Dataset Information

Habitat selection and ecological speciation in Galapagos warbler finches (Certhidea olivacea and Certhidea fusca).

ABSTRACT: We investigated phylogeographic divergence among populations of Galápagos warble finches. Their broad distribution, lack of phenotypic differentiation and low levels of genetic divergence make warbler finches an appropriate model to study speciation in allopatry. A positive relationship between genetic and geographical distance is expected for island taxa. Warbler finches actually showed a negative isolation by distance relationship, causing us to reject the hypothesis of distance-limited dispersal. An alternative hypothesis, that dispersal is limited by habitat similarity, was supported. We found a positive correlation between genetic distances and differences in maximum elevation among islands, which is an indicator of ecological similarity. MtDNA sequence variation revealed monophyletic support for two distinct species. Certhidea olivacea have recently dispersed among larger central islands, while some Certhidea fusca have recently dispersed to small islands at opposite ends of the archipelago. We conclude that females have chosen to breed on islands with habitats similar to their natal environment. Habitat selection is implicated as an important component of speciation of warbler finches, which is the earliest known divergence of the adaptive radiation of Darwin's finches. These results suggest that small populations can harbour cryptic but biologically meaningful variation that may affect longer term evolutionary processes.

SUBMITTER: Tonnis B

PROVIDER: S-EPMC1599867 | biostudies-literature | 2005 Apr

REPOSITORIES: biostudies-literature

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Publications

Habitat selection and ecological speciation in Galápagos warbler finches (Certhidea olivacea and Certhidea fusca).

Tonnis Brandon B Grant Peter R PR Grant B Rosemary BR Petren Kenneth K

Proceedings. Biological sciences 20050401 1565

We investigated phylogeographic divergence among populations of Galápagos warble finches. Their broad distribution, lack of phenotypic differentiation and low levels of genetic divergence make warbler finches an appropriate model to study speciation in allopatry. A positive relationship between genetic and geographical distance is expected for island taxa. Warbler finches actually showed a negative isolation by distance relationship, causing us to reject the hypothesis of distance-limited disper ...[more]

PMID: 15940826

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Project description:In bacteria, physiological change may be effected by a single gene acquisition, producing ecological differentiation without genetic isolation. Natural selection acting on such differences can reduce the frequency of genotypes that arise from recombination at these loci. However, gene acquisition can only account for recombination interference in the fraction of the genome that is tightly linked to the integration site. To identify additional loci that contribute to adaptive differences, we examined orthologous genes in species of Enterobacteriaceae to identify significant differences in the degree of codon selection. Significance was assessed using the Adaptive Codon Enrichment metric, which accounts for the variation in codon usage bias that is expected to arise from mutation and drift; large differences in codon usage bias were identified in more genes than would be expected to arise from stochastic processes alone. Genes in the same operon showed parallel differences in codon usage bias, suggesting that changes in the overall levels of gene expression led to changes in the degree of adaptive codon usage. Most significant differences between orthologous operons were found among those involved with specific environmental adaptations, whereas "housekeeping" genes rarely showed significant changes. When considered together, the loci experiencing significant changes in codon selection outnumber potentially adaptive gene acquisition events. The identity of genes under strong codon selection seems to be influenced by the habitat from which the bacteria were isolated. We propose a two-stage model for how adaptation to different selective regimes can drive bacterial speciation. Initially, gene acquisitions catalyze rapid ecological differentiation, which modifies the utilization of genes, thereby changing the strength of codon selection on them. Alleles develop fitness variation by substitution, producing recombination interference at these loci in addition to those flanking acquired genes, allowing sequences to diverge across the entire genome and establishing genetic isolation (i.e., protection from frequent homologous recombination).

Project description:Urbanization is expanding worldwide with major consequences for organisms. Anthropogenic factors can reduce the fitness of animals but may have benefits, such as consistent human food availability. Understanding anthropogenic trade-offs is critical in environments with variable levels of natural food availability, such as the Galápagos Islands, an area of rapid urbanization. For example, during dry years, the reproductive success of bird species, such as Darwin's finches, is low because reduced precipitation impacts food availability. Urban areas provide supplemental human food to finches, which could improve their reproductive success during years with low natural food availability. However, urban finches might face trade-offs, such as the incorporation of anthropogenic debris (e.g., string, plastic) into their nests, which may increase mortality. In our study, we determined the effect of urbanization on the nesting success of small ground finches (Geospiza fuliginosa; a species of Darwin's finch) during a dry year on San Cristóbal Island. We quantified nest building, egg laying and hatching, and fledging in an urban and nonurban area and characterized the anthropogenic debris in nests. We also documented mortalities including nest trash-related deaths and whether anthropogenic materials directly led to entanglement- or ingestion-related nest mortalities. Overall, urban finches built more nests, laid more eggs, and produced more fledglings than nonurban finches. However, every nest in the urban area contained anthropogenic material, which resulted in 18% nestling mortality while nonurban nests had no anthropogenic debris. Our study showed that urban living has trade-offs: urban birds have overall higher nesting success during a dry year than nonurban birds, but urban birds can suffer mortality from anthropogenic-related nest-materials. These results suggest that despite potential costs, finches benefit overall from urban living and urbanization may buffer the effects of limited resource availability in the Galápagos Islands.

Dataset Information

Habitat selection and ecological speciation in Galapagos warbler finches (Certhidea olivacea and Certhidea fusca).

Publications

Habitat selection and ecological speciation in Galápagos warbler finches (Certhidea olivacea and Certhidea fusca).

Similar Datasets

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