The Combined Effects of Pre- and Post-Insemination Sexual Selection on Extreme Variation in Male Body Size

1. The genus Gambusia represents approximately 45 species of polyandrous livebearing fishes with reversed sexual size dimorphism (i.e. males smaller than females) and with copulation predominantly via male coercion. Male body size has been suggested as an important sexually selected trait, but despite abundant research, evidence for sexual selection on male body size in this genus is mixed. 2. Studies have found that large males have an advantage in both male-male competition and female choice, but that small males perform sneaky copulations better and at higher frequency and thus may sire more offspring in this coercive mating system. Here, we synthesized this discrepant body of evidence in the primary literature. 3. Using pre-registered methods and hypotheses, we performed a systematic review and meta-analysis combining published (n = 19 studies, k = 106 effect sizes) and unpublished data (n = 17, k = 242) to test whether there is overall selection on male body size across studies in Gambusia. We also tested several specific hypotheses to understand sources of heterogeneity across effects. 4. Meta-analysis revealed an overall positive correlation between male size and reproductive performance (r = 0.23, 95% confidence interval: 0.10 – 0.35, n = 36, k = 348, 4514 males, three Gambusia species). Despite high heterogeneity, the large-male advantage appeared robust across all measures studied (i.e. female choice, mating success, paternity, sperm quantity and quality), but was considerably larger for female choice (r = 0.43, 95% confidence interval: 0.28 – 0.59, n = 14, k = 43). Meta-regressions found several important factors explaining heterogeneity across effects, including type of sperm characteristic, male-to-female ratio, female reproductive status, and environmental conditions. We found evidence of publication bias; however, its effect on our estimates was attenuated by including a substantial amount of unpublished effects, highlighting the importance of unpublished (open) data for more accurate meta-analytic estimates. 5. In addition to positive selection on male size, our study suggests that we need to rethink the role and form of sexual selection in Gambusia and, more broadly, to consider the ecological factors that affect reproductive behaviour in livebearing fishes.

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Evolution of sexual dimorphism and Rensch’s rule in the beetle genusLimnebius(Hydraenidae): is sexual selection opportunistic?

PeerJ ◽

10.7717/peerj.3060 ◽

2017 ◽

Vol 5 ◽

pp. e3060 ◽

Cited By ~ 4

Author(s):

Andrey Rudoy ◽

Ignacio Ribera

Keyword(s):

Sexual Selection ◽

Body Size ◽

General Pattern ◽

Strong Support ◽

Male Body ◽

Rensch’S Rule ◽

Male Body Size ◽

Rensch's Rule ◽

The Individual ◽

Male Genital

Sexual size dimorphism (SSD) is widespread among animals, with larger females usually attributed to an optimization of resources in reproduction and larger males to sexual selection. A general pattern in the evolution of SSD is Rensch’s rule, which states that SSD increases with body size in species with larger males but decreases when females are larger. We studied the evolution of SSD in the genusLimnebius(Coleoptera, Hydraenidae), measuring SSD and male genital size and complexity of ca. 80% of its 150 species and reconstructing its evolution in a molecular phylogeny with 71 species. We found strong support for a higher evolutionary lability of male body size, which had an overall positive allometry with respect to females and higher evolutionary rates measured over the individual branches of the phylogeny. Increases in SSD were associated to increases in body size, but there were some exceptions with an increase associated to changes in only one sex. Secondary sexual characters (SSC) in the external morphology of males appeared several times independently, generally on species that had already increased their size. There was an overall significant correlation between SSD, male body size and male genital size and complexity, although some lineages with complex genitalia had low SSD, and some small species with complex genitalia had no SSD. Our results suggest that the origin of the higher evolutionary variance of male body size may be due to lack of constraints rather than to sexual selection, that may start to act in species with already larger males due to random variation.

