Dispersal and Distribution of the Tick Ixodes uriae within and among Seabird Host Populations: The Need for a Population Genetic Approach

Abstract

The aim of this study was to characterize the spatial distribution of the tick Ixodes uriae within and among populations of its seabird hosts and to consider the potential insight that could be gained by a population genetic approach to the issue of dispersal of this tick. Analyses of data collected around the Avalon Peninsula, Newfoundland, indicated that both the prevalence and mean abundance of ticks varied significantly among sample locations. Whereas ticks were found on all 4 host species examined (Rissa tridactyla, Uria aalge, Alca torda, Fratercula arctica), infestation prevalence and mean abundance differed among the species. On R. tridactyla, ticks were significantly aggregated at the among-nest scale and nestling infestation was spatially autocorrelated. Conversely, ticks were not aggregated among chicks within nests. These results enabled us to make a priori predictions regarding tick dispersal and host specificity and suggest there may be spatial structure of Ixodes uriae populations at both macro- and microgeographic scales. Investigating the population genetic structure of ticks within and among populations of hosts with different breeding biologies should provide direct insight into the metapopulation dynamics of such a spatially structured system.

Induced maternal response to the Lyme disease spirochaeteBorrelia burgdorferi sensu latoin a colonial seabird, the kittiwakeRissa tridactyla

“…prior exposure, ability to tolerate). As the presence of ticks is spatially heterogeneous and tick dispersal at inter-colony scales is hostmediated, host movements will alter tick dispersal patterns in the environment (McCoy et al 1999). Thus, the spatial heterogeneity of the di¡erent species involved in this system and the frequency of seabird dispersal will have important consequences for the spread of Borrelia at di¡erent scales and, in turn, will a¡ect the predictability of potential human exposure to Lyme disease (Van Buskirk & Ostfeld 1998).…”

“…The level of tick infestation was determined for each breeding cli¡ the year prior to egg collection, as levels of infestation are determined using parasite loads on chicks (Boulinier et al 1996;Danchin et al 1998;McCoy et al 1999). For some cli¡s, chicks were also searched for ticks the year of egg collection, which permitted us to increase sample sizes by pooling data for the two years.…”

“…In each stage, I. uriae attaches to its host for a single, long, blood meal and then returns to the host nesting substrate to overwinter (Eveleigh & Threlfall 1974). It has previously been shown that tick prevalence and abundance are autocorrelated in both space and time at the scale of the host breeding cli¡ (Danchin et al 1998;McCoy et al 1999). As kittiwakes, like many seabirds, are highly philopatric to their breeding sites between years (Coulson & Thomas 1985), ticks become a predictable part of their breeding environment.…”

Spatial genetic structure of the ectoparasite Ixodes uriae within breeding cliffs of its colonial seabird host

“…The local infestation dynamics of I. uriae in kittiwake colonies has been described at several spatial scales (Danchin, 1992;Danchin et al, 1998;McCoy et al, 1999). Within a single breeding cliff, parasites are highly aggregated among nests, but not among chicks of the same nest , and nest infestation is spatially autocorrelated (Boulinier, 1995;McCoy et al, 1999).…”

“…This tick is a common ectoparasite of colonial-nesting seabirds in the circumpolar areas of both hemispheres (Sonenshine, 1993) and its populations can be subdivided at several spatial scales relative to its host: among breeding colonies, among breeding patches within colonies and among nests within breeding patches McCoy et al, 1999). I. uriae is considered to impact host reproductive success negatively (eg, Morbey, 1996) and to alter host habitat selection decisions (Danchin et al, 1998;Boulinier et al, 2001).…”