Report from a BOU-funded project
Introduced species may bring their pathogens with them, for example, the introduction of non-native bird species to Pacific islands has in many instances resulted in the co-introduction of novel lineages of Plasmodium and Haemoproteus (blood borne parasites that cause malaria and haemoproteosis – aka pseudomalaria). Such introductions are a particular threat to island endemics. For example, in Hawaii endemic species suffer high levels of mortality in response to novel Plasmodium and Haemoproteus lineages (Atkinson & LaPointe, 2009; Warner, 1968). Within French Polynesia, the relatively recent introduction of novel Plasmodium and Haemoproteus lineages, via the introduction of non-native bird species during the late 19th and early 20th centuries, could be contributing to the decline of French Polynesia’s avian endemics. However, so little is known of the origins, prevalence, and geographic distribution of Plasmodium and Haemoproteus lineages within French Polynesia that it is currently impossible to assess the impacts of these introduced pathogens.
Making use of blood samples collected from six introduced species caught across French Polynesia’s Society archipelago, I assessed the prevalence and distribution of malarial infection across this region with the help of a BOU small ornithological research grant. Individuals were screened for avian malaria/haemoproteosis by amplifying a 150bp fragment of Plasmodium/Haemoproteus DNA (part of the Cytochrome oxidase I gene).
Of the 291 individuals screened 92 (31.6%) tested positive for Plasmodium/Haemoproteus infection. Plasmodium/Haemoproteus prevalence was highly variable across islands sampled (Figure 1), with the highest rates of infection observed on Huahine (62%, n = 21) and the lowest rates on Tahiti (22%, n = 41). When grouping sampled islands into their respective geographic regions, the Leeward Island Group (Huahine, Raiatea and Maupiti) had higher prevalence (46.0%, n = 87) than the Windward Island Group (Tahiti and Mo’orea) (25.5%, n = 204).
Figure 1 Prevalence of malarial infection across sampled islands of the Society Archipelago. The location of the Society Archipelago is shown on the globe.
Plasmodium/Haemoproteus prevalence was also highly variable between species (Figure 2). The highest infection rate was observed for the Common Myna (Acridotheres tristis) with 66.6% of individuals sampled testing positive for Plasmodium/Haemoproteus infection. Infected mynas were restricted to the island of Mo’orea (Table 1). This estimate of prevalence was considerably higher than that previously reported for the Common Myna (Blanvillain et al. 2021) in which only 8.5% (n = 59) of individuals caught on a different island (Tahiti) tested positive for Plasmodium/Haemoproteus infection. However, given that my sampling of this species was restricted to two islands (Mo’orea and Raiatea) and only three individuals, further sampling is required to provide a more accurate assessment of malaria prevalence for this species, both within Mo’orea and Raiatea and across the Society Archipelago.
Figure 2 Species by species prevalence of avian malarial infection: (A) Zebra Dove (Geopelia striata); (B) Common Waxbill (Estrilda astrild); (C) Chestnut-breasted Mannikin (Lonchura castaneothorax); (D) Common Myna (Acridotheres tristis); (E) Red-browed Finch (Neochmia temporalis); (F) Silvereye (Zosterops lateralis). All images from Wikipedia.
Table 1 Prevalence of avian malaria infection by species/island/island group sampled. Shown as the proportion of individuals screened that tested positive for Haemoproteus/Plasmodium infection.
Based on current sampling the Red-browed Finch (Neochmia temporalis) does not appear to suffer from avian malaria or haemoproteosis, with zero of the 34 individuals screened testing positive for Plasmodium/Haemoproteus infection. Although further sampling would increase the reliability of results, a previous study (Rosner, 2010) suggests that 25 individuals is sufficient to indicate that a population is negative for the presence of a pathogen. However, further work is required to determine if other populations within this species’ French Polynesian range are also free of infection. If this is indeed the case, this would suggest that the Red-browed Finch has either developed immunity to the Plasmodium/Haemoproteus lineages present within the Society Islands, or founding individuals already had sufficient immunity prior to their introduction to the region. The remaining species had intermediate infection rates (28.6-38.2%) (Figure 2). A breakdown of prevalence estimates per species/per island is provided in Table 1.
These results demonstrate that introduced species within French Polynesia act as a source of harmful parasites and disease. Given the relatively high infection rates observed across the Society Islands, blood borne parasites are likely contributing to the demise of the region’s immunologically naive endemic species.
Ashley Sendell-Price (PhD candidate, University of Oxford, UK) was awarded a small ornithological grant of £1,499 in 2019 for a project entitled ‘Assessing the prevalence, distribution and origins of avian malaria within the introduced avifauna of the Society archipelago, French Polynesia’.
Atkinson, C.T. & LaPointe, D.A. 2009. Introduced avian diseases, climate change, and the future of Hawaiian honeycreepers. Journal of Avian Medicine and Surgery 23: 53–63.VIEW
Warner, R.E. 1968. The role of introduced diseases in the extinction of the endemic Hawaiian avifauna. The Condor 70: 101-120. VIEW
Rosner, B. (ed.) 2010. Fundamentals of Biostatistics Boston: Rooks/ Cole: Boston.
Top right: Common Myna Acridotheres tristis, Hobbyfotowiki, CC BY-SA 4.0, Wikimedia Commons