Rachael Y. Dudaniec

Effects of the parasitic flies of the genus Philornis (Diptera:Muscidae) on birds

Abstract Little is known about the genus Philornis (comprising ~50 species), a group of muscid flies that parasitise birds and may be highly detrimental to host nestlings. Philornis species affect at least 115 species of bird, particularly in the Neotropics. The main distribution of Philornis is in Central and South America, extending to the southern United States. Larvae of the genus Philornis reside in bird nests and may feed on either nestling faeces (coprophagous scavengers), the blood of nestlings (semi-haematophagous parasites), or on nestling tissue and fluid (subcutaneous parasites). Depending on the species of Philornis, larval development can occur in bird faeces, in nesting material or inside nestlings. Nestling mortality depends on the species of Philornis, the intensity of infestation and nestling susceptibility, which in turn depends on the nestling species, age, brood size, body condition and the anatomical site of infestation. Consequently, variable effects of Philornis parasitism are observed in relation to nestling growth, development and fledging success. The impetus for this review is the recent discovery of Philornis downsi on the Galapagos Archipelago, combined with high Philornis-induced mortality in Darwins finches. The potential for ectoparasites such as Philornis to compromise the viability of small, isolated bird populations is highlighted by this recently documented parasite invasion.

Species collapse via hybridization in Darwin's tree finches.

Species hybridization can lead to fitness costs, species collapse, and novel evolutionary trajectories in changing environments. Hybridization is predicted to be more common when environmental conditions change rapidly. Here, we test patterns of hybridization in three sympatric tree finch species (small tree finch Camarhynchus parvulus, medium tree finch Camarhynchus pauper, and large tree finch: Camarhynchus psittacula) that are currently recognized on Floreana Island, Galápagos Archipelago. Genetic analysis of microsatellite data from contemporary samples showed two genetic populations and one hybrid cluster in both 2005 and 2010; hybrid individuals were derived from genetic population 1 (small morph) and genetic population 2 (large morph). Females of the large and rare species were more likely to pair with males of the small common species. Finch populations differed in morphology in 1852–1906 compared with 2005/2010. An unsupervised clustering method showed (a) support for three morphological clusters in the historical tree finch sample (1852–1906), which is consistent with current species recognition; (b) support for two or three morphological clusters in 2005 with some (19%) hybridization; and (c) support for just two morphological clusters in 2010 with frequent (41%) hybridization. We discuss these findings in relation to species demarcations of Camarhynchus tree finches on Floreana Island.

Love thy neighbour? Social nesting pattern, host mass and nest size affect ectoparasite intensity in Darwin’s tree finches

Social nesting behaviour is commonly associated with high prevalence and intensity of parasites in intraspecific comparisons. Little is known about the effects of interspecific host breeding density for parasite intensity in generalist host–parasite systems. Darwin’s small tree finch (Camarhynchus parvulus) on Santa Cruz Island, Galápagos Islands, nests in both heterospecific aggregations and at solitary sites. All Darwin finch species on Santa Cruz Island are infested with larvae of the invasive blood-sucking fly Philornis downsi. In this study, we test the prediction that total P. downsi intensity (the number of parasites per nest) is higher for nests in heterospecific aggregations than at solitary nests. We also examine variation in P. downsi intensity in relation to three predictor variables: (1) nest size, (2) nest bottom thickness and (3) host adult body mass, both within and across finch species. The results show that (1) total P. downsi intensity was significantly higher for small tree finch nests with many close neighbours; (2) finches with increased adult body mass built larger nests (inter- and intraspecific comparison); (3) parasite intensity increased significantly with nest size across species and in the small tree finch alone; and (4) nest bottom thickness did not vary with nest size or parasite intensity. These results provide evidence for an interaction between social nesting behaviour, nest characteristics and host mass that influences the distribution and potential impact of mobile ectoparasites in birds.

