Successful crop pollination occurs through the work of honeybees whether they are native or invasive species. Researchers from the University of California, Davis, studied the impact of honeybees as they moved from Africa to North and South America.
The paper was recently published in the study PLOS Genetics where the researchers traced the movement of African honeybees starting in 1957 when they were first introduced in Brazil. New genetic evidence revealed a barrier between northern and southern bees as well as a gradual decline in African ancestry.
Erin Calfee explained how there was "a gradual transition at the same latitude" in both Americas. It is a natural barrier that may have been maintained by different honeybee species.
Most likely, the climate is what determined the barrier. The team discovered that most honeybee species with African DNA cannot survive colder winter climates.
Introduction of Invasive Bee Species
The first honeybees, Apis mellifera, were brought to the Americas during the 1600s. For centuries, the invasive species coexisted with native species and impacted crop pollination.
By 1957, the African subspecies Apis mellifera scutellate left experimental hives in Brazil and rapidly spread throughout South America while breeding with European bees. Scutellata bees have a unique characteristic of defensive behavior and are resistant to Varroa mites, a trait useful for beekeepers.
The team focused on sequencing the genome of bees from the north and south edges of where the scutellate bees expanded. Results showed that northern bees have less African ancestry.
The entire genome tracked latitude and climate, explained Calfee. Most likely, a lot of the bees' genes are associated with climate sensitivity and survival during the winter. She said that there was also evidence of scutellata ancestry spreading beyond climate limits meaning that some of the advantageous genetic traits are not associated with climate sensitivity.
Their findings also challenge a clear distinction between African and European honeybees in California and Argentina, said Santiago Ramirez. Moreover, the introduced bees to the Americas were also forms of hybrid species.
Hybrid species and scutellate bees had greater genetic diversity than those of European descent. The team also found less genetic diversity loss of those of African descent as scutellata bees moved north toward California.
Breeding for Desirable Traits
The results of the study could help breeders select certain species for desirable genetic traits such as resistance to pathogens. For example, wrote the authors, "Scutellata-European hybrid honey bees have high competitive fitness and, we show here, maintained high genetic diversity despite their rapid expansion."
Although both species were invasive when first introduced, they may be part of the solution of preserving honeybees.
"It makes sense but it's kind of surprising because we have 1.5 million (honeybee) colonies being brought into California every spring to pollinate crops," Ramirez said. The bees have become domesticated and do not mix with the wild bees population in the state.
Check out more news and information on Bees on Science Times.
