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Free keywords:
adaptation; climate change; genetic admixture; historical DNA; range expansion
Abstract:
Poleward range expansions are observed for an increasing number of species, which
may be an effect of global warming during the past decades. However, it is still not
clear in how far these expansions reflect simple geographical shifts of species ranges,
or whether new genetic adaptations play a role as well. Here, we analyse the expansion
of the wasp spider Argiope bruennichi into Northern Europe during the last century.
We have used a range-wide sampling of contemporary populations and historical
specimens from museums to trace the phylogeography and genetic changes associated
with the range shift. Based on the analysis of mitochondrial, microsatellite and SNP
markers, we observe a higher level of genetic diversity in the expanding populations,
apparently due to admixture of formerly isolated lineages. Using reciprocal transplant
experiments for testing overwintering tolerance, as well as temperature preference and
tolerance tests in the laboratory, we find that the invading spiders have possibly
shifted their temperature niche. This may be a key adaptation for survival in Northern
latitudes. The museum samples allow a reconstruction of the invasion’s genetic history.
A first, small-scale range shift started around 1930, in parallel with the onset of
global warming. A more massive invasion of Northern Europe associated with genetic
admixture and morphological changes occurred in later decades. We suggest that the
latter range expansion into far Northern latitudes may be a consequence of the admixture
that provided the genetic material for adaptations to new environmental regimes.
Hence, global warming could have facilitated the initial admixture of populations and
this resulted in genetic lineages with new habitat preferences.
