Parental investment and sex differences in juvenile mortality in birds and mammals

  title={Parental investment and sex differences in juvenile mortality in birds and mammals},
  author={Tim H. Clutton‐Brock and Steve D Albon and Fiona E. Guinness},
The common finding that juvenile male mammals show higher mortality than females1,2 is usually attributed either to the expression of deleterious recessive alleles on the X chromosome3 or to adaptive manipulation of the postnatal sex ratio by mothers who are unable to rear successful sons4,5. As a general explanation of differential juvenile mortality, the first of these two theories is unsatisfactory because increased male mortality is known to occur in several bird species where females are… 

When Should Avian Parents Differentially Provision Sons and Daughters?

The topic of sex-biased provisioning in birds would seem to be a fertile field for further discussion and empirical studies, given the scarcity of data on sex differences in the behavior, provisioning, growth, and development of young birds.

Variations in the birth sex ratio and neonatal mortality in a natural herd of horses

It is shown that the environmental conditions that predicted lower survival of males were negatively related to their production: the birth sex ratio the following year was female-biased; and mares were less likely to produce a son when they had produced a son the preceding year.

Offspring sex ratio in the Common Tern Sterna hirundo, a species with negligible sexual size dimorphism

Variation in offspring sex ratio in the Common Tern Sterna hirundo, a species with negligible sexual size dimorphism, is examined, finding that the sex ratio of c-eggs, but not of earlier laid eggs, was significantly biased in favour of females.

Size matters: competition between male and female great tit offspring.

  • K. Oddie
  • Biology, Environmental Science
    The Journal of animal ecology
  • 2000
The study suggests that male biased fledging/recruitment sex ratios in great tits may be explained by enhanced competitive ability of male nestlings in poor rearing environments.

Sex allocation and sex‐specific parental investment in an endangered seabird

While further research is needed to confirm this trend, populations with male-skewed ASRs have higher extinction risks and conservation strategies aiming to benefit female African Penguin might need to be developed.

Sex Ratio Variation in Mammals

Valid evidence that sex ratio trends are adaptive must be based on the overall distribution of trends or on cases in which the sex ratio can be shown to vary with the relative fitness of producing sons and daughters.

Population density affects sex ratio variation in red deer

It is shown that the adaptive relationship between maternal dominance and offspring sex ratio previously demonstrated in red deer, where dominant females produced more males, disappeared at high population density.

Sexual dimorphism, survival, and parental investment in relation to offspring sex in a precocial bird

Examination of differential growth rates during early life resulting from sexual size dimorphism and how parents may respond in a precocial bird, the black brant Branta bernicla nigricans, suggest that sex‐biased growth rate can dramatically affect population dynamics through sex-biased survival and recruitment which in turn affects decisions parents make about sex allocation and parental investment.

Evolution of large males is associated with female‐skewed adult sex ratios in amniotes

Evidence is provided that skewed ASRs in amniote populations can result in the rarer sex evolving large size to capitalize on enhanced mating opportunities, and Phylogenetic path analysis indicates that higher mortality in one sex leads to skewed ASR, which in turn may generate selection for SSD biased toward the rare sex.



Balanced Sex Ratios in Dimorphic Altricial Birds: The Contribution of Sex-Specific Growth Dynamics

Sex ratio theory holds that the population sex ratio at the termination of parental care should reflect expenditures on males and females. Where sexual dimorphism occurs in required expenditure, the

Maternal dominance, breeding success and birth sex ratios in red deer

It is shown that, in polygynous red deer (Cervus elaphus), dominant mothers produce significantly more sons than subordinates and that maternal rank has a greater effect on the breeding success of males than females.

Sex Ratio Adjustment Under Food Stress: Maximization of Quality or Numbers of Offspring?

  • J. Myers
  • Economics
    The American Naturalist
  • 1978
The hypothesis that poor environmental conditions will lead to the production of the cheaper sex allowing for maximization of the number of young produced is proposed as an alternative to the hypothesis that females in poor condition should produce female offspring.

Natural Selection of Parental Ability to Vary the Sex Ratio of Offspring

Theory and data suggest that a male in good condition at the end of the period of parental investment is expected to outreproduce a sister in similar condition, while she is expected to outreproduce

Variation in Nestling Sex Ratios in the Yellow-Headed Blackbird

This paper raises an additional facet of sex-ratio theory and presents relevant data on why healthy females hould be more likely to produce male offspring than unhealthy females and requires populations in which males differ in ability to acquire mates.

Sex-Ratio Adjustment in the Common Grackle

The first result suggests an adaptive nonrandom meiosis that anticipates seasonal conditions of food availability and the second implies a brood reduction strategy consistent with Fisher's prediction that differential mortality in sexually dimorphic species should favor the less expensive sex.

Sex Differences in Mortality in Abraxas-Type Species

The sex-linked lethal theory seeks to explain the higher male mortality on the view that the male with but one X chromosome would inevitably suffer more frequently from sexlinked recessive characters which, being often lethal, semi-lethal, or injurious, would tend to reduce average vigor and viability-than would the females with two X chromosomes.

Binomial Sex-Ratio Distribution in the Lesser Snow Goose: A Theoretical Enigma

A large sample of goslings does show a sex-ratio distribution which closely fits the binomial, thus refuting the theoretical argument and speculation that pleiotropic effects of sex-skew mutations place a selective disadvantage on such mutations.

Population Dynamics and Mortality of Reindeer Introduced into South Georgia

Reindeer (Rangifer tarandus) were introduced into South Georgia in 1911 and 1925, and now form 3 herds, which was at a different stage of an irruptive oscillation when they were studied during 1972-76, and increased availability of food appears to initiate the upswing of a population fluctuation or irruption in deer and other ungulates.