Genetic variation in the invasive avian parasite, Philornis downsi (Diptera, Muscidae) on the Galápagos archipelago

BackgroundUnderstanding the dispersal and genetic structure of invasive insects across islands is important for designing management plans that are appropriate at spatial and temporal scales. For invasive parasites, population dynamics are largely determined by the distribution and density of their host species. The introduced parasitic fly, Philornis downsi, parasitises nestlings of endemic birds on all major islands of the Galápagos archipelago. The flys high mortality and fitness impacts are of conservation concern for vulnerable and declining species of Darwins finches. Using microsatellite data in Bayesian clustering and landscape genetic analyses, we examine gene flow and dispersal in P. downsi between three islands and across habitats (highlands, lowlands) and examine for the presence of population bottlenecks. We also examine variation at the mitochondrial gene CO1 across islands to establish if cryptic species were present.ResultsBoth the mitochondrial and microsatellite data were consistent with there being a single species across islands. We found low genetic differentiation between islands and strong evidence for inter-island gene flow, or shared recent ancestry among individuals. Landscape genetic analysis identified two genetic clusters: one encompassing Santa Cruz and Isabela, and one on Floreana Island. There was no evidence of genetic differentiation between habitats and molecular variance was mainly attributable to within individuals. The combined P. downsi population was found to have undergone a population bottleneck.ConclusionPhilornis downsi populations have high connectivity within and between islands, with low levels of genetic differentiation between Floreana and the other two islands examined. The genetic bottleneck found across islands suggests there was a small founding population or few introduction events of P. downsi. The high dispersal capacity and wide habitat use of P. downsi highlights the significant threat that this parasite poses to the Galápagos avifauna. Our findings are relevant for assessing the viability of methods to control P. downsi on Galápagos, such as the sterile insect technique.

Tiliqua rugosa microsatellites: isolation via enrichment and characterisation of loci for multiplex PCR in T. rugosa and the endangered T. adelaidensis

We used an enrichment technique to isolate 18 novel di and tri microsatellites for the socially monogamous lizard Tiliqua rugosa. These loci were amplified in conjunction with previously described loci in two and three PCR multiplexes for T. rugosa and the endangered T. adelaidensis, respectively. The loci were highly polymorphic in both species, exhibiting between 2 and 32 alleles with observed heterozygosity ranging from 0.43 to 0.96. These markers will be useful for population-level analyses and can contribute to a genetic foundation for conservation strategies for the endangered T. adelaidensis.

Parasite infestation and predation in Darwin's small ground finch: contrasting two elevational habitats between islands

Contrasting ecological conditions may affect the distribution, abundance and impact of parasites and predators throughout the ranges of hosts and prey. Such patterns are evident on the archipelagos of Hawaii and the Galapagos, which vary in their distribution and abundance of avian parasites within and across islands. Previous research has documented higher intensity of parasitic fly larvae (Philornis downsi) in nests of Darwins finches on elevated islands of the Galapagos. Here we examine P. downsi intensity and predation in 71 nests of Darwins small ground finch (Geospiza fuliginosa) on Floreana Island. We found significant differences in parasite intensity, nest predation and clutch size between the lowland (0–100 m) and highland (300–400 m) habitats. Lowland finch nests had few P. downsi parasites (mean of 8 per nest), high nest predation (44% of nests) and large clutch size (3.4). Highland finch nests showed the opposite pattern, with many P. downsi parasites (40 per nest), low nest predation (17%) and small clutch size (2.5). This study suggests that the impacts of an introduced parasite are limited by its niche requirements and resource availability within and across islands. Our findings also imply that the vulnerability of bird populations to introduced parasites and predators is linked with variation in life history strategies across habitats. (Less)

Gene expression under thermal stress varies across a geographical range expansion front

