Metapopulation connectivity retains genetic diversity following a historical bottleneck in a federally endangered seabird

Despite intensive management since the 1970s, recovery of the endangered northwestern Atlantic population of the Roseate Tern (Sterna dougallii dougallii) has not offset low productivity from a female-biased sex ratio, low adult survival, and habitat constriction. Now, >90% of individuals breed at three sites within 200 km from Long Island, NY, to Buzzards Bay, MA (warm-water subregion). To characterize the impact of historical bottlenecks, metapopulation structure, and demographic fluctuations on genetic variation, Roseate Terns from the warm-water (1870s, 1970s, 1997, 2016) and cold-water (Nova Scotia, Canada; 2018) subregions were genotyped at 8–16 microsatellites and 2–3 mitochondrial regions. Diversity declined in the warm-water subregion from the 1870s (expected heterozygosity [HE] = 0.44, allelic richness [AR] = 2.86) and 1970s (HE = 0.53, AR = 3.25) to 1997 (HE = 0.38, AR = 2.58). Genetic signatures of bottlenecks persisted in 1997 (P =