Isotopic Niche Segregation among Darwin’s Finches on Santa Cruz Island, Galápagos

Darwin’s finches are a classic example of adaptive radiation involving differential use of dietary resources among sympatric species. Here, we apply stable isotope (δ13C, δ15N, and δ2H) analyses of feathers to examine ecological segregation among eight Darwin’s finch species in Santa Cruz Island, Galápagos collected from live birds and museum specimens (1962–2019). We found that δ13C values were higher for the granivorous and herbivorous foraging guilds, and lower for the insectivorous finches. Values of δ15N were similar among foraging guilds but values of δ2H were higher for insectivores, followed by granivores, and lowest for herbivores. The herbivorous guild generally occupied the largest isotopic standard ellipse areas for all isotopic combinations and the insectivorous guild the smallest. Values of δ2H provided better trophic discrimination than those of δ15N possibly due to confounding influences of agricultural inputs of nitrogen. Segregation among guilds was enhanced by portraying guilds in three-dimensional isotope (δ13C, δ15N, and δ2H) space. Values of δ13C and δ15N were higher for feathers of museum specimens than for live birds. We provide evidence that Darwin’s finches on Santa Cruz Island tend to be generalists with overlapping isotopic niches and suggest that dietary overlap may also be more considerable than previously thought.

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Distribution and abundance of Darwin’s finches and other land birds on Santa Cruz Island, Galápagos: evidence for declining populations

Oryx ◽

10.1017/s0030605311000597 ◽

2011 ◽

Vol 46 (1) ◽

pp. 78-86 ◽

Cited By ~ 33

Author(s):

Michael Dvorak ◽

Birgit Fessl ◽

Erwin Nemeth ◽

Sonia Kleindorfer ◽

Sabine Tebbich

Keyword(s):

Critical Factor ◽

Population Monitoring ◽

Temporal Analysis ◽

Native Forest ◽

Habitat Alteration ◽

Santa Cruz Island ◽

Santa Cruz ◽

Darwin's Finches ◽

Darwin’S Finches ◽

Introduced Predators

AbstractPopulation monitoring is a vital tool for conservation management and for testing hypotheses about population trends in changing environments. Darwin’s finches on Santa Cruz Island in the Galápagos archipelago have experienced habitat alteration because of human activity, introduced predators, parasites and disease. We used point counts to conduct systematic quantitative surveys of Darwin’s finches and other land birds between 1997 and 2010. The temporal analysis revealed that six of the nine species investigated declined significantly and that this decline was most pronounced at higher elevations in humid native forest and agricultural areas; the highland areas have been most affected by introduced species or direct human impact. Five of the six declining species are insectivorous, which suggests that changes in insect abundance or insect availability are a critical factor in the declines. Further study is required to test this idea. Other factors including habitat alteration and introduced parasites or pathogens may be contributing to the observed declines.

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Host phylogeny, diet, and habitat differentiate the gut microbiomes of Darwin’s finches on Santa Cruz Island

Scientific Reports ◽

10.1038/s41598-019-54869-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 3

Author(s):

Wesley T. Loo ◽

Jefferson García-Loor ◽

Rachael Y. Dudaniec ◽

Sonia Kleindorfer ◽

Colleen M. Cavanaugh

Keyword(s):

Evolutionary History ◽

Environmental Filtering ◽

Ecological Niches ◽

Santa Cruz Island ◽

Santa Cruz ◽

Darwin's Finches ◽

Bacterial Phyla ◽

Dietary Preferences ◽

Darwin’S Finches ◽

Host Phylogeny

AbstractDarwin’s finches are an iconic example of an adaptive radiation with well-characterized evolutionary history, dietary preferences, and biogeography, offering an unparalleled opportunity to disentangle effects of evolutionary history on host microbiome from other factors like diet and habitat. Here, we characterize the gut microbiome in Darwin’s finches, comparing nine species that occupy diverse ecological niches on Santa Cruz island. The finch phylogeny showed moderate congruence with the microbiome, which was comprised mostly of the bacterial phyla Firmicutes, Actinobacteria, and Proteobacteria. Diet, as measured with stable isotope values and foraging observations, also correlated with microbiome differentiation. Additionally, each gut microbial community could easily be classified by the habitat of origin independent of host species. Altogether, these findings are consistent with a model of microbiome assembly in which environmental filtering via diet and habitat are primary determinants of the bacterial taxa present with lesser influence from the evolutionary history between finch species.

