scholarly journals Sex-specific early survival drives adult sex ratio bias in snowy plovers and impacts mating system and population growth

2017 ◽  
Vol 114 (27) ◽  
pp. E5474-E5481 ◽  
Author(s):  
Luke J. Eberhart-Phillips ◽  
Clemens Küpper ◽  
Tom E. X. Miller ◽  
Medardo Cruz-López ◽  
Kathryn H. Maher ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Population Growth ◽  
Mating System ◽  
Empirical Support ◽  
Population Models ◽  
Adult Sex Ratio ◽  
Early Survival ◽  
Snowy Plovers ◽  
Sex Biases

Adult sex ratio (ASR) is a central concept in population biology and a key factor in sexual selection, but why do most demographic models ignore sex biases? Vital rates often vary between the sexes and across life history, but their relative contributions to ASR variation remain poorly understood—an essential step to evaluate sex ratio theories in the wild and inform conservation. Here, we combine structured two-sex population models with individual-based mark–recapture data from an intensively monitored polygamous population of snowy plovers. We show that a strongly male-biased ASR (0.63) is primarily driven by sex-specific survival of juveniles rather than adults or dependent offspring. This finding provides empirical support for theories of unbiased sex allocation when sex differences in survival arise after the period of parental investment. Importantly, a conventional model ignoring sex biases significantly overestimated population viability. We suggest that sex-specific population models are essential to understand the population dynamics of sexual organisms: reproduction and population growth are most sensitive to perturbations in survival of the limiting sex. Overall, our study suggests that sex-biased early survival may contribute toward mating system evolution and population persistence, with implications for both sexual selection theory and biodiversity conservation.

scholarly journals Adult sex ratio bias in snowy plovers is driven by sex-specific early survival: implications for mating systems and population growth

2017 ◽  
Author(s):  
Luke J. Eberhart-Phillips ◽  
Clemens Küpper ◽  
Tom E. X. Miller ◽  
Medardo Cruz-López ◽  
Kathryn H. Maher ◽  
...  
Keyword(s):  
Population Dynamics ◽  
Sexual Selection ◽  
Life History ◽  
Sex Ratio ◽  
Population Biology ◽  
Population Viability ◽  
Adult Sex Ratio ◽  
Sexual Selection Theory ◽  
Snowy Plovers ◽  
Sex Biases

ABSTRACTAdult sex ratio (ASR) is a central concept in population biology and a key factor in sexual selection, yet why do most demographic models ignore sex-biases? Vital rates often vary between the sexes and across life history, but their relative contributions to ASR variation remain poorly understood—an essential step to evaluate sex ratio theories in the wild and inform conservation. Here we combine structured two-sex population models with individual-based mark-recapture data from an intensively monitored polygamous population of snowy plovers. We show that a strongly male-biased ASR is primarily driven by sex-specific survival of juveniles, rather than adults or dependent offspring. This provides empirical support for theories of unbiased sex allocation when sex-differences in survival arise after the period of parental investment. Importantly, a conventional model ignoring sex-biases significantly overestimated population viability. We suggest that sex-specific population models are essential to understand the population dynamics of sexual organisms: reproduction and population growth is most sensitive to perturbations in survival of the limiting sex. Overall, our study suggests that sex-biased early survival may contribute towards mating system evolution and population persistence, with implications for both sexual selection theory and biodiversity conservation.SIGNIFICANCE STATEMENTSex biases are widespread in nature and represent a fundamental component of sexual selection and population biology—but at which point in life history do these biases emerge? Here we report a detailed individual-based demographic analysis of an intensively studied wild bird population to evaluate the origins of sex biases and their consequences on mating strategies and population dynamics. We document a strongly male-biased adult sex ratio, which is consistent with behavioral observations of female-biased polygamy. Notably, sex-biased juvenile, rather than adult survival, contributed most to the adult sex ratio. Sex-biases also strongly influenced population viability, which was significantly overestimated when sex ratio and mating system were ignored. Our study therefore has implications for both sexual selection theory and biodiversity conservation.

