Honeybee invaders benefit from genetic endowment of their predecessors

Washington, February 26 : A new study has shown that the honeybee Apis mellifera benefit from the genetic endowment of their predecessors while invading a new place.

University of Illinois entomology professor Charles Whitfield and postdoctoral researcher Amro Zayed analysed specific markers of change in the genes of honeybees in Africa, Europe, Asia, and the Americas. They also focused on geographic regions where multiple honeybee invasions had occurred, such as Brazil in South America.

The researchers were looking for tiny variations in the sequences of nucleotides that make up all genes. While certain versions of the single nucleotide polymorphisms (SNPs) are more common to African honeybees, others occur more frequently in honey bees in western Europe, eastern Europe, or Asia.

The research team compared the SNPs in bees from different geographic territories, and looked at the frequency at which particular variants occur in functional and non-functional parts of the honeybee genome.

All that showed that the invading bees were not just randomly acquiring genetic material from their predecessors by interbreeding with them, but that certain genes from the previously introduced bees were also giving the newcomers an advantage.

Whitfield had confirmed in a previous study that A. mellifera originated in Africa, and that African honey bees had mixed with, but largely displaced, their predecessors in the New World, which were primarily of western European stock.

The earlier analysis also showed that when the European old-timers mixed with the African newcomers, their offspring looked, and in most respects behaved, like the African honeybees.

Whitfield and Zayed wanted to understand the evolutionary mechanism that allowed the African honeybees to move into new territories, and dominate the bees that had arrived in the New World centuries earlier from eastern and western parts of Europe.

Their analysis of about 440 SNPs selected randomly from throughout the Africanised honeybee genome showed that most of the variants were common to African honeybees. But of the alleles common to European bees, those found in functional parts of the genome (in genes) were showing up more frequently than those in non-functional regions (between genes).

Zayed said that when the African honeybees mated with the western European honeybees that had been in South America for centuries, one might expect that the hybrid offspring would randomly pick up both the functional and nonfunctional parts of the genome. "But actually what we found was there was a preference for picking up functional parts of the western European genome over the nonfunctional parts," he said.

Whitfield added that it seemed that the Africanised bees, which kept some of the functional western European genes, were gaining an advantage.

"Those African bees are doing better because there were western European honeybees there for them to mix with. Now we can say we have a signature for evolution in the genome," he said.

While the researchers do not yet know how the European honeybee genes are enhancing the survival and fitness of the Africanised bees in the Americas, Whitfield said that it might be that specific traits from western Europe are beneficial, or it might be that being a hybrid, is a good thing for the bees.

The study has been published online in the journal Proceedings of the National Academy of Sciences.

ANI