Considering extinction of dependent species during translocation, ex situ conservation, and assisted migration of threatened hosts

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.

Using ensemble modeling to predict the impacts of assisted migration on recipient ecosystems

Assisted migration is a controversial conservation measure that aims to protect threatened species by moving part of their population outside its natural range. Although this could save species from extinction, it also introduces a range of risks. The magnitude of the threat to recipient ecosystems has not been investigated quantitatively, despite being the most common criticism leveled at the action. We used an ensemble modeling framework to estimate the risks of assisted migration to existing species within ecosystems. With this approach, we calculated the consequences of an assisted migration project across a very large combination of translocated species and recipient ecosystems. We predicted the probability of a successful assisted migration and the number of local extinctions would result from establishment of the translocated species. Using an ensemble of 1.5×106 simulated 15-species recipient ecosystems, we estimated that translocated species will successfully establish in 83% of cases if introduced to stable, high-quality habitats. However, assisted migration projects were estimated to cause an average of 0.6 extinctions and 5% of successful translocations triggered 4 or more local extinctions. Quantifying the impacts to species within recipient ecosystems is critical to help managers weigh the benefits and negative consequences of assisted migration.

Coprological Survey of Protostrongylid Infections in Antelopes from Souss-Massa National Park (Morocco)

Protostrongylids, small nematode lungworms, are an integral part of the wild ruminant helminth community, which can damage animals' health when they are held in captivity or semi-captive conditions. The Sahelo-Saharan antelope species dorcas gazelle (Gazella dorcas), the scimitar-horned oryx (Oryx dammah), and the addax (Addax nasomacculatus), reintroduced to Souss-Massa National Park in Morocco, could be host to many species of Protostrongylids. This study was conducted from January to July 2015 to identify infecting parasite species, and determine their prevalence and abundance in all three antelope species. A total of 180 individual fecal samples were collected, morphologically examined by the Baermann technique, and molecularly identified by PCR amplification and sequencing of the second internal transcribed spacer region of the rDNA (ITS-2). Two parasite species were found in the three antelope populations: Muellerius capillaris and Neostrongylus linearis. The prevalence scores recorded for M. capillaris were 98.40 % in the addax, 96.70 % in dorcas gazelle, and 28.40 % in the oryx. The prevalence rates of N. linearis were 60 % in the addax, 23.40 % in dorcas gazelle, and 90 % in the oryx. Excreted larvae were quantified by LPG (larvae per gram) counting: for M. capillaris, the LPG mean values were 92.94 in the addax, 133.09 in dorcas gazelle, and 1.48 in the oryx; and for N. linearis, the LPG mean values were 6.02 in the addax, 1.37 in dorcas gazelle, and 32.81 in the oryx. These findings indicate that the three species of antelopes are infected with Muellerius capillaris and Neostrongylus linearis to varying degrees in intensity and prevalence.

Altered parasite community structure in an endangered marsupial following translocation

Fauna translocations play an integral role in the management of threatened wildlife, though we are limited by our understanding of how the host-parasite community changes during translocation. During this longitudinal field-based study, we monitored gastrointestinal, blood-borne and ectoparasite taxa infecting woylies (Bettongia penicillata) for up to 12 months following two fauna translocations to supplement existing wild woylie populations in three different sites (Dryandra, Walcott and Warrup East) within the south-west of Western Australia. We aimed to (a) identify changes in parasite community structure of both translocated and resident woylies following translocation; and (b) evaluate the efficacy of ivermectin treatment in translocated hosts. Destination site and time since translocation had the strongest effects on parasite prevalence and mean faecal egg counts following translocation. Ivermectin treatment did not significantly reduce parasite prevalence or mean faecal egg counts in treated hosts. Prior to translocation, parasite community composition differed significantly between woylies selected for translocation and resident woylies within each release site. Following translocation, the parasite communities of translocated and resident hosts converged to become more similar over time, with loss of parasite taxa and novel host-parasite associations emerging. This is the first study to examine changes to the broader parasite community in translocated and resident animals following translocation. The dominant site-specific response of parasites following translocation reinforces the importance of incorporating parasite studies to enhance our fundamental understanding of perturbations in host-parasite systems during translocation, in particular the site-level drivers of parasite dynamics.

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Perturbations to host-parasite systems during translocation are poorly understood.

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Parasite dynamics were strongly impacted by site and time since translocation.

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The parasite communities of translocated and resident hosts converged over time.

