Although thousands of miles from the ice-sheets of Europe, the genetic record of bee species in the islands of the South Pacific carries evidence of the dramatic global effects of climate change over the past 20,000 years.
Research by Flinders University biology PhD student Scott Groom investigating the history of genetic diversity and population size in bee species across Vanuatu, Fiji and Samoa has been published in the journal Proceedings of the Royal Society B. The research was a collaboration with Dr Mark Stevens of the South Australian Museum, with funding from the Australia and Pacific Science Foundation.
The last Ice Age was focused on the northern hemisphere, but its effects were widespread, with sea levels falling markedly and global climate becoming drier and colder.
Using molecular phylogenetic techniques to plot genetic development against time, and mathematical modelling to reconstruct population size, Mr Groom’s research showed bee populations shrinking as the glacial maximum approached, then bouncing back in both population size and genetic diversity.
“We see really negative declines with the onset of the glacial period, but during the following warmer, wetter periods they responded positively and moved into a new environmental niche, accumulating genetic diversity quite rapidly and radiating out throughout the entire archipelagos,” Mr Groom said.
“We’ve been able to show that this occurred simultaneously between each of the archipelagos, which strongly suggests a shared factor that is likely to be climate.”
As with all environmental change, there are evolutionary winners and losers.
Mr Groom said that as the climate warmed, species of bees that successfully evolved to live in the cold found it necessary to retreat to the contracting reaches of mountain rainforests to survive, while a smaller range of species that showed an ability to adapt to warm conditions thrived.
Current diversity, however, remains under threat: “The bad news is that these rare lineages found at higher altitudes will be susceptible to further change,” Mr Groom said.
“If it continues to warm, they’ll have nowhere to go.”
Associate Professor Mike Schwarz, who supervised the research, said the ability to reconstruct bee populations in the past gives new insights into climate change, demonstrating the bees’ near extinction and their abundant resurgence.
“People tend to think of the tropics as being buffered from climate change and periods of cold, but Scott’s studies show that this wasn’t the case – they were really being impacted dramatically in ways that people just hadn’t thought about,” he said.
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