scholarly journals Sexually selected females in the monogamous Western Australian seahorse

2006 ◽  
Vol 274 (1609) ◽  
pp. 521-525 ◽  
Author(s):  
Charlotta Kvarnemo ◽  
Glenn I Moore ◽  
Adam G Jones
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Mating System ◽  
Genetic Study ◽  
Mating Success ◽  
Male Preference ◽  
Monogamous Species ◽  
Adult Sex Ratio ◽  
Western Australian ◽  
Selection Differentials

Studies of sexual selection in monogamous species have hitherto focused on sexual selection among males. Here, we provide empirical documentation that sexual selection can also act strongly on females in a natural population with a monogamous mating system. In our field-based genetic study of the monogamous Western Australian seahorse, Hippocampus subelongatus , sexual selection differentials and gradients show that females are under stronger sexual selection than males: mated females are larger than unmated ones, whereas mated and unmated males do not differ in size. In addition, the opportunity for sexual selection (variance in mating success divided by its mean squared) for females is almost three times that for males. These results, which seem to be generated by a combination of a male preference for larger females and a female-biased adult sex ratio, indicate that substantial sexual selection on females is a potentially important but under-appreciated evolutionary phenomenon in monogamous species.

Sexual dimorphism of the major chela and sex ratio as indicators of the mating system in the estuarine snapping shrimp Alpheus colombiensis Wicksten, 1988 (Decapoda: Caridea: Alpheidae)

2020 ◽  
Vol 40 (6) ◽  
pp. 649-656
Author(s):  
Juan C Azofeifa-Solano ◽  
Jeffrey A Sibaja-Cordero ◽  
Ingo S Wehrtmann
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Sex Ratio ◽  
Mating System ◽  
Mate Guarding ◽  
Female Size ◽  
Monogamous Species ◽  
Low Degree ◽  
Adult Sex Ratio ◽  
Snapping Shrimps

Abstract The sexual selection over traits that favor access to mating partners could promote the emergence of sexual dimorphism when the pressure is different between sexes. Monogamous species are considered to have a low degree of sexual dimorphism. The highly diverse snapping shrimps are usually regarded as monogamous, but the mating system has been studied only in few species. We aimed to provide insights into the mating system and sexual dimorphism of Alpheus colombiensisWicksten, 1988. The adult sex ratio was female biased, and solitary ovigerous females were found, suggesting a temporary mate guarding type of mating system. Our results also revealed sexual dimorphism on the snapping claw, which is larger in males than in females. The male’s snapping claw is probably under sexual selection, which can be mediated by male-male competition or female choice. We also estimated the A. colombiensis female size at maturity at 5.2 ± 0.76 mm. Our results contradict the common idea that snapping shrimps are monogamous species, and support that A. colombiensis probably have a temporary mate guarding (e.g., males can sexually interact with more than one female, in opposition to sexual monogamy). This study also sustains the growing evidence that alpheid shrimps display snapping claw sexual dimorphism.

scholarly journals Sex ratio effects on reproductive strategies in humans

2015 ◽  
Vol 2 (1) ◽  
pp. 140402 ◽  
Author(s):  
Ryan Schacht ◽  
Monique Borgerhoff Mulder
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Ethnic Group ◽  
Reproductive Strategies ◽  
Situational Factors ◽  
Male Mating ◽  
Mating Effort ◽  
Short Term ◽  
Adult Sex Ratio ◽  
Using Data

Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.

