Data from: Multiple introductions, polyploidy and mixed reproductive strategies are linked to genetic diversity and structure in the most widespread invasive plant across Southern Ocean archipelagos

Biological invasions in remote areas that experience low human activity
provide unique opportunities to elucidate processes responsible for
invasion success. Here we study the most widespread invasive plant species
across the isolated islands of the Southern Ocean, the annual bluegrass,
Poa annua. To analyze geographic variation in genome size, genetic
diversity, and reproductive strategies, we sampled all major sub-Antarctic
archipelagos in this region and generated microsatellite data for 470
individual plants representing 31 populations. We also estimated genome
sizes for a subset of individuals using flow cytometry. Occasional events
of island colonization are expected to result in high genetic structure
among islands, overall low genetic diversity, and increased
self-fertilization, but we show that this is not the case for Poa annua.
Microsatellite data indicated low population genetic structure and lack of
isolation-by-distance among the sub-Antarctic archipelagos we sampled, but
high population structure within each archipelago. We identified high
levels of genetic diversity, low clonality, and low selfing rates in
sub-Antarctic P. annua populations (contrary to rates typical of
continental populations). In turn, estimates of autogamy declined in
populations as genetic diversity increased. Additionally, we found that
most P. annua individuals are likely tetraploid and that only slight
variation exists in genome size across the Southern Ocean. Our findings
suggest multiple independent introductions of P. annua into the
sub-Antarctic, which promoted the establishment of genetically diverse
populations. Despite multiple introductions, the adoption of convergent
reproductive strategies (outcrossing) happened independently in each major
archipelago. The combination of polyploidy and a mixed reproductive
strategy likely benefited P. annua in the Southern Ocean by increasing
genetic diversity and its ability to cope with the novel environmental
conditions.