Phylogeographic Structure in Penguin Ticks across an Ocean Basin Indicates Allopatric Divergence and Rare Trans-Oceanic Dispersal.

Katherine L Moon,Michael Knapp,Sam C Banks,Ceridwen I Fraser

doi:10.1371/journal.pone.0128514

Abstract

The association of ticks (Acarina) and seabirds provides an intriguing system for assessing the influence of long-distance dispersal on the evolution of parasitic species. Recent research has focused on host-parasite evolutionary relationships and dispersal capacity of ticks parasitising flighted seabirds. Evolutionary research on the ticks of non-flighted seabirds is, in contrast, scarce. We conducted the first phylogeographic investigation of a hard tick species (Ixodes eudyptidis) that parasitises the Little Blue Penguin (Eudyptula minor). Using one nuclear (28S) and two mitochondrial (COI and 16S) markers, we assessed genetic diversity among several populations in Australia and a single population on the South Island of New Zealand. Our results reveal two deeply divergent lineages, possibly representing different species: one comprising all New Zealand samples and some from Australia, and the other representing all other samples from Australian sites. No significant population differentiation was observed among any Australian sites from within each major clade, even those separated by hundreds of kilometres of coastline. In contrast, the New Zealand population was significantly different to all samples from Australia. Our phylogenetic results suggest that the New Zealand and Australian populations are effectively isolated from each other; although rare long-distance dispersal events must occur, these are insufficient to maintain trans-Tasman gene flow. Despite the evidence for limited dispersal of penguin ticks between Australia and New Zealand, we found no evidence to suggest that ticks are unable to disperse shorter distances at sea with their hosts, with no pattern of population differentiation found among Australian sites. Our results suggest that terrestrial seabird parasites may be quite capable of short-distance movements, but only sporadic longer-distance (trans-oceanic) dispersal.

Highlights

Dispersal is a driving force in the isolation and subsequent evolution of species on both local and global scales [1]
Little Blue Penguins are reported to be parasitised by three hard tick species within their distribution (Ixodes eudyptidis, I. kohlsi and I. uriae), and these can be morphologically separated by the shape of the anal groove [33]
The strong phylogenetic divisions identified between ticks collected from Little Blue Penguins in New Zealand and those from Australia suggest that dispersal events between the two countries have occurred, but that these have been too rare to maintain gene flow and so have led to allopatric diversification

Summary

Introduction

Dispersal is a driving force in the isolation and subsequent evolution of species on both local and global scales [1]. June 17, 2015 adherence to PLOS ONE Editorial policies and criteria. Species whose own capabilities for movement are limited often rely on others for their dispersal [4], and this can be important for dispersal of non-motile or slow-moving parasites with their hosts [5]. Parasites and their hosts are considered to be engaged in a permanent coevolutionary arms race, with host resistance and parasite virulence under intense reciprocal selective pressure [6]. Differences in host versus parasite migration rates can, strongly affect the co-adaptation process [7,8,9]

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Conclusion