Native fly parasites are the principal cause of nestling mortality in endangered Tasmanian pardalotes

Conservation of parasites: A primer

Although parasites make up a substantial proportion of the biotic component of ecosystems, in terms of both biomass and number of species, they are rarely considered in conservation planning, except where they are thought to pose a threat to the conservation of their hosts. In this review, we address a number of unresolved questions concerning parasite conservation. Arguments for conserving parasite species refer to the intrinsic value conferred by their evolutionary heritage and potential, their functional role in the provision of ecosystem services, and their value as indicators of ecosystem quality. We propose that proper consideration of these arguments mean that it is not logically defensible to automatically exclude parasite species from conservation decisions; rather, endangered hosts and parasites should be considered together as a threatened ecological community. The extent to which parasites are threatened with extinction is difficult to estimate with any degree of confidence, because so many parasite species have yet to be identified and, even for those which have been formally described, we have limited information on the factors affecting their distribution and abundance. This lack of ecological information may partially explain the under-representation of parasites on threatened species lists. Effective conservation of parasites requires maintaining access to suitable hosts and the ecological conditions that permit successful transmission between hosts. When implementing recovery plans for threatened host species, this may be best achieved by attempting to restore the ecological conditions that maintain the host and its parasite fauna in dynamic equilibrium. Ecosystem-centred conservation may be a more effective strategy than species-centred (or host-parasite community-centred) approaches for preventing extinction of parasites, but the criteria which are typically used to identify protected areas do not provide information on the ecological conditions required for effective transmission. We propose a simple decision tree to aid the identification of appropriate conservation actions for threatened parasites.

Effects of forest loss and fragmentation on bat-ectoparasite interactions

Human land use causes habitat loss and fragmentation, influencing host-parasite associations through changes in infestation rates, host mortality and possibly local extinction. Bat-ectoparasite interactions are an important host-parasite model possibly affected by such changes, as this system acts as both reservoirs and vectors of several pathogens that can infect different wild and domestic species. This study aimed to assess how the prevalence and abundance of bat ectoparasites respond to forest loss, fragmentation, and edge length. Bats and ectoparasites were sampled at twenty sites, forming a gradient of forest cover, in southwestern Brazil during two wet (2015 and 2016) and two dry (2016 and 2017) seasons. Effects of landscape metrics on host abundance as well as parasite prevalence and abundance were assessed through structural equation models. Nine host-parasite associations provided sufficient data for analyses, including one tick and eight flies on four bat species. Forest cover positively influenced the prevalence or abundance of three fly species, but negatively influenced one fly and the tick species. Prevalence or abundance responded positively to edge length for three fly species, and negatively for the tick. In turn, number of fragments influenced the prevalence or abundance of four fly species, two positively and two negatively. Our results support species-specific responses of ectoparasites to landscape features, and a tendency of host-generalist ticks to benefit from deforestation while most host-specialist flies are disadvantaged. Differences in host traits and abundance, along with parasite life cycles and environmental conditions, are possible explanations to our findings.

Using conservation genetics to prioritise management options for an endangered songbird

Genetic data can be highly informative for answering questions relevant to practical conservation efforts, but remain one of the most neglected aspects of species recovery plans. Framing genetic questions with reference to practical and tractable conservation objectives can help bypass this limitation of the application of genetics in conservation. Using a single-nucleotide polymorphism dataset from reduced-representation sequencing (DArTSeq), we conducted a genetic assessment of remnant populations of the endangered forty-spotted pardalote (Pardalotus quadragintus), a songbird endemic to Tasmania, Australia. Our objectives were to inform strategies for the conservation of genetic diversity in the species and estimate effective population sizes and patterns of inter-population movement to identify management units relevant to population conservation and habitat restoration. We show population genetic structure and identify two small populations on mainland Tasmania as 'satellites' of larger Bruny Island populations connected by migration. Our data identify management units for conservation objectives relating to genetic diversity and habitat restoration. Although our results do not indicate the immediate need to genetically manage populations, the small effective population sizes we estimated for some populations indicate that they are vulnerable to genetic drift, highlighting the urgent need to implement habitat restoration to increase population size and to conduct genetic monitoring. We discuss how our genetic assessment can be used to inform management interventions for the forty-spotted pardalote and show that by assessing contemporary genetic aspects, valuable information for conservation planning and decision-making can be produced to guide actions that account for genetic diversity and increase chances of recovery in species of conservation concern.

Larval morphology of the avian parasitic genus Passeromyia: playing hide and seek with a parastomal bar

The enigmatic larvae of the Old World genus Passeromyia Rodhain & Villeneuve, 1915 (Diptera: Muscidae) inhabit the nests of birds as saprophages or as haematophagous agents of myiasis among nestlings. Using light microscopy, confocal laser scanning microscopy and scanning electron microscopy, we provide the first morphological descriptions of the first, second and third instar of P. longicornis (Macquart, 1851) (Diptera: Muscidae), the first and third instar of P. indecora (Walker, 1858) (Diptera: Muscidae), and we revise the larval morphology of P. heterochaeta (Villenueve, 1915) (Diptera: Muscidae) and P. steini Pont, 1970 (Diptera: Muscidae). We provide a key to the third instar of examined species (excluding P. steini and P. veitchi Bezzi, 1928 (Diptera: Muscidae)). Examination of the cephaloskeleton revealed paired rod-like sclerites, named 'rami', between the lateral arms of the intermediate sclerite in the second and third instar larva. We reveal parastomal bars fused apically with the intermediate sclerite, the absence of which has so far been considered as apomorphic for second and third instar muscid larvae. Examination of additional material suggests that modified parastomal bars are not exclusive features of Passeromyia but occur widespread in the Muscidae, and rami may occur widespread in the Cyclorrhapha.

