Camarhynchus Parvulus Research Articles

Exploration behavior differs between Darwin’s finch species and predicts territory defense and hatching success

Darwin’s finch species in the Galápagos Islands are famously distinguished by their morphology but less attention has been given to behavioral differences between species. In this study, we compared behavior between four Darwin’s finch species on Floreana Island: small ground finch (Geospiza fuliginosa), medium ground finch (G. fortis), small tree finch (Camarhynchus parvulus), and medium tree finch (C. pauper). After capturing birds using mist-nets, we measured three behavioral traits: (1) boldness during human handling, (2) exploration in a novel environment, and (3) aggressiveness towards their mirror image. First, we found that ground finches were bolder and more exploratory than tree finches, consistent with their distinct ecological niches on Floreana Island and with the theoretical prediction that diet generalists should be less wary of novelty. Second, we tested the ecological validity of these behavioral variables at the individual level by relating them to territory defense behavior and breeding success. We found that males that were more exploratory in the novel environment also reacted more aggressively to a simulated territory intruder and showed lower offspring hatching success during the breeding season. Hence, our findings support previous work showing behavioral differences between Darwin’s finch species and also suggest pathways by which behavioral differences among individuals might influence fitness.Significance statementClosely-related species that overlap in their geographical range may differ in their morphology and/or behavior, allowing them to occupy different ecological niches. In this study, we explored behavioral differences between four Darwin’s finch species on Floreana Island in the Galápagos Archipelago. We found clear interspecies differences in behavior, with the ground finches struggling more often during handling (boldness) and visiting more sectors in a novel environment (exploration) compared to the tree finches. After birds were released, we continued to observe a subset of male finches in the wild. An individual’s exploration behavior significantly predicted both its aggressive response to a territory intruder (simulated using song playback) and offspring hatching success during the breeding season. This suggests that individual differences in exploration behavior can potentially be used as a proxy for territorial behavior in the wild and may also predict fitness outcomes.

Buzzes are used as signals of aggressive intent in Darwin’s finches

Abstract Signals of aggression may potentially reduce the fitness costs of conflict during agonistic interactions if they are honest. Here we examined whether the ‘buzz’ vocalization in two species of Darwin’s finches, the small tree finch, Camarhynchus parvulus, and the critically endangered medium tree finch, C. pauper, found in Floreana Island, Galápagos Archipelago, is a signal of aggression. Specifically, we assessed three criteria for aggressive signalling (context, predictive, and response criteria) in an observational study and a playback experiment. In the observational study, buzzes by the resident male were more common when an intruder was present on the territory in medium tree finches but not small tree finches (context criterion). In the playback experiment, buzzes increased during and after a simulated intrusion for both species (context criterion). Buzzes before the playback period predicted aggressive responses by males (predictive criterion) but buzzes during playback did not. Finally, both species responded more strongly to playbacks of conspecific buzzes compared to conspecific songs and heterospecific buzzes (response criterion). Together the results support the aggressive signal hypothesis for buzz vocalizations, although future studies are needed to understand the evolution and development of this interesting signal.

Evolutionary divergence of body size and wing and leg structure in relation to foraging mode in Darwin’s Galapagos finches

Abstract The wings, legs, and tail in Darwin’s finches show many clear adaptations to different types of locomotion used during foraging. We use size scaling to analyse how various characters vary with body mass to clarify dimensional relationships. The selective advantage of a character is judged in terms of energy savings. The wing aspect ratio (4.6–4.9) is very low, so the energy costs for flight are high. Low body mass, low wing loading, and short arm wings in the warbler finch, small tree finch, and small ground finch promote agility and manoeuvrability among vegetation, along with short wings in the warbler finch. Evolution towards a shorter arm wing seems to be favoured in the smaller finch species. Long legs, long toes, and long curved claws are adaptations for climbing/clinging locomotion without tail support (woodpecker finch, small and large tree finches, cactus finch but having short legs). Selection for longer legs seems to act towards a lengthening of the tarsometatarsus. The climbing technique in the woodpecker finch is described. We discuss how the diversification in the beaks relates to the locomotion organs.

