Sex-Ratio Determination in Three Wasp Species Ectoparasitic on Bean Weevil Larvae

Sex ratio theory predicts both mean sex ratio and variance under a range of population structures. Here, we compare two genera of phoretic nematodes (Parasitodiplogaster and Ficophagus spp.) associated with twelve fig-pollinating wasp species in Panama. The host wasps exhibit classic Local Mate Competition: only inseminated females disperse from natal figs, and their offspring form mating pools that consist of scores of the adult offspring contributed by one or a few foundress mothers. In contrast, in both nematode genera, only sexually undifferentiated juveniles disperse, and their mating pools routinely consist of eight or fewer adults. Across all mating pool sizes, the sex ratios observed in both nematode genera are consistently female-biased (~0.34 males), which is markedly less female-biased than is often observed in the host wasps (~0.10 males). In further contrast with their hosts, variances in nematode sex ratios are also consistently precise (significantly less than binomial). The constraints associated with predictably small mating pools within highly subdivided populations appear to select for precise sex ratios that contribute both to the reproductive success of individual nematodes, and to the evolutionary persistence of nematode species. We suggest that some form of environmental sex determination underlies these precise sex ratios.

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The efficacy of natural selection in producing optimal sex ratio adjustments in a fig wasp species

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.1377 ◽

2020 ◽

Vol 287 (1934) ◽

pp. 20201377 ◽

Cited By ~ 1

Author(s):

Jaco M. Greeff ◽

Karina Pentz ◽

Marié Warren

Keyword(s):

Natural Selection ◽

Sex Ratio ◽

A Priori ◽

Fine Tuning ◽

Fig Wasp ◽

Fig Wasps ◽

Wasp Species ◽

Local Mate ◽

Sex Ratio Adjustment ◽

Dual Mechanism

Ever since Darwin's discovery of natural selection, we expect traits to evolve to increase organisms' fitness. As a result, we can use optimization models to make a priori predictions of phenotypic variation, even when selection is frequency-dependent. A notable example is the prediction of female-biased sex ratios resulting from local mate competition (LMC) and inbreeding. LMC models incorporate the effects of LMC and inbreeding. Fig wasp sex ratio adjustments fit LMC predictions well. However, the appropriateness of LMC models to fig wasps has been questioned, and the role that a coincidental by-product plays in creating the apparent fit has been clearly illustrated. Here, we show that the sex ratio adjustments of a fig wasp are the result of a dual mechanism. It consists of a standard facultative LMC response favoured by natural selection, as well as a mechanism that may be the result of selection, but that could also be a coincidental by-product. If it is a by-product, the fitness increase is coincidental and natural selection's role was limited to fine-tuning it for higher fitness returns. We further document a case of an apparent fitness-reducing sex ratio adjustment. We conclude that the use of the adaptationist approach demands that our understanding of traits must be remodelled continually to rectify spurious assumptions.

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Gender Imbalance: The Male/Female Sex Ratio Determination

Journal of Bioeconomics ◽

10.1007/s10818-006-9006-x ◽

2006 ◽

Vol 8 (3) ◽

pp. 253-268 ◽

Cited By ~ 2

Author(s):

Yong J. Yoon

Keyword(s):

Sex Ratio ◽

Gender Imbalance ◽

Female Sex ◽

Ratio Determination

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Sex ratio determination and worker reproduction in the slave-making ant Harpagoxenus sublaevis

Behavioral Ecology and Sociobiology ◽

10.1007/bf00302946 ◽

1988 ◽

Vol 23 (4) ◽

pp. 233-245 ◽

Cited By ~ 39

Author(s):

A. F. G. Bourke ◽

T. M. van der Have ◽

N. R. Franks

Keyword(s):

Sex Ratio ◽

Worker Reproduction ◽

Ratio Determination

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Sex ratio determination by queens and workers in the ant Pheidole desertorum

Animal Behaviour ◽

10.1006/anbe.1999.1343 ◽

2000 ◽

Vol 59 (3) ◽

pp. 523-527 ◽

Cited By ~ 25

Author(s):

Ken R. Helms ◽

Jennifer H. Fewell ◽

Steven W. Rissing

Keyword(s):

Sex Ratio ◽

Ratio Determination

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Genetics of Mother-Dependent Sex Ratio in Blue Mussels (Mytilus spp.) and Implications for Doubly Uniparental Inheritance of Mitochondrial DNA

Genetics ◽

10.1093/genetics/161.4.1579 ◽

2002 ◽

Vol 161 (4) ◽

pp. 1579-1588 ◽

Cited By ~ 1

Author(s):

Ellen Kenchington ◽

Barry MacDonald ◽

Liqin Cao ◽

Defkalion Tsagkarakis ◽

Eleftherios Zouros

Keyword(s):

Mitochondrial Dna ◽

Sex Ratio ◽

Female Parent ◽

Population Level ◽

Uniparental Inheritance ◽

Doubly Uniparental Inheritance ◽

Ratio Bias ◽

Sex Ratio Bias ◽

Mitochondrial Genotype ◽

Ratio Determination

Abstract Previous studies have shown that in most pair matings of Mytilus edulis, M. trossulus, and M. galloprovincialis there is a large sex-ratio bias in favor of either males or females. The degree of bias is a characteristic property of the female parent, as matings of the same female with different males produce the same sex ratio, but matings of the same male with different females produce different sex ratios. All three species possess the unusual feature of doubly uniparental inheritance of mitochondrial DNA (mtDNA); i.e., they contain two distinct types of mtDNA, one that is transmitted matrilinearly and one that is transmitted patrilinearly. This coupling of sex and mtDNA transmission raises the possibility that the mechanism of sex-ratio determination in mussels might be under the control of the mtDNA of the female parent. Here we present data from pedigreed crosses that confirm the previous observations that in mussel matings there is a strong sex-ratio bias and that the bias is under the control of the female parent. In addition, these data strongly suggest that this control is exercised by the mother's nuclear rather than mitochondrial genotype. Making use of these findings we develop a model of mother-dependent sex determination and use data from crosses involving wild females to test the model's predictions at the population level.

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Cooperative interactions among females and even more extraordinary sex ratios

10.1101/2020.06.08.118786 ◽

2020 ◽

Cited By ~ 1

Author(s):

Ryosuke Iritani ◽

Stuart A West ◽

Jun Abe

Keyword(s):

Sex Ratio ◽

Sex Ratios ◽

Structured Populations ◽

Local Mate Competition ◽

Mate Competition ◽

Wasp Species ◽

Cooperative Interactions ◽

Competition Theory ◽

Local Mate ◽

Biased Sex Ratio

AbstractHamilton’s local mate competition theory provided an explanation for extraordinary female biased sex ratios in a range of organisms. When mating takes place locally, in structured populations, a female biased sex ratio is favoured to reduce competition between related males, and to provide more mates for males. However, there are a number of wasp species where the sex ratios appear to more female biased than predicted by Hamilton’s theory. We investigated theoretically the extent to which cooperative interactions between related females can interact with local mate competition to favour even more female biased sex ratios. We found that: (i) cooperative interactions between females can lead to sex ratios that are more female biased than predicted by local competition theory alone; (ii) sex ratios can be more female biased when the cooperative interactions are offspring helping parents before dispersal, rather than cooperation between siblings after dispersal. Our results can be applied to a range of organisms, and provide an explanation for the extreme sex ratio biases that have been observed in Sclerodermus and Melittobia wasps.

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