Geospiza Magnirostris Research Articles

CONSUMPTION OF THE LICHEN ROCCELLA GRACILIS BY THE LARGE GROUND-FINCH GEOSPIZA MAGNIROSTRIS ON THE ISLAND OF DAPHNE MAJOR (GALÁPAGOS)

This note reports a trophic interaction of a passerine consuming lichens. On the islet of Daphne Major (Galápagos Archipelago), we made five observations of the Large Ground-Finch Geospiza magnirostris eating the fruticose lichen Roccella gracilis. This is an example of how island birds broaden their feeding niche in resource-poor environments.

Insight into the characteristics of an important evolutionary model bird (Geospiza magnirostris) mitochondrial genome through comparison

Darwin’s finches are the most classic case of evolution. Early studies on the evolution of this species were mainly based on morphology. Until now, the mitochondrial genome of Geospiza magnirostris has been sequenced and the study explored the characteristics of the complete genome of G. magnirostris and verified the evolutionary position of it. The 13 PCGs initiated by ATN codons. The stop codons of three PCGs (ND2, COX3 and ND4) were incomplete, with only T- or TA- replacing complete form TAA or TAG. All the tRNA genes expressed a typical cloverleaf secondary structure, except for tRNASer1(AGY), whose dihydrouridine (DHU) arm was lack and instead with a simple loop. In the sequence of the control region of G. magnirostris, we found six simple repeat tandem sequences with a total length of 42 bp. Two characteristic conserved overlapping junction (ATGCTAA) and (CAAGAAAG) were observed as reported for eight selected Passeriformes birds. A special conserved overlapping junction (ATCTTACC) involved in mitochondrial transcription termination was found between tRNATyr and COX1 in G. magnirostris’s control region. Four most frequently used amino acids in G. magnirostris’s PCGs were Leu1 (CUN), Ile, Thr, Ala. The codon usage of G. magnirostris was relatively average, and there was no particular bias. The ratio Ka/Ks results showed that G. magnirostris receives less natural selection pressure. The phylogenetic relationships and cluster analysis of relative codon usage showed that G. magnirostris and Thraupis episcopus clustered in one branch. The phylogenetic position of G. magnirostris was consistent with the traditional taxonomic of Thraupis. The results supported the conclusion that G. magnirostris belongs to the morphological classification of the family Thraupidae.

Morphological ghosts of introgression in Darwin’s finch populations

Many species of plants, animals, and microorganisms exchange genes well after the point of evolutionary divergence at which taxonomists recognize them as species. Genomes contain signatures of past gene exchange and, in some cases, they reveal a legacy of lineages that no longer exist. But genomic data are not available for many organisms, and particularly problematic for reconstructing and interpreting evolutionary history are communities that have been depleted by extinctions. For these, morphology may substitute for genes, as exemplified by the history of Darwin's finches on the Galápagos islands of Floreana and San Cristóbal. Darwin and companions collected seven specimens of a uniquely large form of Geospiza magnirostris in 1835. The populations became extinct in the next few decades, partly due to destruction of Opuntia cactus by introduced goats, whereas Geospiza fortis has persisted to the present. We used measurements of large samples of G. fortis collected for museums in the period 1891 to 1906 to test for unusually large variances and skewed distributions of beak and body size resulting from introgression. We found strong evidence of hybridization on Floreana but not on San Cristóbal. The skew is in the direction of the absent G. magnirostris We estimate introgression influenced 6% of the frequency distribution that was eroded by selection after G. magnirostris became extinct on these islands. The genetic residuum of an extinct species in an extant one has implications for its future evolution, as well as for a conservation program of reintroductions in extinction-depleted communities.

