Analysis shows bees increasingly stressed by changes in climate

An analysis of bumblebee wings from a network of UK museums indicates bees have been increasingly stressed by changes in the climate over the past 100 years.

Bumblebees and other insects have faced population declines in recent years.

The research, published in two papers from scientists at Imperial College London and the Natural History Museum, can help predict when and where bees will face most stress and potential decline in the future.

The first paper investigated the body shapes of bee specimens dating back to 1900. Using digital images, the group investigated asymmetry in bumblebee wings as an indicator of stress.

High asymmetry (very differently shaped right and left wings) indicates the bees experienced stress during development – an external factor that affected their normal growth.

Studying four UK bumblebee species, the group found evidence for stress getting higher as the century progressed from its lowest point around 1925. Further analysis showed that each bee species displayed a consistently higher proxy of stress in the latter half of the century.

By taking the climate conditions during the year of collection – namely annual mean temperature and annual rainfall – the team found that in hotter and wetter years bees showed higher wing asymmetry.

Author Aoife Cantwell-Jones, from the Department of Life Sciences (Silwood Park) at Imperial, said: ‘By using a proxy of stress visible on the bee’s external anatomy and caused by stress during development just days or weeks before, we can look to more accurately track factors placing populations under pressure through historic space and time.’

Author Dr Andres Arce, now at the University of Suffolk, stated: ‘Our goal is to better understand responses to specific environmental factors and learn from the past to predict the future. We hope to be able to forecast where and when bumblebees will be most at risk and target effective conservation action.’

Senior author Dr Richard Gill, from the Department of Life Sciences (Silwood Park) at Imperial, added: ‘With hotter and wetter conditions predicted to place bumblebees under higher stress, the fact these conditions will become more frequent under climate change means bumblebees may be in for a rough time over the 21st century.’

As well as measuring the wing shapes of bees, in a second parallel study the team successfully sequenced the genomes of over a hundred bumblebee museum specimens dating back more than 130 years. In a pioneering advance, ancient DNA methods typically used for studying woolly mammoths and ancient humans, were for the first time used on an insect population.

Scientists from the Natural History Museum and the Earlham Institute quantified DNA preservation using just a single bee leg from each of the bees studied. From these developments, published today in Methods in Ecology & Evolution, the researchers can now look to determine how the reported stress may lead to genetic diversity loss.

In conjunction with providing a new reference genome, the team will now use this data to study how bee genomes have changed over time, gaining an understanding of how whole populations have adapted – or not – to changing environments.

Author Dr Victoria Mullin, from the Natural History Museum, said: ‘Museum insect collections offer an unparalleled opportunity to directly study how the genomes of populations and species have been affected by environmental changes through time. However, they are a finite resource and understanding how best to utilise them for genetic studies is important.’

Photo by Dmitry Grigoriev