Climate change killing sperm

With rising climate temperature, heat waves are becoming more frequent and more intense, but what impact is this having on the plants and insects around us? As the temperature of our planet goes up, biodiversity tends to fall, but researchers have been stumped as to why. Now, a team at the University of East Anglia have found that heat waves can compromise sperm counts in insects. Izzie Clarke heard how from Matt Gage...

Matt - So although there's been a lot of research looking at warm blooded species and how heat can impact on male fertility and sperm function, there's been very little work looking at cold blooded species like insects for example which we thought was quite a knowledge gap because most of biodiversity on our planet is cold blooded. They may even be more sensitive to environmental temperature change because our own core body temperature will change as the external thermal environment changes as well.

Izzie - Okay so what did you find looking at these cold blooded species?

Matt - We were basically interested in how experimentally induced heat wave conditions impacted on reproductive performance and reproductive biology. We chose a beetle because first of all it's an insect. About a quarter of insects are beetles. So what we did was we quite simply took adult male and female beetles and we expose them to simulated heatwave conditions and our heatwave conditions were those that are widely accepted as a definition of a heat wave which is when their normal temperature rises by 5 degrees for five, days and then what we found was that male fertility or male reproductive output declined markedly with heat wave exposure. So one heat wave about halved a male’s reproductive performance and when we gave males a second heat wave they basically became sterile.

Izzie - What about female beetles? 

Matt - So the females were in themselves resistant to heat wave so if you heat wave a female Beetle and then mate her to a male who hasn't been heat wave she's fine. Her reproductive output is exactly the same as if she's never experienced the heat wave. But if you mate the female so she's got mature inseminated sperm in her sperm storage organs which most female insects have then she suffers as a consequence a heat wave. So somehow the heat waves are damaging the sperm that she has stored inside her. And then we see about a 30 percent decline in a female subsequent fertility.

Izzie - So they essentially they'll mate with a male they store that sperm and use it as and when they like but if they experience a heat wave the female isn't really affected but the sperm that she's carrying is.

Matt - That's right. But what we also found was a trans generational impact of heat waves so if you're an offspring born from a dad who experienced the heat wave or indeed from a sperm we found a lifespan cut in those offspring so they live to about 20 percent shorter than the offspring whose dad’s or sperm never experienced the heat wave. And if you're a son from a dad or a sperm that experienced the heat wave your reproductive potential also was reduced.

Izzie - Oh gosh. And do you know what is actually going on in that reproductive biology to cause this effect?

Matt - We don't at the moment but our prime suspect is DNA damage. We know that heat can damage DNA inside sperm and we know that sperm that have damaged DNA also have fertility and indeed pregnancy problems for example in humans. But we haven't actually shown yet what the mechanism is that this transgenerational damage occurs by.

Izzie - And what about the impact if we're seeing these reproductive issues and climate change affecting male fertility. What impact could that have?

Matt - Well I guess if you're thinking from a biodiversity perspective it could be a pretty big impact because if you can't reproduce, your population viability is not very good, so we've shown under control conditions that sperm sensitivity could lead to population declines we're seeing in the natural environment. But we really want to pin that down more closely and we're planning to do that both in the lab at population level and maybe to try and take that to the field as well and have a look at it in insects under more field relevant conditions.

We'd like to know whether populations can adapt evolutionarily to changes in the climate and how quickly they can adapt. And of course we'd really like to understand what the mechanism that is that's leading to that transgenerational damage because that could have relevance for a lot of species including our own.