Insular nestling growth and its relationship to parental care effort in Silvereyes, Zosterops lateralis

The rate at which avian offspring grow can have consequences for survival and reproductive output as an adult and is known to vary widely among and within species. This variation is thought to be an adaptive response to cope with environmental variation. The principal environmental factors affecting growth are food availability and predation risk, predominantly acting as constraints on parental care. Islands pose an interesting system to explore growth rate dynamics, because the characteristic insular features of high population densities and depauperate predator diversity translate into a potentially food limited environment with low predation risk. Insular environments typically produce populations with slower life history strategies and larger body size in small-bodied species, features that are likely to be mediated by growth rate. We describe the nestling growth of an insular population of Silvereyes and how it relates to parental size and parental care. Neither parental size nor parental care explained insular nestling growth rate, even though food acquisition is thought to underpin avian growth rates. This could be due to a mismatch between acquisition and allocation of resources by nestlings. Compared to a small number of mainland nestlings, the island growth curve asymptotes were significantly larger and inflection points much later, but insular growth rates were only marginally slower. This is in line with proposed insular adaptations required to produce larger body size on islands, however understanding the mechanism underlying this pattern will require data on the relationship between food quality and acquisition, and physiological allocation of resources within individuals

Geographical surrogates of genetic variation for selecting island populations for conservation

Aim: Threatened species often exist in small numbers in isolated populations. Limited financial resources usually constrain conservationists to allocate funds to a subset of these populations. Because obtaining information required to maximize the amount of genetic and phenotypic variation protected can be costly and time-consuming, the utility of surrogates should be explored. This study tests the efficacy of three simple and cost-effective geographical measures in capturing genetic and phenotypic variation in fragmented populations when setting conservation priorities. Location: Vanuatu archipelago. Methods: We used neutral genetic data (mtDNA and microsatellites) and morphometric data (a proxy for functional variation) for two bird species displaying different patterns of regional population genetic structure: Zosterops flavifrons and Zosterops lateralis. We tested the performance of three geographical surrogates (maximizing: geographical distance between islands; area of islands; geographical representation of islands), in representing divergence between and diversity within populations, constrained to the number of islands being protected. Results: Maximizing geographical separation of sites provided the best surrogate for a constrained budget ( 50% of the populations), the spatially most representative sites were often more effective. Selecting islands based on size retained about half of within-population genetic diversity; however, this was not much higher than selecting the islands randomly. Main conclusions: The ability of surrogates to capture genetic or phenotypic variation varied depending on the species, genetic markers and number of islands selected. While imperfect, selection of populations based on simple geographical surrogates for genetic and phenotypic variation will generally be better than random selection for conserving the evolutionary potential of threatened populations when time and money limit a more thorough and direct analyses of genetic and phenotypic variation

Limited domestic introgression in a final refuge of the wild pigeon

Domesticated animals have been culturally and economically important throughout history. Many of their ancestral lineages are extinct or genetically en dangered following hybridization with domesticated relatives. Consequently, they have been understudied compared to the ancestral lineages of domestic plants. The domestic pigeon Columba livia, which was pivotal in Darwin’s studies, has maintained outsized cultural significance. Its role as a model organism spans the fields of behavior, genetics, and evolution. Domestic pigeons have hybridized with their progenitor, the Rock Dove, rendering the latter of dubious genetic sta tus. Here, we use genomic and morphological data from the putative Rock Doves of the British Isles to identify relictual undomesticated populations. We reveal that Outer Hebridean Rock Doves have experienced minimal levels of introgres sion. Our results outline the contemporary status of these wild pigeons, high lighting the role of hybridization in the homogenization of genetic lineages.publishedVersio

A simple dynamic model explains the diversity of island birds worldwide

International audienc

The influence of vagrant hosts and weather patterns on the colonization and persistence of blood parasites in an island bird

