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Sperm Size (sperm + size)
Selected AbstractsSperm competition and maternal effects differentially influence testis and sperm size in Callosobruchus maculatusJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2009L. GAY Abstract The evolutionary factors affecting testis size are well documented, with sperm competition being of major importance. However, the factors affecting sperm length are not well understood; there are no clear theoretical predictions and the empirical evidence is inconsistent. Recently, maternal effects have been implicated in sperm length variation, a finding that may offer insights into its evolution. We investigated potential proximate and microevolutionary factors influencing testis and sperm size in the bruchid beetle Callosobruchus maculatus using a combined approach of an artificial evolution experiment over 90 generations and an environmental effects study. We found that while polyandry seems to select for larger testes, it had no detectable effect on sperm length. Furthermore, population density, a proximate indicator of sperm competition risk, was not significantly associated with sperm length or testis size variation. However, there were strong maternal effects influencing sperm length. [source] Sperm design and function in the redside dace Clinostomus elongatusJOURNAL OF FISH BIOLOGY, Issue 4 2009T. E. Pitcher A study was undertaken to examine sperm morphometry in relation to sperm velocity and sperm longevity in the redside dace Clinostomus elongatus. There was significant between-male variance in sperm size and shape metrics (total sperm length, sperm head length, flagellum length and sperm head length to width ratio) and positive relationships were found between these morphometrics and sperm velocity. There were no significant relationships found between sperm morphometry and sperm longevity, nor was there a trade-off between sperm velocity and sperm longevity. [source] Consistent significant variation between individual males in spermatozoal morphometryJOURNAL OF ZOOLOGY, Issue 2 2001Edward H. Morrow Abstract Comparative studies show that variation in sperm morphometry across taxa is associated with the environment in which sperm function, and the species' mating pattern dictating the risk of sperm competition. Accordingly, sperm have evolved to function in a non-self environment (in contrast to somatic cells) and sperm morphometry is predicted to be optimized independently of the individual male producing them, but is the result of selective forces arising directly from the fertilization and competitive environment in which sperm will operate. Males within a population are therefore under stabilizing selection to produce an optimal distribution of sperm sizes. The nature of this distribution was explored using consistent techniques to measure detailed sperm morphometry for 10 species in a range of taxa from insects to humans. Although we expected variance in sperm morphometry to be optimized by every individual male through stabilizing selection at a population or species level, we found the exact opposite; for every species examined there was significant variation between individual males in the total lengths of the sperm they produced. A significant variation is reported between individual males for every species in the sizes of each sperm head, mid-piece and flagellum component. The between-male variation exists consistently in wild, domestic and human populations, subject to a wide range of levels of inbreeding. In gryllid crickets sperm length is shown to be male-specific and is repeatable between successive ejaculates. Between-female variation in ova size (data are presented for trout) is explainable by individual female fecundity optimization strategies; however, the adaptive significance of widespread between-individual variance in male gamete size is counter-intuitive and difficult to interpret, particularly as the limited evidence available shows that sperm morphometry is not condition-dependent or resource-constrained. The differences, however, do suggest negligible influences from haploid expression in the development of sperm morphometry , if haplotypic expression were manifested we would expect more profound variation within a male's sperm population (to reflect the inherent within-male variance in haplotypes derived from recombination) rather than the significant between-male differences we found that suggests the diploid control of spermatozoal phenotype [source] | ||||||||||