Elsevier

Animal Behaviour

Volume 76, Issue 1, July 2008, Pages 105-112
Animal Behaviour

Sexual selection in mosquito swarms: may the best man lose?

https://doi.org/10.1016/j.anbehav.2008.01.014Get rights and content

One of the greatest paradoxes in evolutionary biology is the continued maintenance of genetic variation for phenotypic traits that appear to confer strong fitness advantages. Of these traits, body size is perhaps the one that has been most consistently linked to increased longevity and reproductive success in males. We investigated two hypotheses for how events occurring during mating in the mosquito Anopheles gambiae could impede directional selection on male body size: (1) whether male copulation probability is random with respect to body size in aerial swarms, and (2) whether large males are less competitive during mating than smaller, shorter-lived rivals. By manipulation of larval nutritional conditions (low, intermediate and high food allocation), we generated cohorts of male A. gambiae mosquitoes that differed in adult body size and energy reserves (body size and energy reserves being positively correlated with larval nutrition). When competing against one another in aerial swarms, males from the intermediate food treatment were six and two times more successful at acquiring mates than those from the high and low food treatments, respectively. The median survival of males from this most sexually competitive group was approximately 13% lower than that of the larger males with high larval nutrition. We conclude that phenotypic determinants of long-term survival and mating success may not be correlated in this system, and thus that stabilizing selection as well as environmental condition-dependent expression of traits could account for the maintenance of variation in male body size in this species and in other swarming insects.

Section snippets

Rearing

We studied A. gambiae sensu stricto mosquitoes from a population at the Ifakara Health Research and Development (IHRDC), Tanzania. This population was established from a wild population near Njage village, Tanzania, in 1996. We randomly assigned first-instar larvae to one of three food quantity treatments: 0.1 mg, 0.2 mg or 0.4 mg of dried fish food (Tetramin, Melle, Germany) per larva per day (Lyimo et al. 1992). Larvae of the same food treatment were housed together in groups of 100 in standard

RESULTS

By varying larval food, we succeeded in generating three distinct adult male phenotypes, which differed with respect to each of the male traits we measured. First, body size varied substantially between groups (GLM: F2,234 = 94. 128, P < 0.01; Fig. 1), with males from the high food treatment being 18% and 9% bigger than those in the low and medium food treatments, respectively (low food: 2.49 ± 0.015 mm; medium food: 2.69 ± 0.014 mm; high food: 2.94 ± 0.01 mm). The average size of females used in these

DISCUSSION

The mating success of male A. gambiae mosquitoes within swarms in our study was not random, but depended on nutrient uptake during larval development and its impact on adult body size. Contrary to expectation, we observed that the ‘best male’ with respect to frequently observed predictors of male insect fitness (longevity, body size and energy reserves) was not the most competitive in acquiring females within a mating swarm. Instead, we observed that males most likely to win females were those

Acknowledgments

We express our sincere gratitude to Japhet Kihonda, Nicolas Kasigudi and Hassani Ngonyani from the IHRDC Public Health Entomology section and thank the IHRDC, University of Dar es Salaam and Wageningen University for institutional support. This work was supported by a VIDI grant (no. 864.03.004) awarded by the Dutch Scientific Organization (NWO) to B.G.J.K. and a project grant from the International Atomic Energy Agency (IAEA/URT 13295) and BBSRC David Phillips Fellowship to H.M.F.

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  • Cited by (0)

    1

    G. Nkwengulila is at the University of Dar es Salaam, P.O. Box 35064 Dar es Salaam, Tanzania.

    2

    B. G. J. Knols is at the Laboratory of Entomology, Wageningen University and Research Centre, P.O. Box 8031, 6700 EH Wageningen, The Netherlands.

    3

    G. F. Killeen is at Ifakara Health Research and Development Centre Coordination Office, P.O. Box 78373, Kiko Avenue, Dar es Salaam, Tanzania.

    4

    H. M. Ferguson is at the Division of Immunity & Infection, and Division of Environmental & Evolutionary Biology, University of Glasgow, Glasgow G12 8TA, U.K.

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