A century of temporal stability of genetic diversity in wild bumblebees.

Kevin Maebe,Jean-Luc Boevé,Guy Smagghe,Thomas Claeys,Pierre Rasmont,Wouter Dekoninck,Ivan Meeus,Sarah Vray

doi:10.1038/srep38289

Abstract

Since the 1950s, bumblebee (Bombus) species are showing a clear decline worldwide. Although many plausible drivers have been hypothesized, the cause(s) of this phenomenon remain debated. Here, genetic diversity in recent versus historical populations of bumblebee species was investigated by selecting four currently restricted and four currently widespread species. Specimens from five locations in Belgium were genotyped at 16 microsatellite loci, comparing historical specimens (1913–1915) with recent ones (2013–2015). Surprisingly, our results showed temporal stability of genetic diversity in the restricted species. Furthermore, both historical and recent populations of restricted species showed a significantly lower genetic diversity than found in populations of co-occurring widespread species. The difference in genetic diversity between species was thus already present before the alleged recent drivers of bumblebee decline could have acted (from the 1950’s). These results suggest that the alleged drivers are not directly linked with the genetic variation of currently declining bumblebee populations. A future sampling in the entire distribution range of these species will infer if the observed link between low genetic diversity and population distribution on the Belgium scale correlates with species decline on a global scale.

Highlights

One of the important variables in evolutionary biology and population genetics is the effective population size (Ne)[1]
Still today, restricted bumblebee species compared to widespread species had, and have, a significantly lower genetic diversity (Fig. 1)
The here unique experimental setup of comparing recent with historical genetic diversity of different bumblebee species coming from the same locations in Belgium enabled us to show, that the levels of genetic diversity remained fairly stable over time in the studied populations

Summary

Introduction

One of the important variables in evolutionary biology and population genetics is the effective population size (Ne)[1]. Temporal studies, which estimate Ne by examining allele frequency changes over time, showed the best results (reviewed by refs 6,10–12). In bumblebee species, which are all essential pollinators in natural and managed ecosystems (e.g. refs 9,19), new data has recently raised the debate whether the population structure remained temporally stable or whether shifts in genetic diversity occurred during recent times[20,21]. In populations of the restricted and currently declining bumblebee species, a lower genetic diversity than contemporary widespread and stable bumblebee species was observed[20,21,27] It remained unclear whether this difference is caused by the decrease in population size or whether it is an intrinsic characteristic of the currently declining species[20,21,27]. Land cover changed substantially during the last three millennia due to anthropogenic activity[32], the increasing loss of habitats and forage resources due to the agricultural intensification, is thought to be the key driver of the observed bumblebee decline in Europe which started around the 1950s24,30,33

Methods

Results

Conclusion