Poor Reproductive Fitness of Sperm in Aging Males

Poor Reproductive Fitness of Sperm in Aging Males Deterioration of germline DNA found to produce low quality offspring in aged male houbara bustards. A study in houbara bustards, an African bird species gives insight on what is happening with aging men. The scientists suggest that the decline in hatching success observed is caused by senescent decline of both male and female gametes. On the other hand, the development of chicks within the egg appear to be influenced solely by maternal aging which can be explained by reduction in older females’ abilities to provision their eggs. The researchers then monitored the artificial insemination of houbara bustards ranging in age from 1 to 23, recorded the egg hatching success as well as the growth of resulting chicks. Their results found that eggs produced from inseminating older females with ejaculate from older males have lower hatching success as compared to eggs of parents at peak age. The scientists suggest that the decrease in hatching success observed is caused by senescent decline of both male and female gametes. Of the eggs that did hatch, it was discovered that the mass of chicks at hatching were heaviest in chicks born to young mothers, suggesting that the development of chicks within the egg appear to be influenced solely by maternal aging. This can be explained by reduction in older females’ abilities to provision their eggs. Additionally, it was found that chicks born to young fathers had the best overall growth within the first month of life than those born to older fathers. The reason for this is that since males only contribute their DNA to offspring, the growth of the How Reproductively Fit is the Sperm of Older Males? A study in houbara bustards, an African bird species gives insight on the production of low quality offspring in aging men. Gametes are reproductive cells such as ovum or sperm, containing the genetic material required to form a new organism. This genetic material is essential in determining the quality of offspring produced. According to the paper by Brian Preston and his colleagues in Nature Communications, gametes from animals of advanced years undergo degradation by a process called senescence. Senescence is a gradual decline of function and can occur by two mechanisms. The first is the decline in the performance of their spermatogenic machinery such that the sperm has difficulty in carrying out its function. The second mechanism involves the build-up of genetic mutations within the germline of gametes, resulting in the degradation of the DNA carried within. These mechanisms lead to a reduction in both the viability and quality of offspring produced. To determine whether male aging has influence on reproductive fitness, Brian Preston and his colleagues examined 10 years’ worth of data regarding the post insemination success of male houbara bustards part of a captive breeding programme. To begin with, female bustards were inseminated with ejaculates collected from males. The male and female bustards involved in this study ranged from 1 to 23 years of age. Eggs produced were collected and the hatching success recorded. The researchers found that eggs produced from inseminating older females with ejaculate from older males have lower hatching success as compared to eggs of parents at peak age, suggesting that this is caused by senescent decline of both male and female gametes. Furthermore, of the eggs that did hatch, it was discovered that the mass of chicks at hatching were heavier in chicks born to young fathers compared to older fathers. Additionally, a measure of overall growth within the first month of life showed that chicks born to old fathers had the worst overall growth. The scientists reasoned that the cause for growth patterns observed in chicks born to old fathers confirms that the dominant mechanism of senescence in the bird species is mutation-based aging of germline DNA. This is because, since males only contribute their DNA to offspring, the growth of the chicks is inhibited. Eggs produced were collected for incubation and hatched chicks were hand-reared so as to avoid any confounding variables. The researchers monitored the artificial insemination of houbara bustards ranging from 1 to 23 years old, recorded the egg hatching success as well as the growth of resulting chicks. Their results found that eggs produced from inseminating older females with ejaculate from older males have lower hatching success as compared to eggs of parents at peak age, suggesting that this is caused by senescent decline of both male and female gametes. Of the eggs that did hatch, it was discovered that the mass of chicks at hatching were heaviest in chicks born to young fathers. Furthermore, it was found that chicks born to old fathers had the worst overall growth within the first month of life than those born to younger fathers. The scientists suggest that the development of chicks within the egg appears to be influenced solely by maternal aging. This can be explained by reduction in older females’ abilities to provide their eggs with nutrients. On the other hand, the researchers reasoned that the cause for growth patterns observed in chicks born to old fathers confirms that the dominant mechanism of senescence in the bird species is mutation-based aging of germline DNA. This is because, since males only contribute their DNA to offspring, the growth of the chicks is inhibited. According to a recent study by Brian Preston and his colleagues in Nature Communications, gametes (ovum or sperm) from animals of advanced years undergo degradation by a process called senescence. Senescence is a gradual decline of function and occurs by two mechanisms. The first involves the decline of the spermatogenic machinery performance while the second mechanism involves the build-up of genetic mutations within the germline DNA of gametes. To determine whether male aging has influence on reproductive fitness, the researchers examined 10 years’ worth of data on the post insemination success of male houbara bustards aged between 1 to 23 years that were part of a captive breeding programme. First, female bustards were inseminated with the male ejaculates collected so that gametes are the only influencing factor on offspring quality. The eggs produced from older parents were seen to have lower hatching success when compared to eggs of peak age parents. Of the eggs that did hatch, researchers observed that the lightest chicks at hatching were a result of maternal aging. Alternatively, a measure of overall growth within the first month after hatching revealed that chicks born to older fathers had the worst overall growth. In other words, as males age, their ability to produce offspring that are viable and of high quality diminishes. These findings lead scientists to conclude that the dominant mechanism of senescence in the bird species is mutation-based aging of germline DNA. Additionally, it seems that the decline in offspring development linked to paternal aging is similar in scale to that linked to maternal aging. Interestingly, when findings were compared with that of human studies similar patterns were observed, deepening concern for the recent trend of delayed parenthood in both sexes. In future, Brian Preston and his colleagues wish to be able to identify and quantify the reproductive cost associated with male aging in a long-lived species. In their most recent work, published in Nature Communications, they found that, not only did males appear less able to produce offspring successfully as they aged, they also appeared to produce offspring that were of intrinsically lower quality. Perhaps most surprisingly, these declines in offspring quality were of a similar size to those resulting from maternal aging. Patterns observed in humans are in line with the findings in houbara bustards and their interpretation, with paternal aging being linked to adverse reproductive outcomes, a number of genetic diseases, and some mental disorders. The evidence is beginning to accumulate that delaying parenthood until later life can potentially have negative consequences for the children of both older men and women. Read more at: http://phys.org/news/2015-02-male-birds-reproduction-life.html#jCp