Postcopulatory Sexual Selection Is Associated with Reduced Variation in Sperm Morphology

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

doi:10.1371/journal.pone.0000413

Cited by 140 publications

(166 citation statements)

References 68 publications

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“…Our results are, however, comparable to what has been found in the red deer C. elaphus hispanicus (Malo et al 2006), where, although repeatability was statistically significant, within-male variance in total sperm length accounted for 43% of the total variance. These results also contradict theoretical developments predicting that postcopulatory sexual selection should result in stabilizing selection, disfavoring extreme sperm morphologies, and reducing variation in sperm size (Calhim et al 2007;Kleven et al 2009). The substantial within-male variance we found in house sparrows raises two questions: How is variance in sperm morphology maintained and has sperm morphology evolved toward a single optimum that maximizes male fertilization success?…”

Section: Discussioncontrasting

confidence: 65%

Sperm morphology, swimming velocity, and longevity in the house sparrow Passer domesticus

Helfenstein

Podevin

Richner

2009

Behav Ecol Sociobiol

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Sperm competition exerts strong selection on males to produce spermatozoa with an optimal morphology that maximizes their fertilization success. Long sperm were first suggested to be favored because they should swim faster. However, studies that investigated the relationship between sperm length and sperm competitive ability or sperm swimming velocity yielded contradictory results. More recently, ratios of the different sections of a spermatozoon (the head, midpiece, and flagellum) were suggested to be more crucial in determining swimming velocity. Additionally, sperm ability to remain and survive in the female storage organs may also influence fertilization success, so that optimal sperm morphology may rather maximize sperm longevity than velocity. In this study, we investigated how sperm morphology is related to sperm velocity and sperm longevity in the house sparrow Passer domesticus. Sperm velocity was found to be correlated with head/flagellum ratio. Sperm with small heads relative to their flagellum showed higher swimming velocity. Additionally, shorter sperm were found to live longer. Finally, we found sperm morphological traits to vary substantially within males and the head/flagellum ratio to be unrelated to total sperm length. We discuss the hypothesis that the substantial within-male variation in sperm morphology reflects a male strategy to produce a diversity of sperm from long, fast-swimming to short, long-living sperm to maximize their fertilization success in a context of sperm competition.

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Section: Discussioncontrasting

confidence: 65%

Sperm morphology, swimming velocity, and longevity in the house sparrow Passer domesticus

Helfenstein

Podevin

Richner

2009

Behav Ecol Sociobiol

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“…Links between reduced function, relaxed natural selection and greater variation has been acknowledged by more recent studies [19] and demonstrated to characterize certain vestigial traits of insects [20]. More distantly related but still relevant examples of reduced selection and increased variation include certain birds and fishes, which show greater sperm morphological variation coincident with a release of sexual selection [21,22]. In addition, reduced competition in Garter snakes may have increased variation heritability of colour patterns [23].…”

Section: Introductionmentioning

confidence: 99%

High morphological variation of vestibular system accompanies slow and infrequent locomotion in three-toed sloths

et al. 2012

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The semicircular canals (SCs), part of the vestibular apparatus of the inner ear, are directly involved in the detection of angular motion of the head for maintaining balance, and exhibit adaptive patterns for locomotor behaviour. Consequently, they are generally believed to show low levels of intraspecific morphological variation, but few studies have investigated this assumption. On the basis of high-resolution computed tomography, we present here, to our knowledge, the first comprehensive study of the pattern of variation of the inner ear with a focus on Xenarthra. Our study demonstrates that extant three-toed sloths show a high level of morphological variation of the bony labyrinth of the inner ear. Especially, the variation in shape, relative size and angles of their SCs greatly differ from those of other, faster-moving taxa within Xenarthra and Placentalia in general. The unique pattern of variation in three-toed sloths suggests that a release of selection and/or constraints on their organ of balance is associated with the observed wide range of phenotypes. This release is coincident with their slow and infrequent locomotion and may be related, among other possible factors, to a reduced functional demand for a precise sensitivity to movement.

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“…Again, an unequivocal, single explanation for this variation is lacking, although sperm size may have a function in post-copulatory sexual selection, including sperm competition, in at least some cases (e.g. Gage and Morrow, 2003;Calhim et al, 2007; for a review, see Pitnick et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Response to selection and realized heritability of sperm length in the yellow dung fly (Scathophaga stercoraria)

Dobler

Hosken

2009

Heredity

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Sperm length shows considerable phenotypic variation both inter-and intra-specifically, but a general explanation for this variation is lacking. In addition, our understanding of the genetic variation underlying sperm length variation is also limited because there have been few studies on the genetics of sperm size. One factor that could explain the variation in sperm length is that length influences sperm competitiveness, and there is some evidence for this. However, in yellow dung flies (Scathophaga stercoraria), microevolutionary responses to experimental variation at levels of sperm competition indicate that sperm length does not influence sperm competitiveness, although this lack of response may simply indicate sperm length lacks evolutionary potential (that is, it is constrained in some way), in spite of evidence that sperm length is heritable. Here we report on a laboratory study, in which we artificially selected upwards and downwards on sperm length in S. stercoraria. We found that sperm length significantly diverged after four generations of selection, but the response to selection was asymmetrical: upward selection generated a rapid response, but downward did not. We estimated the realized heritability of sperm length to be approximately 50%, which is consistent with previous sire-son estimates. We also assessed the fertility of males from upward and downward lines and found they did not differ. Results are discussed in the context of sperm competition.

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Postcopulatory Sexual Selection Is Associated with Reduced Variation in Sperm Morphology

Cited by 140 publications

References 68 publications

Sperm morphology, swimming velocity, and longevity in the house sparrow Passer domesticus

Sperm morphology, swimming velocity, and longevity in the house sparrow Passer domesticus

High morphological variation of vestibular system accompanies slow and infrequent locomotion in three-toed sloths

Response to selection and realized heritability of sperm length in the yellow dung fly (Scathophaga stercoraria)

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