Climate
change damaging male fertility
University of East
Anglia
Climate change could
pose a threat to male fertility -- according to new research from the
University of East Anglia.
New findings published
today in the journal Nature Communications reveal that
heatwaves damage sperm in insects -- with negative impacts for fertility across
generations.
The research team say
that male infertility during heatwaves could help to explain why climate change
is having such an impact on species populations, including climate-related
extinctions in recent years.
Research group leader
Prof Matt Gage said: "We know that biodiversity is suffering under climate
change, but the specific causes and sensitivities are hard to pin down.
"We've shown in
this work that sperm function is an especially sensitive trait when the
environment heats up, and in a model system representing a huge amount of
global biodiversity.
"Since sperm function is essential for reproduction and population viability, these findings could provide one explanation for why biodiversity is suffering under climate change.
"A warmer
atmosphere will be more volatile and hazardous, with extreme events like
heatwaves becoming increasingly frequent, intense and widespread.
"Heatwaves are
particularly damaging extreme weather events. Local extinctions are known to
occur when temperature changes become too intense. We wanted to know why this
happens. And one answer could be related to sperm."
The research team
investigated the red flour beetle (Tribolium castaneum) to explore the
effects of simulated heatwaves on male reproduction.
The beetles were
exposed to either standard control conditions or five-day heatwave
temperatures, which were 5°C to 7°C above their thermal optimum.
Afterwards, a variety
of experiments assessed the potential damage to reproductive success, sperm
function and offspring quality.
Heatwaves killed sperm
The team found that
heatwaves halved the amount of offspring males could produce, and a second
heatwave almost sterilised males.
Females, by contrast,
were unaffected by heatwave conditions. However, female reproduction was
affected indirectly because experiments showed that heatwaves damaged
inseminated sperm within female reproductive tracts.
Following experimental
heatwaves, males reduced sperm production by three-quarters, and any sperm
produced then struggled to migrate into the female tract and were more likely
to die before fertilisation.
Kirs Sales, a
postgraduate researcher who led the research, said: "Our research shows
that heatwaves halve male reproductive fitness, and it was surprising how
consistent the effect was."
The group also
explored the underlying causes of male vulnerability. Heatwaves caused some
impact on male sexual behaviour -- with males mating half as frequently as
controls.
Heatwaves caused
damage across generations
"Two concerning
results were the impact of successive heatwaves on males, and the impacts of
heatwaves on future generations," said Sales.
"When males were
exposed to two heatwave events 10 days apart, their offspring production was
less than 1 per cent of the control group. Insects in nature are likely to
experience multiple heatwave events, which could become a problem for
population productivity if male reproduction cannot adapt or recover."
The research also
shows that offspring sired by heatwaved dads -- or their sperm -- live shorter
lives -- by a couple of months.
And the reproductive
performance of sons produced by dads -- or sperm -- exposed to heatwave
conditions was also impacted. Sons were found to be less able to fertilise a
series of potential mates, and produced less offspring.
The researchers warn
that this could add extra pressure to populations already suffering through
climate change over time.
"Beetles are
thought to constitute a quarter of biodiversity, so these results are very
important for understanding how species react to climate change. Research has
also shown that heat shock can damage male reproduction in warm blooded animals
too, and past work has shown that this leads to infertility in mammals,"
added Sales.
The researchers hope
that the effects can be incorporated into models predicting species
vulnerability, and ultimately help inform societal understanding and
conservation actions.
The work was funded by
Natural Environment Research Council (NERC) and the EnvEast DTP, UEA, and the
Leverhulme Trust.