Structural variation and phylogenetic relationship of Geospiza magnirostris based on mitochondrial control region

The control region of mitochondrial genome is the main non-coding region. There is no details about Geospiza magnirostris’s control region, who is the only species of Geospiza in Darwin finches whose mitochondrial genome has been sequenced. In this study, the control region mitochondrial genome of G. magnirostris was analyzed. Compare research for 15 Passerine species, belonging to 4 families (Darwin ground finch, Thraupidae, Icteridae, Emberizidae), was also been done. The result showed the length was 1202 bp and it could been divided into three parts, domainI, domainII and domainIII. Genetic distances showed average divergence of different family ranged from 0.36% (Darwin ground finch) to 9.20% (Emberizidae), indicated that the Darwin ground finch may be a very conservative single-source species. Some specific sequence fragments such as conservative sequence box, boxes C, D, F and E, HSP/LSP, CSB-1, TAS-1 were also found in the control region of G. magnirostris, while B-box, CSB-2 and CSB-3 were not found in it. The F-box was detected in all selected 15 species and was 29 bp in length with no variant sites. In the E-box, 20 of the 21 nucleotide positions were identical as conserved among the selected species. There are two variant sites in the D-box, and five variant sites in the C-box. Basing the phylogenetic tree, it can be clearly seen that the relationship of G. magnirostris and family Thraupidae is the closest in all selected family. Through this study, the structure characteristics of G. magnirostris control region were explored and understood. This study provided more basic information for in-depth research of G. magnirostris. It’s also reminded us that we should pay more attention to explore the characteristics of the control region of Darwin’s finches.

Decomposing the Causes for Niche Differentiation Between Species Using Hypervolumes

Hutchinson’s n-dimensional hypervolume concept holds a central role across different fields of ecology and evolution. The question of the amount of hypervolume overlap and differentiation between species is of great interest to understand the processes that drive niche dynamics, competitive interactions and, ultimately, community assembly. A framework is proposed to decompose overall differentiation among hypervolumes into two distinct components: niche shifts and niche contraction / expansion processes. Niche shift corresponds to the replacement of space between the hypervolumes occupied by two species, whereas niche contraction / expansion processes correspond to net differences between the amount of space enclosed by each hypervolume. A procedure to implement non-continuous trait data in the estimation of n-dimensional hypervolumes is proposed. Hypervolumes were constructed for three Darwin' finches, Geospiza conirostris, Geospiza magnirostris and Geospiza difficilis using intraspecific trait data. Results showed that significant niche shifts, not niche contraction, occurred between G. conirostris and G. magnirostris in Genovesa island, where they live in sympatry. This means that G. conirostris occupied a different niche space and not a reduced space on Genovesa. G. difficilis was well differentiated from the other two species. The proposed framework allows disentangling different processes underlying niche partitioning between coexisting species. This framework offers novel insights to understand the drivers of niche partitioning strategies among coexisting species.

The complete mitochondrial genome and phylogeny of Geospiza magnirostris (Passeriformes: Thraupidae)

Geospiza magnirostris, an island species, was listed as of Least Concern (LC) on the IUCN Red List of Threatened Species; human entrapment, habitat destruction, predators, and competitors from the mainland have reduced its population. In this study, we first determined and described the complete mitochondrial genome of G. magnirostris; the circular genome of G. magnirostris is 16.798 bp in length, and contains 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and one non-coding control region (D-loop). The overall base composition of the mitochondrial DNA is 29.9% for A, 22.8% for T, 33.2% for C, and 14.1% for G. The percentage of G + C content is 47.3%. A phylogenetic tree was conducted to explore the taxonomic status of G. magnirostris, and showed that G. magnirostris is clustered in a clade with other Thraupidae species. This information will contribute to future phylogenetic studies of Passeriformes and further conservation strategies for this species.

Sisyphean evolution in Darwin's finches.

