Transcriptomic responses of Galápagos finches to avian poxvirus infection.

Emerging pathogens can have devastating effects on naïve hosts, but disease outcomes often vary among host species. Comparing the cellular response of different hosts to infection can provide insight into mechanisms of host defence. Here, we used RNA-seq to characterize the transcriptomic response of Darwin's finches to avian poxvirus, a disease of concern in the Galápagos Islands. We tested whether gene expression differs between infected and uninfected birds, and whether transcriptomic differences were related either to known antiviral mechanisms and/or the co-option of the host cellular environment by the virus. We compared two species, the medium ground finch (Geospiza fortis) and the vegetarian finch (Platyspiza crassirostris), to determine whether endemic Galápagos species differ in their response to pox. We found that medium ground finches had a strong transcriptomic response to infection, upregulating genes involved in the innate immune response including interferon production, inflammation, and other immune signalling pathways. In contrast, vegetarian finches had a more limited response, and some changes in this species were consistent with viral manipulation of the host's cellular function and metabolism. Many of the transcriptomic changes mirrored responses documented in model and in vitro studies of poxviruses. Our results thus indicate that many pathways of host defence against poxviruses are conserved among vertebrates and present even in hosts without a long evolutionary history with the virus. At the same time, the differences we observed between closely related species suggests that some endemic species of Galápagos finch could be more susceptible to avian pox than others.

Resumen Los patógenos emergentes pueden generar efectos devastadores en huéspedes nuevos, sin embargo, los efectos de la enfermedad varían según el tipo de huésped. Al comparar la respuesta celular de las diferentes especies afectadas se puede determinar el mecanismo de defensa del huésped, y la base de susceptibilidad a la enfermedad. A través de la secuenciación de ARN, se caracterizó la respuesta de transcripción de viruela aviar, un virus introducido, en los pinzones de Darwin. Probamos si una expresión genética difiere entre aves infectadas y no infectadas, y si la diferencia de transcripción estaba relacionada con mecanismos antivirales conocidos y/o con la co-opción del entorno celular del hospedero por parte del virus. Comparamos dos especies, pinzón mediano de tierra (Geospiza fortis) y pinzón vegetariano (Platyspiza crassirostris), para determinar si estas especies tienen variación en sus respuestas al mismo patógeno nuevo. Encontramos que el pinzón mediano de tierra presenta una fuerte respuesta de transcripción a la infección, involucrando a la regulación de genes inmunes que incluyen la producción de interferón, inflamación y otras vías de respuesta inmunológica. A diferencia del pinzón vegetariano que presenta una respuesta más limitada a la infección. Nuestros resultados revelaron evidencia de manipulación viral en la función celular del hospedador y en el metabolismo del huésped, proporcionando información sobre como la viruela aviar afecta al huésped. Varias de las respuestas de transcripción a la infección se ven reflejadas en estudios in vitro y en modelos animales, lo cual indica que muchas vías de defensa del huésped contra la viruela son conservadas en vertebrados incluso en huéspedes sin una historia evolutiva larga del virus. Al mismo tiempo, la variación que observamos entre especies estrechamente relacionadas indica que algunas especies endémicas de pinzones de Galápagos podrían ser más susceptibles a la viruela aviar que otras especies.

Habitat restoration to conserve the Little Vermilion Flycatcher on Santa Cruz Island, Galapagos.

