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© 1996 International Society for Behavioral Ecology
research-article |
Fitness effects of sex ratio response to host quality and size in the parasitoid wasp Spalangia cameroni
Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115, USA
ABSTRACT
The parasitoid wasp Spalangia cameroni oviposited a greater proportion of daughters in stable fly pupae than in house fly pupae, even when I controlled for stable flies being smaller than house flies. Sex ratio manipulation in response to host quality has been modeled as being adaptive through an effect of host quality on the size and hence offspring production of daughters. 5. cameronis response to host species may instead be adaptive through an effect on larval survivorship, the development time of daughters, and the size of sons. There was greater survival of daughters than sons on stable flies. Controlling for host size, I found that development time of daughters was about 2% less on stable flies than on house flies. The decrease in development time corresponds to a 2% increase in fitness as estimated by r, the intrinsic rate of increase, and is equivalent to about a 9% increase in offspring production. Sons were about 2% larger from house flies than stable flies, which may increase offspring production by up to 3%. Host species had no consistent effect on size of daughters or development time of sons. In addition to the response to host species, mothers oviposited a greater proportion of daughters in larger stable fly hosts. Whether this behavior is adaptive is unclear. Although offspring were larger when they developed on larger stable flies, the rate of increase was less for daughters dian for sons. Effects of stable fly size on offspring development time were negligible.
Key words: development time, fitness, host size, Hymenoptera, natural selection, parasitoid wasp, sex ratio.