Not good news According to a new study published in the journal Nature Communications , male fertility appears to decline as temperatures skyrocket. The work has shown “clear evidence” that heat wave stress reduces “sperm number and viability” in insects, thus damaging sperm quality. Although, as we see, the effect has only been demonstrated in insects, it could also be present in other types of organisms.
Although some of the effects of climate change have been well documented, others remain insidious and unclear. For example, the decline of many species has been linked to global warming, but we don’t know exactly how high temperatures are killing these creatures. Now, a team of researchers from the University of East Anglia (England) propose a potential reason: it is affecting the quality of male sperm.
“We know that biodiversity is suffering under climate change, but the specific causes and sensitivities are difficult to pin down,” says Matt Gage, leader of the work.
“We have shown in this work that sperm function is an especially sensitive trait when the environment is heated, and within a model system that represents a large amount of global biodiversity. Since sperm function is essential for reproduction and population viability, these findings could provide an explanation for why biodiversity is suffering under climate change . “
The experts examined the effects of simulated heat waves on the red beetle ( Tribolium castaneum ). They divided the beetles into two groups : a control group that lived in normal temperatures and a group exposed to temperatures of 5 ° C to 7 ° C above these conditions.
After these experiments, the scientists measured the quality of the sperm and the reproductive effects caused by these changes. They found that heat waves halved the number of offspring the males could produce, and a second heat wave nearly sterilized the males.
The sperm count was also reduced by about 75% , and the sperm had to work much harder than usual to fertilize the female. Males subjected to heat waves also mated twice less than the control group.
In general, this represents a damning picture for insects, which are going through a crisis known as “ecological Armageddon”: insect populations have declined dramatically in recent decades: more than 75% of flying insect populations have declined in the last 25 years.
Experts have been surprised at how strong and consistent the effect of heat waves was on the beetles.
“Beetles are thought to make up a quarter of biodiversity, so these results are very important in understanding how species react to climate change,” explains study co-author Kris Sales. “Research has also shown that heat shock can damage male reproduction in warm-blooded animals, and previous work has shown that this leads to infertility in mammals, ” he added.
How is an insect study related to humans?
The truth is that in humans, male sperm count and quality have declined considerably over a few decades, but researchers are still not sure why. While this study did not attempt to address this problem, it shows that many times, the impact of changing environmental conditions can be far reaching, and humans are not spared from these effects.
Reference: Kris Sales et al, Experimental heatwaves compromise sperm function and cause transgenerational damage in a model insect, Nature Communications (2018). DOI: 10.1038 / s41467-018-07273-z
Image credit: University of East Anglia.
