York University biologist and bee expert, Professor Amro Zayed, continues to produce and publish original research of global importance. This time, he has contributed a news and views article in Nature (November 2016) that puts into context the work of an Australian researcher who discovered how natural selection allows an invader bee population to overcome the genetic odds stacked against it. The study, led by Professor Rosalyn Gloag of the University of Sydney, New South Wales, examined the invasion of Asian honeybees over an eight-year time frame.
Zayed: Home-grown York success story and global leader in bee research
York researchers have played key roles in many of the most important discoveries of the past half-century. In many areas, the have become global leaders. This is the case with Amro Zayed. A home-grown success story, he earned his BSc (2000) and PhD (2006) from York; and he has contributed to internationally leading journals − including Nature, Science and Proceedings of the National Academy of Sciences − for many years. His research has greatly added to our global knowledge on bees.
Zayed’s leadership has been recognized many times: In 2007, he was awarded the Governor General’s Gold Medal for his doctoral research on bee conservation genetics. In 2010, he received the Ontario Government of Research and Innovation’s Early Researcher Award; and in 2014, he won the Faculty of Science’s Early Career Researcher Award.
Zayed was recently awarded the Entomological Society of Canada’s Hewitt Award for outstanding contributions to entomology in Canada by a young researcher. He currently serves as the York Research Chair in Genomics (Tier II).
Zayed provides framework in which to understand the new research
While a great deal of bee research is focused on preserving honey bees whose numbers are dwindling (and this could have catastrophic effects on the food chain), Asian bees have piqued the curiosity of researchers for the opposite reason: they are destructive invaders, Zayed explains. These bees are successful invasive insects because they can act as individuals or as part of the colony, and this adaptability allows them to adjust to different environmental conditions.
“Asian bees are invading Australia, which is itself is not great for Australian beekeepers who use the European honey bee; the two may compete or hybridize, which is undesirable,” Zayed says. “Invasive insects can be particularly damaging and we don’t fully understand which process facilitates invasion success,” he adds.
According to the Australian government’s Department of the Environment and Energy, in 2007, an incursion of the Asian honey bee was found in Cairns, Queensland. Attempts to eradicate it proved futile by 2011. However, a containment program was launched to restrict its spread and minimize its impacts.
These bees could have a negative environmental impact, most likely associated with competition for floral resources or nesting sites, inadequate pollination of native flora or undesirable pollination of exotic flora, according to the Australian government.
Australian study focuses on Asian Honey Bees
The Australian study led by Professor Rosalyn Gloag was published in Nature Ecology & Evolution in November 2016 under the title “An invasive social insect overcomes genetic load at the sex locus.” It looked at the invasion of Asian honey bees (Apis cerana).
Zayed explains that these invading insects may appear to be doomed, because they have a sex-determination system that creates sterile or inviable males in small populations that lack genetic diversity, but they were in fact thriving.
The Australian team of researchers realized that natural section was somehow allowing this bee population to thrive, and the group needed to figure out why this was happening.
Eight-year study observes biological invasion in real time
Gloag’s team of researchers went into the field and observed this natural selection during a real-time biological invasion. Over an eight-year time frame, starting in 2007, they studied the csd gene in honey bees – csd being an acronym for complementary sex determiner, hence the gene governs sex determination.
As Zayed explains, a female bee possesses two copies of the csd gene and mates with a male bee, which has only one copy of the gene. The csd gene exists in different forms called alleles, as depicted in different colours in the diagram below.
If a female mates with a male that has an identical csd allele, shown in situation A of Zayed’s diagram, then half of the offspring will have two identical csd alleles and will develop as sterile males, that will die off leaving no future generations. Conversely, the offspring that have two different csd alleles develop as fertile females.
Situation B in Zayed’s diagram tells a different story: All of the offspring from a mating between a male that has a rare allele, such as the one indicated in purple, and a female that does not have this rare allele will develop into fertile females. This would, therefore, increase the frequency of the rare allele in future generations until all csd alleles have the same frequency, says Zayed.
This is how Gloag’s team was able to confirm the phenomenon of natural selection in the invading Apis cerana bees in Australia. “Gloag and colleagues’ study provides a clear example of how rapid evolutionary changes can affect the fitness of invasive populations,” Zayed explains.
Zayed’s article, “Evolution: Insect invasions and natural selection,” was published in Nature in 2016. Gloag’s study, “An invasive social insect overcomes genetic load at the sex locus,” was also published in 2016. Amro Zayed’s lab website at York University contains more information about this researcher and bee expert.
By Megan Mueller, manager, research communications, Office of the Vice-President Research & Innovation, York University, muellerm@yorku.ca