The trajectory of speciation involves geographic isolation of ancestral populations followed by divergence by natural selection, genetic drift or sexual selection. Once started, the process may experience fits and starts, as sometimes diverging populations intermittently reconnect. In theory populations might cycle between stages of differentiation and never attain species status, a process we refer to as Sisyphean evolution. We argue that the six putative ground finch species (genus Geospiza) of the Galápagos Islands represent a dramatic example of Sisyphean evolution that has been confused with the standard model of speciation. The dynamic environment of the Galápagos, closely spaced islands, and frequent dispersal and introgression have prevented the completion of the speciation process. We suggest that morphological clusters represent locally adapted ecomorphs, which might mimic, and have been confused with, species, but these ecomorphs do not form separate gene pools and are ephemeral in space and time. Thus the pattern of morphological, behavioural and genetic variation supports recognition of a single species of Geospiza, which we suggest should be recognized as Darwin's ground finch (Geospiza magnirostris). We argue that instead of providing an icon of insular speciation and adaptive radiation, which is featured in nearly every textbook on evolutionary biology, Darwin's ground finch represents a potentially more interesting phenomenon, one of transient morphs trapped in an unpredictable cycle of Sisyphean evolution. Instead of revealing details of the origin of species, the mechanisms underlying the transient occurrence of ecomorphs provide one of the best illustrations of the antagonistic effects of natural selection and introgression.

Insights into the evolution of Darwin’s finches from comparative analysis of the Geospiza magnirostris genome sequence

BackgroundA classical example of repeated speciation coupled with ecological diversification is the evolution of 14 closely related species of Darwin’s (Galápagos) finches (Thraupidae, Passeriformes). Their adaptive radiation in the Galápagos archipelago took place in the last 2–3 million years and some of the molecular mechanisms that led to their diversification are now being elucidated. Here we report evolutionary analyses of genome of the large ground finch, Geospiza magnirostris.Results13,291 protein-coding genes were predicted from a 991.0 Mb G. magnirostris genome assembly. We then defined gene orthology relationships and constructed whole genome alignments between the G. magnirostris and other vertebrate genomes. We estimate that 15% of genomic sequence is functionally constrained between G. magnirostris and zebra finch. Genic evolutionary rate comparisons indicate that similar selective pressures acted along the G. magnirostris and zebra finch lineages suggesting that historical effective population size values have been similar in both lineages. 21 otherwise highly conserved genes were identified that each show evidence for positive selection on amino acid changes in the Darwin's finch lineage. Two of these genes (Igf2r and Pou1f1) have been implicated in beak morphology changes in Darwin’s finches. Five of 47 genes showing evidence of positive selection in early passerine evolution have cilia related functions, and may be examples of adaptively evolving reproductive proteins.ConclusionsThese results provide insights into past evolutionary processes that have shaped G. magnirostris genes and its genome, and provide the necessary foundation upon which to build population genomics resources that will shed light on more contemporaneous adaptive and non-adaptive processes that have contributed to the evolution of the Darwin’s finches.

Predation on Seeds of Invasive Lantana camara by Darwin's Finches in the Galapagos Islands

Observations on birds feeding on fruits of the invasive shrub Lantana camara (Supirrosa) were conducted on Santa Cruz Island, Galapagos (Ecuador) in the Dry Zone during the 2009 dry season. The endemic ground finches Geospiza magnirostris (Large Ground Finch) and G. fortis (Medium Ground Finch) were recorded eating Lantana seeds with G. fortis the main consumer (>90% of records). Both finch species crushed the seeds and ate the embryos, discarding the exocarp and empty seed coats. They also dropped entire fruits to the ground, which could contribute to short-distance dispersal, but both finches also consumed fruits of L. camara on the ground. Density of L. camara seedlings under adult plants was higher in rockier areas than in bare soil since seeds were less accessible to predators and/or found more suitable microsites for germination and establishment. Both species of finches serve as short-distance dispersers, but mainly as seed predators of L. camara fruits.