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Ivermectin treatment had no significant impact on target parasites.

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Translocation protocols should consider the intrinsic biodiversity value of parasites.

Increased Trypanosoma spp. richness and prevalence of haemoparasite co-infection following translocation

Background

Understanding how fauna translocation and antiparasitic drug treatment impact parasite community structure within a host is vital for optimising translocation outcomes. Trypanosoma spp. and piroplasms (Babesia and Theileria spp.) are known to infect Australian marsupials, including the woylie (Bettongia penicillata). However relatively little is known about these haemoparasites, or how they respond to management practices such as translocation. We monitored haemoparasites infecting woylies for up to 12 months during two fauna translocations to supplement existing woylie populations in three different sites (Dryandra, Walcott and Warrup East) within south-western Australia between 2014 and 2016, with the aim of investigating (i) how haemoparasite prevalence, Trypanosoma spp. richness and Trypanosoma spp. community composition varied over time and between different sites following translocation; and (ii) whether ivermectin treatment indirectly impacts haemoparasite prevalence. Using molecular methods, 1211 blood samples were screened for the presence of trypanosomes, and a subset of these samples (n = 264) were also tested for piroplasms.

Results

Trypanosomes and piroplasms were identified in 55% and 94% of blood samples, respectively. We identified five Trypanosoma species, two Theileria species, a single species of Babesia and a novel Bodo species. Trypanosoma spp. richness and the prevalence of haemoparasite co-infection increased after translocation. Prior to translocation, Trypanosoma spp. community composition differed significantly between translocated and resident woylies within Walcott and Warrup East, but not Dryandra. Six months later, there was a significant difference between translocated and resident woylies within Dryandra, but not Walcott or Warrup East. The response of haemoparasites to translocation was highly site-specific, with predominant changes to the haemoparasite community in translocated woylies occurring within the first few months following translocation. Ivermectin treatment had no significant effect on haemoparasite prevalence.

Conclusions

This study contributes to our understanding of haemoparasite dynamics in woylies following translocation. The highly site-specific and rapid response of haemoparasites to translocation highlights the need to better understand what drives these effects. Given that haemoparasite prevalence and composition of translocated and resident animals changed significantly following translocation, we propose that parasite monitoring should form an essential component of translocation protocols, and such protocols should endeavour to monitor translocated hosts and cohabiting species.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3370-6) contains supplementary material, which is available to authorized users.

A global database and "state of the field" review of research into ecosystem engineering by land animals

Ecosystem engineers have been widely studied for terrestrial systems, but global trends in research encompassing the range of taxa and functions have not previously been synthesised. We reviewed contemporary understanding of engineer fauna in terrestrial habitats and assessed the methods used to document patterns and processes, asking: (a) which species act as ecosystem engineers and with whom do they interact? (b) What are the impacts of ecosystem engineers in terrestrial habitats and how are they distributed? (c) What are the primary methods used to examine engineer effects and how have these developed over time? We considered the strengths, weaknesses and gaps in knowledge related to each of these questions and suggested a conceptual framework to delineate "significant impacts" of engineering interactions for all terrestrial animals. We collected peer-reviewed publications examining ecosystem engineer impacts and created a database of engineer species to assess experimental approaches and any additional covariates that influenced the magnitude of engineer impacts. One hundred and twenty-two species from 28 orders were identified as ecosystem engineers, performing five ecological functions. Burrowing mammals were the most researched group (27%). Half of all studies occurred in dry/arid habitats. Mensurative studies comparing sites with and without engineers (80%) were more common than manipulative studies (20%). These provided a broad framework for predicting engineer impacts upon abundance and species diversity. However, the roles of confounding factors, processes driving these patterns and the consequences of experimentally adjusting variables, such as engineer density, have been neglected. True spatial and temporal replication has also been limited, particularly for emerging studies of engineer reintroductions. Climate change and habitat modification will challenge the roles that engineers play in regulating ecosystems, and these will become important avenues for future research. We recommend future studies include simulation of engineer effects and experimental manipulation of engineer densities to determine the potential for ecological cascades through trophic and engineering pathways due to functional decline. We also recommend improving knowledge of long-term engineering effects and replication of engineer reintroductions across landscapes to better understand how large-scale ecological gradients alter the magnitude of engineering impacts.