Age effects in Darwin’s finches: older males build more concealed nests in areas with more heterospecific singing neighbors

Nesting success tends to increase with age in birds, in part because older birds select more concealed nest sites based on experience and/or an assessment of prevailing predation risk. In general, greater plant diversity is associated with more biodiversity and more vegetation cover. Here, we ask if older Darwin’s finch males nest in areas with greater vegetation cover and if these nest sites also have greater avian species diversity assessed using song. We compared patterns in Darwin’s Small Tree Finch (Camarhynchus parvulus) and Darwin’s Small Ground Finch (Geospiza fuliginosa) as males build the nest in both systems. We measured vegetation cover, nesting height, and con- vs. heterospecific songs per minute at 55 nests (22 C. parvulus, 33 G. fuliginosa). As expected, in both species, older males built nests in areas with more vegetation cover and these nests had less predation. A novel finding is that nests of older males also had more heterospecific singing neighbors. Future research could test whether older males outcompete younger males for access to preferred nest sites that are more concealed and sustain a greater local biodiversity. The findings also raise questions about the ontogenetic and fitness consequences of different acoustical experiences for developing nestlings inside the nest.

Functional traits and foraging behaviour: Avian vampire fly larvae change the beak and fitness of their Darwin's finch hosts

AbstractThe avian beak is a key morphological trait used for foraging. If parasites alter beak shape, we may expect changes in host foraging behaviour. Larvae of the avian vampire flyPhilornis downsicause naris enlargement in Darwin's finch nestlings when first and second instar larvae consume keratin, blood and tissue from inside the beak of the developing host. This naris malformation persists into adulthood, where nares that are >15% of total beak length are considered enlarged.We measured effects of parasite‐induced naris enlargement on foraging behaviour, foraging niche overlap and body condition in Darwin's finches on Floreana Island. Foraging behaviour was ranked by the stress per foraging technique exerted on the beak and ranged from least stress for ‘gleaning’ to most stress for ‘chip off bark’.Naris enlargement occurred in 34% of adult birds. The most common foraging technique differed among species: medium tree finches (Camarhynchus pauper) often chipped off bark to extract subsurface prey, small tree finches (C. parvulus) often gleaned surface prey from foliage, hybrids gleaned prey from bark and foliage, and small ground finches (Geospiza fuliginosa) mostly foraged on the ground. InC. pauper, birds with naris enlargement did more gleaning and less subsurface prey excavation. Foraging niche across species was most similar in birds with naris enlargement. Finally, body condition was lower in insectivorous tree finches with malformed beaks.A novel aspect of this study is the idea that parasite‐induced alterations to phenotype affect ecological processes and interspecific interactions at large temporal and spatial scales. The parasitism occurs early in life but the ecological effects of this parasitism, if causative, are happening later.Read the freePlain Language Summaryfor this article on the Journal blog.

Female in-nest attendance predicts the number of ectoparasites in Darwin's finch species.

Selection should act on parental care and favour parental investment decisions that optimize the number of offspring produced. Such predictions have been robustly tested in predation risk contexts, but less is known about alternative functions of parental care under conditions of parasitism. The avian vampire fly (Philornis downsi) is a myasis-causing ectoparasite accidentally introduced to the Galápagos Islands, and one of the major mortality causes in Darwin's finch nests. With an 11-year dataset spanning 21 years, we examine the relationship between parental care behaviours and number of fly larvae and pupae in Darwin's finch nests. We do so across three host species (Camarhynchus parvulus, C. pauper, Geospiza fuliginosa) and one hybrid Camarhynchus group. Nests with longer female brooding duration (minutes per hour spent sitting on hatchlings to provide warmth) had fewer parasites, and this effect depended on male food delivery to chicks. Neither male age nor number of nest provisioning visits were directly associated with number of parasites. While the causal mechanisms remain unknown, we provide the first empirical study showing that female brooding duration is negatively related to the number of ectoparasites in nests. We predict selection for coordinated host male and female behaviour to reduce gaps in nest attendance, especially under conditions of novel and introduced ectoparasites.

Avian vampire fly (Philornis downsi) mortality differs across Darwin\u2019s finch host species

In invasive parasites, generalism is considered advantageous during the initial phase of introduction. Thereafter, fitness costs to parasites, such as host-specific mortality, can drive parasites towards specialism to avoid costly hosts. It is important to determine changes in host specificity of invasive populations to understand host-parasite dynamics and their effects on vulnerable host populations. We examined changes in mortality in the introduced avian vampire fly (Philornis downsi) (Diptera: Muscidae), a generalist myasis-causing ectoparasite, between 2004 and 2020 on Floreana Island (Galápagos). Mortality was measured as the proportion of immature larvae found upon host nest termination. Over the time period, the avian vampire fly was most abundant and had low mortality in nests of the critically endangered medium tree finch (Camarhynchus pauper) and had the highest mortality in nests of hybrid tree finches (Camarhynchus spp.). Low larval mortality was also found in small tree (Camarhynchus parvulus) and small ground finch (Geospiza fuliginosa) nests. Selection could favour avian vampire flies that select medium tree finch nests and/or avoid hybrid nests. Overall, the finding of differences in avian vampire fly survival across host species is parsimonious with the idea that the introduced fly may be evolving towards host specialisation.

