Cryptic species in a Vulnerable seabird: shorttailed albatross consists of two species

Abstract

The occurrence of cryptic species within a threatened taxon is rare, but where they do occur, understanding species boundaries is essential for planning an effective conservation strategy. The short-tailed albatross Phoebastria albatrus is a Vulnerable seabird that mainly breeds on Torishima and the Senkaku Islands in the western North Pacific. Although it has been tacitly regarded as a single management unit with 2 breeding sites, the species is known to comprise 2 genetically separated populations (Senkaku-type and Torishima-type). However, morphological examination of birds from both populations has not been conducted owing to the difficulty in accessing the Senkaku Islands. In this study, we examined the morphological differences between immigrants from the Senkaku Islands to Torishima (Senkaku-type) and native birds on Torishima (Torishima-type) and found significant differences in morphological characteristics between the 2 bird types. In general, Torishima-type birds were larger than Senkaku-type birds, whereas Senkaku-type birds had relatively longer beaks. Based on the morphological differences found in this study as well as genetic and ecological differences revealed in previous studies, we believe that Senkaku- and Torishima-type birds should be classified as different cryptic species. To the best of our knowledge, this is the first case of cryptic species being identified in a threatened avian species.

Documenting the short‐tailed albatross (Phoebastria albatrus) clades historically present in British Columbia, Canada, through ancient DNA analysis of archaeological specimens

“…These data suggest Clade 1 birds did indeed forage in other areas of the Northeast Pacific. If supported by additional data, Clade 1 and 2 short‐tailed albatrosses having differing distributions would lend support to Eda and colleagues' (Eda et al, 2020 ; Yamasaki et al, 2022 ) argument that these two clades represent distinct species.…”

“…As such, we hypothesize this spatial variation in haplotype frequencies reflects historical differences in the distribution of Clade 1 and 2 short-tailed albatrosses. While the results of previous studies indicate both clades were historically abundant in the Northwest Pacific (Eda et al, 2006(Eda et al, , 2012Eda, Koike, & Higuchi, 2016) (Eda et al, 2020;Yamasaki et al, 2022) argument that these two clades represent distinct species.…”

“…In addition to being genetically distinct, stable isotope analysis of archaeological specimens from the Hamanaka 2 site on Rebun Island, Japan, (Figure 1 ) suggests Clade 1 and 2 birds have differing foraging ecologies (Eda et al, 2012 ). Analyses of archaeological and modern short‐tailed albatrosses also suggest these clades vary in their morphology, with both their size and beak shape differing (Eda et al, 2012 , 2020 ). The distinctiveness of these breeding populations is maintained by within‐clade assortative mating, which limits gene flow (Eda, Izumi, et al, 2016 ).…”

“…This assortative mating is believed to be due to prezygotic barriers, including inter‐clade differences in courtship displays and breeding season timing (Eda, Izumi, et al, 2016 ). Recently, (Eda et al, 2020 ; Yamasaki et al, 2022 ) have argued that the morphological, genetic, and ecological differences between these clades as well as the propensity for within‐clade assortative mating suggest they may in fact represent two cryptic species. Understanding the distribution of these clades has been identified as being critical to developing effective conservation and recovery plans for the species (Eda et al, 2020 ).…”

“…suggests Clade 1 and 2 birds have differing foraging ecologies (Eda et al, 2012). Analyses of archaeological and modern short-tailed albatrosses also suggest these clades vary in their morphology, with both their size and beak shape differing (Eda et al, 2012(Eda et al, , 2020.…”