Host-parasite dynamics in the endangered yellow-eyed penguin (Megadyptes antipodes) : investigations of Plasmodium and Eimeria in geographically distinct populations : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science in Wildlife Health at Massey University, Palmerston North, Manawatu, New Zealand
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2021
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Massey University
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Abstract
The yellow-eyed penguin (Megadyptes antipodes) is an endangered species endemic to New Zealand, facing ongoing threats to the persistence of the species. The yellow-eyed penguin occupies a restricted range including mainland New Zealand and adjacent islands, and the subantarctic Auckland Islands and Campbell Island. There has been no effective migration between the birds occupying mainland New Zealand, and the subantarctic islands, creating two population centres that are both geographically and genetically distinct. The two population centres of the yellow-eyed penguin, defined by the geographical range, occupy vastly different habitat ranges and face ongoing site-specific threats. The mainland population has declined by up to 65% in the last 20 years, while the sub-Antarctic population appears stable through limited monitoring. Examining host-pathogen dynamics of geographically distinct wildlife populations can inform predictions of a population’s response to major climate shifts or translocations. This study therefore explored possible differences in the host-pathogen dynamics between the two population centres of the yellow-eyed penguin. The study sampled wild penguins from the two major population centres, the mainland and sub-Antarctic population centres, to examine the prevalence and pathogen load differences of two known parasites Eimeria and Plasmodium. In addition, the study documented differences in the prevalence of Plasmodium infection between penguins in rehabilitation and those in the wild. Eimeria is a host-adapted parasite that principally causes disease in wild birds when the host is immunosuppressed through stress or intercurrent disease. Therefore, this study used Eimeria as an ecological biomarker to assess the distinct wild yellow-eyed penguin populations. The first morphological description of a novel species of Eimeria protozoa from a yellow-eyed penguin host is provided in this study. A high prevalence and pathogen load of Eimeria oocysts in faecal samples from wild yellow-eyed penguins was identified from the wild sub-Antarctic (apparent prevalence 76.6%, 95% CI 62.78-86.40% and mean pathogen load 9723 +/- 5831 oocysts/gram) and mainland populations surveyed (apparent prevalence 58.5%, 95% CI 43.37-72.24% and mean pathogen load 1050 +/- 398 oocysts/gram), with only weak evidence for a difference in the apparent prevalence and pathogen load between the two population centres. There was, however, a significant difference in body condition scores of infected penguins between the two populations, suggesting possible differences in the host-pathogen dynamics between the two distinct population centres. These results confirm the hypothesis that these coccidia are characteristic of a highly host-adapted endemic parasite in the yellow-eyed penguins. Penguins have a known susceptibility to Plasmodium sp., with infection capable of causing significant morbidity and mortality. This study provides the first report of a positive result for Plasmodium sp. from wild yellow-eyed penguins using LSU-RNA qPCR, and documents the estimated pathogen load (mean pathogen load 122 +/-29 Plasmodium DNA copies / 10,000 avian cells) of infected wild birds. There was good evidence for a difference in apparent prevalence between the two population centres, with a higher apparent prevalence of avian malaria in the wild mainland population (6.8%, 95% CI 2.96-15.05%), and an apparent absence of infection in the sub-Antarctic population surveyed (0%, 95% CI 0-5.58%). The study also documented a high apparent prevalence (65.9%, 95% CI 51.14-78.12%) of Plasmodium sp. infection in yellow-eyed penguins in rehabilitation, identifying three separate strains of avian malaria (Plasmodium sp. Lineage LINN1, Plasmodium relictum lineage SGS1 and Plasmodium elongatum lineage GRW06) via molecular sequencing. These results confirm the hypothesis that avian malaria is characteristic of a vector-borne parasite in the yellow-eyed penguins, and despite the presence of competent vectors in both habitats, only the northernmost population of yellow eyed penguins is currently infected. However, this disease is likely to emerge in the sub-Antarctic population in response to predicted climate shifts. The results of this work provide a platform for further research into the host-pathogen dynamics of the novel Eimeria species identified, and the potential host effects of this parasite during environmental stressors. In addition, the findings of this study suggest future monitoring of avian malaria prevalence and mortality rates in the yellow-eyed penguin are critical to understand the emerging risk of this pathogen in the context of ongoing climate shifts. Finally, the high prevalence of Plasmodium infection documented in yellow-eyed penguins in rehabilitation demonstrates the threat of this parasite to the success of ongoing rehabilitation efforts, and the need to investigate measures to mitigate infection risk for this species in the future.