scholarly journals Male phenotypic quality influences offspring sex ratio in a polygynous ungulate

2006 ◽  
Vol 274 (1610) ◽  
pp. 727-733 ◽  
Author(s):  
Knut H Røed ◽  
Øystein Holand ◽  
Atle Mysterud ◽  
Aage Tverdal ◽  
Jouko Kumpula ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Rangifer Tarandus ◽  
Paternity Analysis ◽  
Differential Allocation ◽  
Offspring Sex Ratio ◽  
Phenotypic Quality ◽  
Secondary Sex Ratio ◽  
Breeding Herd ◽  
Sex Ratio Adjustment ◽  
Attractive Male

Evolutionary models of sex ratio adjustment applied to mammals have ignored that females may gain indirect genetic benefits from their mates. The differential allocation hypothesis (DAH) predicts that females bias the sex ratio of their offspring towards (more costly) males when breeding with an attractive male. We manipulated the number of available males during rut in a polygynous ungulate species, the reindeer ( Rangifer tarandus ), and found that a doubling of average male mass (and thus male attractiveness) in the breeding herd increased the proportion of male offspring from approximately 40 to 60%. Paternity analysis revealed indeed that males of high phenotypic quality sired more males, consistent with the DAH. This insight has consequences for proper management of large mammal populations. Our study suggests that harvesting, by generating a high proportion of young, small and unattractive mates, affects the secondary sex ratio due to differential allocation effects in females. Sustainable management needs to consider not only the direct demographic changes due to harvest mortality and selection, but also the components related to behavioural ecology and opportunities for female choice.

scholarly journals Is biasing offspring sex ratio adaptive? A test of Fisher's principle across multiple generations of a wild mammal in a fluctuating environment

2018 ◽  
Vol 285 (1891) ◽  
pp. 20181251 ◽  
Author(s):  
Andrea E. Wishart ◽  
Cory T. Williams ◽  
Andrew G. McAdam ◽  
Stan Boutin ◽  
Ben Dantzer ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Adult Sex Ratio ◽  
Secondary Sex Ratio ◽  
North American Red Squirrels ◽  
Negative Frequency Dependent Selection ◽  
Fisher’S Principle

Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have more grandoffspring. In a wild population of North American red squirrels ( Tamiasciurus hudsonicus ) that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1 : 1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, the adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring at their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.

scholarly journals Do differences in Toxoplasma prevalence influence global variation in secondary sex ratio? Preliminary ecological regression study

Parasitology ◽  
2016 ◽  
Vol 143 (9) ◽  
pp. 1193-1203 ◽  
Author(s):  
MADHUKAR S. DAMA ◽  
LENKA MARTINEC NOVÁKOVÁ ◽  
JAROSLAV FLEGR
Keyword(s):  
Sex Ratio ◽  
Female Offspring ◽  
Human Populations ◽  
Offspring Sex Ratio ◽  
Global Variation ◽  
Ecological Regression ◽  
Large Populations ◽  
Secondary Sex Ratio ◽  
Genetically Determined ◽  
Male To Female

SUMMARYSex of the fetus is genetically determined such that an equal number of sons and daughters are born in large populations. However, the ratio of female to male births across human populations varies significantly. Many factors have been implicated in this. The theory that natural selection should favour female offspring under suboptimal environmental conditions implies that pathogens may affect secondary sex ratio (ratio of male to female births). Using regression models containing 13 potential confounding factors, we have found that variation of the secondary sex ratio can be predicted by seroprevalence of Toxoplasma across 94 populations distributed across African, American, Asian and European continents. Toxoplasma seroprevalence was the third strongest predictor of secondary sex ratio, β = −0·097, P < 0·01, after son preference, β = 0·261, P < 0·05, and fertility, β = −0·145, P < 0·001. Our preliminary results suggest that Toxoplasma gondii infection could be one of the most important environmental factors influencing the global variation of offspring sex ratio in humans. The effect of latent toxoplasmosis on public health could be much more serious than it is usually supposed to be.

scholarly journals Maternal stress to partner quality is linked to adaptive offspring sex ratio adjustment

2011 ◽  
Vol 22 (4) ◽  
pp. 717-722 ◽  
Author(s):  
Sarah R. Pryke ◽  
Lee A. Rollins ◽  
William A. Buttemer ◽  
Simon C. Griffith
Keyword(s):  
Sex Ratio ◽  
Maternal Stress ◽  
Offspring Sex Ratio ◽  
Offspring Sex ◽  
Sex Ratio Adjustment

An unstable social environment affects sex ratio in guinea pigs: an adaptive maternal effect?

