Translocation reverses birth sex ratio bias depending on its timing during gestation: evidence for the action of two sex-allocation mechanisms

Many sex allocation mechanisms are proposed but rarely have researchers considered and tested more than one at a time. Four facultative birth sex ratio (BSR) adjustment mechanisms are considered: (1) hormone-induced conception bias; (2) sex-differential embryo death from excess glucose metabolism; (3) sex-differential embryo death from embryo–uterine developmental asynchrony; and (4) pregnancy hormone suppression and resource deprivation. All mechanisms could be switched on by the corticoadrenal stress response. A total of 104 female rhinoceroses (Rhinocerotidae), translocated from 1961 to 2004 at different stages of gestation or conceived soon after arrival in captivity, were used to test for a reversal in BSR bias as evidence for the action of multiple sex-allocation mechanisms. Translocation induced a statistically significant BSR reversal between early gestation (86% male births from 0 to 0.19 gestation) and mid-gestation (38% male from 0.2 to 0.79 gestation). Captivity also induced a strongly male-biased (67% male) BSR for conceptions after arrival in captivity. The results indicate the action of at least two sex-allocation mechanisms operating in sequence, confirm the important role of sex-differential embryo death around implantation and of stress in sex allocation, and lend support to suggestions that sex-differential glucose metabolism by the preimplantation embryo likely plays a role in facultative BSR adjustment.

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Sperm sex ratio adjustment in a mammal: perceived male competition leads to elevated proportions of female-producing sperm

Biology Letters ◽

10.1098/rsbl.2019.0929 ◽

2020 ◽

Vol 16 (6) ◽

pp. 20190929

Author(s):

Renée C. Firman ◽

Jamie N. Tedeschi ◽

Francisco Garcia-Gonzalez

Keyword(s):

Sex Ratio ◽

Sex Allocation ◽

Sex Ratios ◽

Female Offspring ◽

Male Competition ◽

Offspring Sex ◽

Sex Ratio Adjustment ◽

Adaptive Adjustment ◽

Male House

Mammal sex allocation research has focused almost exclusively on maternal traits, but it is now apparent that fathers can also influence offspring sex ratios. Parents that produce female offspring under conditions of intense male–male competition can benefit with greater assurance of maximized grand-parentage. Adaptive adjustment in the sperm sex ratio, for example with an increase in the production of X-chromosome bearing sperm (CBS), is one potential paternal mechanism for achieving female-biased sex ratios. Here, we tested this mechanistic hypothesis by varying the risk of male–male competition that male house mice perceived during development, and quantifying sperm sex ratios at sexual maturity. Our analyses revealed that males exposed to a competitive ‘risk’ produced lower proportions of Y-CBS compared to males that matured under ‘no risk’ of competition. We also explored whether testosterone production was linked to sperm sex ratio variation, but found no evidence to support this. We discuss our findings in relation to the adaptive value of sperm sex ratio adjustments and the role of steroid hormones in socially induced sex allocation.

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Flow cytometric sexing of spider sperm reveals an equal sperm production ratio in a female-biased species

Biology Letters ◽

10.1098/rsbl.2014.0159 ◽

2014 ◽

Vol 10 (5) ◽

pp. 20140159 ◽

Cited By ~ 4

Author(s):

B. Vanthournout ◽

K. Deswarte ◽

H. Hammad ◽

T. Bilde ◽

B. Lambrecht ◽

...

Keyword(s):

Sex Ratio ◽

Sex Allocation ◽

Evolutionarily Stable Strategy ◽

General Rule ◽

Sperm Cells ◽

Sperm Production ◽

Male And Female ◽

Ratio Bias ◽

Sex Ratio Bias ◽

Production Ratio

Producing equal amounts of male and female offspring has long been considered an evolutionarily stable strategy. Nevertheless, exceptions to this general rule (i.e. male and female biases) are documented in many taxa, making sex allocation an important domain in current evolutionary biology research. Pinpointing the underlying mechanism of sex ratio bias is challenging owing to the multitude of potential sex ratio-biasing factors. In the dwarf spider, Oedothorax gibbosus , infection with the bacterial endosymbiont Wolbachia results in a female bias. However, pedigree analysis reveals that other factors influence sex ratio variation. In this paper, we investigate whether this additional variation can be explained by the unequal production of male- and female-determining sperm cells during sperm production. Using flow cytometry, we show that males produce equal amounts of male- and female-determining sperm cells; thus bias in sperm production does not contribute to the sex ratio bias observed in this species. This demonstrates that other factors such as parental genes suppressing endosymbiont effects and cryptic female choice might play a role in sex allocation in this species.

