Abstract In each of at least two locations within the Galapagos Islands, breeding band‐rumped storm‐petrels ( Oceanodroma castro ) form two distinct populations that use the same colony site at separate times of the year for reproduction. Temporal segregation of these populations raises the possibility that they are reproductively isolated and represent cryptic species. We examined variation in mitochondrial DNA, morphology, and vocalizations of storm‐petrel populations nesting 6 months apart on the islet of Plaza Norte in the Galapagos. Seasonal populations displayed low but significant levels of differentiation in the mitochondrial control region, five morphological variables, and one feature of male vocalizations. Breeding populations appear to have been separated for approximately 1700 years. Given the recent divergence date and relatively high effective population sizes (4000–5600 females each), seasonal populations are unlikely to be in genetic equilibrium. As a result, the low divergence estimate probably reflects historical association and not contemporary genetic exchange. These populations are not sufficiently differentiated to be considered cryptic species. However, they are probably in the early stages of divergence. Consequently, we recommend that cool‐ and hot season populations on Plaza Norte be recognized as separate management units.
SUMMARY BIRT, T .P ., MACKINNON, D ., PIATT, J .F . & FRIESEN, V .L . 2011 . Genetic differentiation of the Kittlitz’s Murrelet Brachyramphus brevirostris in the Aleutian Islands and Gulf of Alaska . Marine Ornithology 39: 45–51 . Information about the distribution of genetic variation within and among local populations of the Kittlitz’s Murrelet Brachyramphus brevirostris is needed for effective conservation of this rare and declining species . We compared variation in a 429 base pair fragment of the mitochondrial control region and 11 microsatellite loci among 53 Kittlitz’s Murrelets from three sites in the western Aleutian Islands (Attu Island) and Gulf of Alaska (Glacier Bay and Kachemak Bay) . We found that birds in these two regions differ genetically in three assessments: (1) global and pairwise indices of genetic differentiation were significantly greater than zero, (2) mitochondrial haplotypes differed by a minimum of nine substitutions, and (3) molecular assignments indicated little gene flow between regions . The data suggest that birds in these regions have been genetically isolated for an extended period . We conclude that Kittlitz’s Murrelets from Attu Island and from the Gulf of Alaska represent separate evolutionarily significant units, and should be treated as such for conservation . Genetic data for Kittlitz’s Murrelets from the remainder of the breeding range are urgently needed .
Abstract Understanding the forces that shape population genetic structure is fundamental both for understanding evolutionary trajectories and for conservation. Many factors can influence the geographic distribution of genetic variation, and the extent to which local populations differ can be especially difficult to predict in highly mobile organisms. For example, many species of seabirds are essentially panmictic, but some show strong structure. Pigeon Guillemots ( Cepphus columba ; Charadriiformes: Alcidae) breed in small colonies scattered along the North Pacific coastline and feed in shallow nearshore waters year‐round. Given their distribution, gene flow is potentially lower and population genetic structure is stronger than in most other high‐latitude Northern Hemisphere seabirds. We screened variation in the mitochondrial control region, four microsatellite loci, and two nuclear introns in 202 Pigeon Guillemots representing three of five subspecies. Mitochondrial sequences and nuclear loci both showed significant population differences, although structure was weaker for the nuclear loci. Genetic differentiation was correlated with geographic distance between sampling locations for both the mitochondrial and nuclear loci. Mitochondrial gene trees and demographic modeling both provided strong evidence for two refugial populations during the Pleistocene glaciations: one in the Aleutian Islands and one farther east and south. We conclude that historical fragmentation combined with a stepping‐stone model of gene flow led to the relatively strong population differentiation in Pigeon Guillemots compared to other high‐latitude Northern Hemisphere seabird species. Our study adds to growing evidence that Pleistocene glaciation events affected population genetic structure not only in terrestrial species but also in coastal marine animals.