Feral horse demography and population growth in the Kaimanawa Ranges, New Zealand

2004 ◽  
Vol 31 (2) ◽  
pp. 119 ◽  
Author(s):  
Wayne L. Linklater ◽  
Elissa Z. Cameron ◽  
Ed O. Minot ◽  
Kevin J. Stafford
Keyword(s):  
New Zealand ◽  
Sex Ratio ◽  
Population Growth ◽  
Management Problem ◽  
Feral Horses ◽  
Sex Structure ◽  
Young Males ◽  
Feral Horse ◽  
Adult Sex Ratio ◽  
Female Bias

Although feral horses are a common management problem in numerous countries, detailed and long-term demographic studies are rare. We measured the age and sex structure, and pregnancy, birth and death rates in a population of 413 feral horses in New Zealand during 1994–98 and used them to construct a model simulating population growth. Survivorship increased with age (0–1 years old = 86.8%, 1–2 = 92.3%, 2–4 = 92.4%, ≥�4 years old = females 94%, males 97% per annum). Birth sex ratio parity, a slight female bias in the adult sex ratio (92 males per 100 females) and higher adult male survivorship indicated lower average survivorship for young males than females that was not detectable in mortality statistics. Pregnancy and foaling rates for mares ≥�2 years old averaged 79 and 49%, respectively. Foaling rates increased as mares matured (2–3-year-old mares = 1.9%, 3–4 = 20.0%, 4–5 = 42.1%, ≥�5 = 61.5% per annum). Young mares had higher rates of foetal and neonatal mortality (95% of pregnancies failed and/or were lost as neonatal foals in 2–3-year-old mares, 70.6% in 3–4, 43.2% in 4–5, and 31% in mares ≥�5 years old). Population growth was 9.6% per annum (9.5–9.8, 95% CI) without human-induced mortalities (i.e. r = 0.092). Our model, standardised aerial counts, and historical estimates of annual reproduction suggest that the historical sequence of counts since 1979 has overestimated growth by ~50% probably because of improvements in count effort and technique.

scholarly journals Evolution of sex ratio through gene loss

2019 ◽  
Vol 116 (26) ◽  
pp. 12919-12924 ◽  
Author(s):  
Da Yin ◽  
Eric S. Haag
Keyword(s):  
Sex Ratio ◽  
Population Growth ◽  
Mating System ◽  
Mating Success ◽  
Population Subdivision ◽  
Male Mating ◽  
Mixed Mating ◽  
Male Mating Success ◽  
Caenorhabditis Briggsae ◽  
Male Frequency

The maintenance of males at intermediate frequencies is an important evolutionary problem. Several species ofCaenorhabditisnematodes have evolved a mating system in which selfing hermaphrodites and males coexist. While selfing produces XX hermaphrodites, cross-fertilization produces 50% XO male progeny. Thus, male mating success dictates the sex ratio. Here, we focus on the contribution of themale secreted short(mss) gene family to male mating success, sex ratio, and population growth. Themssfamily is essential for sperm competitiveness in gonochoristic species, but has been lost in parallel in androdioecious species. Using a transgene to restoremssfunction to the androdioeciousCaenorhabditis briggsae,we examined how mating system and population subdivision influence the fitness of themss+genotype. Consistent with theoretical expectations, whenmss+andmss-null (i.e., wild type) genotypes compete,mss+is positively selected in both mixed-mating and strictly outcrossing situations, though more strongly in the latter. Thus, while sexual mode alone affects the fitness ofmss+, it is insufficient to explain its parallel loss. However, in genetically homogenous androdioecious populations,mss+both increases male frequency and depresses population growth. We propose that the lack of inbreeding depression and the strong subdivision that characterize naturalCaenorhabditispopulations impose selection on sex ratio that makes loss ofmssadaptive after self-fertility evolves.

Pairing Success of Kirtland's Warblers in Marginal vs. Suitable Habitat

The Auk ◽  
1987 ◽  
Vol 104 (2) ◽  
pp. 234-241 ◽  
Author(s):  
John R. Probst ◽  
Jack P. Hayes
Keyword(s):  
Sex Ratio ◽  
Population Growth ◽  
Nest Success ◽  
Breeding Population ◽  
Lower Proportion ◽  
Control Measures ◽  
Suitable Habitat ◽  
Annual Productivity ◽  
Adult Sex Ratio ◽  
Marginal Habitat

