# Polyandry may mitigate the negative impact of reproductive interference among bumblebees in Japan

## TL;DR

Bumblebee queens in Japan may mate with multiple males to avoid negative effects from mating with invasive species.

## Contribution

The study shows that polyandry in native bumblebees may evolve to mitigate reproductive interference from invasive species.

## Key findings

- Native B. hypocrita sapporoensis queens in sympatry with B. terrestris are polyandrous.
- B. terrestris queens in Japan are polyandrous, unlike in their native range.
- Polyandry may reduce negative impacts of interspecific mating in sympatric bumblebees.

## Abstract

In social hymenopterans, monandry of the queen is an ancestral trait, and polyandry is a derived trait. Polyandry of the queen is the norm in a limited number of lineages, such as honeybees, leaf-cutting ants, Pogonomyrmex ants, and Vespula wasps, which presumably provide fitness advantages for the whole colony. The queen of the introduced bumblebee, Bombus terrestris, is polyandrous in Japan, whereas it is monandrous in native regions. We hypothesize that polyandry can evolve in a process that avoids the negative impacts of reproductive interference caused by interspecific mating and conducted genetic studies of the invasive species B. terrestris and two native subspecies, Bombus hypocrita sapporoensis and Bombus hypocrita hypocrita, in Japan. Our results revealed that although the native queens of B. hypocrita hypocrita allopatric with B. terrestris were strictly monandrous, the native queens of B. hypocrita sapporoensis sympatric with B. terrestris were polyandrous. These results suggested that the queens of native B. hypocrita sapporoensis do not experience negative impacts on interspecific mating from the invasive B. terrestris. We discuss the possibility that reproductive interference is a driving force in selection for multiple mating through an arms race between sympatric species.

The online version contains supplementary material available at 10.1007/s00114-024-01917-5.