No severe genetic bottleneck in a rapidly range-expanding bumblebee pollinator

Area of Science:

• Evolutionary biology
• Population genetics
• Invasive species biology

Background:

• Genetic bottlenecks can impede population establishment in new environments.
• The genetic paradox of invasion describes successful colonization despite bottlenecks.
• Eusocial insects like bumblebees are vulnerable to bottlenecks due to diploid male production (DMP).

Purpose of the Study:

• To investigate the genetic basis of the Tree Bumblebee (Bombus hypnorum) invasion in the UK.
• To test bottleneck and gene flow hypotheses for UK B. hypnorum colonization.
• To estimate diploid male production (DMP) in the invasive UK population.

Main Methods:

• Microsatellite genotyping of UK Bombus hypnorum.
• Genetic estimation of diploid male production (DMP).
• Comparison of genetic diversity with continental populations.

Main Results:

• The UK B. hypnorum population shows no evidence of a recent severe genetic bottleneck.
• Genetic diversity levels are intermediate, between widespread and range-restricted Bombus species.
• Diploid males were found in 15.4% of colonies, with an estimated 21.5 alleles at the sex-determining locus.

Conclusions:

• The UK B. hypnorum population is not bottlenecked.
• Continued gene flow from Europe likely maintains genetic diversity.
• The Tree Bumblebee invasion in the UK does not exemplify the genetic paradox of invasion.