Songs of Darwin's finches diverge when a new species enters the community

Bird species sing different songs and as a result rarely breed with each other. Species are not static but can shift in acoustic and morphological space, yet maintain their distinctiveness. Investigating such a situation in a community of Darwin's finches sheds light on the origin and maintenance of premating barriers between species. Explanations for songs divergence generally invoke morphological changes to the sound-producing apparatus, environmental changes influencing transmitting properties of song, avoidance of acoustical interference with other species, and random processes including copying errors. We investigated changes in songs of Geospiza fortis (medium ground finch) and Geospiza scandens (cactus ground finch) from 1978 to 2010 on Daphne Major Island, Galápagos. The habitat did not change significantly; however, the finch community changed. The socially aggressive congener Geospiza magnirostris (large ground finch), singing in the same frequency band (2–4 kHz), colonized Daphne in 1983 and increased in numbers. Temporal features of the songs of G. fortis and G. scandens , especially trill rate and song duration, diverged from G. magnirostris songs as it became increasingly common. Changes in song were not a passive consequence of a change in beak morphology. Instead they arose as a bias during song imprinting and production. Sons of both G. fortis and G. scandens sang faster songs than their respective fathers and thereby differed more from G. magnirostris in their songs than did their fathers. Divergence from an aversive or confusing stimulus during learning illustrates a “peak shift” that may be a common feature of song evolution and speciation.

Divergence with gene flow as facilitated by ecological differences: within-island variation in Darwin's finches

Divergence and speciation can sometimes proceed in the face of, and even be enhanced by, ongoing gene flow. We here study divergence with gene flow in Darwin's finches, focusing on the role of ecological/adaptive differences in maintaining/promoting divergence and reproductive isolation. To this end, we survey allelic variation at 10 microsatellite loci for 989 medium ground finches (Geospiza fortis) on Santa Cruz Island, Galápagos. We find only small genetic differences among G. fortis from different sites. We instead find noteworthy genetic differences associated with beak. Moreover, G. fortis at the site with the greatest divergence in beak size also showed the greatest divergence at neutral markers; i.e. the lowest gene flow. Finally, morphological and genetic differentiation between the G. fortis beak-size morphs was intermediate to that between G. fortis and its smaller (Geospiza fuliginosa) and larger (Geospiza magnirostris) congeners. We conclude that ecological differences associated with beak size (i.e. foraging) influence patterns of gene flow within G. fortis on a single island, providing additional support for ecological speciation in the face of gene flow. Patterns of genetic similarity within and between species also suggest that interspecific hybridization might contribute to the formation of beak-size morphs within G. fortis.

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

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.

Pedigrees, assortative mating and speciation in Darwin's finches.

Pedigree analysis is a useful tool in the study of speciation. It can reveal trans-generational influences on the choice of mates. We examined mating patterns in a population of Darwin's medium ground finches (Geospiza fortis) on Daphne Major Island to improve our understanding of how a barrier to the exchange of genes between populations arises in evolution. Body sizes of mates were weakly correlated. In one year, the smallest females were paired non-randomly with the males of similar size, and in another year the largest males were paired with the largest females. An influence of parental morphology on the choice of mates, as expected from sexual imprinting theory, was found; the body size of mates was predicted by the body sizes of both parents, and especially strongly by the father's. These associations imply that the seeds of reproductive isolation between species are present within a single variable population. The implication was subject to a natural test: two exceptionally large birds of the study species, apparently immigrants, bred with each other, as did their offspring, and not with the members of the resident population. The intense inbreeding represents incipient speciation. It parallels a similar phenomenon when another species, the large ground finch, immigrated to Daphne and established a new population without interbreeding with the resident medium ground finches.

