Unregulated transportation of colonies by apiculturists in the Americas has led to increasing standardization of the genetic profile of stingless bees (Apidae: Meliponini), which are key pollinators of many native plants and commercial crops.
One of the possible consequences of this genetic homogenization could be the disappearance of bee populations that are better adapted to certain climate and environmental conditions, according to an international study conducted by Brazilian researchers in collaboration with colleagues in the United States, Portugal and Spain.
Rodolfo Jaffé, lead author of the paper and a researcher at Vale Institute of Technology (ITV) in Brazil, told Agência FAPESP, “We found that the unregulated and uncontrolled practice of transporting colonies has made stingless bee populations in the Americas more genetically homogeneous.”
The study focused on a number of factors that might hypothetically influence stingless bee gene flow, such as geographic distance between populations, beekeepers’ management practices, bee body size, deforestation and other changes in land use, and environmental conditions in the bees’ natural habitats such as temperature, elevation and rainfall.
The researchers analyzed data on these variables for 135 wild and managed populations of 17 stingless bee species from various tropical biomes in the Americas for which estimates of genetic distances between populations based on microsatellite molecular markers were available in the literature. Microsatellites are short segments of DNA that are inherited from both parents, making them useful for kinship analysis and population genetic studies.
Based on these microsatellite markers, they estimated isolation by distance (IBD) for the 135 bee populations studied. IBD is a measure of local genetic variation under conditions of geographically limited dispersal.
The results showed that IBD was significantly affected by beekeeper transportation of colonies. It was weaker for managed populations than for wild populations.
“What we would normally expect is an increase in genetic differentiation as the distance between managed populations increases, but this is not what we found,” Jaffé said. “That probably means beekeepers are transporting colonies from one region to another, and it is this practice that has caused standardization of the bees’ genetic profiles.”
Transporting colonies of stingless bees is a common practice and recommended by beekeepers in deforested areas that have lost their native bee populations. In the case of protected areas, the recommendation is to maintain the natural dynamics of existing bee populations and to avoid introducing bees from other regions.
“Transporting stingless bee colonies is a delicate matter,” Jaffé said. “It should be regulated and controlled. Transportation could be allowed within the same species’ natural habitat provided colonies are healthy and populations are evaluated beforehand.”
He added that one possible impact of unregulated colony transportation between regions is the introduction of diseases to places where none had previously existed.
Bringing new populations into a region can also lead to the loss of local populations that have hitherto been isolated and well adapted to local climate and environmental conditions in their native habitats.
“When colonies are transported, this can wipe out the genetic differentiation previously existing between bees in different areas,” Jaffé said.
Stingless bees are believed to be especially susceptible to environmental degradation owing to their limited dispersal. Because a daughter colony relies on resources from the mother colony during its initial establishment, it is typically located not very far away.
Jaffé said limited dispersal of stingless bees, which are essential to the reproduction of many plant species and critical pollinators for several commercial crops, makes them particularly sensitive to changes in land use such as those caused by deforestation.
“If an area of primary forest is cleared, the bees that used to live there will have difficulty relocating to a new habitat because of limited dispersal,” he explained.
Earlier research showed that the degradation of stingless bees’ natural habitats could hinder gene flow and lead to depletion of genetic diversity, heightening the risk of extinction, and that topography, temperature and precipitation could also influence patterns of genetic differentiation in bee populations.
However, this study found that environmental factors and deforestation did not influence gene flow for the stingless bee species analyzed.
“These species are able to disperse and maintain gene flow across different altitudinal gradients and temperature patterns, and in deforested areas,” Jaffé said.
This finding suggests maintaining connectivity between populations is not especially important to the conservation of these stingless bee species since they are already connected, even in deforested areas, he added. Instead, the focus should be on maintaining and rehabilitating environments that are “friendly” to pollinators.
“In other words, there should be sufficient resources in these areas for bees to establish colonies and forage,” Jaffé said.
“Given their ability to disperse across heterogeneous environments, they need environments where they can build nests and with enough flowers for them to obtain nectar.”