Heatwaves damage insect sperm

Despite what some politicians would have you believe, climate change is happening, and it is taking its toll on life on earth. New research published in the journal Nature Communications seeks to explain the negative impact global warming is having on biodiversity worldwide by demonstrating that increasing heat is damaging insect fertility.

As the Earth warms, so too the atmosphere, producing volatility that numerous studies suggest that it will result in extreme climatic events, such as heatwaves being longer, more frequent, more intense and spread across a wider area of the globe. 

Such warming is causing many organisms to change their range, and sometimes leading to population declines that in many cases end with extinction. Exactly how this happens remains something of a mystery, and given the import of the issue, one group of researchers described the state of scientific knowledge on the topic as “disturbingly limited”.

Now a team of scientists from the University of East Anglia in Norwich, UK, has set about trying to understand how heatwaves, defined as a period of five days or more when the temperature is five degrees above the local maximum, affect insect populations.{%recommended 5490%}

Heatwaves are increasingly common and deadly, not only for non-human animals but for us as well: the 2003 European heatwave resulted in some 70,000 deaths. But they don’t just kill individuals: they can have a profound effect on populations too.

“Heatwaves are particularly damaging extreme weather events,” says research leader Matt Gage. 

“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.” 

It’s well understood that sperm production in mammals is incredibly sensitive to increases in temperature: subjecting male mice to 24 hours of 32 degree Celsius temperature results in a 75% decline in fertility, for example. However, no such research has been carried out for insects, which are ectothermic, or cold blooded, relying on the environment for warmth, a trait that makes them highly susceptible to global warming.

The team chose the red flour beetle (Tribolium castaneum) as its experimental model for investigation into the link between heat and sperm in insects because it has “developmental and reproductive physiology representative of most insect groups”. Beetles also make up about 25% of global biodiversity.

They discovered that heatwaves negatively impact sperm and reproductive function in a number of troubling ways. A single heatwave halved the amount of offspring and caused a 75% decline in male fertility, with the surviving sperm unable to successfully reach the appropriate female organs when delivered, and often dying before fertilisation. 

Rather than acclimatising to the new conditions, the team showed that a second heatwave 10 days later caused near-sterilisation in males. 

“Our research shows that heatwaves halve male reproductive fitness, and it was surprising how consistent the effect was,” says co-author Kris Sales. 

Worryingly, the offspring of heatwave-affected males had reduced fertility and produced fewer offspring, while at the same time exhibiting shorter lifespans. 

“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,” says Sales. 

“Since sperm function is essential for reproduction and population viability, these findings could provide one explanation for why biodiversity is suffering under climate change.”