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Increased male bias in eider ducks can be explained by sex-specific survival of prime-age breeders.

ABSTRACT: In contrast to theoretical predictions of even adult sex ratios, males are dominating in many bird populations. Such bias among adults may be critical to population growth and viability. Nevertheless, demographic mechanisms for biased adult sex ratios are still poorly understood. Here, we examined potential demographic mechanisms for the recent dramatic shift from a slight female bias among adult eider ducks (Somateria mollissima) to a male bias (about 65% males) in the Baltic Sea, where the species is currently declining. We analysed a nine-year dataset on offspring sex ratio at hatching based on molecularly sexed ducklings of individually known mothers. Moreover, using demographic data from long-term individual-based capture-recapture records, we investigated how sex-specific survival at different ages after fledgling can modify the adult sex ratio. More specifically, we constructed a stochastic two-sex matrix population model and simulated scenarios of different survival probabilities for males and females. We found that sex ratio at hatching was slightly female-biased (52.8%) and therefore unlikely to explain the observed male bias among adult birds. Our stochastic simulations with higher survival for males than for females revealed that despite a slight female bias at hatching, study populations shifted to a male-biased adult sex ratio (> 60% males) in a few decades. This shift was driven by prime reproductive-age individuals (?5-year-old), with sex-specific survival of younger age classes playing a minor role. Hence, different age classes contributed disproportionally to population dynamics. We argue that an alternative explanation for the observed male dominance among adults-sex-biased dispersal-can be considered redundant and is unlikely, given the ecology of the species. The present study highlights the importance of considering population structure and age-specific vital rates when assessing population dynamics and management targets.

SUBMITTER: Ramula S

PROVIDER: S-EPMC5892891 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Increased male bias in eider ducks can be explained by sex-specific survival of prime-age breeders.

Ramula Satu S Öst Markus M Lindén Andreas A Karell Patrik P Kilpi Mikael M

PloS one 20180410 4

In contrast to theoretical predictions of even adult sex ratios, males are dominating in many bird populations. Such bias among adults may be critical to population growth and viability. Nevertheless, demographic mechanisms for biased adult sex ratios are still poorly understood. Here, we examined potential demographic mechanisms for the recent dramatic shift from a slight female bias among adult eider ducks (Somateria mollissima) to a male bias (about 65% males) in the Baltic Sea, where the spe ...[more]

PMID: 29634733

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Project description:There are sex differences in age-related bone modifications after puberty. Androgens stimulate radial bone expansion in males, while estrogen stimulates endosteal apposition but limits periosteal expansion in females. The potential effect of age on observed sex biases in height and sex estimation models is most significantly relevant for forensic or bioarchaeological research that relies, at least in part, on hand and foot bone measurements of living or skeletal remains for purposes of identification or demographic reconstruction. This study sought to determine whether age affects sex biases in models for height and sex estimation which are based on hand and foot dimensions. The study was cross-sectional between January and June 2021 at the University for Development Studies. The study included 379 participants (male = 161 and female = 218) between 20 and 29 years. The hand length (HL), hand width (HW), foot length (FL) and foot width (FW) were measured twice from the left side using computer-assisted analysis. Univariable and multivariable discriminant and linear regression models were formulated for sex and height estimation respectively. Females were better classified than males with sex biases (male-female) ranging from −1.3% to −22.6% for all models. Models for height estimation were more precise in males (bias: 0.0–0.3 cm) than in females (bias: 0.3–1.4 cm). However, age did not have an impact on the observed sex biases. Height and sex estimation from foot and height dimensions may not need adjustment for age. This may, however, be limited to a given population and age group. Highlights • There are sex biases in the reliabilities of sex and height estimation models based on hand and foot dimensions.• While females are better classified, height estimation models were more precise in males than in females• Age may not explain the observed sex biases in hand and foot-based models for height and sex estimation in 20 to 29-year-olds• The relationship between height and dimensions of the hand and foot may not be moderated by sex in 20 to 29-year-olds• Models for sex and height estimation from hand and foot dimensions may not need adjustment for age

Dataset Information

Increased male bias in eider ducks can be explained by sex-specific survival of prime-age breeders.

Publications

Increased male bias in eider ducks can be explained by sex-specific survival of prime-age breeders.

Similar Datasets

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