Parasites at Risk – Insights from an Endangered Marsupial

High levels of inbreeding with spatial and host-associated structure in lice of an endangered freshwater seal

Host-specialist parasites of endangered large vertebrates are in many cases more endangered than their hosts. In particular, low host population densities and reduced among-host transmission rates are expected to lead to inbreeding within parasite infrapopulations living on single host individuals. Furthermore, spatial population structures of directly-transmitted parasites should be concordant with those of their hosts. Using population genomic approaches, we investigated inbreeding and population structure in a host-specialist seal louse (Echinophthirius horridus) infesting the Saimaa ringed seal (Phoca hispida saimensis), which is endemic to Lake Saimaa in Finland, and is one of the most endangered pinnipeds in the world. We conducted genome resequencing of pairs of lice collected from 18 individual Saimaa ringed seals throughout the Lake Saimaa complex. Our analyses showed high genetic similarity and inbreeding between lice inhabiting the same individual seal host, indicating low among-host transmission rates. Across the lake, genetic differentiation among individual lice was correlated with their geographic distance, and assignment analyses revealed a marked break in the genetic variation of the lice in the middle of the lake, indicating substantial population structure. These findings indicate that movements of Saimaa ringed seals across the main breeding areas of the fragmented Lake Saimaa complex may in fact be more restricted than suggested by previous population-genetic analyses of the seals themselves.

Verification of the Spotted-Tail Quoll, Dasyurus maculatus, as a Definitive Host for the Pentastomid Linguatula sp. in Australia

PURPOSE

Specimens of a pentastomid, identified as a nymphal Linguatula serrata, have previously been reported from the nasal cavity of the endangered Australian marsupial, the spotted-tail quoll, Dasyurus maculatus. These specimens were made available for morphological and molecular characterisation to confirm their species identity.

METHODS

Specimens were examined by light microscopy. Molecular sequencing attempts were unsuccessful.

RESULTS

Examination showed that the specimens were adult pentastomes of the genus Linguatula. Morphological differences are reported between these specimens and published measurements of specimens from other hosts collected from the same region.

CONCLUSIONS

This is the first confirmed report of an adult Linguatula pentastome in a native Australian animal. Due to the small number of specimens and the lack of successful molecular characterisation, the pentastomes have been referred to Linguatula sp. until future work can confirm the species identity. The need for combined molecular and morphological analysis of pentastome specimens is reiterated.

Nematodes from the Tasmanian devil (Sarcophilus harrisii (Boitard)), with the description of Sarcophiloxyuris longus n. gen. and n. sp. (Oxyuridae)

The Tasmanian devil (Sarcophilus harrisii (Boitard)) is an endangered carnivorous marsupial, limited to the islands of Tasmania in southern Australia. The parasites of the Tasmanian devil are understudied. This study aimed to increase the knowledge of the nematode fauna of Tasmanian devils. Ten Tasmanian devils were examined for parasites from northern and southern Tasmania. Nematodes that were collected were morphologically characterized as two separate species. Molecular sequencing was undertaken to verify the identity of these species. A new genus and species of oxyurid nematode was collected from a single Tasmanian devil from the northern part of Tasmania. The nematode is differentiated from oxyurids described from other Australian amphibians, reptiles and marsupials by the characters of the male posterior end - that is, in having three pairs of caudal papillae, two pairs peri-cloacal, one large pair post-cloacal, a long tapering tail, a stout spicule and a gubernaculum and accessory piece, as well as its much larger overall size. Molecular sequencing was unsuccessful. The remaining nematodes collected from the Tasmanian devil in this study were all identified as Baylisascaris tasmaniensis Sprent, 1970, through morphology and molecular sequencing. This paper presents the first description of a new genus and species of oxyurid nematode from the Tasmanian devil, Sarcophiloxyuris longus n. gen., n. sp. The need to undertake more sampling of the parasites of endangered hosts, such as the Tasmanian devil, to assist with a better understanding of their conservation management, is discussed.

Anthropogenic disturbance favours generalist over specialist parasites in bird communities: Implications for risk of disease emergence

Niche theory predicts specialists which will be more sensitive to environmental perturbation compared to generalists, a hypothesis receiving broad support in free-living species. Based on their niche breadth, parasites can also be classified as specialists and generalists, with specialists infecting only a few and generalists a diverse array of host species. Here, using avian haemosporidian parasites infecting wild bird populations inhabiting the Western Ghats, India as a model system, we elucidate how climate, habitat and human disturbance affects parasite prevalence both directly and indirectly via their effects on host diversity. Our data demonstrate that anthropogenic disturbance acts to reduce the prevalence of specialist parasite lineages, while increasing that of generalist lineages. Thus, as in free-living species, disturbance favours parasite communities dominated by generalist versus specialist species. Because generalist parasites are more likely to cause emerging infectious diseases, such biotic homogenisation of parasite communities could increase disease emergence risk in the Anthropocene.

Fish out of water: Aquatic parasites in a drying world

Although freshwater ecosystems are among the most diverse and endangered in the world, little attention has been paid to either the importance of parasitic disease as a threatening process for freshwater organisms, or the co-extinction risk of freshwater parasites. In this review, we use theoretical and empirical studies of host/parasite interactions to examine these issues, particularly with respect to the threat posed by climate change to fish and parasite communities in intermittent rivers. Intermittent rivers are those that cease to flow at any point in time or space, with isolated pools providing ecological refuges for freshwater biota between streamflow events. Intermittent rivers are the dominant river type in arid, semi-arid and Mediterranean regions; areas of the world that have experienced dramatic decreases in streamflow as a result of climate change. Reduced streamflow decreases the number, size and connectivity of refuge pools in intermittent rivers, with important consequences for free-living aquatic organisms, particularly fishes, and their parasitic fauna. As a result of more frequent and sustained periods of no flow, parasite diversity within refuge pools is expected to decrease, with a concomitant increase in the prevalence and intensity of those parasite species which do survive, particularly host generalists. Decreased connectivity between refuge pool communities should increase the spatial modularity of host/parasite interactions, leading to a greater structuring of host and parasite communities along the river. This increases the probability of species loss (for both hosts and their parasites), as local extinctions cannot be reversed by colonisation from other localities.

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Parasites in intermittent rivers must adapt to alternating lotic and lentic conditions.

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A drying climate will decrease number, size and connectivity of lentic refuges.

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As a result, parasite α-diversity will decrease, but β-diversity will increase.

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Increased parasite abundance in refuge pools may drive hosts to local extinction.

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Increased modularity of interactions increases host and parasite extinction risk.

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.

Exotic Parasite Threats to Australia's Biosecurity-Trade, Health, and Conservation

Parasites have threatened Australia’s biosecurity since the early days of European settlement. Tick fever in cattle and liver fluke, along with their invertebrate hosts, and hydatid disease head the list of parasites that are still impacting livestock industries. In addition, there are many parasites that have been introduced that are of significance to public health as well as the conservation of native wildlife. As a consequence of these early arrivals, Australia has become much more aware of its vulnerability should parasites such as Trichinella and Trypanosoma evansi become established in Australia. However, recent discoveries concerning Leishmania and other trypanosomes have demonstrated that Australia must not become complacent and reliant on dogma when considering the potential emergence of new threats to its biosecurity. In this short review, the major parasite threats to Australia’s biosecurity are summarised, some misconceptions are emphasised, and attention is given to the importance of challenging dogma in the face of a dearth of information about Australian native fauna.