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Infertility poses major threat to biodiversity during climate change, study warns

A new study by ecologists in international collaboration warns that heat-induced male infertility will see some species succumb to the effects of climate change earlier than thought.

Fruit fly. Photo: Mostphotos
Fruit fly. Photo: Mostphotos

Currently, scientists are trying to predict where species will be lost due to climate change so they can plan effective conservation strategies. However, research on temperature tolerance has generally focused on the temperatures that are lethal to organisms, rather than the temperatures at which organisms can no longer breed.

Published in Nature Climate Change, the study of 43 fruit fly (Drosophila) species showed that in almost half of the species, males became sterile at lower than lethal temperatures. Importantly, the worldwide distribution of these species could be predicted much more accurately by including the temperature at which they become sterile, rather than just using their lethal temperature. To give an example, Drosophila lummei males are sterile four degrees below their lethal limit. To put that in context, four degrees is the temperature difference between summer in northern England and the south of France.

“We have known for a long time that fertility is affected by heat, that’s for example a reason for mammals to have descended testicles. Other organisms than fruit flies will likely suffer from reduced fertility in a warmer climate. Insects can’t regulate body temperature, and for animals with small ranges, finding a place cool enough might not be possible,” says Rhonda Snook, professor at the Department of Zoology, Stockholm University, co-author of the article.

Lead researcher Dr Steven Parratt from University of Liverpool said: “Our findings strongly suggest that where species can survive in nature is determined by the temperature at which males become sterile, not the lethal temperature.

“Unfortunately, we do not have any way to tell which organisms are fertile up to their lethal temperature, and which will be sterilised at cooler temperatures. So, a lot of species may have a hidden vulnerability to high temperatures that has gone unnoticed. This will make conservation more difficult, as we may be overestimating how well many species will do as the planet warms.”

The researchers went on to model this for one of the Drosophila species using temperature predictions for 2060 and found more than half of areas with temperatures cool enough to survive will be too hot for the males to remain fertile.

Senior researcher Dr Tom Price commented: “Our work emphasises that temperature-driven fertility losses may be a major threat to biodiversity during climate change. We already had reports of fertility losses at high temperature in everything from pigs to ostriches, to fish, flowers, bees, and even humans. Unfortunately, our research suggests they are not isolated cases, and perhaps half of all species will be vulnerable to thermal infertility. 

“We now urgently need to understand the range of organisms likely to suffer thermal fertility losses in nature, and the traits that predict vulnerability. We must understand the underlying genetics and physiology, so we can predict which organisms are vulnerable, and perhaps produce breeds of livestock more robust to these challenges,” he added.

The researchers still don’t know if sterility is reversible and how different species can recover.

“The life span of the species is important. If a short-lived organism is infertile, even if for a short while, this temporary sterility could still have quite negative consequences. To find out if and how different species recover is the next step in our research. We also want to find out how females are affected and which genes are involved,” says Rhonda Snook.

Head of Terrestrial Ecosystems at the UK Natural Environment Research Council Dr Simon Kerley said: “This is a highly exciting piece of work that turns on its head our thinking and assumption of the role, rate, and impact of climate change. It really starts to shed light on the hidden and subtle impact of the changing conditions on the myriad of animals that we perhaps take for granted and have not previously considered ‘at risk’ from our changing climate. Importantly, it alerts us to the understanding this risk could occur sooner than we thought.”

The study involved collaborators from Stockholm University, University of Liverpool, the University of Leeds, University of Melbourne, University of Zürich and Stockholm University and was funded by the UK Natural Environment Research Council (NERC).

The paper ‘Temperatures that sterilise males better match global species distributions than lethal temperatures’ is published in Nature Climate Change.