Heatwaves sharply reduce insect fertility

Red flour beetles saw significant fertility reduction in the laboratory. Source: Wikimedia Commons

By Jonathan Learmont

At this point it’s no secret that human induced climate change and its associated rising global temperatures have harmed biodiversity. A report last year including data from nature reserves across Germany proclaimed that there had been a 75% reduction in the population of flying insects over the past 25 years. More recently, insect numbers in Puerto Rico’s Luquillo rainforest have been found to have dropped by 10 to 60 times since the mid-1970s. In the UK moth, bee and butterfly populations have all significantly declined over a similar time period. These findings are fuelling fears of a global ecosystem collapse caused by plants not being pollinated, insectivores starving as food chains break down, and other ecological functions carried out by flying insects ceasing.

Habitat destruction for urban spaces and pesticide use are thought to be major contributing factors to these figures. However scientists have sought to isolate the temperature effect on this worrying decline, curious about why local extinctions happened when a significant increase occurred. This was done by putting red flour beetles in a five day heatwave, about 5 to 7 degrees above their optimum living conditions, in the laboratory. What they discovered was a three quarters reduction in sperm production in male beetles, while female beetles were unaffected.

Professor Matt Gage from the University of East Anglia, who led the research, said “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. Since sperm function is essential for reproduction and population viability, these findings could provide one explanation for why biodiversity is suffering under climate change.

Subsequent tests on the heatwave exposed male beetles found that higher temperatures had lingering effects on their fertility, as well as reducing the life expectancy of their offspring by a couple of months. Kira Sales, a postgraduate co-researcher, said “When males were exposed to two heatwave events 10 days apart, their offspring production was less than 1 per cent of the control group. 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.”

Beetles are thought to make up a quarter of biodiversity, and their global presence makes this study ominous; in locations where heatwaves last for weeks rather than days as is becoming more common, insect population declines may hasten.

Prior research has shown heat damages male fertility in mammals including mice, sheep and cows. This link could also be relevant to humans; fertility in men has been declining, with a 2017 study reporting a 50% reduction in collective sperm count sampling from Western countries. In addition to the environmental considerations, we may yet realise the implications of not controlling global temperatures are very personal indeed.

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