Is the grass always greener on the other side? Weak relationships between vegetation cover and parasitic fly infestations

Understanding parasite-host ecology is increasingly important for conservation efforts in a changing world. Parasitic nest flies in the genus Philornis (Diptera: Muscidae) have been implicated in the decline of endemic island species and are also known to negatively impact breeding success of the critically endangered Ridgway's hawk (B. ridgwayi) on the island of Hispaniola. Despite the importance of these effects on hosts, and extensive research of Philornis downsi in the Galápagos, the ecology of most species of philornid nest flies is poorly understood. We examined biotic factors related to Philornis pici infestations of nestling Ridgway's hawks in the Dominican Republic, where both fly and hawk are native. We found grass-cover was negatively associated with P. pici infestations, while coverage and height of other vegetation classes (tree, shrub, herbaceous, and bare ground) had no association, which is interesting considering recent landscape-level changes to Ridgway's hawk habitat. Anthropogenic activities in Los Haitises National Park, the last strong-hold of Ridgway's hawk, have shifted the landscape from primary forest to a fragmented secondary forest with smallholder or subsistence farms and grassy patches. New information on the ecology of nest flies in their native habitat can inform conservation efforts and allow us to make recommendations for future research.

Use of anthropogenic-related nest material and nest parasite prevalence have increased over the past two centuries in Australian birds

Global plastic production has increased exponentially since the 1940s, resulting in the increased presence of anthropogenic debris in the environment. Recent studies have shown that birds incorporate anthropogenic debris into their nests, which can reduce nest ectoparasite loads. However, we know little about the long-term history of interactions among birds, anthropogenic debris, and ectoparasites. Our study took a unique approach to address this issue by determining the prevalence of anthropogenic debris and ectoparasitic nest flies (Protocalliphora and Passeromyia spp.) in 893 bird nests from 224 species between 1832 and 2018, which were sourced from Australian museum collections. The prevalence of anthropogenic material increased from approximately 4% in 1832 to almost 30% in 2018. This change was driven by an increase in the incorporation of synthetic rather than biodegradable anthropogenic debris (by 2018 ~ 25% of all nests contained synthetics), with the first synthetic item being found in a nest from 1956 in the city of Melbourne. Nest parasite prevalence increased over time but contrary to other studies, there was no relationship between habitat type or anthropogenic material and parasite presence. Our study is the first to use museum specimens to quantify temporal and spatial impacts of anthropogenic material on birds, the results of which justifies contemporary concerns regarding the ubiquitous nature of human impacts on terrestrial wildlife.

Sex-biased parasitism and expression of a sexual signal

Given that sexual signals are often expressed more highly in one sex than the other, they can impose a sex-specific cost of reproduction through parasitism. The two primary paradigms regarding the relationship of parasites to sexual signals are the good genes hypothesis and the immunocompetence handicap hypothesis; however, there are other ecological, morphological and energetic factors that might influence parasite infections in a sex-specific fashion. We tested the relationship between expression of a sexual signal (the dewlap) and ecological, morphological and energetic factors mediating ectoparasite (mite) load between male and female Panamanian slender anoles (Anolis apletophallus). We found that males were more highly parasitized than females because of the preponderance of ectoparasites on the larger dewlap of males. Indeed, ectoparasite infection increased with both body size and dewlap size in males but not in females, and parasite infection was related to energy storage in a sex-specific fashion for the fat bodies, liver and gonads. Our work and previous work on testosterone in anoles suggests that this pattern did not arise solely from immunosuppression by testosterone, but that mites prefer the dewlap as an attachment site. Thus, the expression of this sexual signal could incur a fitness cost that might structure life-history trade-offs.

Sub-lethal effects of permethrin exposure on a passerine: implications for managing ectoparasites in wild bird nests

Permethrin is increasingly used for parasite control in bird nests, including nests of threatened passerines. We present the first formal evaluation of the effects of continued permethrin exposure on the reproductive success and liver function of a passerine, the zebra finch (Taeniopygia guttata), for two generations. We experimentally treated all nest material with a 1% permethrin solution or a water control and provided the material to breeding finches for nest building. The success of two consecutive clutches produced by the parental generation and one clutch produced by first-generation birds were tracked. Finches in the first generation were able to reproduce and fledge offspring after permethrin exposure, ruling out infertility. Permethrin treatment had no statistically significant effect on the number of eggs laid, number of days from clutch initiation to hatching, egg hatch rate, fledgling mass or nestling sex ratio in either generation. However, treating nest material with permethrin significantly increased the number of hatchlings in the first generation and decreased fledgling success in the second generation. Body mass for hatchlings exposed to permethrin was lower than for control hatchlings in both generations, but only statistically significant for the second generation. For both generations, an interaction between permethrin treatment and age significantly affected nestling growth. Permethrin treatment had no effect on liver function for any generation. Permethrin was detected inside 6 of 21 exposed, non-embryonated eggs (28.5% incidence; range: 693-4781 ng of permethrin per gram of dry egg mass). Overall, results from exposing adults, eggs and nestlings across generations to permethrin-treated nest material suggest negative effects on finch breeding success, but not on liver function. For threatened bird conservation, the judicious application of this insecticide to control parasites in nests can result in lower nestling mortality compared to when no treatment is applied. Thus, permethrin treatment benefits may outweigh its sub-lethal effects.