Specialist enemies, generalist weapons and the potential spread of exotic pathogens: malaria parasites in a highly invasive bird

Abstract

Pathogens can influence the success of invaders. The Enemy Release Hypothesis predicts invaders encounter reduced pathogen abundance and diversity, while the Novel Weapons Hypothesis predicts invaders carry novel pathogens that spill over to competitors. We tested these hypotheses using avian malaria (haemosporidian) infections in the invasive myna (Acridotheres tristis), which was introduced to southeastern Australia from India and was secondarily expanded to the eastern Australian coast. Mynas and native Australian birds were screened in the secondary introduction range for haemosporidians (Plasmodium and Haemoproteus spp.) and results were combined with published data from the myna's primary introduction and native ranges. We compared malaria prevalence and diversity across myna populations to test for Enemy Release and used phylogeographic analyses to test for exotic strains acting as Novel Weapons. Introduced mynas carried significantly lower parasite diversity than native mynas and significantly lower Haemoproteus prevalence than native Australian birds. Despite commonly infecting native species that directly co-occur with mynas, Haemoproteus spp. were only recorded in introduced mynas in the primary introduction range and were apparently lost during secondary expansion. In contrast, Plasmodium infections were common in all ranges and prevalence was significantly higher in both introduced and native mynas than in native Australian birds. Introduced mynas carried several exotic Plasmodium lineages that were shared with native mynas, some of which also infected native Australian birds and two of which are highly invasive in other bioregions. Our results suggest that introduced mynas may benefit through escape from Haemoproteus spp. while acting as important reservoirs for Plasmodium spp., some of which are known exotic lineages.

Migration strategy and pathogen risk: non‐breeding distribution drives malaria prevalence in migratory waders

“…Despite extensive sampling, migratory marine + freshwater species were represented by only 300 samples from five species in Australia, the vast majority of which were sampled at high latitudes where prevalence is likely to be lower. Monitoring for natural prevalence levels is crucial in disease ecology (Grogan et al , Clark et al ), and sample size is an important consideration for identifying populations at risk.…”

“…We constructed molecular phylogenies from parasite cyt‐b sequences recovered in Australian samples using identical protocols to the methods outlined above for waders. To investigate whether parasite phylogenies could yield information about where infections were acquired, we included all published avian malaria sequences recovered in Australia and Southeast Asia (see Clark et al for details on parasite sequence acquisition). In addition, we included parasite sequences previously recovered from waders and other non‐passerine shorebirds (Mendes et al , , Levin et al , ) to investigate whether waders in Australia carry similar lineages to shorebirds around the world.…”

Co‐infections and environmental conditions drive the distributions of blood parasites in wild birds

“…A Bayesian phylogeny was constructed to estimate malaria relationships, following Clark et al . (). For malaria lineages presenting all developmental stages in corresponding single‐infection smears, we identified parasites to species (see Supporting information for parasite identifications).…”

“…Avian malaria PCR screening and sequencing followed Clark et al . (), with the following variations. Sequences suggested amplification bias towards Plasmodium spp.…”

Why fly the extra mile? Using stress biomarkers to assess wintering habitat quality in migratory shorebirds

“…Therefore, the choice of wintering habitat may be important for minimising the rate at which these animals encounter harmful infections. This includes haemosporidian malaria parasites of the genera Haemoproteus and Plasmodium, which are a diverse vector-borne group of parasites known to infect a wide range of avian taxa, including shorebirds (Clark et al 2014(Clark et al , 2015b. These parasites can adversely affect the fitness of their hosts (Valkiunas 2005), and potentially influence migration patterns exhibited by shorebirds (Piersma 1997;Figuerola and Green 2000).…”