Population differentiation in whiskered auklets Aethia pygmaea: do diurnal and nocturnal colonies differ in genetics, morphometry and acoustics?

Abstract

Despite a great number of empirical studies, the mechanisms of population differentiation and the factors that influence this process, particularly in seabirds, remain insufficiently understood. Here we analyzed population structure in the whiskered auklet Aethia pygmaea, a previously poorly studied alcid species with unusual differentiation in colony attendance rhythms (i.e. diurnal in the Sea of Okhotsk vs nocturnal in the Bering Sea), and examined the influence of it on intraspecific differentiation. For this study, we analyzed morphometric measurements, acoustic variables, mitochondrial control region fragment and five microsatellite loci from nine whiskered auklet colonies spanning the breeding range. Previous research has shown a clinal morphometric variation in this species. We build on this analysis by adding auklets from more colonies, for the first time analyzing vocalizations from different colonies and genetic structure of this species. Our data supports a clinal variation in morphometric and acoustic characters with the largest size and the lowest call frequency in western birds, and the smallest size and highest call frequency in the east. We also found two mitochondrial lineages – whiskered auklets from colonies in the Sea of Okhotsk and the Commander Is. (Bering Sea) and from the Aleutian Is. (Bering Sea), that were presumably formed during Sangamonian interglacial period (115 000–130 000 years ago). Genetic clusters found did not reflect differences in colony attendance rhythms, suggesting that they were shaped by other factors (e.g. differences in predator pressure) and are unlikely to have participated in the formation of population structure. Colony fidelity, mobility of birds, proximity of foraging grounds and location of colonies in relation to seasonal ice pack, seem to be more likely determinants of population differentiation.

Confirmed year-round residence and land roosting of Whiskered Auklets (Aethia pygmaea) at Buldir Island, Alaska

“…Additionally, all recorded Aleutian sightings of Whiskered Auklets at sea have been concentrated close to land and near known or suspected breeding sites Williams 1993, Piatt andDrew 2015). A rangewide pattern of residence near breeding colonies without long-distance movement (leading to a lack of mixing among populations) would be consistent with the high levels of genetic divergence in Whiskered Auklets recently described by Pshenichnikova et al (2017). Nevertheless, some variability in movement activity across the species' breeding range is expected because breeding islands in the Okhotsk Sea (Iony Island and Penzhina Bay; Figure 1) are surrounded by heavy pack ice cover in winter (Nihashi et al 2009).…”

“…Migration to and from these sites would appear to be inevitable, although these birds could still roost on land at nearby ice-free locations such as the Kurile Islands, part of the species' breeding range (Gaston and Jones 1998; Figure 1). Okhotsk Whiskered Auklets also differ from Aleutian populations in morphology (larger body size and ornaments; Pshenichnikova et al 2017) and colony attendance (diurnal instead of nocturnal; Andreev et al 2012).…”

Geolocator tagging links distributions in the non-breeding season to population genetic structure in a sentinel North Pacific seabird

“…But the rhinoceros auklet nests in large colonies, is mainly neritic, and exhibits extensive genetic structuring. Those same traits are also characteristic of the whiskered auklet [111], a species that forages in tide-rips close to shore [111], and a species in which birds outfitted with geolocator tags attended the breeding colony year-round [112]. Neritic seabirds might tend to structure extensively because they conform to a one-dimensional, stepping-stone model of dispersal [105], and/or because they are unlikely to come into contact at sea with individuals from populations other than their own [79].…”

“…First, the ancient murrelet is panmictic across the North Pacific Ocean [82], and geolocator tagging revealed that some individuals crossed from the eastern into the western Pacific in the winter [81]. Second, population genetic structure exists in the whiskered auklet [111], and geolocator tagging showed that individuals in this species overwinter close to breeding colonies [112]. Third, the winter distribution of most Cassin's auklets breeding on two very large colonies in British Columbia (Triangle, Frederick islands) overlapped with that of individuals from Southeast Farallon Island in California [117,118], and the two groups are genetically homogeneous [50].…”

Identifying mechanisms of genetic differentiation among populations in vagile species: historical factors dominate genetic differentiation in seabirds

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