Population structure and genetic diversity analyses reveal isolation that may imperil the northernmost colony of the endangered Australian sea lion

Marine environments are experiencing rapid warming, substantially altering
ecosystems. Populations at the edge of a species’ range are more
vulnerable to environmental change as they are first affected and may have
limited dispersal opportunities. This vulnerability may be exacerbated in
species with specialised foraging and breeding strategies. The Australian
sea lion (Neophoca cinerea) is an endangered otariid species that breeds
across a ~3000 km range in southern Australia. At the most north-westerly
edge of the species’ distribution, Australian sea lions breed across
multiple islands within the Houtman Abrolhos Archipelago, Western
Australia, a tropical-temperate location affected by marine heatwaves.
This study aimed to examine the genetic structure and diversity of the
Australian sea lions from the Houtman Abrolhos Archipelago compared to
other populations in the species’ range. One hundred and twenty-five
individuals, nineteen from Houtman Abrolhos, were genotyped from nineteen
sample sites across Western Australia and South Australia. Our findings
showed that individuals from the Houtman Abrolhos grouped into a single
population, which was highly differentiated and had extremely low genetic
diversity. The isolation and limited genetic variation of the Houtman
Abrolhos Australian sea lion population suggest that it is extremely
vulnerable to extirpation. Our study highlights the vulnerability of
isolated populations of a species to rapid environmental change and
stochastic events.