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Species Range Expansion Case Study

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Species range expansion is a global phenomenon (Holt 2003) driven primarily by factors such as climate change (Walther et al. 2009, Chen et al. 2011) and land use change (e.g. Dawe et al. 2014). Such events have resulted in the rapid emergence of several zoonotic diseases (Crowl et al. 2008, Engering et al. 2013) as pathogen, disease vector, or reservoir host species introduce disease into a previously naïve region (e.g. Legér et al. 2013, Fuller et al. 2012). Since the process of species range expansion always produces observable genetic signals, such as lower genetic diversity and greater genetic structuring among populations at range edges (Excoffier et al. 2009, Cristescu 2015)we can apply concepts from population genetic theories to identify …show more content…

2009, Institut National de Santé Publique du Quebec 2014), a phenomenon largely attributed to the to the range expansion of the Lyme disease vector, the black-legged tick (Ixodes scapularis (Say)) into the country (Ogden et al. 2008). The number of known and suspected established black-legged tick populations in Canada has increased substantially from one at Long Point, Ontario in the 1990s (Ogden et al. 2009), to the numerous populations now found across five Canadian provinces (Ogden et al. 2014). This rapid range expansion of black-legged tick has been credited to several factors, including climate change (Ogden et al. 2006) and shifting ranges of common black-legged tick hosts (Madhav et al. …show more content…

Variation in allele frequency through time will be the net result of colonizing and extinction processes in the population. In other words, while species abundance in the population may remain stable over time, genetic diversity may vary (Figure 1). For instance, we would expect populations at earlier stages of establishment to exhibit greater genetic turnover rate compared to populations that are well established (Figure 1). For the black-legged tick in southern Quebec, all populations regardless of establishment stage will likely be experiencing regular influxes of new genetic material from the introduction of new individuals. However, the relative amount of novel genetic material relative to that already present locally will differ depending on the establishment stage (Figure 1). For populations still undergoing recolonization-extinction cycles, the relative amounts of novel genetic material will likely be much greater compared to local genetic material due to high local mortality rates (Figure 1). In this case, we would expect to observe great amounts of genetic turnover over time, assuming that introduced individuals originated from multiple random source populations. Conversely, populations that are well established with a self-sustaining pool of local individuals would likely have enough local genetic material to mask the signal of any introduced material (Figure 1). Therefore,

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