Behaviour ◽  
2009 ◽  
Vol 146 (11) ◽  
pp. 1513-1529 ◽  
Author(s):  
Nikolaus Von Engelhardt ◽  
Sylvia Kaiser ◽  
Norbert Sachser ◽  
Kristina Kemme ◽  
Ton Groothuis ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Sex Ratio ◽  
Social Environment ◽  
Guinea Pigs ◽  
Social Situation ◽  
Offspring Sex Ratio ◽  
Social Instability ◽  
Environmental Disasters ◽  
Offspring Sex ◽  
Secondary Sex Ratio

AbstractEvolutionary theory suggests that offspring sex should be adjusted to environmental conditions in order to maximize future reproductive success. In several animal taxa environmental factors indeed affect the secondary sex ratio. In humans, changes in the sex ratio at birth have been associated with population stressors like war, environmental disasters or economic strife during pregnancy. Here we compared litter sex ratios of female guinea pigs, exposed experimentally to a stable and an unstable social environment. In the latter group composition was changed every three days. Under unstable social conditions the sex ratio was significantly more biased towards daughters than in the stable social situation. This finding was consistent among four independent experiments, conducted independently from each other. Life expectancy can be dramatically reduced under conditions of social instability. Hence mothers in such conditions should bias their investment towards the sex that reaches sexual maturity first, which is the female sex in this species. Thus, to shift the offspring sex ratio towards more daughters under conditions of social instability may represent a maternal strategy to maximize future reproductive success.

scholarly journals Meiotic drive and sex determination: molecular and cytological mechanisms of sex ratio adjustment in birds

2007 ◽  
Vol 363 (1497) ◽  
pp. 1675-1686 ◽  
Author(s):  
Joanna Rutkowska ◽  
Alexander V Badyaev
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Sex Chromosomes ◽  
Sex Ratios ◽  
Relative Fitness ◽  
Compensatory Mechanisms ◽  
Offspring Sex Ratio ◽  
Epigenetic Effects ◽  
Offspring Sex ◽  
Sex Ratio Adjustment

Differences in relative fitness of male and female offspring across ecological and social environments should favour the evolution of sex-determining mechanisms that enable adjustment of brood sex ratio to the context of breeding. Despite the expectation that genetic sex determination should not produce consistent bias in primary sex ratios, extensive and adaptive modifications of offspring sex ratio in relation to social and physiological conditions during reproduction are often documented. Such discordance emphasizes the need for empirical investigation of the proximate mechanisms for modifying primary sex ratios, and suggests epigenetic effects on sex-determining mechanisms as the most likely candidates. Birds, in particular, are thought to have an unusually direct opportunity to modify offspring sex ratio because avian females are heterogametic and because the sex-determining division in avian meiosis occurs prior to ovulation and fertilization. However, despite evidence of strong epigenetic effects on sex determination in pre-ovulatory avian oocytes, the mechanisms behind such effects remain elusive. Our review of molecular and cytological mechanisms of avian meiosis uncovers a multitude of potential targets for selection on biased segregation of sex chromosomes, which may reflect the diversity of mechanisms and levels on which such selection operates in birds. Our findings indicate that pronounced differences between sex chromosomes in size, shape, size of protein bodies, alignment at the meiotic plate, microtubule attachment and epigenetic markings should commonly produce biased segregation of sex chromosomes as the default state, with secondary evolution of compensatory mechanisms necessary to maintain unbiased meiosis. We suggest that it is the epigenetic effects that modify such compensatory mechanisms that enable context-dependent and precise adjustment of primary sex ratio in birds. Furthermore, we highlight the features of avian meiosis that can be influenced by maternal hormones in response to environmental stimuli and may account for the precise and adaptive patterns of offspring sex ratio adjustment observed in some species.

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