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Sexual selection on male body size and assortative pairing in Gammarus pulex (Crustacea: Amphipoda): field surveys and laboratory experiments

Journal of Zoology ◽

10.1017/s0952836904005643 ◽

2004 ◽

Vol 264 (2) ◽

pp. 135-141 ◽

Cited By ~ 33

Author(s):

L. Bollache ◽

F. Cézilly

Keyword(s):

Sexual Selection ◽

Body Size ◽

Laboratory Experiments ◽

Gammarus Pulex ◽

Male Body ◽

Field Surveys ◽

Male Body Size ◽

Assortative Pairing

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Sexual selection on male body size and mating behaviour in American toads, Bufo americanus

Animal Behaviour ◽

10.1016/s0003-3472(88)80119-2 ◽

1988 ◽

Vol 36 (6) ◽

pp. 1796-1808 ◽

Cited By ~ 27

Author(s):

Richard D. Howard

Keyword(s):

Sexual Selection ◽

Body Size ◽

Mating Behaviour ◽

Male Body ◽

Bufo Americanus ◽

Male Body Size

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Disruptive sexual selection on male body size in the polyphenic black scavenger fly Sepsis thoracica

Behavioral Ecology ◽

10.1093/beheco/ary038 ◽

2018 ◽

Vol 29 (3) ◽

pp. 769-777 ◽

Cited By ~ 1

Author(s):

Juan Pablo Busso ◽

Wolf U Blanckenhorn

Keyword(s):

Sexual Selection ◽

Body Size ◽

Reproductive Success ◽

Mating Success ◽

Directional Selection ◽

Disruptive Selection ◽

Simultaneous Occurrence ◽

Male Body ◽

Male Body Size ◽

Starting Point

Abstract Sexual selection has 2 main components, female preference and male–male competition, which can lead males to adopt alternative reproductive tactics to optimize their reproductive success. Two traits that significantly influence reproductive success are body size and coloration, as they can facilitate access to females through male contests or as female attractors. We investigated whether, and if so which mechanism of sexual selection contributes to the maintenance, and possibly even the establishment, of 2 almost discrete male morphs in the polyphenic black scavenger fly Sepsis thoracica (Diptera: Sepsidae): small and black, or large and amber. We performed 2 complementary laboratory experiments to evaluate the mating success of the different male morphs and the behaviors (of both males and females) presumably mediating their mating success. We found evidence for intraspecific disruptive sexual selection on male body size that is mediated by male–male interactions, and significant positive directional selection on body size that interacted with (directional) selection on coloration, likely contributing to the origin and/or maintenance of the threshold relationship between the 2 traits in this species. The simultaneous occurrence of disruptive selection and polyphenism in S. thoracica supports the role of sexual selection in the intraspecific diversification of coupled traits (here body size and coloration), which could be a speciation starting point.

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Autosomal variation for male body size and sperm competition phenotypes is uncorrelated in Drosophila melanogaster

Biology Letters ◽

10.1098/rsbl.2008.0283 ◽

2008 ◽

Vol 4 (5) ◽

pp. 500-503 ◽

Cited By ~ 4

Author(s):

Rui Zhang ◽

Linda Amah ◽

Anthony C Fiumera

Keyword(s):

Drosophila Melanogaster ◽

Sexual Selection ◽

Body Size ◽

Genetic Correlations ◽

Male Body ◽

Substitution Lines ◽

Male Body Size ◽

Chromosome Substitution Lines ◽

Significant Line ◽

Sexually Antagonistic Coevolution

Correlations between male body size and phenotypes impacting post-copulatory sexual selection are commonly observed during the manipulation of male body size by environmental rearing conditions. Here, we control for environmental influences and test for genetic correlations between natural variation in male body size and phenotypes affecting post-copulatory sexual selection in Drosophila melanogaster . Dry weights of virgin males from 90 second-chromosome and 88 third-chromosome substitution lines were measured. Highly significant line effects ( p <0.001) documented a genetic basis to variation in male body size. No significant correlations were identified between male body size and the components of sperm competitive ability. These results suggest that natural autosomal variation for male body size has little impact on post-copulatory sexual selection. If genetic correlations exist between male body size and post-copulatory sexual selection then variation in the sex chromosomes are likely candidates, as might be expected if sexually antagonistic coevolution was responsible.

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