Living on the edge: genetic variability and range dynamics of the American dog tick

点击翻译按钮获取中文摘要

Each species has a unique geographical distribution. Range expansion by some species is in response to climate change. Detailed knowledge of the range and abundance of species across the landscape is particularly important if they are a vital food source, of cultural significance, keystone species at risk of extinction, invasive species, or parasites or microbes that affect the health of wildlife, domestic animals and humans. Tick-borne pathogens, for example, cause significant economic losses for cattle producers worldwide. Understanding what factors restrict the ranges of species remains a key issue in ecology and evolutionary biology. My long-term research goals are to understand how ecological and evolutionary factors influence the distribution and abundance of parasites, and to unveil the strength of parasitism and endosymbiosis as fundamental ecological interactions and drivers of selection. The centre-periphery hypothesis (CPH) postulates that individuals at the range edge experience harsher ecological conditions and have reduced fitness than those in more `core' populations. Populations at range edges are smaller, genetically less diverse and have reduced adaptive potential to cope with environmental conditions in habitats beyond the distributional limits. Although the CPH provides a general explanation as to what limits species distributions, its does not in its current form, represent a universal rule. Also, few studies have examined if the CPH is applicable to parasites, which comprise 30-50% of all animals. Over the next five years, we will use a unique combined approach (laboratory and field experiments with molecular tools) to uncover how genetic variation and species interactions influence tick distribution and abundance by examining three interrelated objectives: (1) compare the genetic diversity and divergence of tick populations near the range edges with more `core' populations, (2) examine the effect of predatory ants on tick survival and (3) elucidate if tick survival is influenced by bacterial endosymbionts. The third objective is unique, in that, the effect of endosymbionts on the survival of their tick hosts has largely been overlooked. The American dog tick (Dermacentor variabilis) is the focal organism of this study because it has a broad geographic range in North America that is expanding northwards and westwards in Saskatchewan. Advancing our understanding of what limits range expansion of D. variabilis will also be of importance for other researchers in the development of effective strategies to control this species, and other parasitic arthropod vectors and their pathogens that are currently expanding their ranges into Canada. My research program also facilitates the training of graduate and undergraduate students, future research leaders in Canada and other parts of the world, who will be well equipped to deal with the increasing economic and social burden of parasitic arthropods and their pathogenic microbes.