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ESR 53:213-225 (2024)  -  DOI:

Incomplete isolation in the nonbreeding areas of two genetically separated but sympatric short-tailed albatross populations

Naoki Tomita1,*, Fumio Sato1, Jean-Baptiste Thiebot2,3, Bungo Nishizawa2,3, Masaki Eda4, Hiroe Izumi4, Satoshi Konno5, Miwa Konno5, Yutaka Watanuki3

1Yamashina Institute for Ornithology, Konoyama 115, Abiko, Chiba 270-1145, Japan
2National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan
3Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1, Minato-cho, Hakodate, Hokkaido 041-8611, Japan
4Hokkaido University Museum, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
5Nishi 15, Minami 37, 1-14, Obihiro, Hokkaido 080-0025, Japan
*Corresponding author:

ABSTRACT: The short-tailed albatross Phoebastria albatrus, a globally Vulnerable species recovering from near-extinction, breeds mainly on 2 island groups in the north-western Pacific: Torishima and Senkaku Islands. Recently, it became clear that this is a species complex, composed of 2 populations (‘Torishima’ and ‘Senkaku’ types) that are distinct from both genetic and morphological perspectives, and which mate assortatively on Torishima. We tested the hypothesis of premating isolation as a possible mechanism for genetic differentiation and shifted breeding date in short-tailed albatrosses. Using light-based geolocation and molecular analysis, we examined whether adults from the 2 populations breeding on Torishima differed in their at-sea distribution during the nonbreeding period (June-September) and in their return dates. From 22 bird tracks collected from 12 birds over 4 yr, we identified 2 distinct nonbreeding areas: around the Aleutian Islands in the Bering Sea and near the Kuril Islands in the Okhotsk Sea. All 6 tracks of Torishima-type birds migrated directly to the Bering Sea in all years. In contrast, most of the Senkaku-type birds migrated along northeast Japan to the Okhotsk Sea (9 tracks), with the others moving to the Bering Sea (7 tracks). There was no clear difference in the dates of return to Torishima between the 2 bird types. Overall, no absolute pre-mating isolation in space or time was observed in short-tailed albatrosses, but we highlighted notable divergences in the nonbreeding distribution of both types. This result suggests that Torishima- and Senkaku-type populations should be treated as separate management units.

KEY WORDS: Phoebastria albatrus · Isolation mechanism · At-sea distribution · Timing of breeding · Genetics · Management unit · Geolocator

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Cite this article as: Tomita N, Sato F, Thiebot JB, Nishizawa B and others (2024) Incomplete isolation in the nonbreeding areas of two genetically separated but sympatric short-tailed albatross populations. Endang Species Res 53:213-225.

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