Avian vampire fly (Philornis downsi) mortality differs across Darwin\u2019s finch host species

Lauren K Common,Rachael Y Dudaniec,Diane Colombelli-Négrel,Petra Sumasgutner,Sonia Kleindorfer

doi:10.1038/s41598-021-94996-7

Abstract

In invasive parasites, generalism is considered advantageous during the initial phase of introduction. Thereafter, fitness costs to parasites, such as host-specific mortality, can drive parasites towards specialism to avoid costly hosts. It is important to determine changes in host specificity of invasive populations to understand host-parasite dynamics and their effects on vulnerable host populations. We examined changes in mortality in the introduced avian vampire fly (Philornis downsi) (Diptera: Muscidae), a generalist myasis-causing ectoparasite, between 2004 and 2020 on Floreana Island (Galápagos). Mortality was measured as the proportion of immature larvae found upon host nest termination. Over the time period, the avian vampire fly was most abundant and had low mortality in nests of the critically endangered medium tree finch (Camarhynchus pauper) and had the highest mortality in nests of hybrid tree finches (Camarhynchus spp.). Low larval mortality was also found in small tree (Camarhynchus parvulus) and small ground finch (Geospiza fuliginosa) nests. Selection could favour avian vampire flies that select medium tree finch nests and/or avoid hybrid nests. Overall, the finding of differences in avian vampire fly survival across host species is parsimonious with the idea that the introduced fly may be evolving towards host specialisation.

Highlights

Niche breadth is a fundamental concept that underpins key hypotheses in species e cology[1,2,3]
Given the apparent ubiquity of the avian vampire fly across Galápagos passerine species and the increasing number of avian vampire fly larvae and pupae per host nest in studies carried out between 2000 to 201336,39, theory predicts that parasite generalism should prevail if there are negligible resource differences between host species
Host specialisation or host preference should occur if there are differences in fitness costs for the avian vampire fly between host species

Summary

Introduction

Niche breadth is a fundamental concept that underpins key hypotheses in species e cology[1,2,3]. Generalist parasites tend to occur on host species that are phylogenetically closely related[7,13,14,15] They incur the cost of maintaining variation in life history, genetic and behavioural traits that enable exploitation of different host s pecies[16]. When a generalist parasite colonises a novel environment and suite of potential host species, the differences in fitness due to altered selection creates a window of opportunity to study niche and host specialisation shifts. Given the apparent ubiquity of the avian vampire fly across Galápagos passerine species and the increasing number of avian vampire fly larvae and pupae per host nest in studies carried out between 2000 to 201336,39, theory predicts that parasite generalism should prevail if there are negligible resource differences (i.e. nutritional value or fitness costs to parasites) between host species. Host specialisation or host preference should occur if there are differences in fitness costs for the avian vampire fly between host species

Methods

Results

Conclusion