Evaluating the Effects of Ivermectin Treatment on Communities of Gastrointestinal Parasites in Translocated Woylies (Bettongia penicillata)

Wildlife species are often treated with anti-parasitic drugs prior to translocation, despite the effects of this treatment being relatively unknown. Disruption of normal host-parasite relationships is inevitable during translocation, and targeted anti-parasitic drug treatment may exacerbate this phenomenon with inadvertent impacts on both target and non-target parasite species. Here, we investigate the effects of ivermectin treatment on communities of gastrointestinal parasites in translocated woylies (Bettongia penicillata). Faecal samples were collected at three time points (at the time of translocation, and 1 and 3 months post-translocation) and examined for nematode eggs and coccidian oocysts. Parasite prevalence and (for nematodes) abundance were estimated in both treated and untreated hosts. In our study, a single subcutaneous injection of ivermectin significantly reduced Strongyloides-like egg counts 1 month post-translocation. Strongyle egg counts and coccidia prevalence were not reduced by ivermectin treatment, but were strongly influenced by site. Likewise, month of sampling rather than ivermectin treatment positively influenced body condition in woylies post-translocation. Our results demonstrate the efficacy of ivermectin in temporarily reducing Strongyloides-like nematode abundance in woylies. We also highlight the possibility that translocation-induced changes to host density may influence coinfecting parasite abundance and host body condition post-translocation.

Morphological and molecular description of Ixodes woyliei n. sp. (Ixodidae) with consideration for co-extinction with its critically endangered marsupial host

Background

Taxonomic identification of ticks obtained during a longitudinal survey of the critically endangered marsupial, Bettongia penicillata Gray, 1837 (woylie, brush-tailed bettong) revealed a new species of Ixodes Latrielle, 1795. Here we provide morphological data for the female and nymphal life stages of this novel species (Ixodes woyliei n. sp.), in combination with molecular characterisation using the mitochondrial cytochrome c oxidase subunit 1 gene (cox1). In addition, molecular characterisation was conducted on several described Ixodes species and used to provide phylogenetic context.

Results

Ixodes spp. ticks were collected from the two remaining indigenous B. penicillata populations in south-western Australia. Of 624 individual B. penicillata sampled, 290 (47%) were host to ticks of the genus Ixodes; specifically I. woyliei n. sp., I. australiensis Neumann, 1904, I. myrmecobii Roberts, 1962, I. tasmani Neumann, 1899 and I. fecialis Warburton & Nuttall, 1909. Of these, 123 (42%) were host to the newly described I. woyliei n. sp. In addition, 268 individuals from sympatric marsupial species (166 Trichosurus vulpecula hypoleucus Wagner, 1855 (brushtail possum), 89 Dasyurus geoffroii Gould, 1841 (Western quoll) and 13 Isoodon obesulus fusciventer Gray, 1841 (southern brown bandicoot)) were sampled for ectoparasites and of these, I. woyliei n. sp. was only found on two I. o. fusciventer.

Conclusions

Morphological and molecular data have confirmed the first new Australian Ixodes tick species described in over 50 years, Ixodes woyliei n. sp. Based on the long-term data collected, it appears this tick has a strong predilection for B. penicillata, with 42% of Ixodes infections on this host identified as I. woyliei n. sp. The implications for this host-parasite relationship are unclear but there may be potential for a future co-extinction event. In addition, new molecular data have been generated for collected specimens of I. australiensis, I. tasmani and museum specimens of I. victoriensis Nuttall, 1916, which for the first time provides molecular support for the subgenus Endopalpiger Schulze, 1935 as initially defined. These genetic data provide essential information for future studies relying on genotyping for species identification or for those tackling the phylogenetic relationships of Australian Ixodes species.

Translocation strategies for multiple species depend on interspecific interaction type

Conservation translocations, anthropogenic movements of species to prevent their extinction, have increased substantially over the last few decades. Although multiple species are frequently moved to the same location, current translocation guidelines consider species in isolation. This practice ignores important interspecific interactions and thereby risks translocation failure. We model three different two-species systems to illustrate the inherent complexity of multispecies translocations and to assess the influence of different interaction types (consumer-resource, mutualism, and competition) on translocation strategies. We focus on how these different interaction types influence the optimal founder population sizes for successful translocations and the order in which the species are moved (simultaneous or sequential). Further, we assess the effect of interaction strength in simultaneous translocations and the time delay between translocations when moving two species sequentially. Our results show that translocation decisions need to reflect the type of interaction. While all translocations of interacting species require a minimum founder population size, which is demarked by an extinction boundary, consumer-resource translocations also have a maximum founder population limit. Above the minimum founder size, increasing the number of translocated individuals leads to a substantial increase in the extinction boundary of competitors and consumers, but not of mutualists. Competitive and consumer-resource systems benefit from sequential translocations, but the order of translocations does not change the outcomes for mutualistic interaction partners noticeably. Interspecific interactions are important processes that shape population dynamics and should therefore be incorporated into the quantitative planning of multispecies translocations. Our findings apply whenever interacting species are moved, for example, in reintroductions, conservation introductions, biological control, or ecosystem restoration.

