sylvicola from the same high-elevation alpine localities in Colorado. (2015) compared morphometric measurements of contemporary samples and historical specimens of the species B. In addition to range shifts there is evidence that the morphology of certain populations of bumblebees has shifted in recent decades. Arctic and alpine species are particularly threatened by these trends, and can be considered “canaries in the coal mine” for detecting early effects ( Elsen & Tingley, 2015). In particular, a general worldwide trend for species to shift to higher elevations and latitudes has been documented, with losses occurring at a faster rate than expansions ( Kerr et al., 2015 Marshall et al., 2020). Many bumblebee species are experiencing range shifts or declines due to climate change or habitat loss ( Cameron et al., 2011 Cameron & Sadd, 2020 Goulson, Lye, & Darvill, 2008a Soroye, Newbold, & Kerr, 2020). Bumblebees are large-bodied, mainly cold-adapted species with broad significance for agricultural production and plant-pollinator networks in the wild ( Goulson, 2003).
The importance of pollinators for ecology and the maintenance of biodiversity is widely recognized ( Goulson, Nicholls, Botías, & Rotheray, 2015). Our results provide evidence for ongoing modification of a morphological trait important for pollination and indicate that this trait likely has a complex genetic and environmental basis. We identified evidence of covariance between kinship and both tongue length and body size, which is suggestive of a genetic component of these traits, although it is possible that shared environmental effects between colonies are responsible. We did not discover any genetic associations with tongue length, but a SNP related to production of a proteolytic digestive enzyme was implicated in body size variation. We found a significant decrease in tongue length between bees collected between 2012-2014 and in 2017, indicating that morphological shifts are ongoing. However, an absence of genetic structure within species suggests that gene flow is common between mountains. sylvicola, 67 formed a separate genetic cluster comprising a newly-discovered cryptic species (“incognitus”). Out of 281 samples originally identified as B. We then analyzed whole-genome sequencing data and morphometric measurements of 580 samples of both species from seven high-altitude localities. Here we used morphometrics and population genomics to determine whether morphological change is ongoing, investigate the genetic basis of morphological variation, and analyze population structure in these populations. It has been hypothesized that this observation reflects selection resulting from shifts in floral composition under climate change. Over the last six decades, populations of the bumblebees Bombus sylvicola and Bombus balteatus in Colorado have experienced decreases in tongue length, a trait important for plant-pollinator mutualisms.
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