Senescent sperm performance in old male birds.
ABSTRACT Senescence is the deterioration of the phenotype with age caused by negative effects of mutations acting late in life or the physiological deterioration of vital processes. Birds have traditionally been assumed to senescence slowly despite their high metabolic rates, high blood sugar levels and high body temperature. Here we investigate the patterns of age-related performance of sperm of a long distance migrant, the barn swallow Hirundo rustica, varying in age from 1 to 6 years, analysed by the computer-assisted sperm analysis equipment. Sperm showed deteriorating performance in terms of linear movement, track velocity, straight line velocity and reduced proportions of rapidly moving, progressive and motile sperm with age. In a second series of experiments, we assessed performance of sperm from the same males in neutral medium and in medium derived from the reproductive tract of females in an attempt to test if sperm of old males performed relatively better in female medium, as expected from extra-pair paternity being negatively related to male age, but not to female age. Older males showed consistently better performance in female medium than in neutral medium in terms of track velocity, straight line velocity and reduced proportions of rapidly moving, progressive and motile sperm, whereas young males showed better performance in neutral medium. These results provide evidence of declining sperm performance for important reproductive variables not only with age, but also with the sperm of old males performing differentially better in female medium than young males.
Article: Identification, RNAi knockdown, and functional analysis of an ejaculate protein that mediates a postmating, prezygotic phenotype in a cricket.[show abstract] [hide abstract]
ABSTRACT: Postmating, prezygotic phenotypes, especially those that underlie reproductive isolation between closely related species, have been a central focus of evolutionary biologists over the past two decades. Such phenotypes are thought to evolve rapidly and be nearly ubiquitous among sexually reproducing eukaryotes where females mate with multiple partners. Because these phenotypes represent interplay between the male ejaculate and female reproductive tract, they are fertile ground for reproductive senescence--as ejaculate composition and female physiology typically change over an individual's life span. Although these phenotypes and their resulting dynamics are important, we have little understanding of the proteins that mediate these phenotypes, particularly for species groups where postmating, prezygotic traits are the primary mechanism of reproductive isolation. Here, we utilize proteomics, RNAi, mating experiments, and the Allonemobius socius complex of crickets, whose members are primarily isolated from one another by postmating, prezygotic phenotypes (including the ability of a male to induce a female to lay eggs), to demonstrate that one of the most abundant ejaculate proteins (a male accessory gland-biased protein similar to a trypsin-like serine protease) decreases in abundance over a male's reproductive lifetime and mediates the induction of egg-laying in females. These findings represent one of the first studies to identify a protein that plays a role in mediating both a postmating, prezygotic isolation pathway and reproductive senescence.PLoS ONE 01/2009; 4(10):e7537. · 4.09 Impact Factor
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ABSTRACT: The realization that senescence, age-dependent declines in survival and reproductive performance, pervades natural populations has brought its evolutionary significance into sharper focus. However, reproductive senescence remains poorly understood because it is difficult to separate male and female mechanisms underpinning reproductive success. We experimentally investigated male reproductive senescence in feral fowl, Gallus gallus domesticus, where socially dominant males monopolize access to females and the ejaculates of multiple males compete for fertilization. We detected the signal of senescence on multiple determinants of male reproductive success. The effect of age on status was dependent upon the intensity of intrasexual competition: old males were less likely to dominate male-biased groups where competition is intense but were as likely as young males to dominate female-biased groups. Mating and fertilization success declined sharply with male age largely as a result of population-level patterns. These age-dependent declines translated into sexually antagonistic payoffs: old males fertilized more eggs when they were dominant, but this resulted in females suffering a drastic reduction in fertility. Thus, male senescence causes potential for sexual conflict over mating, and the intensity of this conflict is modulated socially, by the probability of old males dominating reproductive opportunities.Current biology: CB 07/2010; 20(13):1192-6. · 10.99 Impact Factor