A sex ratio theory of gregarious parasitoids |
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Authors: | Yoshito Suzuki Yoh Iwasa |
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Institution: | (1) Institute of Biological Control, Faculty of Agriculture, Kyushu University, 812 Fukuoka, Japan;(2) Department of Biophysics, Faculty of Science, Kyoto University, 606 Kyoto, Japan;(3) Present address: Department of Biophysics, Faculty of Science, Kyoto University, 606 Kyoto, Japan |
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Abstract: | Summary A mathematical model is constructed to explain a density-dependent increase in the progeny sex ratios of gregarious parasitoids.
In the model we considered non-cooperative game between females concerned with their own inclusive fitness. Equilibrium progeny
sex ratios of the first and second females ovipositing on the same host are expressed in terms of the probability of double
parasitism (p), the ratio of a male to a female in contribution to resource competition (α), the clutch size ratio between the two females
(β), the crowding effect on female reproductive success (γ), and the inbreeding coefficient (f). Major predictions from the model are: 1) the progeny sex ratios of both the first and second females increase withp, 2) as β becomes smaller, the progeny sex ratios of the first females decrease, while those of the second females dramatically
increases, 3) when a host is attacked by at most two wasps, the sex ratio of the total number of eggs laid on the host does
not exceed 0.25. The effects of α and preferential death by female progeny in doubly parasitized hosts are considered as factors
responsible for an excess number of males at emergence. Some possible modes of density-dependent increase in the sex ratios
of the overall progeny populations is also discussed on the basis of the present model. |
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Keywords: | Clutch Size Inclusive Fitness Female Parasitoid Female Wasp Female Progeny |
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