Behavioural response to songs between genetically diverged allopatric populations of Darwin's small tree finch in the Galápagos.

Empirical data that identify contemporary mechanisms of divergence shed light on how species could multiply. In this study, we measured population genetic structure, song syllable diversity and response to simulated intruder song in Darwin's small tree finch (Camarhynchus parvulus) on Santa Cruz and Floreana Islands, Galápagos archipelago. Our aim was to test whether the magnitude of contemporary behavioural response in resident birds was consistent with patterns of genetic or cultural differences between populations. We analysed genetic structure and the occurrence of song syllable types, and experimentally measured the response of resident birds to intruder bird song from different geographical origin (i.e., island) or syllable type. We discovered a weak signal of population genetic structure between Santa Cruz and Floreana Islands. Although some song syllables occurred on both islands, others were unique to each island; Santa Cruz Island males used more unique syllables than Floreana Island males. Both Santa Cruz and Floreana resident males discriminated their response towards a simulated intruder song based on the geographical origin of the intruder song, but not on the syllable type sung by the intruder. We conclude that the populations are diverging in genetic and cultural traits and identified a signal of contemporary behavioural response that could maintain divergence upon secondary contact.

Timing of infestation influences virulence and parasite success in a dynamic multi-host\u2013parasite interaction between the invasive parasite, Philornis downsi, and Darwin\u2019s finches

Recently commenced host–parasite interactions provide an excellent opportunity to study co-evolutionary processes. Multi-host systems are especially informative because variation in virulence between hosts and temporal changes provides insight into evolutionary dynamics. However, empirical data under natural conditions are scarce. In the present study, we investigated the interaction between Darwin’s finches and the invasive fly Philornis downsi whose larvae feed on the blood of nestlings. Recently, however, the fly has changed its behavior and now also attacks incubating females. Two sympatric hosts are affected differently by the parasite and parasite load has changed over time. Our study observed a reversal of trends described two decades ago: while, currently, small tree finches (Camarhynchus parvulus) experience significantly higher parasite load than warbler finches (Certhidea olivacea), this was the opposite two decades ago. Currently, fledging success is higher in warbler finches compared to small tree finches. Our data indicate that not only intensity but also timing of infestation influences hosts’ reproductive success and parasite fitness. During incubation, prevalence was higher in warbler finches, but once chicks had hatched, prevalence was 100% in both species and parasite load was higher in small tree finches. Furthermore, our results suggest faster development and higher reproductive success of P. downsi in small tree finch nests. A change in host preference driven by larvae competition could have led to the reversal in parasite load.

Under adverse conditions, older small tree finch males (Camarhynchus parvulus) produce more offspring than younger males.

Females of many bird species prefer mating with older males, presumably because they provide superior parental care and possibly superior genes. A previous study found that female small tree finches (Camarhynchus parvulus) preferred pairing with old males and had a higher breeding success when paired with old males because their nests were more concealed, higher up in the canopy and therefore less likely to be depredated. However, causes for brood loss have changed over the last decade: predation of small tree finch nests has decreased, whereas brood losses due to parasitism by the invasive parasitic fly Philornis downsi have increased. In the present study, we investigated (a) how the change in predation and parasitism by P. downsi influenced the breeding success of small tree finches, (b) whether there were still differences in breeding success between young and old males, (c) whether P. downsi infestation had a differential effect on nests of young and old males and (d) whether young and old males differed in foraging success. During 2012–2016, we found an overall low influence of predation and a high influence of P. downsi, but neither differed between nests of young and old males. Nests of old males had more fledglings than those of young males. However, the difference in breeding success disappeared when P. downsi numbers were experimentally reduced by injecting an insecticide into nests. This indicates that older males were able to compensate for the detrimental effects of parasitism.

Parental care in the Small Tree Finch Camarhynchus parvulus in relation to parasitism and environmental factors.

