Patterns of avian malaria in tropical and temperate environments: testing the "The enemy release hypothesis"

Yasmine Antonini,Ana Cláudia Norte,Patrícia De Abreu Moreira,Erika Martins Braga,Jaime A Ramos,Debora Nogueira Campos Lobato

doi:10.1590/1676-0611-bn-2018-0716

Abstract

Abstract: According to the enemy release hypothesis (ERH) the spread of invasive species will be facilitated by release from their enemies as they occupy new areas. However, the ERH has rarely been tested by comparing populations of native (non-invasive, long established) species with expanding or shifting ranges, to the same species as invasive in another area. We tested the ERH with respect to blood parasite levels (prevalence and intensity of Plasmodium spp. and Haemoproteus spp.) of (a) two closely related, widely distributed species of thrush (Turdus leucomelas and T. merula), and (b) an invasive sparrow (Passer domesticus) whose range has expanded from the Old World to the New World since the 18th century. A total of 158 birds were sampled in Portugal and 99 in Brazil. All bird species were parasitized, and 55% of the individuals collected were parasitized, and the mean intensity of infection was of 28 parasites per 10,000 erythrocytes. We assessed whether differences in levels of infection (prevalence and intensity) were due to site (tropical/New World and temperate/Old World) or host species. The ERH was supported: Passer domesticus and Turdus merula had higher levels of parasitism in the Old World than in the New World. Thus, P. domesticus seems to be benefitting from its "recent" range expansion, compared to T. leucomelas, through ecological release from its native parasites and because the parasites of the recently invaded area seem to be infesting native species instead.

Highlights

Avian Haemosporidian infections is caused by blood parasites of the phylum Apicomplexa, which includes the genera Plasmodium, Haemoproteus, Leucocytozoon and Fallisia (Valkiūnas 2005)
We focused on addressing three questions: (1) Do Haemosporidian prevalence and density differ between host species? (2) Do Haemosporidian prevalence and density differ between populations of the same host species/genus, sampled in temperate (Western Europe, Portugal) and tropical (South America, Brazil) environments? (3) Does Haemosporidian infection cause negative consequences to host health in both temperate and tropical areas?
The Enemy Release Hypothesis predicts that a species whose range is expanding should have lower levels of parasitism in ‘new’ sites versus ‘old’ sites

Summary

Introduction

Avian Haemosporidian infections is caused by blood parasites of the phylum Apicomplexa, which includes the genera Plasmodium, Haemoproteus, Leucocytozoon and Fallisia (Valkiūnas 2005). Plasmodium and Haemoproteus infections have negative consequences to host fitness by reducing clutch sizes and nest defense behavior, increasing probability of clutch desertion, reducing hatching and fledging success and weaning nestlings with poorer body condition (Korpimaki et al 1993, Dulfa 1996, Hakkarainen et al 1998, Sanz et al 2004, Andrezj 2005, Marzal et al 2005). Introduced species might encounter novel parasites whose virulence will partly determine whether they become invasive

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