A rigorous comparison of sexual selection indexes via simulations of diverse mating systems

Henshaw, Jonathan M.; Kahn, Andrew T.; Fritzsche, Karoline

doi:10.1073/pnas.1518067113

Cited by 62 publications

(70 citation statements)

References 78 publications

(61 reference statements)

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“…The absence of a relationship between the OSR and strength of sexual selection in U. mjoebergi is a reminder that the OSR is an imperfect predictor (Jones, ; Shuster, ). Indeed, a recent simulation study of various mating systems that tested a range of proposed indices of sexual selection showed that the OSR tended to be a consistently poor predictor of sexual selection on a focal trait (Henshaw et al ., ).…”

Section: Discussionmentioning

confidence: 97%

Mate choice and the operational sex ratio: an experimental test with robotic crabs

Hayes

Callander

Booksmythe

et al. 2016

J of Evolutionary Biology

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The operational sex ratio (OSR: sexually active males: receptive females) predicts the intensity of competition for mates. It is less clear, however, under what circumstances, the OSR predicts the strength of sexual selection -that is, the extent to which variation in mating success is attributable to traits that increase the bearer's attractiveness and/or fighting ability. To establish causality, experiments that manipulate the OSR are required. Furthermore, if it is possible to control for any OSR-dependent changes in the chosen sex (e.g. changes in male courtship), we can directly test whether the OSR affects the behaviour of the choosing sex (e.g. female choice decisions). We conducted female mate choice experiments in the field using robotic models of male fiddler crabs (Uca mjoebergi). We used a novel design with two females tested sequentially per trial. As in nature, the choice of the first female to mate therefore affected the mates available to the next female. In general, we detected significant sexual selection due to female choice for 'males' with larger claws. Importantly, the strength of sexual selection did not vary across five different OSR/density treatments. However, as the OSR decreased (hence the number of available males declined), females chose the 'males' with the largest claws available significantly more often than expected by chance. Possible reasons for this mismatch between the expected and observed effects of the OSR on the strength of sexual selection are discussed. whether the OSR affects the behaviour of the choosing sex (e.g. female choice 48 decisions). We conducted female mate choice experiments in the field using robotic 49 models of male fiddler crabs (Uca mjoebergi). We used a novel design with two 50 females tested sequentially per trial. As in nature, the choice of the first female to 51 mate therefore affected the mates available to the next female. In general we detected 52 significant sexual selection due to female choice for 'males' with larger claws. 53Importantly, the strength of sexual selection did not vary across five different 54 OSR/density treatments. However, as the OSR decreased (hence the number of 55 available males declined), females chose the 'males' with the largest claws available 56 significantly more often than expected by chance. Possible reasons for this mismatch 57 between the expected and observed effects of the OSR on the strength of sexual 58 selection are discussed. 59 60

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Section: Discussionmentioning

confidence: 97%

Mate choice and the operational sex ratio: an experimental test with robotic crabs

Hayes

Callander

Booksmythe

et al. 2016

J of Evolutionary Biology

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“…Various post-birth sex ratio biases are regularly invoked to explain sex roles ) (see Table 1). Traditionally, theoreticians have argued that the operational sex ratio (OSR) in the mating pool plays the central role because of stronger sexual selection on the more common sex due to greater competition for mates (Trivers 1972;Emlen & Oring 1977;review: Clutton-Brock, this volume), although the actual relationship is less straightforward than once assumed (Klug et al 2010;Kokko et al 2012;Henshaw et al 2015; but see Krakauer et al 2011). More recently, others have noted that the adult sex ratio (ASR) is influential, not just because it affects the OSR, but because it determines the reproductive rate (offspring production per time unit) and reproductive value (i.e.…”

Section: Introductionmentioning

confidence: 99%

Not all sex ratios are equal: the Fisher condition, parental care and sexual selection

Jennions

Fromhage

2017

Phil. Trans. R. Soc. B

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The term ‘sex roles’ encapsulates male–female differences in mate searching, competitive traits that increase mating/fertilization opportunities, choosiness about mates and parental care. Theoretical models suggest that biased sex ratios drive the evolution of sex roles. To model sex role evolution, it is essential to note that in most sexually reproducing species (haplodiploid insects are an exception), each offspring has one father and one mother. Consequently, the total number of offspring produced by each sex is identical, so the mean number of offspring produced by individuals of each sex depends on the sex ratio (Fisher condition). Similarly, the total number of heterosexual matings is identical for each sex. On average, neither sex can mate nor breed more often when the sex ratio is even. But equally common in which sex ratio? The Fisher condition only applies to some reproductive measures (e.g. lifetime offspring production or matings) for certain sex ratios (e.g. operational or adult sex ratio; OSR, ASR). Here, we review recent models that clarify whether a biased OSR, ASR or sex ratio at maturation (MSR) have a causal or correlational relationship with the evolution of sex differences in parental care and competitive traits—two key components of sex roles. We suggest that it is more fruitful to understand the combined effect of the MSR and mortality rates while caring and competing than that of the ASR itself. In short, we argue that the ASR does not have a causal role in the evolution of parental care. We point out, however, that the ASR can be a cue for adaptive phenotypic plasticity in how each sex invests in parental care. This article is part of the themed issue ‘Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies’.

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“…). One proxy directly derived from the Bateman gradient, the Jones index s ’ max , shows particularly good performance (Henshaw, Kahn & Fritzsche ; Table ) and captures upper limits to sexual selection differentials on any given trait (Jones ). We wish to stress that our methodological arguments extend to all other recently advocated metrics of sexual selection (Table ) that share a necessity to quantify individual reproductive success and individual mating success in a population.…”

Section: Introductionmentioning

confidence: 99%

Measuring and interpreting sexual selection metrics: evaluation and guidelines

et al. 2016

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Summary Routine assessments of overall sexual selection, including comparisons of its direction and intensity between sexes or species, rely on summary metrics that capture the essence of sexual selection. Nearly all currently employed metrics require population‐wide estimates of individual mating success and reproductive success. The resulting sexual selection metrics, however, can heavily and systematically vary with the chosen approaches in terms of sampling, measurement, and analysis. Our review illustrates this variation, using the Bateman gradient, a particularly prominent sexual selection metric. It represents the selection gradient on mating success and – given the latter's pivotal role in defining sexual selection – reflects a trait‐independent integrative proxy for the maximum strength of sexual selection. Drawing from a recent meta‐analysis, we evaluate potential biases arising from study design, data collection and parameter estimation, and provide suggestions to mitigate such biases in future studies. With respect to study design, we argue that currently almost inexistent manipulative studies must complement the dominating correlative studies to inform us about causality in sexual selection. With respect to data collection, we outline how different measures of mating and reproductive success affect the components of sexual (and natural) selection that are reflected in standard summary metrics. With respect to parameter estimation, we show the potential impact of decisions about data inclusion and the chosen quantitative approach on inferences of sexual selection and its sex difference. We expect this meta‐analytical review to aid future studies in providing less biased and more informative estimates of sexual selection.

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A rigorous comparison of sexual selection indexes via simulations of diverse mating systems

Cited by 62 publications

References 78 publications

Mate choice and the operational sex ratio: an experimental test with robotic crabs

Mate choice and the operational sex ratio: an experimental test with robotic crabs

Not all sex ratios are equal: the Fisher condition, parental care and sexual selection

Measuring and interpreting sexual selection metrics: evaluation and guidelines

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