Invasive Asian honeybees defy evolutionary expectations

In North Queensland, invasive Asian honeybees (Apis cerana) have surprisingly flourished, expanding from a single swarm to over 10,000 colonies across a 10,000 square kilometer area, akin to the size of Greater Sydney. 

This enormous growth challenges the conventional evolutionary theory that a significant genetic bottleneck would hinder such expansion.

Unexpected adaptability with limited diversity

“Our study of this bee population shows that some species can quickly adjust to new environments despite starting with very low genetic diversity relative to their native-range populations,” said co-lead author Rosalyn Gloag from the University of Sydney School of Life and Environmental Sciences 

Gloag’s observation highlights the adaptability of species even with minimal genetic variation, contradicting the widespread belief that high genetic diversity is crucial for adapting to new or rapidly changing environments.

This finding underscores the resilience of populations with diminished genetic diversity, offering insights into broader ecological adaptability. “This is even more important as we observe many species dealing with anthropogenic climate change,” Gloag said.

The Queensland invasion 

The team’s investigation into the Queensland invasion provides a comprehensive genetic chronology of a natural incursion, tracing back to the bees’ 2007 arrival, likely from Papua New Guinea. This event raised biosecurity alarms in Australia due to potential parasite threats. 

However, these bees were found to be free of the feared varroa mite, which has since entered Australia through unknown means, posing a risk to the local honey industry.

Valuable biological dataset 

The Queensland Department of Agriculture and Fisheries‘ exhaustive early sampling efforts, aimed at eradicating the bees, yielded a valuable biological dataset. 

“We were lucky to have a complete sample timeline of this invasive population thanks to the incredible efforts of the Queensland Department of Agriculture and Fisheries, which sampled the population extensively during the early years of the incursion as part of an eradication attempt,” Gloag explained.

“Although that attempt was unsuccessful, the biological material collected has been incredibly valuable for understanding how these invasions proceed. And that in turn helps us prepare better for future invasions.”

Observing natural selection

Analyzing genomes from 118 bees collected over a decade, the researchers witnessed natural selection in action within a genetically constrained population. “We could essentially observe natural selection acting over time in a population that started with low genetic diversity,” Gloag said. 

“From this unique vantage point, we could see that selection was acting on the variation in genomes that had arrived with the handful of original bees. It wasn’t variation that arose later by mutations. In other words, some species with very low genetic diversity can adapt very quickly.”

This finding that species can swiftly adapt with scant genetic diversity presents a mixed outcome. While it poses challenges for managing invasive species, it also offers hope for populations endangered by climate change or catastrophes, demonstrating potential resilience despite genetic losses.

Invasive Asian honeybees

Invasive Asian honeybees, particularly Apis cerana, have become a topic of concern in various parts of the world due to their ability to adapt to diverse environments and compete with local bee populations. 

These bees are smaller than the European honeybees (Apis mellifera) commonly found in agriculture and beekeeping industries worldwide.

Major challenges

The spread of Asian honeybees outside of their native range poses several environmental and economic challenges. 

First, they compete with local bee species for resources such as nectar and pollen, which can lead to a decrease in the populations of native bees. This is particularly concerning for areas with unique native bee species that are essential pollinators for local flora.

In addition, the introduction and establishment of invasive bee species can disrupt local ecosystems. Asian honeybees are known for their aggressive foraging behavior and efficient utilization of floral resources, which can lead to changes in the pollination dynamics of native plant species. Such changes can have cascading effects on the structure and function of ecosystems.

Economic threats

From an economic perspective, the spread of Asian honeybees can impact the beekeeping industry. They often become pests to beekeepers by invading and colonizing European honeybee hives. 

Furthermore, in areas where these bees become dominant, they can change the dynamics of pollination services, potentially affecting crop yields.

Management and mitigation

Efforts to manage and mitigate the impact of invasive Asian honeybees include monitoring their spread, implementing biosecurity measures to prevent their introduction into new areas, and researching biological control methods. 

Conservationists and researchers are particularly focused on protecting native bee populations and ensuring that the ecological balance is maintained to support both agriculture and biodiversity.

The study is published in the journal Current Biology.

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