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Estimating the Frequency of Constrained Sex Allocation in Field Populations of Hymenoptera

Behaviour ◽

10.1163/156853990x00086 ◽

1990 ◽

Vol 114 (1-4) ◽

pp. 137-147 ◽

Cited By ~ 33

Author(s):

H.C.J. Godfray ◽

I.C.W. Hardy

Keyword(s):

Sex Ratio ◽

Sex Allocation ◽

Sex Ratios ◽

Parasitoid Species ◽

Ratio Bias ◽

Sex Ratio Bias ◽

Sex Ratio Theory

Abstract1) Sex ratio theory has assumed that females can produce offspring of both sexes. It has been suggested that some females in haplodiploid populations are only able to produce sons (constrained sex allocation), for example because they are virgin. The presence of such females influences the optimal sex ratio of unconstrained females. The relevance of these ideas to field sex ratios is largely untested. 2) The frequencies of constrained oviposition in three Drosophila parasitoid species are estimated. Constrained, ovipositing females were distinguished by the absence of sperm in the spermatheca. Constrained females were absent or rare in these species. 3) We review data from the literature that allow an estimate of the frequency of constrained females. 4) We conclude that the available evidence suggests that while constrained oviposition is uncommon, there are some species in which constrained females are sufficiently common to select for an observable sex ratio bias by unconstrained females.

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Breeding ecology and bias in offspring sex ratio in little grassbirds (Megalurus gramineus)

Australian Journal of Zoology ◽

10.1071/zo03002 ◽

2003 ◽

Vol 51 (5) ◽

pp. 505 ◽

Cited By ~ 5

Author(s):

Rebecca R. McIntosh ◽

Romke Kats ◽

Mathew Berg ◽

Jan Komdeur ◽

Mark A. Elgar

Keyword(s):

Sex Ratio ◽

Breeding Season ◽

Salt Marshes ◽

Sex Allocation ◽

Breeding Ecology ◽

Offspring Sex Ratio ◽

Reed Beds ◽

Primary Sex Ratio ◽

Sex Ratio Bias ◽

Offspring Sex

Little grassbirds (Megalurus gramineus) are small, sexually monomorphic passerines that live in reed beds, lignum swamps and salt marshes in southern Australia. The breeding biology and patterns of sex allocation of the little grassbird were investigated over a single breeding season. Our observations of this species in the Edithvale Wetland Reserve revealed a highly male-biased population sex ratio, with some breeding territories containing several additional males. Nevertheless, there was little compelling evidence that little grassbirds breed cooperatively. The growth rates of male and female nestlings were similar and, as predicted by theory, there was no overall primary sex ratio bias. However, the primary sex ratio was female-biased early in the breeding season and became increasingly male-biased later in the breeding season.

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No Evidence for Adaptive Differential Sex Allocation in Red Junglefowl (Gallus Gallus)

The Auk ◽

10.1093/auk/122.4.1161 ◽

2005 ◽

Vol 122 (4) ◽

pp. 1161-1168

Author(s):

Timothy H. Parker

Keyword(s):

Sex Ratio ◽

Brood Size ◽

Sex Allocation ◽

Gallus Gallus ◽

Ratio Analysis ◽

Maternal Condition ◽

Sperm Donor ◽

Sex Ratio Bias ◽

Red Junglefowl ◽

Ratio Data

Abstract In many situations, selection should favor females that bias the sex ratio of their offspring. Two commonly examined factors potentially influencing off- spring sex ratio are paternal ornamentation and maternal condition. Male junglefowl with larger combs are attractive to females. I housed female Red Junglefowl (Gallus gallus) with sterile male consorts and artificially inseminated them with sperm from other males that the females never saw. I found no relationship between either the comb size of the consort or the comb size of the sperm donor and the sex ratio of the offspring. I previously reported a significant sex ratio bias related to maternal mass in Red Junglefowl. However, that analysis was based on sex ratio data not weighted for brood size and assuming a normal distribution. Here, I show that this effect disappears when I conduct a more appropriate analysis weighting sex ratio according to brood size and accounting for the binomial error distribution. I also failed to find evidence that male chicks hatch from larger eggs than female chicks. These results suggest that Red Junglefowl females may not bias the sex ratio of their brood in response to either their own condition or the attractiveness of the males with whom they copulate. Furthermore, these results demonstrate the importance of choosing the correct methods of sex ratio analysis. Falta de Evidencia de Asignación Adaptativa Diferencial entre Sexos en Gallus gallus

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