Dataset Information

Multiple losses of flight and recent speciation in steamer ducks.

ABSTRACT: Steamer ducks (Tachyeres) comprise four species, three of which are flightless. The flightless species are believed to have diverged from a flying common ancestor during the Late Pleistocene; however, their taxonomy remains contentious. Of particular interest is the previously unstudied population of flying steamer ducks in the Falkland Islands. We present the first genetic data from this insular population, and illustrate that the flying and flightless steamer ducks on the Falkland Islands are genetically indistinguishable, in contrast to their traditional classification as separate species. The three species that reside in continental South America form a genetically distinct lineage from the Falkland Island ducks. The Falkland steamer ducks diverged from their continental relatives 2.2-0.6 million years ago, coincident with a probable land bridge connecting the Falkland Islands to the mainland. The three continental species share a common ancestor approximately 15 000 years ago, possibly owing to isolation during a recent glacial advance. The continental steamer duck species are not reciprocally monophyletic, but show some amount of genetic differentiation between them. Each lineage of Tachyeres represents a different stage between flight and flightlessness. Their phylogenetic relationships suggest multiple losses of flight and/or long-term persistence of mixed-flight capability. As such, steamer ducks may provide a model system to study the evolution of flightlessness.

SUBMITTER: Fulton TL

PROVIDER: S-EPMC3350674 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Multiple losses of flight and recent speciation in steamer ducks.

Fulton Tara L TL Letts Brandon B Shapiro Beth B

Proceedings. Biological sciences 20120208 1737

Steamer ducks (Tachyeres) comprise four species, three of which are flightless. The flightless species are believed to have diverged from a flying common ancestor during the Late Pleistocene; however, their taxonomy remains contentious. Of particular interest is the previously unstudied population of flying steamer ducks in the Falkland Islands. We present the first genetic data from this insular population, and illustrate that the flying and flightless steamer ducks on the Falkland Islands are ...[more]

PMID: 22319122

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Project description:Background: The Dobzhansky-Muller (D-M) model of speciation by genic incompatibility is widely accepted as the primary cause of interspecific postzygotic isolation. Since the introduction of this model, there have been theoretical and experimental data supporting the existence of such incompatibilities. However, speciation genes have been largely elusive, with only a handful of candidate genes identified in a few organisms. The Saccharomyces sensu stricto yeasts have small genomes, can be easily cultured, and can mate interspecifically to produce sterile hybrids, are thus an ideal model for studying postzygotic isolation. Among them, only a single D-M pair has been found, between S. bayanus and S. cerevisiae, comprising the mitochondrially targeted product of a nuclear gene, AEP2, and a mitochondrially encoded locus, OLI1, the 5' region of whose transcript is bound by Aep2. Thus far, no D-M pair of nuclear genes has been identified between any sensu stricto yeasts. Methods: We report here the first detailed genome-wide analysis of rare F2 progeny from an otherwise sterile hybrid, and show that no classic D-M pairs of speciation genes exist between the nuclear genomes of the closely related yeasts S. cerevisiae and S. paradoxus. Instead, our analyses suggest that more complex interactions may be responsible for their post-zygotic separation. These interactions most likely involve multiple loci having weak effects, as there were multiple significant pairwise combinations of loci, with no single combination being completely excluded from the viable F2s. Conclusions: The lack of a nuclear encoded classic D-M pair between these two yeasts, yet the existence of multiple loci that may each exert a small effect through complex interactions, suggests that initial speciation events might not always be mediated by D-M pairs. An alternative explanation may be that "death by a thousand cuts" leads to speciation, whereby an accumulation of polymorphisms can lead to an incompatibility between the species "transcriptional and metabolic networks, with no single pair at least initially being responsible for the incompatibility. After such a speciation event, it is possible that one or more D-M pairs might subsequently arise following isolation. Genotypes for hybrids between S. cerevisiae and S. paradoxus. A genotyping experiment design type classifies an individual or group of individuals on the basis of alleles, haplotypes, SNP's.

Project description:Background and aimsHybridization is known to drive plant speciation through the establishment of homoploid or allopolyploid hybrid species. Here we investigate the origin of Pulmonaria helvetica, a narrow endemic species described across a restricted area of Switzerland that was entirely covered by ice during the last glacial maximum. This species presents an original number of chromosomes (2n = 24) and morphological traits suggestive of a hybrid origin.MethodsWe sequenced a plastid locus and 1077 double-digest restriction-site-associated DNA (ddRAD) loci in 67 individuals from across the distribution range of P. helvetica and candidate progenitor species growing in the same area. Assignment of genotypes to main genetic clusters within and among taxa using STRUCTURE tested whether P. helvetica represents a genetically differentiated lineage and addressed the hypothesis of its hybrid origin. Comparative ecological modelling further addressed possible niche differentiation among taxa.Key resultsPulmonaria helvetica was highlighted as a genetically homogeneous species distinct from co-occurring taxa. Consistent with a scenario of hybrid speciation, it presented clear evidence of balanced admixture between Pulmonaria officinalis (2n = 16) and Pulmonaria mollis s.l. (2n = 18, 22), which was also highlighted as a maternal progenitor based on plastid sequences. Limited genetic structure within the maternal progenitor is consistent with an origin of P. helvetica through either homoploid hybridization with considerable karyotype changes or via complex scenarios of allopolyploidy involving a dysploid taxon of P. mollis s.l. Comparative niche modelling indicated non-significant ecological differences between P. helvetica and its progenitors, supporting intrinsic factors resulting from hybridization as main drivers of speciation.ConclusionsHybridization appears as a major process having promoted the postglacial origin of the narrow endemic P. helvetica, suggesting hybrid speciation as an effective process that rapidly produces new species under climate changes.

Dataset Information

Multiple losses of flight and recent speciation in steamer ducks.

Publications

Multiple losses of flight and recent speciation in steamer ducks.

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