Data from: Translocation precipitates natural hybridisation and pervasive introgression between marine gastropods with divergent developmental modes

Assisted colonisation, the introduction of species beyond their historical
range, is increasingly necessary for conserving species. However,
empirical evidence of the long-term genetic outcomes of assisted
colonisation is grossly lacking. A risk associated with moving species
beyond their native range is the possibility of interspecific
hybridisation with a closely related species, potentially
resulting in outbreeding depression or the genetic
swamping of a parental species. Here, we use a combination of
genome-wide Single Nucleotide Polymorphism (SNP) markers
and mitochondrial DNA sequencing to determine the long-term genetic
consequences of introducing the intertidal periwinkle Bembicium
vittatum (a direct developer) beyond its native range and into
the native range of its congener Bembicium auratum (a
species with planktotrophic larval dispersal). We found novel evidence of
natural, multigenerational hybridisation between marine invertebrates with
different modes of development.
Intriguingly, introgression was highly asymmetrical
initially, but became more evenly bidirectional as the population became
more admixed. There was a significant decline in the frequency of alleles
from the introduced B. vittatum over time, providing
evidence of genetic swamping. The present study also provides potential
evidence of outbreeding depression, in the form of cytonuclear
incompatibilities, leading to the observed pattern of
asymmetrical introgression. This study reveals the potential for
unexpected mixing between species when reproductive barriers are not well
understood, resulting in failure of pure B. vittatum to
persist at the translocation site, a major concern associated with
assisted colonisation. Without long-term genetic monitoring interspecific
hybridisation between B. vittatum and B.
auratum would have gone undetected, highlighting the importance of
long-term monitoring to detect unintentional negative consequences of
conservation translocations. Successful assisted colonisation requires an
understanding of the potential for interspecific hybridisation between the
threatened species and closely related native species, to reduce the risk
of adverse outcomes.