The parental food compensation hypothesis suggests that parents may compensate for the negative effects of parasites on chicks by increased food provisioning. However, this ability differs widely among host species and may also depend on ecological factors such as adverse weather conditions and habitat quality. Although weed management can improve habitat quality, management measures can bring about a temporary decrease in food availability and thus may reduce parents’ ability to provide their nestlings with enough energy. In our study we investigated the interaction of parasitism and weed management, and the influence of climate on feeding rates in a Darwin’s tree finch species, which is negatively impacted by two invasive species. The larvae of the invasive parasitic fly Philornis downsi ingest the blood and body tissues of tree finch nestlings, and the invasive Blackberry Rubus niveus affects one of the main habitats of Darwin’s tree finches. We compared parental food provisioning of the Small Tree Finch Camarhynchus parvulus in parasitized and parasite‐free nests in three different areas, which differed in invasive weed management (no management, short‐term and long‐term management). In a parasite reduction experiment, we investigated whether the Small Tree Finch increases food provisioning rates to nestlings when parasitized and whether this ability depends on weed management conditions and precipitation. Our results provide no evidence that Small Tree Finches can compensate with additional food provisioning when parasitized with P. downsi. However, we found an increase in male effort in the short‐term management area, which might indicate that males compensate for lower food quality with increased provisioning effort. Furthermore, parental food provisioning was lower during rainfall, which provides an explanation for the negative influence of rain on breeding success found in earlier studies. Like other Darwin’s finches, the Small Tree Finch seems to lack the ability to compensate for the negative effects of P. downsi parasitism, which is one explanation for why this invasive parasite has such a devastating effect on this host species.

Introduced parasite changes host phenotype, mating signal and hybridization risk: Philornis downsi effects on Darwin's finch song.

Introduced parasites that alter their host's mating signal can change the evolutionary trajectory of a species through sexual selection. Darwin's Camarhynchus finches are threatened by the introduced fly Philornis downsi that is thought to have accidentally arrived on the Galapagos Islands during the 1960s. The P. downsi larvae feed on the blood and tissue of developing finches, causing on average approximately 55% in-nest mortality and enlarged naris size in survivors. Here we test if enlarged naris size is associated with song characteristics and vocal deviation in the small tree finch ( Camarhynchus parvulus), the critically endangered medium tree finch ( C. pauper) and the recently observed hybrid tree finch group ( Camarhynchus hybrids). Male C. parvulus and C. pauper with enlarged naris size produced song with lower maximum frequency and greater vocal deviation, but there was no significant association in hybrids. Less vocal deviation predicted faster pairing success in both parental species. Finally, C. pauper males with normal naris size produced species-specific song, but male C. pauper with enlarged naris size had song that was indistinguishable from other tree finches. When parasites disrupt host mating signal, they may also facilitate hybridization. Here we show how parasite-induced naris enlargement affects vocal quality, resulting in blurred species mating signals.

Genetic admixture predicts parasite intensity: evidence for increased hybrid performance in Darwin's tree finches.

Hybridization can increase adaptive potential when enhanced genetic diversity or novel genetic combinations confer a fitness advantage, such as in the evolution of anti-parasitic mechanisms. Island systems are especially susceptible to invasive parasites due to the lack of defence mechanisms that usually coevolve in long-standing host–parasite relationships. We test if host genetic admixture affects parasite numbers in a novel host–parasite association on the Galápagos Islands. Specifically, we compare the number of Philornis downsi in nests with offspring sired by Darwin's small tree finch (Camarhynchus parvulus), Darwin's medium tree finch (C. pauper) and hybrids of these two species. The number of P. downsi decreased with an increasing genetic admixture of the attending male, and nests of hybrid males had approximately 50% fewer parasites than C. parvulus nests, and approximately 60% fewer parasites than C. pauper nests. This finding indicates that hybridization in this system could be favoured by selection and reveal a mechanism to combat an invasive parasite.

Weed management increases the detrimental effect of an invasive parasite on arboreal Darwin's finches

The detrimental effects of invasive parasites on hosts often increase under poor environmental conditions. Both natural fluctuations in environmental conditions and habitat management measures can temporarily cause adverse environmental effects. In this study, we investigated the interaction between the invasive parasitic fly Philornis downsi, control of invasive plants and precipitation on the breeding success of Darwin's finches. Introduced plant species have invaded a unique forest on the Galapagos island of Santa Cruz, which is a key habitat for Darwin's finches. The Galapagos National Park Directorate applies manual control and herbicides to combat this invasion. We hypothesized that these measures led to a reduction in the arthropod food supply during chick rearing, which in turn caused mortality in chicks that were already weakened by parasitism. We compared food availability in three study sites of varying degrees of weed management. To assess the interaction of parasitism and weed management, we experimentally reduced P. downsi abundance in nests in all three study sites. The key result suggests that there is an increase in the adverse effect of parasitism under unfavourable habitat conditions. As predicted, we found a negative additive effect of parasitism and weed management on the breeding success of the insectivorous warbler finch (Certhidea olivacea), but not on the omnivorous small tree finch (Camarhynchus parvulus), which was strongly affected by parasitism independently of weed management. Management measures can temporarily decrease environmental quality and reduce resistance/tolerance to invasive species. This should be considered when applying management measures to habitats of vulnerable species.