Self-regulation of embryonic pattern in Xenopus embryos

Presidential symposium Program/Abstract # 1 Self-regulation of embryonic pattern in Xenopus embryos Eddy De Robertis, Lucho Fuentealba, Edward Eivers, Cecilia Hurtado, Andrea Ambrosio, Vincent Taelman, Jean-Louis Plouhinec, Hojoon X. Lee HHMI and University of California, Los Angeles, USA How do cells at opposite ends of the embryo communicate with each other? We found that dorsal and ventral BMP signals and their extracellular antagonists, expressed under opposing transcriptional regulation, provide a molecular mechanism for embryonic self-regulation. Quadruple knockdown of ADMP and BMP2/4/7 in Xenopus embryos caused ubiquitous neural induction throughout the ectoderm. ADMP and Chordin transcription in the Spemann organizer is activated at low BMP levels. When ventral BMP2/4/7 signals are depleted, Admp expression increases, allowing for self-regulation. ADMP has BMP-like activity but is unable to signal dorsally because of inhibition by Chordin. Ventrally, high BMP signalling increases transcription of the BMP antagonists Crossveinless-2, Bambi and Sizzled. We are developing an Electronic Frog model to analyze how this network of extracellular proteins works. The model has a single output, the levels of phosphorylation of Smad1 by BMPR. There are multiple molecular pathways that must be integrated so that a perfect embryonic pattern can be generated. We will discuss how three major signaling pathways BMPR, MAPK/RTK and GSK3/Wnt are integrated at the level of the phosphorylation of the Smad 1 transcription factor. We will describe how this network of intracellular regulation controls the intensity and the duration of the Smad1 signal. De Robertis, E.M. (2006). Spemann's organizer and self-regulation in amphibian embryos. Nature Reviews Molecular Cell Biology 7, 296–302. doi:10.1016/j.ydbio.2007.03.528 Program/Abstract # 2 Stem cells and lineage decisions in the early mammalian embryo Janet Rossant , A. Ralston , Y. Yamanaka , R. Stephenson , J. Draper , C. Seguin 1 1 Dev and StemCell Biol, Hosp for Sick Children, Toronto, Canada 2 Med Genet and Microbio, Univ of Toronto, Canada Three types of permanent cell lines can be derived from the mouse blastocyst; embryonic stem (ES) cells, trophoblast stem (TS) cells and extraembryonic endoderm (XEN) cells. All three express markers and show properties in chimeras consistent with their origin from the epiblast (EPI), trophectoderm (TE) and primitive endoderm (PE) of the blastocyst respectively. A hierarchy of transcription factors, Cdx2, Eomes, Ets2 and ERRb, are key to different phases of trophoblast stem cell development and maintenance in vitro and in vivo. Cdx2 acts at the blastocyst stage to inhibit Oct4 and Nanog expression in the outer cells of the blastocyst in a cell-autonomous manner and so is required to repress the pluripotent state. However, the formation of the initial polarized outer epithelium of the blastocyst does not depend on zygotic Cdx2. This suggests that the cell polarity pathways are upstream of and may activate Cdx2. We have explored this by interfering with various aspects of cell polarization and show a relationship between apical polarity and maintenance of Cdx2 expression. We have previously shown that formation of EPI and PEmay dependmore on sorting of precommitted precursors than on cell polarity. We propose a model for blastocyst formation that combines asymmetric cell divisions and cell sorting to generate the final three committed lineages. We also will present comparative data on the response of mouse and human embryonic stem cells to expression of lineage-specific transcription factors that indicates that lineage decisions in early human development may differ temporally from the mouse. doi:10.1016/j.ydbio.2007.03.529 Program/Abstract # 3 Evo–Devo studies on Latin American fauna Cliff Tabin Harvard Med Sch, Boston, MA, USA The diversity of Darwin's finches primarily lies in the size and shape of their beaks. Using a candidate gene approach, we found that expression of Bmp4 strongly correlates with deep and broad beak morphology. When misexpressed in chicken embryos, Bmp4 causes morphological transformations paralleling the beak morphology of the large ground finch. The candidate approach failed, however to identify genes correlating with Developmental Biology 306 (2007) 285–286 www.elsevier.com/locate/ydbio doi:10.1016/j.ydbio.2007.03.040

Darwin’s finches

Darwin’s finches

THE FOUNDING OF A NEW POPULATION OF DARWIN'S FINCHES.