Aim: Colonization and extinction are important drivers of island biogeography, but they are difficult to study. We used a long-term dataset to determine the mechanisms that contribute to colonization and persistence for vector-borne blood parasites in an island population of birds that regularly receives infected vagrant conspecifics and wind-assisted potential vectors from the mainland. Location: Heron Island (Australia) and the Australian mainland. Methods: We determined the prevalence, temporal stability and host-specificity of Haemoproteus and Plasmodium parasites in resident and mainland-vagrant silvereyes (Zosterops lateralis) on Heron Island over seven years (1999-2003 and 2012-2013). We carried out simulations using mainland infection data and vagrant arrival scenarios to test whether transmission from vagrants influences infection patterns in island residents. We tested whether variation in island parasite prevalence was predicted by abiotic factors associated with vector breeding and dispersal. Results: Parasite prevalence and composition on the island varied considerably across years. Host-specialist Haemoproteus species exhibited lower prevalence than expected and frequent absence despite a high probability of arriving via vagrants. In contrast, host-generalist Plasmodium species exhibited a low probability of arriving via vagrants but were temporally persistent in island silvereyes. Increases in prevalence and diversity of Plasmodium species were associated with episodes of offshore winds. Main conclusions: This study shows that parasites that are abundant in source populations do not necessarily exhibit increased colonization success via vagrant host movement. Vagrant silvereyes are not likely to shape infection patterns in island-resident silvereyes. Instead, indirect evidence of associations between weather patterns and parasite dynamics suggests that the insular parasite community may be limited by vector establishment. Our results support the hypothesis that host-specificity is important in determining a parasite's ability to persist on islands, with host-specialists at greater risk of failing to establish after their initial arrival

Data from: The relative roles of cultural drift and acoustic adaptation in shaping syllable repertoires of island bird populations change with time since colonization

In birds, song divergence often precedes and facilitates divergence of other traits. We assessed the relative roles of cultural drift, innovation and acoustic adaptation in divergence of island bird dialects, using silvereyes (Zosterops lateralis). In recently colonized populations, syllable diversity was not significantly lower than source populations, shared syllables between populations decreased with increasing number of founder events and dialect variation displayed contributions from both habitat features and drift. The breadth of multivariate space occupied by recently colonized Z. l. lateralis populations was comparable to evolutionarily old forms that have diverged over thousands to hundreds of thousands of years. In evolutionarily old subspecies, syllable diversity was comparable to the mainland and the amount of variation in syllable composition explained by habitat features increased by two- to three-fold compared to recently colonized populations. Together these results suggest that cultural drift influences syllable repertoires in recently colonized populations, but innovation likely counters syllable loss from colonization. In evolutionarily older populations, the influence of acoustic adaptation increases, possibly favoring a high diversity of syllables. These results suggest that the relative importance of cultural drift and acoustic adaptation changes with time since colonization in island bird populations, highlighting the value of considering multiple mechanisms and timescale of divergence when investigating island song divergence

Data from: Migration strategy and pathogen risk: non-breeding distribution drives malaria prevalence in migratory waders

Pathogen exposure has been suggested as one of the factors shaping the myriad of migration strategies observed in nature. Two hypotheses relate migration strategies to pathogen infection: the ‘avoiding the tropics hypothesis’ predicts that pathogen prevalence and transmission increase with decreasing non-breeding (wintering) latitude, while the “habitat selection hypothesis” predicts lower pathogen prevalence in marine than in freshwater habitats. We tested these scarcely investigated hypotheses by screening wintering and resident wading shorebirds (Charadriiformes) for avian malaria blood parasites (Plasmodium and Haemoproteus spp.) along a latitudinal gradient in Australia. We sequenced infections to determine if wintering migrants share malaria parasites with local shorebird residents, and we combined prevalence results with published data in a global comparative analysis. Avian malaria prevalence in Australian waders was 3.56% and some parasite lineages were shared between wintering migrants and residents, suggesting active transmission at wintering sites. In the global dataset, avian malaria prevalence was highest during winter and increased with decreasing wintering latitude, after controlling for phylogeny. The latitudinal gradient was stronger for waders that use marine and freshwater habitats (marine + freshwater) than for marine-restricted species. Marine + freshwater wader species also showed higher overall avian malaria parasite prevalence than marine-restricted species. By combining datasets in a global comparative analysis, we provide empirical evidence that migratory waders avoiding the tropics during the non-breeding season experience a decreased risk of malaria parasite infection. We also find global support for the hypothesis that marine-restricted shorebirds experience lower parasite pressures than shorebirds that also use freshwater habitats. Our study indicates that pathogen transmission may be an important driver of site selection for non-breeding migrants, a finding that contributes new knowledge to our understanding of how migration strategies evolve

All syllables recorded and categorized from study

This file contains acoustic details of all syllables recorded from all Zosterops lateralis individuals and populations included in the current study. Data was gathered by DAP, all acoustic measurements were made in RavenPro 1.4 (Cornell Lab of Ornithology)