Infertility poses major threat to biodiversity during climate change

Heat-induced male infertility will see some species succumb to the effects of climate change earlier than thought, new research warns.

A study of 43 fruit fly (Drosophila) species by a team including ecologists at the University of Leeds showed that in almost half of the species, males became sterile at lower than lethal temperatures.  

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. 

“Whilst we predicted these thermal effects on fertility, our results are much more striking than I envisaged.”

Importantly, the worldwide distribution of the fruit fly 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. 

The findings are published in Nature Climate Change today. 

Dr Amanda Bretman, Associate Professor in Behavioural Ecology in Leeds’ School of Biology, said: “Our work highlights the importance of thinking about the impacts of climate change on biodiversity from multiple angles.  

“Whilst we predicted these thermal effects on fertility, our results are much more striking than I envisaged.  

“This emphasises an urgent need to uncover the breadth of the effects and the underlying biological processes. It also shows the value of applying knowledge about the fundamental biology of reproduction to this global problem.  

“It is a privilege to work on such important questions with a dedicated international team.” 

Hidden vulnerability 

Lead researcher Dr Steven Parratt, from the 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, from the University of Liverpool, 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.” 

Shedding light 

Head of Terrestrial Ecosystems at the 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.  

“This piece of work takes biology, at its most fundamental level, and explores it in a well-known and understood laboratory animal, but then takes that crucial extra step of relating it to the real world and the potential impact if may have on global biodiversity. 

“With the COP15 and COP26 conferences taking place this year, this study serves as a timely reminder of the need to research and better understand the relationship between climate change and biodiversity loss. The Natural Environmental Research Council will continue to fund this vital research, and UKRI as a whole will work as part of the global effort to safeguard the natural environment for generations to come.” 

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

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