Like most seabirds, red-tailed tropicbirds (Phaethon rubricauda) spend most of their lives at sea, returning to islands only to breed. Despite their well-known capacity for long-distance movement, little is known about how new colonies are established or how genetic diversity is maintained across isolated, highly philopatric breeding populations. Here, we investigate patterns of genetic diversity using SNP genotyping across three breeding colonies forming a triangular spatial configuration between the Great Barrier Reef and Ashmore Reef in the eastern Indo-Pacific. We focus first on Lady Elliot Island, the most recently colonised site in the region, and compare it to Raine Island (the only other Great Barrier Reef colony), and Ashmore Reef off north-western Australia. Red-tailed tropicbirds were first recorded nesting on Lady Elliot Island in the 1980s, following revegetation efforts after historical guano mining. Raine Island lies approximately equidistant from Lady Elliot Island (1965 km south) and Ashmore Reef (2280 km west). Despite its smaller size, the Lady Elliot Island colony exhibited genetic diversity that was greater than the larger Raine Island colony and comparable to the larger Ashmore Reef colony. Weak genetic population structuring was observed between the three colonies, with Raine Island positioned between the other two in a pattern consistent with their geographic layout. These findings suggest well-established connectivity among colonies, with Lady Elliot and Ashmore Reef populations likely drawing from a broader genetic pool. Further sampling across the Indian and Pacific Oceans may reveal additional drivers of genetic structure.
Potvin et al. (Tue,) studied this question.