Level of Genetic Diversity in European Bumblebees is Not Determined by Local Species Abundance

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.

Assessment of genetic diversity and population structure of Eulaema nigrita (Hymenoptera: Apidae: Euglossini) as a factor of habitat type in Brazilian Atlantic forest fragments

“…These parameters were calculated using GenAlEx, version 6.5 Smouse 2006, 2012) and the diveRsity package in R (Keenan et al 2013), respectively. To test if habitat and relative abundance influenced genetic diversity (here, it refers only to allelic richness values) in each locality, linear mixed models were performed for allelic richness with the lmer function in the R package, lme4, version 1.1-10 (Bates et al 2015), as described in Soro et al (2017) and Maebe et al (2019aMaebe et al ( , 2019b. The model included habitat (considering the two physiognomies, rainforest and semi-deciduous forest), relative abundance as the fixed factors, and microsatellite loci as a random factor (Soro et al 2017;Barton 2020).…”

“…The model included habitat (considering the two physiognomies, rainforest and semi-deciduous forest), relative abundance as the fixed factors, and microsatellite loci as a random factor (Soro et al 2017;Barton 2020). The best model that fits our data was selected based on the Akaike's information criterion by using the "dredge" command within the MUMIn package (Barton 2020;Maebe et al 2019a and references therein). The main effect of the factor of interest was analysed for each selected linear mixed model by performing likelihood ratio tests comparing the models with factors to a "null" model without these factors (Soro et al 2017;Maebe et al 2019a and references therein).…”

“…The best model that fits our data was selected based on the Akaike's information criterion by using the "dredge" command within the MUMIn package (Barton 2020;Maebe et al 2019a and references therein). The main effect of the factor of interest was analysed for each selected linear mixed model by performing likelihood ratio tests comparing the models with factors to a "null" model without these factors (Soro et al 2017;Maebe et al 2019a and references therein). We estimated the variance of each of habitat and abundance alone versus the variance for microsatellite loci variability, as the marginal and conditional coefficient of determination, respectively (Nakagawa and Schielzeth 2013;Soro et al 2017).…”

“…Our comprehension of genetic diversity in natural populations requires knowledge of genetic variation within and among populations (Avise and Hamrick 1996). Gene flow among populations and the dispersal capacity of individuals are essential for the maintenance of genetic diversity over time, which is crucial for species survival (Maebe et al 2019a). Indeed, low levels of intraspecific genetic diversity can restrict the potential of species to adapt to environmental change (Frankham 2005;Zayed 2009;Habel et al 2014;Koch et al 2017;Maebe et al 2019aMaebe et al , 2019b.…”

“…Gene flow among populations and the dispersal capacity of individuals are essential for the maintenance of genetic diversity over time, which is crucial for species survival (Maebe et al 2019a). Indeed, low levels of intraspecific genetic diversity can restrict the potential of species to adapt to environmental change (Frankham 2005;Zayed 2009;Habel et al 2014;Koch et al 2017;Maebe et al 2019aMaebe et al , 2019b. Among the effects of limited dispersal capability, populations that were previously but are no longer well-connected can attain significant population structure (Frankham 2005;Kokko and López-Sepulcre 2006;Zayed 2009;Maebe et al 2019b).…”