Spatial and temporal patterns of genetic diversity in Bombus terrestris populations of the Iberian Peninsula and their conservation implications

Abstract

The bumblebee Bombus terrestris is used worldwide for crop pollination. Despite its positive impact on crop yield, it has become a widespread threat to biodiversity due to its interactions with local bumblebee populations. Commercial subspecies introduced to the Iberian Peninsula since the 1990s without any regulation have colonized the environment, with evidence of naturalization and introgression with the endemic subspecies Bombus terrestris lusitanicus. We have used mitochondrial and nuclear genetic data to describe the current genetic diversity of the Iberian population and to estimate the expansion of commercial bumblebees. Samples from the natural distribution range of the commercial subspecies, the natural intergradation area between the two subspecies and from a period prior to the use of commercial colonies (i.e., before the 1990s) have been used for comparison. Our results show that the mitochondrial haplotype of the commercial breeds has spread throughout the territory, which, together with subtle changes observed in the nuclear genetic diversity of the populations, indicates that hybridization and consequent introgression are occurring in most of the peninsula. It is, therefore, necessary to improve the existing legislation concerning the management and exportation of commercial bumblebees to conserve locally adapted populations.

Selection despite low genetic diversity and high gene flow in a rapid island invasion of the bumblebee, Bombus terrestris

“…Although there can be strong correlation between metrics from SNPs and microsatellites, the magnitude of the diversity and differentiation between metrics can be quite different (Zimmerman et al, 2020). In Tasmania, B. terrestris also has substantially lower than expected heterozygosity compared to in New Zealand (H exp = 0.729), continental Europe (H exp = 0.826) (Schmid-Hempel et al, 2007), the Iberian Peninsula (H O = 0.588-0.739) (Cejas et al, 2021) and invasive populations in Japan that were colonized by several queens over several years (H exp = mean 0.751-0.780) (Nagamitsu & Yamagishi, 2009). High inbreeding coefficients were observed at all sites (Table 2), which is consistent with a small number of founding individuals.…”

Limited introgression from non‐native commercial strains and signatures of adaptation in the key pollinator Bombus terrestris

“…Furthermore, if invasion leads to the establishment of populations of commercially bred bumblebee subspecies, and/or hybridization between these bees and native subspecies occurs, a multitude of key biological traits in native populations may be affected, with impacts on their genetic diversity, ecological adaptation, as well as key plant–pollinator interactions. However, the effects of commercially bred subspecies on native pollinator genetic integrity and evolution have been the focus of few studies to date (Cejas et al, 2021; Kardum Hjort et al, 2022; Seabra et al, 2019).…”