Minimum longevity and age-related male plumage in Darwin’s finches on Floreana Island

Several Darwin’s finch populations on the Galapagos Islands are declining and/or locally extinct. Acoustic surveys provide useful information about population size, but do not provide information on the age or morphology of birds. This study uses mist netting data collected during 2004–2016 on Floreana Island with the aim of evaluating minimum longevity in Darwin’s finches. The study species are the Small Tree Finch (Camarhynchus parvulus), hybrid tree finches (Camarhynchus spp.), Medium Tree Finch (Camarhynchus pauper), and Small Ground Finch (Geospiza fuliginosa). In total, 1032 Darwin’s finches were mist netted and 86 of 707 males and 14 of 325 females were recaptured across years. We used the proportion of black plumage to age males, and the age at first capture plus the number of years between recapture to estimate minimum longevity. Minimum longevity ranged from 12 to 15 years and was lowest in the critically endangered C. pauper (12 years). The average number of years between first capture and last recapture was significantly lower in females than in males. Because long-term mist netting provides information on age structure, recruitment and longevity in males and females, it should be a key component of effective conservation planning.

Females drive asymmetrical introgression from rare to common species in Darwin's tree finches.

The consequences of hybridization for biodiversity depend on the specific ecological and evolutionary context in which it occurs. Understanding patterns of gene flow among hybridizing species is crucial for determining the evolutionary trajectories of species assemblages. The recently discovered hybridization between two species of Darwin's tree finches (Camarhynchus parvulus and C.pauper) on Floreana Island, Galápagos, presents an exciting opportunity to investigate the mechanisms causing hybridization and its potential evolutionary consequences under conditions of recent habitat disturbance and the introduction of invasive pathogens. In this study, we combine morphological and genetic analysis with pairing observations to explore the extent, direction and drivers of hybridization and to test whether hybridization patterns are a result of asymmetrical pairing preference driven by females of the rarer species (C.pauper). We found asymmetrical introgression from the critically endangered, larger-bodied C.pauper to the common, smaller-bodied C.parvulus, which was associated with a lack of selection against heterospecific males by C.pauper females. Examination of pairing data showed that C.parvulus females paired assortatively, whereas C.pauper females showed no such pattern. This study shows how sex-specific drivers can determine the direction of gene flow in hybridizing species. Furthermore, our results suggest the existence of a hybrid swarm comprised of C.parvulus and hybrid birds. We discuss the influence of interspecific abundance differences and susceptibility to the invasive parasite Philornis downsi on the observed hybridization and recommend that the conservationof this iconic species group should be managed jointly rather than species-specific.

The impact of invasive plant management on the foraging ecology of the Warbler Finch (Certhidea olivacea) and the Small Tree Finch (Camarhynchus parvulus) on Gal\xe1pagos

In recent decades, arboreal Darwin’s Finches have suffered from a dramatic population decline, which has been attributed to parasitism by the invasive botfly Philornis downsi. However, changes to their primary habitat caused by invasive plant species may have additionally contributed to the observed population decline. The humid cloud forest on Santa Cruz Island is a stronghold of arboreal Darwin’s Finches but has been invaded by blackberry (Rubus niveus). In some areas, manual control and herbicide application are used to combat this invasion, both causing a temporary removal of the entire understory. We hypothesized that the removal of the understory reduces the availability of arthropods, which are a main food source during chick rearing. We compared the foraging behaviour of Warbler Finches (Certhidea olivacea) and Small Tree Finches (Camarhynchus parvulus) at three study sites that varied in the degree of R. niveus invasion and the length of time since the last herbicide application. We used prey attack rate and foraging success as an index for food availability and predicted a lower attack rate and foraging success in areas that had recently been sprayed with herbicides. We found that both the invasion and the management of R. niveus influenced microhabitat use, foraging substrate and prey choice in both species. Contrary to our hypothesis, we did not find a lower attack rate or foraging success in the area with recent herbicide application. This may be explained by the finding that both species mainly foraged in the canopy but also used dead plant structures of the understory of the recently controlled area that resulted from the invasive plant management.

