25 October 2013
A paper by South Australian Museum scientist Dr Remko Leijs and colleagues that looks at the way Carpenter bee extinctions mirrored dinosaur deaths millions of years ago, has this week been published in PLOS ONE.
Dr Leijs, the University of New Hampshire’s Dr Sandra Rehan and Flinders University’s Dr Michael Schwarz have shown that Carpenter bees underwent a mass extinction event similar to that experienced by dinosaurs millions of years ago.
Their remarkable research traced the evolution of Carpenter bees (subfamily Xylocopinae) using molecular analysis of living bees, as fossils were not available.
“Bee fossils are very rare and most of them are relatively young – around 20-40 million years old – unlike dinosaur fossils which stretch back further in time,” said Dr Leijs.
“Without access to fossils, we needed to use molecular phylogenetic analysis to trace the bees throughout history. We analysed DNA sequences to find out how the different groups were related throughout time. This gave us a window into the past and valuable information on the evolutionary relationships between organisms,” Dr Leijs said.
The scientists used this analysis to create a phlyogenetic tree. This diagram (below) looks similar to a family tree and shows how different organisms have evolved from a common ancestor.
During their research, the group discovered that the ancestors of each of the remaining four tribes of Carpenter bees lived around 85–90 million years ago. Once they discovered the age of the ancestral Carpenter bee, they realised it had lived through a massive extinction event.
“We started working on the historical biogeography of the bees – where they lived and when – but then we realised that they lived across the K-T boundary around 66 million years ago,” said Dr Leijs.
The K-T boundary spans from the end of the Cretaceous period to the beginning of the Tertiary period in geological time. From the fossil record, scientists say many forms of life, including dinosaurs and some flowering plants, became extinct at this time. A meteor impact is thought to have caused the massive extinctions, although major environmental changes were also taking place.
“This was a catastrophe. We don’t know exactly what happened, but many life forms died out and we thought that this could be the case in bees as well,” Dr Leijs said.
When the team looked at the Carpenter bee lineage across time, they found that these bees showed diversification very early in their history and then a long period without new lineages across the K-T boundary.
“Diversification would normally keep increasing over time, so this plateau is either due to a massive extinction event or an equal rate of species’ births and deaths over a long time. We think that a massive extinction event is the most likely answer, as up to 90% of the species were lost during this time before rapid diversification began again in each of the four tribes,” said Dr Leijs.
The global extinction of dinosaurs around the K-T boundary also suggests that events at this time had a massive and geographically widespread effect on terrestrial ecosystems.
“Carpenter bees generally nest in dead wood and plant stems – their relationship with plants isn’t just about food, they also use them for shelter. In an event like a meteor strike, it is likely that their habitat was destroyed as well as their food source. Other bees nest in the ground so although they need plants to eat, they may have been less susceptible to extinction,” said Dr Leijs.
At this point it’s not possible to determine whether other bee groups suffered similar massive extinction events. This Carpenter bee research is only possible because a large number of Carpenter bees have been analysed. DNA has been sequenced from over 200 species by scientists at the South Australian Museum and Flinders University over many years.
As technology advances and DNA analyses become faster and cheaper, researchers will be able to bring the history of more organisms to life – particularly those that aren’t represented in the fossil record. Understanding the past relationships between different species may also help us to predict the consequences of future environmental change for our important pollinators.