Evol Ecol Res 11: 95-107 (2009)     Full PDF if your library subscribes.

For a few males more: do changes in sex ratio predict reproductive success and offspring survival?

Thierry Lodé

Ethologie-Evolution-Ecologie, Université de Rennes 1, Rennes, France

Correspondence: T. Lodé, UMR-CNRS 6552, Ethologie-Evolution-Ecologie, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes, France.
e-mail: thierry.lode@univ-rennes1.fr


Background: Sexual selection theory predicts that if the operational sex ratio is male-biased, females will be choosy, whereas males, for the most part, will compete with each other for mates. However, the influence of the operational sex ratio on reproductive success and offspring survival has rarely been studied.

Question: Does the operational sex ratio influence reproductive success and offspring survival?

Methods: I surveyed the sex ratio and reproductive success of agile frog (Rana dalmatina) populations at 19 breeding sites in western France. I assessed reproductive success using ratios among the number of clutches, the number of froglets, and the daily number of adult frogs. I also determined the survival rate of offspring.

Conclusions: Males dominated in 90% of ponds; the mean adult sex ratio and operational sex ratio ranged from 0.84 to 3.14 and from 2.84 to 13.71 respectively. The number of post-metamorphic froglets per clutch averaged 9.37 (S.D. = 2.37). Variations in the adult sex ratio and operational sex ratio did affect reproductive success. Froglet survival was diminished in populations with higher proportions of males. Furthermore, although each female produced a single clutch regardless of sex ratio, higher proportions of males depressed the average number of clutches per male. Evidently, adult male competition and sexual conflict reduce the fitness of both males and females.

Keywords: fitness, mating success, operational sex ratio, survival.

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