Effective population size as a driver for divergence of an antimicrobial peptide (Hymenoptaecin) in two common European bumblebee species

Abstract

Social insects are the target of numerous pathogens. This is because the high density of closely‐related individuals frequently interacting with each other enhances the transmission and establishment of pathogens. This high selective pressure results in the rapid evolution of immune genes, which might be counteracted by a reduced effective population size (Ne) lowering the effectiveness of selection. We tested the effect of Ne on the evolutionary rate of an important immune gene for the antimicrobial peptide Hymenoptaecin in two common central European bumblebee species: Bombus terrestris and Bombus lapidarius. Both species are similar in their biology and are expected to be under similar selective pressures because pathogen prevalence does not differ between species. However, previous studies indicated a higher Ne in B. terrestris compared to B. lapidarius. We found high intraspecific variability in the coding sequence but low variability for silent polymorphisms in B. lapidarius. Estimates of long‐ and short‐term Ne were three‐ to four‐fold higher Ne in B. terrestris, although the species did not differ in census population sizes. The difference in Ne might result in less efficient selection and suboptimal adaptation of immune genes (e.g. hymenoptaecin) in B. lapidarius, and thus this species might become less resistant and more tolerant, turning into a superspreader of diseases.

Direct estimation of the spontaneous mutation rate by short-term mutation accumulation lines in Chironomus riparius

“…Lattorf et al . ) may be taken as support for the drift‐barrier hypothesis (Lynch et al . ), stating that the realised μ of a species is determined by the balance between selection and drift and thus N e and mutation rates should be negatively correlated.…”

The tragedy of the common? A comparative population genomic study of two bumblebee species

“…What is surprising, however, is that the Ne values observed for B. pratorum are of similar orders of magnitude to B. monticola (Table 1), despite the former being generally considered as widespread and common in the UK (and Ireland). Lattorff et al (2016) reported much higher Ne values than those observed here for other common bumblebee species using the same approach, although as those were continental European populations this would be expected ( B. terretris 2.7 × 10 6 ; B. lapidarius 6.4 × 10 5 , estimates that would be higher when applied to the Bombus mutation rate that has since become available (Liu et al, 2017)). We note the danger of over‐interpreting raw values using single point datasets (Nadachowske‐Bryska et al, 2022), and instead focus on the general pattern of decline observed in both species over recent generations (Figure 4).…”

“…To estimate long‐term effective population size, Watterson's theta ( θ W ) (Watterson, 1975) was calculated in SambaR (de Jong et al, 2021) as has been estimated for other Bombus species (Lattorff et al, 2016). This parameter is equivalent to 3N e μ in haplodiploids.…”

Conservation insights from wild bee genetic studies: Geographic differences, susceptibility to inbreeding, and signs of local adaptation

“…Declines in the blue orchard bee, O. lignaria, may also be due to trans-continental movement of pathogens associated with the closely related and invasive O. cornifrons (Bartomeus et al, 2013;Hedtke et al, 2015). The spread of parasites is a conservation concern because bee species and populations with lower genetic diversity are disproportionately affected (Lattorff et al, 2016;Parsche & Lattorff, 2018;Whitehorn et al, 2014). Populations with lower genetic diversity are known to have higher parasite prevalence (Parsche & Lattorff, 2018;Whitehorn et al, 2011Whitehorn et al, , 2014.…”