Data from: Combined evidence reveals the origin of a rapid range expansion despite retained genetic diversity and a weak founder effect

Many species are currently experiencing range shifts in response to
changing environmental conditions, but with potentially serious genetic
consequences. Repeated founder events and strong genetic drift are
expected to erode genetic variation at the range front, reducing adaptive
potential and slowing or even halting the expansion. However, the severity
of these consequences for the more common and highly mobile species
undergoing environment-driven range shifts (c.f. invasions) is less clear.
Here we combined historical observations of the common reed warbler
(Acrocephalus scirpaceus) with contemporary movement data from ringing
re-encounters and genomic (RAD-seq) data from across its European
breeding range to (1) infer the origin and (2) quantify the genetic
consequences of a recent and rapid northward range expansion. While there
were no reductions in levels of nucleotide diversity or allelic richness,
nor a signal of founder effect in the directionality index (ψ), our
combined dataset approach was able to infer an expansion origin from the
southwest. Furthermore, we found that private allelic richness retained a
slight but significant linear decline along the colonisation route. These
results suggest that high dispersal capabilities can allow even
philopatric species to avoid the loss of genetic diversity during rapid
range expansions. Nevertheless, if multiple lines of evidence enable
identification of an expansion pathway, we may still detect genetic
signals of expansion.