Abstract
BackgroundDispersal and reproduction are key life-history traits that jointly determine species’ potential to expand their distribution, for instance in light of ongoing climate change. These life-history traits are known to be under selection by changing local environmental conditions, but they may also evolve by spatial sorting. While local natural selection and spatial sorting are mainly studied in model organisms, we do not know the degree to which these processes are relevant in the wild, despite their importance to a comprehensive understanding of species’ resistance and tolerance to climate change.MethodsThe wasp spider Argiope bruennichi has undergone a natural range expansion - from the Mediterranean to Northern Europe during the recent decades. Using reciprocal common garden experiments in the laboratory, we studied differences in crucial traits between replicated core (Southern France) and edge (Baltic States) populations. We tested theoretical predictions of enhanced dispersal (ballooning behaviour) and reproductive performance (fecundity and winter survival) at the expansion front due to spatial sorting and local environmental conditions.ResultsDispersal rates were not consistently higher at the northern expansion front, but were impacted by the overwintering climatic conditions experienced, such that dispersal was higher when spiderlings had experienced winter conditions as occur in their region. Hatching success and winter survival were lower at the range border. In agreement with theoretical predictions, spiders from the northern leading edge invested more in reproduction for their given body size.ConclusionsWe found no evidence for spatial sorting leading to higher dispersal in northern range edge populations of A. bruennichi. However, reproductive investment and overwintering survival between core and edge populations differed. These life-history traits that directly affect species’ expansion rates seem to have diverged during the recent range expansion of A. bruennichi. We discuss the observed changes with respect to the species’ natural history and the ecological drivers associated with range expansion to northern latitudes.
Highlights
Dispersal and reproduction are key life-history traits that jointly determine species’ potential to expand their distribution, for instance in light of ongoing climate change
Repeated spatial assortment for dispersal further increases the rates of dispersal on the advancing front and can even result in accelerated range expansion or shifts in expansion dynamics (e.g., [20, 21])
Spatial sorting and local natural selection are strong determinants of contemporary evolution at expansion fronts, and genetic divergence along range gradients will be determined by their joint action [17, 25, 26]
Summary
Dispersal and reproduction are key life-history traits that jointly determine species’ potential to expand their distribution, for instance in light of ongoing climate change. These life-history traits are known to be under selection by changing local environmental conditions, but they may evolve by spatial sorting. For example, local adaptation of life-history traits in relation to climate and seasonality has been described (2020) 8:2 expected to be smaller, to show a lower resilience and to be more prone to extinction under environmental fluctuations [13] They typically show reduced genetic diversity due to the effects of genetic drift [11]. Spatial sorting and local natural selection are strong determinants of contemporary evolution at expansion fronts, and genetic divergence along range gradients will be determined by their joint action [17, 25, 26]
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