Many ectothermic species are currently expanding their distributions polewards due to anthropogenic global warming. Molecular genetic mechanisms facilitating range expansion under these conditions are largely unknown, but understanding these could help mitigate expanding pests and disease vectors, or help explain why some species fail to track changing climates. Here, using RNA‐seq data, we examine genomewide changes in gene expression under heat and cold stress in the range‐expanding damselfly Ischnura elegans in northern Europe. We find that both the number of genes involved and levels of gene expression under heat stress have become attenuated during the expansion, consistent with a previously reported release from selection on heat tolerances as species move polewards. Genes upregulated under cold stress differed between core and edge populations, corroborating previously reported rapid adaptation to cooler climates at the expansion front. Expression of sixty‐nine genes exhibited a region x treatment effect; these were primarily upregulated in response to heat stress in core populations but in response to cold stress at the range edge, suggesting that some cellular responses originally adapted to heat stress may switch to cold‐stress functionality upon encountering novel thermal selection regimes during range expansion. Transcriptional responses to thermal stress involving heat‐shock and neural function genes were largely geographically conserved, while retrotransposon, regulatory, muscle function and defence gene expression patterns were more variable. Flexible mechanisms of cold‐stress response and the ability of some genes to shift their function between heat and cold stress might be key mechanisms facilitating rapid poleward expansion in insects.

Dealing with uncertainty in landscape genetic resistance models: a case of three co-occurring marsupials

Landscape genetics lacks explicit methods for dealing with the uncertainty in landscape resistance estimation, which is particularly problematic when sample sizes of individuals are small. Unless uncertainty can be quantified, valuable but small data sets may be rendered unusable for conservation purposes. We offer a method to quantify uncertainty in landscape resistance estimates using multimodel inference as an improvement over single model‐based inference. We illustrate the approach empirically using co‐occurring, woodland‐preferring Australian marsupials within a common study area: two arboreal gliders (Petaurus breviceps, and Petaurus norfolcensis) and one ground‐dwelling antechinus (Antechinus flavipes). First, we use maximum‐likelihood and a bootstrap procedure to identify the best‐supported isolation‐by‐resistance model out of 56 models defined by linear and non‐linear resistance functions. We then quantify uncertainty in resistance estimates by examining parameter selection probabilities from the bootstrapped data. The selection probabilities provide estimates of uncertainty in the parameters that drive the relationships between landscape features and resistance. We then validate our method for quantifying uncertainty using simulated genetic and landscape data showing that for most parameter combinations it provides sensible estimates of uncertainty. We conclude that small data sets can be informative in landscape genetic analyses provided uncertainty can be explicitly quantified. Being explicit about uncertainty in landscape genetic models will make results more interpretable and useful for conservation decision‐making, where dealing with uncertainty is critical.

Integrating microorganism and macroorganism dispersal: modes, techniques and challenges with particular focus on co-dispersal

ABSTRACT Whatever their size and the ecosystem they live in, all organisms may disperse at some stage of their life cycle. Dispersal dynamics are to a varying extent dependent on organismal size, life history, ecological niche, survival capacities and phylogeny. Moves towards a synthesis in dispersal ecology have focused primarily on vertebrates and higher plants, yet recent studies suggest that the dispersal of microorganisms and macroorganisms has much more in common than previously assumed. The dispersal of one organism enables co-dispersal for many others, smaller in size. There is an increasing need for a more integrated approach to study dispersal within the context of organismal interactions and their environments. Such an approach is facilitated by recent developments of powerful indirect techniques that enable tracking of microorganisms and macroorganisms over multiple spatial and temporal scales. Likewise, dispersal modelling and theoretical models of the consequences of dispersal can inspire empirical studies across the entire size spectrum. Simultaneously studying the relationships between dispersal of microorganisms and macroorganisms, and accounting for dispersal through time and space, will allow us to better understand the functioning and dynamics of communities and ecosystems, and to make better predictions of future dispersal patterns, changes in biodiversity and connectivity.

Isolation, characterization and multiplex polymerase chain reaction of novel microsatellite loci for the avian parasite Philornis downsi (Diptera: Muscidae)

An enrichment technique was used to isolate 11 di‐, tri‐, and tetra microsatellites for the parasitic fly Philornis downsi (Diptera: Muscidae). These loci were polymerase chain reaction amplified in singleplexes or two‐plexes for P. downsi. The loci showed low to moderate polymorphism, exhibited between three and four alleles, and observed heterozygosity ranged from 0.05 to 0.86. These new markers will be useful for population‐level and paternity analyses and will provide valuable information about the ecology of this high‐impact parasite of vulnerable bird species.