MALE FERTILITY: Global warming also knocks out sperm

 Global warming harms male fertility, concludes this study from the University of East Anglia (UK), which shows, in particular, the deleterious effects of heat peaks on sperm. Work presented in the journal Nature Communications, carried out at this stage in insects, which specifies these negative effects on fertility from one generation to the next, and helps to explain the reduction in biodiversity and the extinction of certain species with global warming.

The research team hypothesizes that male infertility during heat waves could also help explain why climate change has such an impact on the reproduction and survival of different species. “We know that biodiversity is suffering with climate change, but the specific causes and sensitivities are difficult to pinpoint,” notes lead author Professor Matt Gage: “We show with this research that sperm function is a trait particularly sensitive to global warming.

Local extinctions of some species are known to occur when temperature changes become too intense. The explanation for these phenomena could be linked to sperm, suggests the study carried out on the beetle, a small red flour beetle (Tribolium castaneum). The insects were exposed to standard control conditions or 5-day heat wave temperatures, which were 5°C to 7°C above the standard temperature. The researchers then evaluated, via different experiments, the damage of heat on reproduction, sperm function and the quality of the offspring.

Heat waves kill sperm, this is the first observation of the team which notes a halving of the number of offspring with a first exposure of males, then a virtual absence of offspring after a second heat wave. Females, on the other hand, do not seem to be affected by heat waves. After several heat waves, all sperm have difficulty migrating through the female tract and are likely to die before fertilization.

Heat waves halve the reproductive abilities of males, say researchers who suggest different causes for this vulnerability:

heat waves have an initial impact on the sexual behavior of males, which mate approximately twice as often as controls;

heat waves cause "damage" to sperm over several generations;

2 heat waves, 10 days apart, are enough to reduce the sperm production of exposed males to less than 1% of that of the control group;

finally, heat waves shorten - always in these insects - the lifespan of offspring, by the equivalent of a few months;

the reproductive performance of first-generation males descended from males exposed to heat wave conditions is also affected: these sons have reduced fertility and produce fewer offspring.

Additional pressure on populations already affected by climate change? This is the hypothesis of researchers who believe that "thermal shock" can also harm the reproduction of males in warm-blooded animals and lead mammals to sterility...