Data from: Effects of admixture in native and invasive populations of Lythrum salicaria

Intraspecific hybridization between diverged populations can enhance
fitness via various genetic mechanisms. The benefits of such admixture
have been proposed to be particularly relevant in biological invasions,
when invasive populations originating from different source populations
are found sympatrically. However, it remains poorly understood if
admixture is an important contributor to plant invasive success and how
admixture effects compare between invasive and native ranges. Here, we
used experimental crosses in Lythrum salicaria, a species with
well-established history of multiple introductions to Eastern North
America, to quantify and compare admixture effects in native European and
invasive North American populations. We observed heterosis in
between-population crosses both in native and invasive ranges. However,
invasive-range heterosis was restricted to crosses between two different
Eastern and Western invasion fronts, whereas heterosis was absent in
geographically distant crosses within a single large invasion front. Our
results suggest that multiple introductions have led to already-admixed
invasion fronts, such that experimental crosses do not further increase
performance, but that contact between different invasion fronts further
enhances fitness after admixture. Thus, intra-continental movement of
invasive plants in their introduced range has the potential to boost
invasiveness even in well-established and successfully spreading invasive
species.