Sorry, honey – I can't tonight. Blame climate change.
A new study highlights the risks that heatwaves can alter species' population numbers over time, resulting in drastically lower sperm counts for insects and could impact other groups for years to come. The findings were published in the journal Nature Communications.
"We know that biodiversity is suffering under climate change, but the specific causes and sensitivities are hard to pin down," said Research group leader Prof Matt Gage in a statement. "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 continued: "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."
The researchers looked at the red flour beetle to get the effects of simulated heatwaves on male reproduction. They were exposed to standard control conditions or a five-day heatwave where the temperatures ranged between 5°C and 7°C "above their thermal optimum," the statement added.
As a result, the researchers learned that the climate-controlled group had no problems reproducing, but those that were exposed to the harsher conditions suffered serious setbacks. The heatwaves "halved" the number of offspring produced and a second heatwave almost caused them to become sterile.
"Heatwaves are particularly damaging extreme weather events," Gage added in the statement. "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."
After the rise in temperatures, sperm count fell by three-quarters and "any sperm produced then struggled to migrate into the female tract and were more likely to die before fertilization," according to the statement.
Females, however, were not affected by the warmer conditions.
"Our research shows that heatwaves halve male reproductive fitness, and it was surprising how consistent the effect was," said Kirs Sales, a postgraduate researcher who led the research.
While concerning in the short-term, there are significant longer-term implications as well, with Sales citing "the impacts of heatwaves on future generations."
"When males were exposed to two heatwave events 10 days apart, their offspring production was less than 1 percent of the control group," Sales 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."
Of the offspring that did survive, they lived a shorter life-span, up to a few months shorter, the researcher found. There were also problems with male offspring, as some were found to be less fertile as a result of their fathers' exposure to the heatwave-like conditions.
Beetles are believed to represent a quarter of biodiversity, Sales added, making these results concerning for how other species will 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," Sales added.
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