Conservation status of landbirds on Floreana: the smallest inhabited Galápagos Island

On Floreana, the smallest inhabited island in the Galapagos, populations of several species of birds have either been extirpated or, based on anecdotal evidence and small-scale surveys, are declining. Our objective, therefore, was to conduct a comprehensive survey of landbirds encompassing the entire island during three breeding seasons (2014–2016). We conducted surveys at 59 points in 2014, 257 in 2015, and 295 in 2016. Each survey point was sampled once. We detected 12 species during our surveys. Galapagos Flycatchers, Yellow Warblers, Small and Medium ground-finches, and Small Tree-Finches were widely distributed over the entire island. Common Cactus-Finches and Medium Tree-Finches had more restricted distributions in the lower or higher parts of the island. Few Dark-billed Cuckoos (Coccyzus melacoryphus), Paint-billed Crakes (Neocrex erythrops), Galapagos Doves (Zenaida galapagoensis), and Galapagos Short-eared Owls (Asio flammeus galapagoensis) were recorded. Small Ground-Finches and Small Tree-Finches were found at densities comparable to those on other Galapagos Islands, whereas densities of Galapagos Flycatchers and Yellow Warblers were higher on Floreana than on other islands. Endemic Medium Tree-Finches were confined to an area of 24 km², mainly in the highlands, but were still widespread and common in their restricted habitat, with the number of territories estimated to be between 3900 and 4700. Of 22 originally occurring landbirds on Floreana, no fewer than 10 species have either been extirpated or are likely to have been extirpated since the arrival of the first human inhabitants. The combined effects of introduced mammals, large-scale habitat destruction, and direct human persecution were responsible for the extirpation of six species during the 19th century. Three additional species have been extirpated since 1960, likely due to the introduction of the parasitic fly Philornis downsi, and this fly remains a major threat for the remaining bird species. Developing strategies for reducing the impact of these flies on the birds of the Galapagos Islands must be a high priority. In addition, habitat management and restoration, including the control of invasive plants and promotion of native tree species, will be critically important in conserving landbird populations on Floreana.

Naris deformation in Darwin’s finches: Experimental and historical evidence for a post-1960s arrival of the parasite Philornis downsi

The rate of evolution depends on the strength of selection, which may be particularly strong for introduced parasites and their naive hosts. Because natural selection acts on phenotypes and because parasites can alter host phenotype, one fruitful starting point to measure the impact of novel pathogens is to quantify parasite-induced changes to host phenotype. Our study system is Darwin’s finches on Floreana Island, Galápagos Archipelago, and the virulent fly larvae of Philornis downsi that were first discovered in Darwin’s finch nests in 1997. We use an experimental approach and measure host phenotype in parasitized and parasite-free chicks in Darwin’s small ground finch (Geospiza fuliginosa). Beak size did not differ between the two treatment groups, but naris size was 106% larger in parasitized chicks (∼3.3 mm) versus parasite-free chicks (∼1.6 mm). To test if P. downsi was present prior to the 1960s, we compared naris size in historical (1899–1962) and contemporary birds (2004–2014) on Floreana Island in small ground finches (G. fuliginosa) and medium tree finches (Camarhynchus pauper). Contemporary Darwin’s finches had significantly larger naris size (including extreme deformation), whereas historical naris size was both smaller and less variable. These findings provide the first longitudinal analysis for the extent of P. downsi-induced change to host naris size and show that Darwin’s finches, prior to the 1960s, were not malformed. Thus natural selection on altered host phenotype as a consequence of P. downsi parasitism appears to be contemporary and novel.

Linked loci and Galapagos finch size

Evolutionary Genetics![Figure][1] Medium and large ground finches diverged in beak size after a severe drought. PHOTO: © FRANS LANTING STUDIO/ALAMY STOCK PHOTO Observations of parallel evolution in the finches of the Galapagos, including body and beak size, contributed to Darwin's theories. Lamichhaney et al. carried out whole-genome sequencing of 60 Darwin's finches. These included small, medium, and large ground finches as well as small, medium, and large tree finches. A genomic region containing the HMGA2 gene correlated strongly with beak size across different species. This locus appears to have played a role in beak diversification throughout the radiation of Darwin's finches. Science , this issue p. [470][2] [1]: pending:yes [2]: /lookup/doi/10.1126/science.aad8786