Mating frequency estimation and its importance for colony abundance analyses in eusocial pollinators: A case study of Bombus impatiens (Hymenoptera: Apidae)

Authors: Bird, Sydney; POPE, NATHANIEL - University Of Oregon; MCGRADY, CARLEY - Pennsylvania State University; FLEISCHER, SHELBY - Pennsylvania State University; LOPEZ-URIBE, MARGARITA - Pennsylvania State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2024
Publication Date: 8/13/2024
Citation: Bird, S.A., Pope, N.S., McGrady, C.M., Fleischer, S.J., Lopez-Uribe, M.M. 2024. Mating frequency estimation and its importance for colony abundance analyses in eusocial pollinators: A case study of Bombus impatiens (Hymenoptera: Apidae). Journal of Economic Entomology. Article toae178. https://doi.org/10.1093/jee/toae178.
DOI: https://doi.org/10.1093/jee/toae178

Interpretive Summary: Bumble bees are an important group of pollinators in North America and worldwide. Current estimates of colony abundance rely on the assumption that queen bumble bees have one mate, however, past research has indicated that this species displays low levels of multiple matings. This difference in mating frequency could bias estimates of colony abundance, which are based on genetic data. Here, we quantify effective mating by queen female common eastern bumble bees (Bombus impatiens) using genetic markers, called microsatellites, to determine relatedness and paternity in 30 colonies of wild and commercial bumblebees. Unlike other studies which estimated paternity in social insects, we used a statistical algorithm that estimates both paternity and microsatellite genotyping error. We found that queen bumble bees displayed a low level of multiple mating which was similar to previous estimates. The method used in this study will be useful for determining mating frequency for many other bumblebee species for which mating frequency is currently unknown.

Technical Abstract: The genus Bombus (bumble bees) includes approximately 250 social species, many of which are in decline in North America and Europe. To estimate colony abundance of bumble bees in natural and agricultural habitats, sib-ship relationships are often reconstructed from genetic data with the assumption that colonies have one monandrous queen. However, some species such as the common Eastern North American bumble bee (Bombus impatiens Cresson) can display low levels of polyandry, which may bias estimates of colony abundance based on monandrous sib-ship reconstructions. To accurately quantify rates of polyandry in this species, we empirically estimated mating frequencies of queens using a novel statistical model and genotypes from 730 bees. To genotype individuals, we used a highly polymorphic set of microsatellites to genotype colonies established from 20 wild caught and 10 commercial queens. We found multiple fathers in 15% of wild colonies and 30% of commercial colonies. This resulted in average effective mating frequencies of 1.075 ± 0.18 for wild and 1.154 ± 0.25 for commercial colonies. Paternity was also skewed, with the minority fathers contributing less than 30% of the offspring. These findings agree with previous reports of polyandry for B. impatiens. Using this large empirical dataset, we demonstrate that assuming monandry for colony abundance estimation in species that violate this assumption may result in an overestimation of the number of colonies. Our results emphasize the importance of studying mating frequencies in social species of conservation concern for the accuracy of colony abundance estimation.