Abstract
Dispersal is a key biological process serving several functions including connectivity among populations. Habitat fragmentation caused by natural or anthropogenic structures may hamper dispersal, thereby disrupting genetic connectivity. Investigating factors affecting dispersal and gene flow is important in the current era of anthropogenic global change, as dispersal comprises a vital part of a species' resilience to environmental change. Using finescale landscape genomics, we investigated gene flow and genetic structure of the Sooty Copper butterfly (Lycaena tityrus) in the Alpine Ötz valley system in Austria. We found surprisingly high levels of gene flow in L. tityrus across the region. Nevertheless, ravines, forests, and roads had effects on genetic structure, while rivers did not. The latter is surprising as roads and rivers have a similar width and run largely in parallel in our study area, pointing towards a higher impact of anthropogenic compared with natural linear structures. Additionally, we detected eleven loci potentially under thermal selection, including ones related to membranes, metabolism, and immune function. This study demonstrates the usefulness of molecular approaches in obtaining estimates of dispersal and population processes in the wild. Our results suggest that, despite high gene flow in the Alpine valley system investigated, L. tityrus nevertheless seems to be vulnerable to anthropogenically-driven habitat fragmentation. With anthropogenic rather than natural linear structures affecting gene flow, this may have important consequences for the persistence of species such as the butterfly studied here in altered landscapes.
Highlights
Dispersal, defined as any movement potentially resulting in gene flow, is a key biological process (Bowler & Benton, 2005; Dieckmann et al, 1999)
We tested three hypotheses. (i) As the species is considered to be dispersal-limited, a strong population genetic structure is expected, with individuals caught in close vicinity being more closely related to each other than to individuals caught further apart. (ii) Natural and anthropogenic barriers should constrain dispersal in this species and affect genetic structure. (iii) Butterflies from different altitudes are expected to be adapted to local conditions, leading to the detection of outlier loci with links to relevant biochemical pathways
To subsequently analyse isolation by resistance (IBR) and by environment (IBE, see below), we first modelled the distribution of L. tityrus within the Ötz valley system with maxent version 3.4.1 (Phillips et al, 2017) including bioclimatic variables as well as landscape features
Summary
Dispersal, defined as any movement potentially resulting in gene flow, is a key biological process (Bowler & Benton, 2005; Dieckmann et al, 1999) It has received increasing interest in the current era of anthropogenic global change (Fountain et al, 2018; Schloss et al, 2012; Urban, 2015). Dispersal investigations have been hampered by the lack of appropriate methods to measure long-distance dispersal and gene flow, i.e., successful dispersal (Fountain et al, 2018; Kim & Sappington, 2013) Traditional approaches such as mark-release-recapture or individual tracking can be difficult, and can underestimate dispersal rates and fail to reveal past dispersal events (Sielezniew et al, 2011; Ugelvig et al, 2012). We tested three hypotheses. (i) As the species is considered to be dispersal-limited, a strong population genetic structure is expected, with individuals caught in close vicinity being more closely related to each other than to individuals caught further apart (isolation by distance). (ii) Natural (forests, ravines, rivers) and anthropogenic barriers (roads) should constrain dispersal in this species and affect genetic structure. (iii) Butterflies from different altitudes are expected to be adapted to local conditions, leading to the detection of outlier loci with links to relevant biochemical pathways
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