# Host range and community structure of avian nest parasites in the genus Philornis (Diptera: Muscidae) on the island of Trinidad

## TL;DR

This study examines the host range and community structure of avian nest parasites in the genus Philornis on Trinidad, revealing patterns of host specificity and phylogenetic relationships.

## Contribution

The study introduces a novel combination of host-parasite association data with phylogenetic analysis to explore evolutionary influences on host range in Philornis flies.

## Key findings

- Philornis species on Trinidad exhibit varying degrees of host specificity, with some being generalists and others specialists.
- No significant phylogenetic signal was found for host range measures or parasite species load in bird hosts.
- Philornis parasites tend to feed on closely related bird species more often than expected by chance.

## Abstract

Parasite host range can be influenced by physiological, behavioral, and ecological factors. Combining data sets on host–parasite associations with phylogenetic information of the hosts and the parasites involved can generate evolutionary hypotheses about the selective forces shaping host range. Here, we analyzed associations between the nest-parasitic flies in the genus Philornis and their host birds on Trinidad. Four of ten Philornis species were only reared from one species of bird. Of the parasite species with more than one host bird species, P. falsificus was the least specific and P. deceptivus the most specific attacking only Passeriformes. Philornis flies in Trinidad thus include both specialists and generalists, with varying degrees of specificity within the generalists. We used three quantities to more formally compare the host range of Philornis flies: the number of bird species attacked by each species of Philornis, a phylogenetically informed host specificity index (Poulin and Mouillot's STD), and a branch length-based STD. We then assessed the phylogenetic signal of these measures of host range for 29 bird species. None of these measures showed significant phylogenetic signal, suggesting that clades of Philornis did not differ significantly in their ability to exploit hosts. We also calculated two quantities of parasite species load for the birds – the parasite species richness, and a variant of the STD index based on nodes rather than on taxonomic levels – and assessed the signal of these measures on the bird phylogeny. We did not find significant phylogenetic signal for the parasite species load or the node-based STD index. Finally, we calculated the parasite associations for all bird pairs using the Jaccard index and regressed these similarity values against the number of nodes in the phylogeny separating bird pairs. This analysis showed that Philornis on Trinidad tend to feed on closely related bird species more often than expected by chance.