We report the natural colonization of the small Galápagos island Daphne Major by the large ground finch (Geospiza magnirostris). Immigrants of this species were present in every year of a 22-yr study, 1973-1994. Typically they arrived after a breeding season and left at the beginning of the next one. Geospiza magnirostris bred on the island for the first time in the exceptionally wet El Niño year of 1982-1983, and bred in all subsequent years except drought years. In agreement with theoretical expectations the frequency of inbreeding was unusually high. Pronounced fluctuating asymmetry in tarsus length, together with slightly reduced breeding success of inbreeding pairs, suggests a low level of inbreeding depression. Despite this, the population increased from 5 breeding individuals in 1983 to 20 breeding individuals in 1992, and probably more than twice that number in 1993, largely through recruitment of locally born birds.

Isospora daphnensis n. sp. (Apicomplexa: Eimeriidae) from the Medium Ground Finch (Geospiza fortis) from the Galapagos Islands

In March and April 1987 fecal samples from 237 nestling birds, including 199 from 85 nest sites of Geospiza fortis, 23 from 12 nest sites of Geospiza scandens, 6 from 2 nest sites of Geospiza magnirostris, and 9 from 2 nest sites of hybrids involving Geospiza fuliginosa and G. fortis, were collected from Daphne Major in the Galapagos archipelago and examined for coccidia. Only 3 of 4 nestlings from 1 nest site of G. fortis (1.5%) had oocysts in their feces. Two of the 3 infected nestlings had concurrent infections of Isospora temeraria, and all 3 nestlings were infected with a new species. Isospora daphnensis n. sp. Sporulated oocysts of I. daphnensis n. sp. are ellipsoidal, 27.3 x 23.6 (22-30 x 20-27) microns; a polar body is present, but no oocyst residuum or micropyle occurs. The oocyst wall, approximately 1.5 microns thick, is composed of a mammillated outer layer and thinner inner layer. Sporocysts are ovoid, 15.2 x 10.2 (15-16 x 9-11) microns and have a nipplelike Stieda body and a small substieda body. The sporocysts contain an irregularly shaped, smoothly contoured residuum with uniform granules and 4 sporozoites with a large refractile body at one end and lying randomly in the sporocysts.

Ecological Consequences of an Exceptionally Strong El Nino Event on Darwin's Finches

We studied the effects of heavy rainfall associated with the El Nino event of 1982-1983 on the demography of Darwin's Ground Finch (Geospizinae) populations and their resources on Isla Daphne Major, Galapagos. Total rainfall during this period (1359 mm) was 10 times the previously recorded wet season maximum. Most plant species responded by dramatically increasing seed production; total seed biomass increased by an order of magnitude, and small seed biomass increased in relative abundance, from 20% of total seed biomass before 1983 to >80% at the peak of the event. Caterpillars, the main food used by finches while breeding, also became extremely abundant. Ground finch species, mainly the Medium Ground Finch (Geospiza fortis) and the Cactus Finch (G. scandens), responded to the increase in food supply by breeding repeatedly. Females of both species produced up to 10 clutches of eggs; normally they produce 1-5 clutches. The most productive female fortis and scandens individuals fledged 25 and 19 young, respectively. Some birds born at the beginning of the season bred successfully before the end. Clutch sizes were scarcely larger than before and overall fledging success per nest was lower than in a normal breeding season. The large number of young produced resulted in (1) increases in population sizes of both species by a factor of four, (2) a dramatic skew in the age structure of both species, with birds born in 1982-1983 making up >75% of each population in January 1984, and (3) >50% of the lifetime fledgling production of females born in 1978 occurring in this breeding season. Individuals of both species immigrated from nearby islands, and a nonresident species, the Large Ground Finch (G. magnirostris) immigrated and bred on the island. Severe El Nino events have important ecological and evolutionary effects on these birds. For example, the high proportion of lifetime reproductive success contributed under exceptionally favorable conditions may have influenced the evolution of life history characteristics in the finches. Overall, our results support the view that rare events can have a major influence on key population processes in long-lived birds living in temporally varying environments, and that long-term studies are necessary to detect such effects.