Abstract We compared pairing success of male Kirtland's Warblers (Dendroica kirtlandii) in different habitats to test the hypothesis that a lower proportion of males in marginal habitat are mated. Fewer than 60% of the males in marginal habitat were paired, but 95% of the males in suitable habitat were paired. We estimated the overall pairing success of the known breeding population at 85%. We could not estimate the number of females because the adult sex ratio is unknown, and an unknown proportion of Kirtland's Warblers are polygynous. The Kirtland's Warbler population was fairly constant from 1971 to 1983, despite markedly improved nest success resulting from cowbird control measures. If there are more males than females, or if many females fail to breed or must accept mated males or marginal habitat, population growth could be impeded. We combined reduced pairing success with an estimate of fledgling mortality, and revised the estimated number of fall immatures to between 369 and 471 birds-about 36% lower than the uncorrected estimate. Lower annual productivity of a static population implies higher annual survivorship of adults, yearlings, or both.

scholarly journals Adaptations to sexual selection and sexual conflict: insights from experimental evolution and artificial selection

2010 ◽  
Vol 365 (1552) ◽  
pp. 2541-2548 ◽  
Author(s):  
Dominic A. Edward ◽  
Claudia Fricke ◽  
Tracey Chapman
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Sexual Conflict ◽  
Artificial Selection ◽  
Experimental Evolution ◽  
Genetic Basis ◽  
Mating Behaviour ◽  
Evolutionary Change ◽  
Operational Sex Ratio ◽  
Adult Sex Ratio

Artificial selection and experimental evolution document natural selection under controlled conditions. Collectively, these techniques are continuing to provide fresh and important insights into the genetic basis of evolutionary change, and are now being employed to investigate mating behaviour. Here, we focus on how selection techniques can reveal the genetic basis of post-mating adaptations to sexual selection and sexual conflict. Alteration of the operational sex ratio of adult Drosophila over just a few tens of generations can lead to altered ejaculate allocation patterns and the evolution of resistance in females to the costly effects of elevated mating rates. We provide new data to show how male responses to the presence of rivals can evolve. For several traits, the way in which males responded to rivals was opposite in lines selected for male-biased, as opposed to female-biased, adult sex ratio. This shows that the manipulation of the relative intensity of intra- and inter-sexual selection can lead to replicable and repeatable effects on mating systems, and reveals the potential for significant contemporary evolutionary change. Such studies, with important safeguards, have potential utility for understanding sexual selection and sexual conflict across many taxa. We discuss how artificial selection studies combined with genomics will continue to deepen our knowledge of the evolutionary principles first laid down by Darwin 150 years ago.

Generation of sex ratio biases in the red-tailed phascogale (Phascogale calura)

2008 ◽  
Vol 20 (2) ◽  
pp. 275 ◽  
Author(s):  
W. K. Foster ◽  
D. A. Taggart
Keyword(s):  
Sex Ratio ◽  
Mating System ◽  
Meta Analysis ◽  
Sex Ratios ◽  
Corpora Lutea ◽  
Sex Ratio At Birth ◽  
Maternal Weight ◽  
Female Age ◽  
Male Bias ◽  
Sex Biases

Male semelparous dasyurid species are annual breeders that use a promiscuous mating system. These species have shown biases in litter sex ratios and, with females producing more young than they have available teats, this provides an opportunity for the manipulation of the sex ratio at birth. The sex ratio of embryos and pouch young, and the degree of embryonic overproduction, in red-tailed phascogales (Phascogale calura) was investigated to gain an understanding of the mechanism by which sex biases may be generated. The sex ratio of embryos did not differ from parity, but a male bias was observed in young attaching to teats. Females produced an average of 15.1 ± 1.9 corpora lutea and 10.5 ± 3.5 viable embryos, with no difference in fecundity observed with female age or weight. Because females only have eight teats, the overproduction of young, and male-biased attachment, was sufficient to explain the observed male bias in pouch young. No relationship was observed between maternal weight and sex ratio, but heavier females did tend to produce more ova. Meta-analysis of studies providing information on litter sex ratios in male semelparous dasyurid species did not show any consistent trend.

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