The endemic Little Vermilion Flycatcher (LVF), Pyrocephalus nanus, has suffered a drastic decline on Santa Cruz Island, where it was common 30 years ago. Currently, less than 40 individuals remain in the last remnants of natural humid forest in the Galapagos National Park on this island. This small population has low reproductive success, which is contributing to its decline in Santa Cruz. Previous studies have identified Avian Vampire Fly, Philornis downsi, parasitism, changes in food sources, and habitat alteration as threats to this species. In Santa Cruz, invasive plants may strongly affect the reproductive success of the LVF because they limit accessibility to prey near the ground, the preferred foraging niche of these birds. Since 2019, we restored the vegetation in seven plots of one hectare each by removing invasive blackberry plants and other introduced plant species. In all nests that reached late incubation, we also reduced the number of Avian Vampire Fly larvae. In this study, we compared foraging and perch height, pair formation, incubation time and reproductive success between managed and unmanaged areas. As predicted, we found significantly lower foraging height and perch height in 2021 in managed areas compared to unmanaged areas. In 2020, daily failure rate (DFR) of nests in the egg stage did not differ between management types; however, in 2021, DFR in the egg stage was significantly lower in managed areas than in unmanaged areas. The DFR during the nestling stage was similar between managed and unmanaged areas in 2020, but in 2021, only nests in managed areas reached the nestling stage. Females brooded significantly more during the incubation phase in managed areas. Additionally, we found significantly higher reproductive success in managed areas compared to unmanaged areas in 2021, but not in 2020. Habitat restoration is a long-term process and these findings suggest that habitat management positively affects this small population in the long term.

Prevalence of Toxoplasma gondii in Galapagos birds: Inference of risk factors associated with diet.

Toxoplasma gondii is a zoonotic intracellular parasite of particular concern in the conservation of wildlife due to its ability to infect all homeotherms and potentially cause acute fatal disease in naive species. In the Galapagos (Ecuador), an archipelago composed of more than a hundred islets and islands, the presence of T. gondii can be attributed to human-introduced domestic cats, but little is known about its transmission in wildlife populations. We compared the prevalence of antibodies against T. gondii in sympatric Galapagos wild bird species that differ in diet and contact with oocyst-contaminated soil to determine the relative importance of trophic habits as an exposure factor. Plasma samples were obtained from 163 land birds inhabiting Santa Cruz, one of the cat-inhabited islands, and from 187 seabirds breeding in cat-free surrounding islands (Daphne Major, North Seymour, and South Plaza). These samples were tested for the presence of T. gondii antibodies using the modified agglutination test (MAT ≥ 1:10). All seven species of land birds and 4/6 species of seabirds presented seropositive results. All great frigatebirds (Fregata minor) (N = 25) and swallow-tailed gulls (Creagrus furcatus) (N = 23) were seronegative. Prevalence ranged from 13% in Nazca boobies (Sula granti) to 100% in Galapagos mockingbirds (Mimus parvulus). It decreased from occasional carnivores (63.43%) to granivores-insectivores (26.22%), and strict piscivores (14.62%). These results indicate that the consumption of tissue cysts poses the highest risk of exposure to T. gondii for Galapagos birds, followed by the ingestion of plants and insects contaminated by oocysts as important transmission pathways.

Behavior of the Avian Parasite Philornis downsi (Diptera: Muscidae) in and Near Host Nests in the Galapagos Islands.

The Avian Vampire Fly, Philornis downsi, has invaded the Galapagos Islands, where it causes high mortality of endemic and native landbird species, including most species of Darwin's finches. Control methods are under development, but key information is missing about the reproductive biology of P. downsi and the behavior of flies in and near nests of their hosts. We used external and internal nest cameras to record the behavior of P. downsi adults within and outside nests of the Galapagos Flycatcher, Myiarchus magnirostris, throughout all stages of the nesting cycle. These recordings showed that P. downsi visited flycatcher nests throughout the day with higher fly activity during the nestling phase during vespertine hours. The observations also revealed that multiple P. downsi individuals can visit nests concurrently, and that there are some interactions among these flies within the nest. Fly visitation to nests occurred significantly more often while parent birds were away from the nest than in the nest, and this timing appears to be a strategy to avoid predation by parent birds. We report fly mating behavior outside the nest but not in the nest cavity. We discuss the relevance of these findings for the adaptive forces shaping P. downsi life history strategies as well as rearing and control measures. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10905-021-09789-7.

Darwin's finches treat their feathers with a natural repellent.

