Increased Postcopulatory Sexual Selection Reduces the Intramale Variation in Sperm Design

Immler, Simone; Calhim, Sara; Birkhead, Tim R.

doi:10.1111/j.1558-5646.2008.00393.x

Cited by 105 publications

(140 citation statements)

References 52 publications

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“…Theoretical models also predict lower variation in sperm dimensions within males under strong sperm competition levels [29,30]. In line with these predictions, comparative studies have shown a strong inverse relationship between sperm competition indices and coefficients of both between-male (CV bm ) and within-male (CV wm ) variation in sperm length in insects [31] and birds [32,33]. In contrast to sperm CV wm , the relationship between sperm CV bm and sperm competition risk does not show any phylogenetic bias (cf.…”

Section: Introductionmentioning

confidence: 61%

Sperm competition in tropical versus temperate zone birds

et al. 2013

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Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, using the coefficient of between-male variation (CV bm ) in sperm size as an index for sperm competition risk, in a comparative analysis of 31 Afrotropical and 99 northern temperate zone passerine species. We found no difference in sperm competition risk between the two groups, nor any relationship with migration distance. However, a multivariate model indicated that sperm competition risk was highest in species with a combination of low body mass and few eggs per clutch. The effect of clutch size was most pronounced in tropical species, which indicates that sperm competition risk in tropical and temperate species is differently associated with particular life-history traits. Although tropical species had lower sperm competition risk than temperate zone species for overlapping clutch sizes, the idea of a generally reduced risk of sperm competition in tropical birds was not supported by our analysis.

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Section: Introductionmentioning

confidence: 61%

Sperm competition in tropical versus temperate zone birds

et al. 2013

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“…To elucidate the origin of these patterns comparative analyses in different bird groups have suggested that betweenindividual variation in sperm size is most pronounced in species subject to low levels of sperm competition, probably due to relaxed selection on an optimal sperm morphometry and so too presumably on other aspects of spermatogenesis (Birkhead et al, 2005;Calhim, Immler & Birkhead, 2007;Kleven et al, 2008;Lüpold, Linz & Birkhead, 2009a). Moreover, there may also be a role for post-mating sexual selection in explaining patterns of within-individual variation in sperm morphometry, since bird species subject to high levels of sperm competition are also those that show the lowest levels of standardised within-individual variation in sperm size (Immler, Calhim & Birkhead, 2008), which has led to the suggestion that sperm competition may select for enhanced quality control during spermatogenesis (see also Lüpold et al, 2011).…”

Section: (2) Variation and Plasticity In Sperm Morphology Within Speciesmentioning

confidence: 99%

The evolutionary ecology of testicular function: size isn't everything

Ramm

Schärer

2014

Biological Reviews

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Larger testes are considered the quintessential adaptation to sperm competition. However, the strong focus on testis size in evolutionary research risks ignoring other potentially adaptive features of testicular function, many of which will also be shaped by post-mating sexual selection. Here we advocate a more integrated research programme that simultaneously takes into account the developmental machinery of spermatogenesis and the various selection pressures that act on this machinery and its products. The testis is a complex organ, and so we begin by outlining how we can think about the evolution of testicular function both in terms of the composition and spatial organisation of the testis ('testicular histology'), as well as in terms of the logical organisation of cell division during spermatogenesis ('testicular architecture'). We then apply these concepts to ask which aspects of testicular function we can expect to be shaped by post-mating sexual selection. We first assess the impact of selection on those traits most strongly associated with sperm competition, namely the number and kind of sperm produced. A broad range of studies now support our contention that post-mating sexual selection affects many aspects of testicular function besides gross testis size, for example, to maximise spermatogenic efficiency or to enable the production of particular sperm morphologies. We then broaden our focus to ask how testicular function is affected by fluctuation in sperm demand. Such fluctuation can occur over an individual's lifetime (for example due to seasonality in reproduction) and may select for particular types of testicular histology and architecture depending on the particular reproductive ecology of the species in question. Fluctuation in sperm demand also occurs over evolutionary time, due to shifts in the mating system, and this may have various consequences for testicular function, for example on rates of proliferation-induced mutation and for dealing with intragenomic conflict. We end by suggesting additional approaches that could be applied to study testicular function, and conclude that simultaneously considering the machinery, products and scheduling of spermatogenesis will be crucial as we seek to understand more fully the evolution of this most fundamental of male reproductive traits.

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“…Marked phenotypic variation across sperm cells within a single ejaculate is ubiquitous, both in terms of sperm morphology [6][7][8] and performance [9]. However, sperm are generally considered products of the diploid paternal genome with no endogenous haploid gene expression, and sperm phenotype is thus thought not to reflect the haploid genome they carry [10].…”

Section: Introductionmentioning

confidence: 99%

Sperm variation within a single ejaculate affects offspring development in Atlantic salmon

et al. 2014

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It is generally believed that variation in sperm phenotype within a single ejaculate has no consequences for offspring performance, because sperm phenotypes are thought not to reflect sperm genotypes. We show that variation in individual sperm function within an ejaculate affects the performance of the resulting offspring in the Atlantic salmon Salmo salar. We experimentally manipulated the time between sperm activation and fertilization in order to select for sperm cohorts differing in longevity within single ejaculates of wild caught male salmon. We found that within-ejaculate variation in sperm longevity significantly affected offspring development and hence time until hatching. Whether these effects have a genetic or epigenetic basis needs to be further evaluated. However, our results provide experimental evidence for transgenerational effects of individual sperm function.

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Increased Postcopulatory Sexual Selection Reduces the Intramale Variation in Sperm Design

Cited by 105 publications

References 52 publications

Sperm competition in tropical versus temperate zone birds

Sperm competition in tropical versus temperate zone birds

The evolutionary ecology of testicular function: size isn't everything

Sperm variation within a single ejaculate affects offspring development in Atlantic salmon

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