SUMMARY Colour morphs associated with different physiological adaptations offer unique opportunities to study the genomic basis of otherwise elusive adaptive traits. These complex balanced polymorphisms are often controlled by groups of tightly linked genes, and understanding how these ‘supergenes’ evolve and are maintained is an active area of research in evolutionary biology (Schwander et al . 2014, Thompson and Jiggins 2014). Within the Atlantic, the common murre ( Uria aalge , a colonial seabird) displays a plumage colour dimorphism (‘bridled’ and ‘unbridled’) that seems to be associated with differences in thermal adaptation (Birkhead 1984; Reiertsen et al . 2012). The genes associated with bridling and how these genes affect thermal adaptation are unknown. Using whole genome resequencing, we investigate the genomic basis of differences in colouration and thermal adaptation between the two morphs, and how the association between the two traits is maintained despite random mating. We identify a 60 kb genomic region of high differentiation laying in the intergenic area amongst three candidate genes for colouration and thermal adaptation: retinoic acid receptor beta ( RARB ), thyroid hormone receptor beta ( THRB ), and nuclear receptor subfamily 1 group D member 2 ( NR1D2 or Rev-erbβ ). Differentiation is due to a complex copy number variant (CNV) that suppresses recombination locally. We show that this CNV acts as a ‘supergene’ and maintain association between regulatory elements likely affecting gene expression of one or more of the identified candidate genes. Our analyses also provide insights into the origin of the dimorphism: while copy number proliferation in the unbridled haplotype was potentially mediated by transposable elements (TEs), the bridled haplotype seems to have introgressed from the more cold-adapted sister species, the thick-billed murre ( U. lomvia ). Our results highlight the role of copy number variants in adaptation, especially when association among traits is maintained in the face of gene flow. They also shed light into the molecular mechanisms of adaptive thermogenesis in birds, which is poorly understood. Highlights Differences in plumage colour in Atlantic common murres are associated with different thermal adaptations A single region is highly differentiated between bridled and unbridled morphs A complex copy number variant in a non-coding region underlies the dimorphism Transposable elements and adaptive introgression from the thick-billed murre seem to explain the origin of the dimorphism
We describe sequence variation in the mitochondrial control region and its nuclear homolog in three species and seven subspecies of guillemots (Cepphus spp.). Nuclear homologs of the 5' end of the control region were found in all individuals. Nuclear sequences were approximately 50% divergent from their mitochondrial counterparts and formed a distinct phylogenetic clade; the mitochondrial-nuclear introgression event must have predated the radiation of Cepphus. As in other vertebrates, the guillemot control region has a relatively conserved central block flanked by hypervariable 5' and 3' ends. Mean pairwise interspecific divergence values among control regions were lower than those in other birds. All individuals were heteroplasmic for the number of simple tandem nucleotide repeats (A(n)C) at the 3' end of the control region. Phylogenetic analyses suggest that black guillemots are basal to pigeon and spectacled guillemots, but evolutionary relationships among subspecies remain unresolved, possibly due to incomplete lineage sorting. Describing molecular variation in nuclear homologs of mitochondrial genes is of general interest in phylogenetics because, if undetected, the homologs may confound interpretations of mitochondrial phylogenies.
Abstract Pitman and Jehl (1998) recently argued that Masked Boobies (formerly Sula dactylatra granti) breeding on the Nazca Plate in the eastern Pacific Ocean are morphologically and ecologically distinct from other Masked Boobies and may represent a full species. The American Ornithologists' Union subsequently elevated that subspecies to a full species: the Nazca Booby (S. granti). To evaluate that change in classification, we compared sequence variation in the mitochondrial cytochrome-b gene among 75 Nazca Boobies and 37 Masked Boobies representing three subspecies from the central and eastern Pacific and Atlantic oceans. Results indicated strong differentiation of cytochrome-b variation among taxa. Sequences constituted three distinct groups: Nazca Boobies, Masked Boobies from the central and eastern Pacific (S. d. personata and S. d. californica), and Masked Boobies (S. d. dactylatra) from the Caribbean and Atlantic. Those three groups probably diverged within a very short period, 400,000–500,000 year...
