Population divergence and gene flow in an endangered and highly mobile seabird

Abstract

Seabirds are highly vagile and can disperse up to thousands of kilometers, making it difficult to identify the factors that promote isolation between populations. The endemic Hawaiian petrel (Pterodroma sandwichensis) is one such species. Today it is endangered, and known to breed only on the islands of Hawaii, Maui, Lanai and Kauai. Historical records indicate that a large population formerly bred on Molokai as well, but this population has recently been extirpated. Given the great dispersal potential of these petrels, it remains unclear if populations are genetically distinct and which factors may contribute to isolation between them. We sampled petrels from across their range, including individuals from the presumably extirpated Molokai population. We sequenced 524 bp of mitochondrial DNA, 741 bp from three nuclear introns, and genotyped 18 microsatellite loci in order to examine the patterns of divergence in this species and to investigate the potential underlying mechanisms. Both mitochondrial and nuclear data sets indicated significant genetic differentiation among all modern populations, but no differentiation was found between historic samples from Molokai and modern birds from Lanai. Population-specific nonbreeding distribution and strong natal philopatry may reduce gene flow between populations. However, the lack of population structure between extirpated Molokai birds and modern birds on Lanai indicates that there was substantial gene flow between these populations and that petrels may be able to overcome barriers to dispersal prior to complete extirpation. Hawaiian petrel populations could be considered distinct management units, however, the dwindling population on Hawaii may require translocation to prevent extirpation in the near future.

Millennial-scale isotope records from a wide-ranging predator show evidence of recent human impact to oceanic food webs

“…However, atmospheric deposition of 15 N decline. This conclusion is supported by genetic analyses, which show that migration was very low among islands before human colonization and is currently low among extant populations (17,18).…”

“…We collected isotope data from over 250 individuals, including birds from every known modern and ancient Hawaiian petrel population. Equally extensive genetic studies (based largely on the same set of individuals) show that despite their high mobility, Hawaiian petrels rarely move between islands, and breeding colonies on different islands have diverged into genetically distinct populations (17,18). Because at least some of those populations also have distinct foraging habits (15), we construct separate isotopic chronologies for each island population.…”

Assessing polar bear (Ursus maritimus) population structure in the Hudson Bay region using SNPs

“…2005) to our STRUCTURE data would suggest K  = 2. However, the efficacy of the ΔK method for detecting hierarchical population structure is debatable (Gao et al., 2011; Goedbloed et al., 2013; Waples & Gaggiotti, 2006; Welch et al., 2012). Evidence of hierarchical structure in our dataset is demonstrated by the increasing likelihood values of our STRUTURE runs (Figure S3); as well by the geographic concordance of individual genetic assignments in relation to capture locations (Figure 3).…”

“…We opted for the plateau criterion because the ΔK method (Evanno et al. 2005) can be biased toward detection of the first structural level in the data, and miss fine‐scale structure (Gao, Bryc, & Bustamante, 2011; Goedbloed et al., 2013; Waples & Gaggiotti, 2006; Welch et al., 2012). …”

No island hopping for Hawaiian petrels

“…A recent study by Welch et al (2012) provides valuable insights into patterns of gene flow in the endangered Hawaiian petrel (Pterodroma sandwichensis), an endemic species found in one of the world's biodiversity hotspots. The authors investigated population genetic structure using samples from one extirpated and four extant colonies on separate islands.…”