Abstract
Introduced populations often lose the parasites they carried in their native range, but little is known about which processes may cause parasite loss during host movement. Conservation-driven translocations could provide an opportunity to identify the mechanisms involved. Using 3,888 blood samples collected over 22 years, we investigated parasite prevalence in populations of Seychelles warblers (Acrocephalus sechellensis) after individuals were translocated from Cousin Island to four new islands (Aride, Cousine, Denis and Frégate). Only a single parasite (Haemoproteus nucleocondensus) was detected on Cousin (prevalence = 52%). This parasite persisted on Cousine (prevalence = 41%), but no infection was found in individuals hatched on Aride, Denis or Frégate. It is not known whether the parasite ever arrived on Aride, but it has not been detected there despite 20 years of post-translocation sampling. We confirmed that individuals translocated to Denis and Frégate were infected, with initial prevalence similar to Cousin. Over time, prevalence decreased on Denis and Frégate until the parasite was not found on Denis two years after translocation, and was approaching zero prevalence on Frégate. The loss (Denis) or decline (Frégate) of H. nucleocondensus, despite successful establishment of infected hosts, must be due to factors affecting parasite transmission on these islands.
Highlights
Introduced populations often lose the parasites they carried in their native range, but little is known about which processes may cause parasite loss during host movement
Among the newly established populations, Haemoproteus infection has only persisted on Cousine (Fig. 1), and DNA sequencing confirmed that this population was infected with the same strain (GRW121) of Haemoproteus nucleocondensus previously and consistently detected in the source population of Cousin[23]
Infection probability did not differ between Cousin and Cousine (Z = 1.67, P = 0.10), and there was a significant correlation in H. nucleocondensus prevalence between these islands across years (r = 0.84, P = 0.005)
Summary
Introduced populations often lose the parasites they carried in their native range, but little is known about which processes may cause parasite loss during host movement. This parasite persisted on Cousine (prevalence = 41%), but no infection was found in individuals hatched on Aride, Denis or Frégate It is not known whether the parasite ever arrived on Aride, but it has not been detected there despite 20 years of post-translocation sampling. Across a wide range of host taxa, parasite diversity and abundance is lower in introduced compared to native populations[1,2] This loss of parasites can have consequences for the establishment and long-term success of host populations that colonise new areas[3,4]. While there is evidence that conservation-driven translocations can result in parasite loss within new host populations[13], as far as we are aware, no study has tried to identify the mechanisms involved
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