### Abstract

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 with p, 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.

Original language | English |
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Pages (from-to) | 366-382 |

Number of pages | 17 |

Journal | Researches on Population Ecology |

Volume | 22 |

Issue number | 2 |

DOIs | |

Publication status | Published - Dec 1 1980 |

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### All Science Journal Classification (ASJC) codes

- Agricultural and Biological Sciences(all)

### Cite this

*Researches on Population Ecology*,

*22*(2), 366-382. https://doi.org/10.1007/BF02530857

**A sex ratio theory of gregarious parasitoids.** / Suzuki, Yoshito; Iwasa, Yoh.

Research output: Contribution to journal › Article

*Researches on Population Ecology*, vol. 22, no. 2, pp. 366-382. https://doi.org/10.1007/BF02530857

}

TY - JOUR

T1 - A sex ratio theory of gregarious parasitoids

AU - Suzuki, Yoshito

AU - Iwasa, Yoh

PY - 1980/12/1

Y1 - 1980/12/1

N2 - 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 with p, 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.

AB - 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 with p, 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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U2 - 10.1007/BF02530857

DO - 10.1007/BF02530857

M3 - Article

VL - 22

SP - 366

EP - 382

JO - Population Ecology

JF - Population Ecology

SN - 1438-3896

IS - 2

ER -