A(caps)s we know, sperm quality generally does decrease with age in human beings. Several studies have shown that as men get older, the quality of their sperm can decline. Age-related changes in sperm quality can include reduced sperm count, decreased sperm motility (movement), and increased DNA damage in sperm cells. However, The team, led by the University of Oxford had a new discovery which is the results of 379 studies and covered a wide range of animals, including mammals, insects, birds, and fish. This found that, overall, advancing age seemed to have no impact on ejaculate size, number of sperm, sperm motility, or sperm viability.
In human being, male fertility and sperm fitness decline with age, but scientists have made the surprising discovery that this pattern is not consistent in other animals. These findings have been published in the journal Nature Communications.
For some animals, age had a positive effect on reproductive traits. In many insect species, for example, ejaculate size, quantity of sperm, and sperm viability all improved with age. However, it is possible that this result may be explained by methodological limitations in the studies. For instance, in many insect studies, males were kept as virgins until old age, during which they are likely to accumulate sperm. From almost all animals examined, only lab rodents showed age-related deterioration in most ejaculate traits measured.
According to the researchers, the sharp contrast in ejaculate ageing patterns between most animals and humans might be because humans now live much longer than they did just a few centuries ago. This may have led to men now living beyond the age at which they evolved to maintain sperm function. Co-lead author Krish Sanghvi (Department of Biology, University of Oxford), said: 'The surprising differences between animals and humans could reflect stronger selection pressures for animals to maintain sperm function across all ages.'
The researchers also investigated whether age impacted reproductive outcomes (such as fertilization success and fecundity) in the males of these species. Similar to ejaculate traits, they found that, overall, reproductive outcomes did not improve or decline with advancing age, which is again in stark contrast to what is seen in humans. According to the authors, the results may be partly explained by methodological limitations, such as studies rarely testing animals that are at an advanced age for their species. They also suggest that deterioration in male fertility might not be occurring for each ejaculate trait in every species.