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Geometry and dynamics link form, function, and evolution of finch beaks

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2105957118 ◽

2021 ◽

Vol 118 (46) ◽

pp. e2105957118

Author(s):

Salem al-Mosleh ◽

Gary P. T. Choi ◽

Arhat Abzhanov ◽

L. Mahadevan

Keyword(s):

Functional Form ◽

Elementary Theory ◽

Three Dimensional ◽

Tissue Level ◽

Cellular Level ◽

Darwin's Finches ◽

Aspect Ratios ◽

Form Function ◽

Darwin’S Finches ◽

Curvature Driven

Darwin’s finches are a classic example of adaptive radiation, exemplified by their adaptive and functional beak morphologies. To quantify their form, we carry out a morphometric analysis of the three-dimensional beak shapes of all of Darwin’s finches and find that they can be fit by a transverse parabolic shape with a curvature that increases linearly from the base toward the tip of the beak. The morphological variation of beak orientation, aspect ratios, and curvatures allows us to quantify beak function in terms of the elementary theory of machines, consistent with the dietary variations across finches. Finally, to explain the origin of the evolutionary morphometry and the developmental morphogenesis of the finch beak, we propose an experimentally motivated growth law at the cellular level that simplifies to a variant of curvature-driven flow at the tissue level and captures the range of observed beak shapes in terms of a simple morphospace. Altogether, our study illuminates how a minimal combination of geometry and dynamics allows for functional form to develop and evolve.

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Ecological speciation in Darwin’s finches: Parsing the effects of magic traits

Current Zoology ◽

10.1093/czoolo/59.1.8 ◽

2013 ◽

Vol 59 (1) ◽

pp. 8-19 ◽

Cited By ~ 7

Author(s):

Jeffrey Podos ◽

Rie Dybboe ◽

Mads Ole Jensen

Keyword(s):

Assortative Mating ◽

Mate Recognition ◽

Ecological Speciation ◽

Santa Cruz ◽

Darwin's Finches ◽

Relative Contribution ◽

Darwin’S Finches ◽

Song Divergence ◽

Recognition Systems ◽

Geospiza Fortis

Abstract Many recent studies of ecological speciation have focused on “magic trait” scenarios, in which divergent selection on viability traits leads inextricably to corresponding divergence in mechanisms, especially mate recognition systems, that facilitate assortative mating. Speciation however may also proceed via other scenarios, such as when populations experience directly selected or random divergence in mate recognition systems. The relative contributions of magic trait versus other scenarios for speciation remain virtually unexplored. The present study aims to test the relative contribution of the magic trait scenario in the divergence of populations of the medium ground finch Geospiza fortis of Santa Cruz Island, Galapagos. First, we assess differences in G. fortis song between a northern population (Borrero Bay) and a southeastern population (El Garrapatero), differences that we propose (along with other within-island geographic song variations) have arisen via scenarios that do not involve a magic trait scenario. Pairwise comparisons of raw and composite (PC) song parameters, as well as discriminant functions analyses, reveal significant patterns of song divergence between sites. Second, we test the ability of territorial males at Borrero Bay to discriminate songs from the two sites. We find that G. fortis males can discriminate within-island song variants, responding more strongly to local than to “foreign” songs, along 3 raw and 1 composite response measures. Third, we compare these findings to prior data sets on song divergence and discrimination in Santa Cruz G. fortis. These comparisons suggest that song divergence and discrimination are shaped less strongly by geographic sources than by morphological (beak-related) sources. We thus argue that interpopulation song divergence and discrimination, fundamental elements of assortative mating in Darwin’s finches, can be fostered in early stages of divergence under magic trait as well as alternative scenarios for speciation, but with more emphasis on the magic trait scenario, at least for this species on this island.

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Multilocus genotypes from Charles Darwin's finches: biodiversity lost since the voyage of the Beagle

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2009.0316 ◽

2010 ◽

Vol 365 (1543) ◽

pp. 1009-1018 ◽

Cited By ~ 13

Author(s):

Kenneth Petren ◽

Peter R. Grant ◽

B. Rosemary Grant ◽

Andrew A. Clack ◽

Ninnia V. Lescano

Keyword(s):

Genetic Diversity ◽

Genetic Analysis ◽

Microsatellite Loci ◽

Charles Darwin ◽

Museum Specimens ◽

Darwin's Finches ◽

Darwin’S Finches ◽

Genetic Source ◽

Autosomal Microsatellite Loci ◽

Beagle Voyage

Genetic analysis of museum specimens offers a direct window into a past that can predate the loss of extinct forms. We genotyped 18 Galápagos finches collected by Charles Darwin and companions during the voyage of the Beagle in 1835, and 22 specimens collected in 1901. Our goals were to determine if significant genetic diversity has been lost since the Beagle voyage and to determine the genetic source of specimens for which the collection locale was not recorded. Using ‘ancient’ DNA techniques, we quantified variation at 14 autosomal microsatellite loci. Assignment tests showed several museum specimens genetically matched recently field-sampled birds from their island of origin. Some were misclassified or were difficult to classify. Darwin's exceptionally large ground finches ( Geospiza magnirostris ) from Floreana and San Cristóbal were genetically distinct from several other currently existing populations. Sharp-beaked ground finches ( Geospiza difficilis ) from Floreana and Isabela were also genetically distinct. These four populations are currently extinct, yet they were more genetically distinct from congeners than many other species of Darwin's finches are from each other. We conclude that a significant amount of the finch biodiversity observed and collected by Darwin has been lost since the voyage of the Beagle .

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