The feeding of darwin's finches on Tribulus cistoides (L.) seeds

Food-handling skills of finches vary as a function of bill size. Geospiza magnirostris crush and shatter the woody mericarps of caltrop ( Tribulus cistoides) to reach the seeds, whereas G. fortis (a smaller species) bite and tear at them. G. magnirostris accept and crack most of the mericarps picked up; fortis reject most mericarps but often feed on fragments. Energy rewards are greater for magnirostris than for fortis. Intraspecific variation in handling skills parallels interspecific variation. G. fortis individuals with large bills spend more time on mericarps and extract more seeds than do those with small bills, and they reject mericarps with a lower frequency. Those observed feeding on seeds from Tribulus mericarps were larger, particularly in bill size, than those not observed feeding on them.

The Breeding and Feeding Characteristics of Darwin's Finches on Isla Genovesa, Galapagos

The breeding and feeding of four species of finches were studied on Isla Genovesa, Galapagos from January to May 1978. Food supply and finch diets were studied in the nonbreeding season (November) as well. The species in order of decreasing body size were Geospiza magnirostris, G. conirostris, G. difficilis, and Certhidea olivacea. Initiation of breeding was not a simple function of body size; the medium—sized cactus finch, G. conirostris, started breeding first, followed by G. difficilis and G. magnirostris in that order. Eggs of G. conirostris were first laid within °1 wk of the first rains. Certhidea laid a maximum of three clutches, G. magnirostris and G. conirostris laid up to four, and one pair of G. difficilis laid five. Similarities among all four species were found in incubation periods (10—14 d, mode 12 d), nestling periods (11—17 d, modes 13—15 d), and uniform success of clutches of different sizes. Similarities among the three Geospiza species were found in the interval between successive clutches (°30 d); the modal size of clutches (four eggs); seasonal variation in clutch sizes, in which average size was largest among second clutches and smallest among fourth clutches; egg and nestling production; and the average interval between fledging from one nest and egg laying by the parents in the next nest. This average interval was 1—4 d, but some pairs of all three species started laying 5—6 d before the nestlings of the previous brood had fledged. The species differed in the number of fledglings produced per pair; from the first three clutches G. difficilis produced 9.5 ± 0.5 per pair, G. conirostris produced 7.9 ± 0.7, G. magnirostris produced 5.1 ± 0.9, and Certhidea produced 3.2 ± 1.5. The relatively low success of G. magnirostris was attributed to predation of nestlings by owls (Asio flammeus), which occurred most frequently within 1 wk of expected fledging. The low success of Certhidea is attributed to disturbance at the nest by G. difficilis and mockingbirds (Nesomimus parvulus), and possible predation by mockingbirds. Compared with finch species in a climatically similar region of the Ecuadorian mainland, Darwin's Finches have large clutches, a much longer nestling period, higher nesting and breeding success, but similar, and low, incidences of egg infertility. Certhidea fed nestlings on an exclusively arthropod diet, whereas the three Geospiza species fed nestlings on a mixed diet of arthropods, fruits, and seeds. All Geospiza species fed size selectively on spiders in proportion to their average body and beak size. Diets of the three Geospiza species were largely overlapping throughout the breeding season. Differences reflected the differences in beak sizes. Seeds of Bursera graveolens, which are difficult to crack, were absent from nestling diets of (the smallest) G. difficilis, and most frequent in nestling diets of (the largest) G. magnirostris. Only G. conirostris fed nestlings on parts of Opuntia helleri (cactus). Diets of the three species diverged markedly in the nonbreeding season, at which time they clearly reflected the adaptations of beak sizes and shapes. The results are discussed in terms of the strong seasonality in food production and availability, coupled with interannual variation in amount, onset, and pattern of rainfall, and hence food production. It is concluded that adaptations for food gathering in the nonbreeding season, when food is scarce, have indirect influences upon reproductive traits, resulting in small but significant demographic differences between species.