Climate change may pose a threat to male fertility, according to a study published Tuesday.
Researchers from the University of East Anglia in the UK found that heatwaves damage sperm in insects -- with negative impacts for fertility across generations.
The study showed 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.
"We know that biodiversity is suffering under climate change, but the specific causes and sensitivities are hard to pin down," said Matt Gage, who led the study published in the journal Nature Communications.
"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," Gage said.
"Since sperm function is essential for reproduction and population viability, these findings could provide one explanation for why biodiversity is suffering under climate change," he said.
A warmer atmosphere will be more volatile and hazardous, with extreme events like heatwaves becoming increasingly frequent, intense and widespread, researchers said.
Heatwaves are particularly damaging extreme weather events. Local extinctions are known to occur when temperature changes become too intense, they said.
"We wanted to know why this happens. And one answer could be related to sperm," Gage said.
The 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 degrees Celsius to 7 degrees Celsius above their thermal optimum.
A variety of experiments assessed the potential damage to reproductive success, sperm function and offspring quality.
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.
"Our research shows that heatwaves halve male reproductive fitness, and it was surprising how consistent the effect was," said Kirs Sales, a postgraduate researcher.
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.
"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, researchers said.
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, they said.
The research also shows that offspring sired by heatwaved dads -- or their sperm -- live shorter lives -- by a couple of months.
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