Biodiversity of parasite assemblages in the genus Petrogale and its relation to the phylogeny and biogeography of their hosts

Parasites form an integral part of overall biodiversity although they are often overlooked in conservation management, where emphasis is primarily directed towards the host. Parasites are often highly specialised to particular hosts, and thus may be just as threatened as the host they inhabit. For many of Australia’s wildlife species, little is known about their associated parasite communities. To begin to address this knowledge gap, we documented the parasite fauna described in the genetically diverse marsupial genus Petrogale, which contains seven species of conservation concern. The literature evaluation showed parasites of Petrogale to be highly diverse, with 17 species of protozoa, 8 species of cestodes, 102 species of nematodes and 30 species of ectoparasites identified in 16 of 17 Petrogale host species. A comparison of the parasite communities amongst Petrogale host species indicated a highly significant correlation between the parasite community similarity, and the phylogeny (P = 0.008) and biogeography (P = 0.0001) of their Petrogale hosts, suggesting high host specificity within their associated parasite assemblages. Five Petrogale species have established species recovery programs and their parasite communities should also be considered threatened, and management of parasite diversity required as part of these conservation programs.

The success of assisted colonization and assisted gene flow depends on phenology

Global warming will jeopardize the persistence and genetic diversity of many species. Assisted colonization, or the movement of species beyond their current range boundary, is a conservation strategy proposed for species with limited dispersal abilities or adaptive potential. However, species that rely on photoperiodic and thermal cues for development may experience conflicting signals if transported across latitudes. Relocating multiple, distinct populations may remedy this quandary by expanding genetic variation and promoting evolutionary responses in the receiving habitat--a strategy known as assisted gene flow. To better inform these policies, we planted seeds from latitudinally distinct populations of the annual legume, Chamaecrista fasciculata, in a potential future colonization site north of its current range boundary. Plants were exposed to ambient or elevated temperatures via infrared heating. We monitored several life history traits and estimated patterns of natural selection to determine the adaptive value of plastic responses. To assess the feasibility of assisted gene flow between phenologically distinct populations, we counted flowers each day and estimated the degree of temporal isolation between populations. Increased temperatures advanced each successive phenological trait more than the last, resulting in a compressed life cycle for all but the southern-most population. Warming altered patterns of selection on flowering onset and vegetative biomass. Population performance was dependent on latitude of origin, with the northern-most population performing best under ambient conditions and the southern-most performing most poorly, even under elevated temperatures. Among-population differences in flowering phenology limited the potential for genetic exchange among the northern- and southern-most populations. All plastic responses to warming were neutral or adaptive; however, photoperiodic constraints will likely necessitate evolutionary responses for long-term persistence, especially when involving populations from disparate latitudes. With strategic planning, our results suggest that assisted colonization and assisted gene flow may be feasible options for preservation.

Diversity of Cryptosporidium in brush-tailed rock-wallabies (Petrogale penicillata) managed within a species recovery programme

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Cryptosporidium diversity was investigated in a BTRW as part of a recovery programme.

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Faecal samples from captive bred, supplemented and wild wallabies were screened.

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Cryptosporidium isolates were identified at three gene loci using PCR.

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Diverse species of Cryptosporidium were identified across populations.

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Both specific, C. fayeri, and broad host species, C. meleagridis, were identified.

