Abstract
Bumblebee species with declining population trends tend to show lower genetic diversity levels than stable species. The observed difference might be explained by abundance differences, with declining bumblebee species having lower genetic diversity levels simply due to their lower local species abundances. However, whether this holds true is not known. Here, we investigated whether bumblebee local abundances determines population genetic diversity levels. Therefore, local species abundances were measured for bumblebee species at four locations in Belgium and two locations in Estonia during bumblebee foraging years 2013–2017. These locations and countries were chosen to ensure the greatest possible variance in both local abundances and population trends for these species. Hence, genetic diversity levels were obtained for seven species by genotyping collected specimens with 16 microsatellites. Our results showed that the observed patterns in genetic diversity did not depend on local species abundance. So, although declining bumblebee species can become locally abundant, they will still show lower genetic diversity levels than stable species. This result implies that measuring bumblebees’ local abundance cannot be used to directly determine the health status of a population. Furthermore, this result has also major impact on future conservation strategies as increasing the genetic diversity levels of declining species will be very difficult, and habitat quality should be high to maintain their populations, otherwise these species are doomed to disappear first.
Highlights
An essential factor for species survival is the level of genetic diversity present within its populations
628 specimens (309 Belgian and 319 Estonian specimens) remained for further genetic analysis out of 729 specimens, due to the removal of full-sibs which were detected by Colony 2.0 and Kinalyzer analyses, and discarding of specimens which have more than five loci of missing data from both Belgian and Estonian dataset
Linear regression showed low and non-significant correlations between local abundance and allelic richness (AR) or HE (R2 = 0.0261, p = 0.393; R2 = 0.0419, p = 0.278; respectively; Figure 2) suggesting that only a low amount of variation of genetic diversity is explained by local abundance
Summary
An essential factor for species survival is the level of genetic diversity present within its populations. In smaller less-connected populations, gene flow may be more limited, decreasing its buffering effect, which leads to lower genetic diversity and increase brother–sister mating chances, and in turn to inbreeding and inbreeding depression (Frankham, 2005; Zayed, 2009; Habel et al, 2014). The latter dynamics can further diminish genetic variability within small populations, potentially creating a vicious circle, known as the extinction vortex, which could lead to extinction (Frankham, 2005; Zayed, 2009; Habel et al, 2014)
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