Climate change harms male fertility

New discoveries published today in the journal Nature Communications reveal that heat waves damage sperm in insects, with negative effects on fertility from one generation to the next.

The research team said male infertility during heatwaves could help explain why climate change is having such an impact on species populations, including climate-related extinctions over the past few years. years.

Professor Matt Gage, head of the research group, said: "We know that biodiversity suffers from climate change, but specific causes and sensitivities are hard to pin down.

"We have shown in this work that sperm function is a particularly sensitive trait when the environment is warming up and in a model system representing a huge amount of global biodiversity.

"Since sperm function is essential for the reproduction and viability of the population, these results could partly explain why biodiversity suffers from climate change.

"A warmer atmosphere will be more volatile and dangerous, with extreme events such as heat waves becoming more frequent, intense and widespread.

"Heat waves are particularly damaging to extreme weather events, local extinctions are known to occur when temperature changes become too intense, and we wanted to know why this was happening, and an answer could be sperm-related."

The research team studied the red flour beetle (Tribolium castaneum) to explore the effects of simulated heat waves on male reproduction.

The beetles were exposed to standard control conditions or to five-day heat wave temperatures, which were 5 ° C to 7 ° C above their thermal optimum.

Subsequently, various experiments evaluated potential damage to reproductive success, sperm function, and offspring quality.

Heat waves killed sperm

The team discovered that heat waves halved the number of offspring that males could produce and that a second heat wave almost sterilized males.

Females, on the other hand, were not affected by heatwaves. However, female reproduction has been affected indirectly, as experiments have shown that heat waves damage sperm inseminated in the female reproductive tract.

As a result of experimental heat waves, males reduced sperm production by three-quarters and all sperm produced subsequently had difficulty migrating into the female tract and were more likely to die before fertilization.

Kirs Sales, a postgraduate researcher who led the research, said, "Our research shows that heat waves halve men's reproductive abilities, and it was surprising to see the consistency of the effect . "

The group also explored the underlying causes of men's vulnerability. Heatwaves had an impact on men's sexual behavior – men mating twice as often as controls.

Heat waves have caused damage over several generations

"Two disturbing results have been the impact of successive heat waves on men and the effects of heat waves on future generations," Sales said.

"When males were exposed to two heat waves 10 days apart, their production was less than 1% of the control group, and insects in the wild are likely to experience multiple heat waves, which could become a problem for the productivity of the population if male reproduction can not adapt or recover. "

Research also shows that the offspring of fathers – or their sperm – has a shorter life – a few months.

And the reproductive performance of yarns produced by dads – or sperm – exposed to heatwave conditions has also been affected. Yarns were found to be less able to fertilize a range of potential partners and produce fewer offspring.

The researchers warned that this could put additional pressure on populations already affected by climate change.

"Beetles are thought to account for a quarter of biodiversity, so these results are very important in understanding how species respond to climate change, and research has also shown that heat shock can also affect male reproduction in wildlife. warm blood, leads to sterility in mammals, "added Sales.

The researchers hope that the effects can be incorporated into species vulnerability prediction models and ultimately help to inform society's understanding and conservation measures.

"Experimental heat waves compromise the function of sperm and cause transgression damage in a model insect" is published in Nature Communications on Tuesday, November 12, 2018.

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More information:
Kris Sales et al, Experimental heat waves compromise sperm function and cause transgenerational damage in a model insect, Nature Communications (2018). DOI: 10.1038 / s41467-018-07273-z