrom L, Chapuisat M, Keller L. Conditional Manipulation of Sex Ratios by Ant Workers: A Test of Kin Selection Theory. Science. 1996 Nov 8;274(5289):993–995. doi: 10.1126/science.274.5289.993. [DOI] [PubMed] [Google Scholar]
- Trivers R. L., Hare H. Haploidploidy and the evolution of the social insect. Science. 1976 Jan 23;191(4224):249–263. doi: 10.1126/science.1108197. [DOI] [PubMed] [Google Scholar]
- Werren J. H., Charnov E. L. Facultative sex ratios and population dynamics. Nature. 1978 Mar 23;272(5651):349–350. doi: 10.1038/272349a0. [DOI] [PubMed] [Google Scholar]