ScienceDaily (Dec. 4, 2012) — Fertility tests
frequently reveal that males have problems with the quality of their sperm. The
problems often relate to sperm senescence, which is a reduction in quality with
age. Sperm senescence can arise either before or after the DNA in the sperm
cells is produced by a process known as meiosis. So-called
"pre-meiotic" senescence results from accumulated damage in the
germline cells with increasing age and results in older males having sperm of
lower quality. Post-meiotic senescence occurs after the sperm cells have been
produced, either during storage of sperm by the male or after ejaculation and
before they fertilize the eggs.
There
is previous evidence that various kinds of sperm senescence occur in insects,
in some domestic animals (birds and mammals) and even in humans but the studies
have generally been carried out under fairly artificial conditions and so it is
not clear how they relate to wild animals -- or to the general human
population. These objections have been overcome in the latest work of Attila
Hettyey and colleagues at the Konrad Lorenz Institute of Ethology, University
of Veterinary Medicine, Vienna (Vetmeduni), together with Balázs Vági in
Budapest, Hungary, where Hettyey himself is now working.
The
researchers investigated the common toad, an interesting model system as it is
known to produce all its sperm before the start of the breeding season. They
found that male toads that re-entered hibernation at the start of the breeding
season, i.e. that lowered their metabolic rates after producing sperm, stored
sperm of significantly higher motility than males kept under pseudo-natural
conditions without females throughout the entire breeding season. The result
means that slowing the normal rate of general physiological processes reduced
the normal rate of sperm aging within the toad's testicles. This constitutes
the first evidence for post-meiotic intra-testicular sperm senescence in a wild
vertebrate. A further surprising result was that in males kept under
pseudo-natural conditions, sperm motility was related to the number of matings
a male achieved, with the presence of females or the occurrence of matings
having a positive effect on the quality of stored sperm. This suggests that
post-meiotic intra-testicular sperm senescence does not occur at a fixed rate
but may be modulated by external factors, such as temperature and number of matings.
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