Selection for increased male size predicts variation in sexual size dimorphism among fish species

Variation in the degree of sexual size dimorphism (SSD) among taxa is generally considered to arise from differences in the relative intensity of male–male competition and fecundity selection. One might predict, therefore, that SSD will vary systematically with (1) the intensity of sexual selection for increased male size, and (2) the intensity of fecundity selection for increased female size. To test these two fundamental hypotheses, we conducted a phylogenetic comparative analysis of SSD in fish. Specifically, using records of body length at first sexual maturity from FishBase, we quantified variation in the magnitude and direction of SSD in more than 600 diverse freshwater and marine fish species, from sticklebacks to sharks. Although female-biased SSD was common, and thought to be driven primarily by fecundity selection, variation in SSD was not dependent on either the allometric scaling of reproductive energy output or fecundity in female fish. Instead, systematic patterns based on habitat and life-history characteristics associated with varying degrees of male–male competition and paternal care strongly suggest that adaptive variation in SSD is driven by the intensity of sexual selection for increased male size.

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Sexual Size Dimorphism and Survival of Male and Female Blackbirds (Icteridae)

The Auk ◽

10.1093/auk/98.3.457 ◽

1981 ◽

Vol 98 (3) ◽

pp. 457-465 ◽

Cited By ~ 15

Author(s):

William A. Searcy ◽

Ken Yasukawa

Keyword(s):

Sexual Size Dimorphism ◽

Relative Survival ◽

Female Size ◽

Male Size ◽

Size Dimorphism ◽

Large Size ◽

Survival Selection ◽

Female Survival ◽

Positive Correlations ◽

Dimorphic Species

Abstract In a between-species comparison of icterids, male survival decreases relative to female survival as the degree of sexual size dimorphism increases. This result is consistent with the hypothesis that male size is limited by survival selection in icterids; the degree of size dimorphism is known to correlate with the degree of polygyny in icterids, however, so the decreased relative survival of males in dimorphic species may be caused by some correlate of polygyny other than large size. Survival estimates based on records of recovery of dead birds show positive correlations between male size and male survival and between female size and female survival, but survival estimates based on recaptures of live birds fail to show such relationships.

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Sexual size dimorphism and sexual selection in artiodactyls

Behavioral Ecology ◽

10.1093/beheco/araa017 ◽

2020 ◽

Vol 31 (3) ◽

pp. 792-797

Author(s):

Marcelo H Cassini

Keyword(s):

Sexual Selection ◽

Sexual Dimorphism ◽

Group Size ◽

Sexual Size Dimorphism ◽

Alternative Hypothesis ◽

Mammalian Species ◽

Generalized Least Squares ◽

Size Dimorphism ◽

Selection For

Abstract Sexual size dimorphism is biased toward males in most mammalian species. The most common explanation is precopulatory intramale sexual selection. Large males win fights and mate more frequently. In artiodactyls, previous tests of this hypothesis consisted of interspecific correlations of sexual dimorphism with group size as a surrogate for the intensity of sexual selection (Is). However, group size is not a proper measure of sexual selection for several reasons as is largely recognized in other mammalian taxa. I conducted an interspecific test on the role of sexual selection in the evolution of sexual dimorphism using the variance in genetic paternity as a proxy for the Is. I reviewed the literature and found 17 studies that allowed estimating Is= V/(W2), where V and W are the variance and mean number of offspring per male, respectively. A phylogenetic generalized least squares analysis indicated that dimorphism (Wm/Wf) showed a significant positive regression with the intensity of sexual selection but not group size (multiple r2= 0.40; F3,17= 12.78, P = 0.002). This result suggests that sexual selection may have played a role in the evolution of sexual size dimorphism in Artiodactyla. An alternative hypothesis based on natural selection is discussed.

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Sexual selection on size and shape in Japanese beetles (Popillia japonica)

Behavioral Ecology ◽

10.1093/beheco/araa054 ◽

2020 ◽

Vol 31 (4) ◽

pp. 1073-1083 ◽

Cited By ~ 1

Author(s):

Clint D Kelly

Keyword(s):

Sexual Selection ◽

Body Size ◽

Mating Success ◽

Insect Pest ◽

Popillia Japonica ◽

Female Size ◽

Male Body ◽

Japanese Beetle ◽

Size Dimorphism ◽

Selection For

Abstract The mobility hypothesis argues that species in which males compete for mates in scrambles often exhibit female-biased size dimorphism because smaller male body size should increase male mobility and success in searching for mates. Sexual dimorphism can be further exaggerated if fecundity or sexual selection concurrently selects for larger female size. Scramble competition can select for trait characteristics that optimize locomotion; for example, long and slender wings should be favored if aerial speed is important to mating success. I tested these predictions in the scrambling Japanese beetle (Popillia japonica), a female-biased size dimorphic insect pest that is invasive to North America. Multivariate selection analyses support the prediction that smaller body size and larger wings in males benefit their mating success. My analyses also revealed significant selection for larger wings in females but, contrary to prediction, direct sexual selection favors smaller body size in females. These results support the mobility hypothesis and partially explain the evolution of female-biased size dimorphism in this species. Sexual selection favored rounder bodies in females and more tapered bodies in males, whereas, in both sexes, the effect of wing shape appears less important to fitness than wing size.

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Using effects of parasitoid size on fitness to test a host quality model assumption with the parasitoid wasp Spalangia endius

Canadian Journal of Zoology ◽

10.1139/z06-162 ◽

2006 ◽

Vol 84 (11) ◽

pp. 1678-1682 ◽

Cited By ~ 7

Author(s):

B.H. King ◽

M.E. Napoleon

Keyword(s):

Sexual Size Dimorphism ◽

Parasitoid Wasp ◽

Host Size ◽

Female Size ◽

Host Quality ◽

Quality Model ◽

Male Size ◽

Model Assumption ◽

Size Dimorphism ◽

Spalangia Endius

How body size affects fitness of males relative to females is relevant to understanding the evolution of sexual size dimorphism and maternal sex-ratio manipulation. In most parasitoid wasps, mothers oviposit a greater proportion of daughters in larger hosts. The host-quality model describes how this may be adaptive. A major assumption of the model is that host size has a greater effect on the fitness of daughters than of sons. The assumption has often been tested indirectly by examining the effects of parasitoid size on fitness, because a parasitoid’s size generally increases with the size of the host on which it develops. The validity of this indirect method is examined here for the parasitoid wasp Spalangia endius Walker, 1839 parasitizing Musca domestica L., 1758. If the method is valid, effects of parasitoid size on fitness should match the effects of host size on fitness that were shown in a previous study. The effects matched in that both parasitoid size and host size affected the fitness of females but not of males. However, the aspects of female fitness that were affected differed. That female size but not male size affected fitness was consistent with the female-biased sexual size dimorphism of S. endius.

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