Darwin's finches are highly innovative. Recently we recorded for the first time a behavioural innovation in Darwin's finches outside the foraging context: individuals of four species rubbed leaves of the endemic tree Psidium galapageium on their feathers. We hypothesised that this behaviour serves to repel ectoparasites and tested the repellency of P. galapageium leaf extracts against parasites that negatively affect the fitness of Darwin's finches, namely mosquitoes and the invasive hematophagous fly Philornis downsi. Mosquitoes transmit pathogens which have recently been introduced by humans and the larvae of the fly suck blood from nestlings and incubating females. Our experimental evidence demonstrates that P. galapageium leaf extracts repel both mosquitoes and adult P. downsi and also inhibit the growth of P. downsi larvae. It is therefore possible that finches use this plant to repel ectopoarasites.

Invasive parasites, habitat change and heavy rainfall reduce breeding success in Darwin's finches.

Invasive alien parasites and pathogens are a growing threat to biodiversity worldwide, which can contribute to the extinction of endemic species. On the Galápagos Islands, the invasive parasitic fly Philornis downsi poses a major threat to the endemic avifauna. Here, we investigated the influence of this parasite on the breeding success of two Darwin's finch species, the warbler finch (Certhidea olivacea) and the sympatric small tree finch (Camarhynchus parvulus), on Santa Cruz Island in 2010 and 2012. While the population of the small tree finch appeared to be stable, the warbler finch has experienced a dramatic decline in population size on Santa Cruz Island since 1997. We aimed to identify whether warbler finches are particularly vulnerable during different stages of the breeding cycle. Contrary to our prediction, breeding success was lower in the small tree finch than in the warbler finch. In both species P. downsi had a strong negative impact on breeding success and our data suggest that heavy rain events also lowered the fledging success. On the one hand parents might be less efficient in compensating their chicks' energy loss due to parasitism as they might be less efficient in foraging on days of heavy rain. On the other hand, intense rainfalls might lead to increased humidity and more rapid cooling of the nests. In the case of the warbler finch we found that the control of invasive plant species with herbicides had a significant additive negative impact on the breeding success. It is very likely that the availability of insects (i.e. food abundance)is lower in such controlled areas, as herbicide usage led to the removal of the entire understory. Predation seems to be a minor factor in brood loss.

Evolutionary dead end in the Galápagos: divergence of sexual signals in the rarest of Darwin's finches.

Understanding the mechanisms underlying speciation remains a challenge in evolutionary biology. The adaptive radiation of Darwin's finches is a prime example of species formation, and their study has revealed many important insights into evolutionary processes. Here, we report striking differences in mating signals (songs), morphology and genetics between the two remnant populations of Darwin's mangrove finch Camarhynchus heliobates, one of the rarest species in the world. We also show that territorial males exhibited strong discrimination of sexual signals by locality: in response to foreign songs, males responded weaker than to songs from their own population. Female responses were infrequent and weak but gave approximately similar results. Our findings not only suggest speciation in the mangrove finch, thereby providing strong support for the central role of sexual signals during speciation, but they have also implications for the conservation of this iconic bird. If speciation is complete, the eastern species will face imminent extinction, because it has a population size of only 5-10 individuals.

How to save the rarest Darwin's finch from extinction: the mangrove finch on Isabela Island.

Habitat destruction and predation by invasive alien species has led to the disappearance of several island populations of Darwin's finches but to date none of the 13 recognized species have gone extinct. However, driven by rapid economic growth in the Galápagos, the effects of introduced species have accelerated and severely threatened these iconic birds. The critically endangered mangrove finch (Camarhynchus heliobates) is now confined to three small mangroves on Isabela Island. During 2006-2009, we assessed its population status and monitored nesting success, both before and after rat poisoning. Population size was estimated at around only 100 birds for the two main breeding sites, with possibly 5-10 birds surviving at a third mangrove. Before rat control, 54 per cent of nests during incubation phase were predated with only 18 per cent of nests producing fledglings. Post-rat control, nest predation during the incubation phase fell to 30 per cent with 37 per cent of nests producing fledglings. During the nestling phase, infestation by larvae of the introduced parasitic fly (Philornis downsi) caused 14 per cent additional mortality. Using population viability analysis, we simulated the probability of population persistence under various scenarios of control and showed that with effective management of these invasive species, mangrove finch populations should start to recover.