Host–parasite relationships are likely to be impacted by conservation management practices, potentially increasing the susceptibility of wildlife to emerging disease. Cryptosporidium, a parasitic protozoan genus comprising host-adapted and host-specific species, was used as an indicator of parasite movement between populations of a threatened marsupial, the brush-tailed rock-wallaby (Petrogale penicillata). PCR screening of faecal samples (n = 324) from seven wallaby populations across New South Wales, identified Cryptosporidium in 7.1% of samples. The sampled populations were characterised as captive, supplemented and wild populations. No significant difference was found in Cryptosporidium detection between each of the three population categories. The positive samples, detected using 18S rRNA screening, were amplified using the actin and gp60 loci. Multi-locus sequence analysis revealed the presence of Cryptosporidium fayeri, a marsupial-specific species, and C. meleagridis, which has a broad host range, in samples from the three population categories. Cryptosporidium meleagridis has not been previously reported in marsupials and hence the pathogenicity of this species to brush-tailed rock-wallabies is unknown. Based on these findings, we recommend further study into Cryptosporidium in animals undergoing conservation management, as well as surveying wild animals in release areas, to further understand the diversity and epidemiology of this parasite in threatened wildlife.

Which host-dependent insects are most prone to coextinction under changed climates?

Coextinction (loss of dependent species with their host or partner species) presents a threat to untold numbers of organisms. Climate change may act synergistically to accelerate rates of coextinction. In this review, we present the first synthesis of the available literature and propose a novel schematic diagram that can be used when assessing the potential risk climate change represents for dependent species. We highlight traits that may increase the susceptibility of insect species to coextinction induced by climate change, suggest the most influential host characteristics, and identify regions where climate change may have the greatest impact on dependent species. The aim of this review was to provide a platform for future research, directing efforts toward taxa and habitats at greatest risk of species loss through coextinction accelerated by climate change.

Neglected wild life: Parasitic biodiversity as a conservation target

Parasites appropriate host resources to feed and/or to reproduce, and lower host fitness to varying degrees. As a consequence, they can negatively impact human and animal health, food production, economic trade, and biodiversity conservation. They can also be difficult to study and have historically been regarded as having little influence on ecosystem organization and function. Not surprisingly, parasitic biodiversity has to date not been the focus of much positive attention from the conservation community. However, a growing body of evidence demonstrates that parasites are extremely diverse, have key roles in ecological and evolutionary processes, and that infection may paradoxically result in ecosystem services of direct human relevance. Here we argue that wildlife parasites should be considered meaningful conservation targets no less relevant than their hosts. We discuss their numerical and functional importance, current conservation status, and outline a series of non-trivial challenges to consider before incorporating parasite biodiversity in conservation strategies. We also suggest that addressing the key knowledge gaps and communication deficiencies that currently impede broad discussions about parasite conservation requires input from wildlife parasitologists.

Plant quality and local adaptation undermine relocation in a bog specialist butterfly

The butterfly Boloria aquilonaris is a specialist of oligotrophic ecosystems. Population viability analysis predicted the species to be stable in Belgium and to collapse in the Netherlands with reduced host plant quality expected to drive species decline in the latter. We tested this hypothesis by rearing B. aquilonaris caterpillars from Belgian and Dutch sites on host plants (the cranberry, Vaccinium oxycoccos). Dutch plant quality was lower than Belgian one conferring lower caterpillar growth rate and survival. Reintroduction and/or supplementation may be necessary to ensure the viability of the species in the Netherlands, but some traits may have been selected solely in Dutch caterpillars to cope with gradual changes in host plant quality. To test this hypothesis, the performance of Belgian and Dutch caterpillars fed with plants from both countries were compared. Dutch caterpillars performed well on both plant qualities, whereas Belgian caterpillars could not switch to lower quality plants. This can be considered as an environmentally induced plastic response of caterpillars and/or a local adaptation to plant quality, which precludes the use of Belgian individuals as a unique solution for strengthening Dutch populations. More generally, these results stress that the relevance of local adaptation in selecting source populations for relocation may be as important as restoring habitat quality.

Coextinction and Persistence of Dependent Species in a Changing World

The extinction of a single species is rarely an isolated event. Instead, dependent parasites, commensals, and mutualist partners (affiliates) face the risk of coextinction as their hosts or partners decline and fail. Species interactions in ecological networks can transmit the effects of primary extinctions within and between trophic levels, causing secondary extinctions and extinction cascades. Documenting coextinctions is complicated by ignorance of host specificity, limitations of historical collections, incomplete systematics of affiliate taxa, and lack of experimental studies. Host shifts may reduce the rate of coextinctions, but they are poorly understood. In the absence of better empirical records of coextinctions, statistical models estimate the rates of past and future coextinctions, and based on primary extinctions and interactions among species, network models explore extinction cascades. Models predict and historical evidence reveals that the threat of coextinction is influenced by both host and affiliate traits and is exacerbated by other threats, including habitat loss, climate change, and invasive species.