The tip of the iceberg: genome wide marker analysis reveals hidden
hybridization during invasion
Biological invasions are accelerating, and invasive species can have
large economic impacts as well as severe consequences for biodiversity.
During invasions, species can interact, potentially resulting in
hybridization. Here, we examined two Cakile species, C. edentula and C.
maritima (Brassicaceae), that co-occur and may hybridize during range
expansion in separate regions of the globe. Cakile edentula invaded each
location first, while C. maritima established later, apparently
replacing the former. We assessed the evidence for hybridization in
western North America and Australia, where both species have been
introduced, and identified source populations with 4561 SNPs using
Genotype-by-Sequencing. Our results indicate that the C. edentula in
Australia originated from one region of eastern North America while in
western North America it is likely from multiple sources. The C.
maritima in Australia were derived from at least two different parts of
Europe while the introduction in western North America is from one.
Although morphological evidence of hybridization is generally limited to
mixed species populations in Australia and virtually absent elsewhere,
our genetic analysis revealed relatively high levels of hybridization in
Australia (58% hybrids) and supported the presence of hybrids in
western North America (16%) and New Zealand. Hybrids might be commonly
overlooked in invaders, as identification based solely on morphological
traits may represent only the tip of the iceberg. Our study reveals a
repeated pattern of invasion, hybridization and apparent replacement of
one species by another, which offers an opportunity to investigate the
role of hybridization and introgression during invasion.