Abstract
Wildlife populations have been introduced to new areas by people for centuries, but this human-mediated movement can disrupt natural patterns of genetic structure by altering patterns of gene flow. Insular populations are particularly prone to these influences due to limited opportunities for natural dispersal onto islands. Consequently, understanding how genetic patterns develop in island populations is important, particularly given that islands are frequently havens for protected wildlife. We examined the evolutionary origins and extent of genetic structure within the introduced island population of red squirrels (Sciurus vulgaris) on the Channel Island of Jersey using mitochondrial DNA (mtDNA) control region sequence and nuclear microsatellite genotypes. Our findings reveal two different genetic origins and a genetic architecture reflective of the introductions 120 years ago. Genetic structure is marked within the maternally inherited mtDNA, indicating slow dispersal of female squirrels. However, nuclear markers detected only weak genetic structure, indicating substantially greater male dispersal. Data from both mitochondrial and nuclear markers support historic records that squirrels from England were introduced to the west of the island and those from mainland Europe to the east. Although some level of dispersal and introgression across the island between the two introductions is evident, there has not yet been sufficient gene flow to erase this historic genetic “footprint.” We also investigated if inbreeding has contributed to high observed levels of disease, but found no association. Genetic footprints of introductions can persist for considerable periods of time and beyond traditional timeframes of wildlife management.
Highlights
Wildlife populations have been relocated and translocated by people for centuries, both accidentally and intentionally (Atkinson 1973; Huxley 2003; Kolbe et al 2008)
The prevalence of the two haplotypes found on Jersey reveals that there is a geographic pattern to where the mitochondrial haplotypes occur on the island (Fig. 2)
Two introductions of red squirrels occurred on the island of Jersey, one from England and one from mainland Europe, likely France, comprising two evolutionarily different source populations, which most likely contributed to high initial levels of genetic structure
Summary
Wildlife populations have been relocated and translocated by people for centuries, both accidentally and intentionally (Atkinson 1973; Huxley 2003; Kolbe et al 2008). Accidental movement of animals is most frequently a consequence of stowaways or escapees (Atkinson 1973; Weir and Grant 2005), whereas intentional movements can be either as introductions of wildlife to new areas, reintroductions to areas where they once previously occurred, or as restocking activities – augmenting existing populations with additional individuals (Shorten 1954; Biebach and Keller 2009; Grandjean et al 2009) This human-mediated movement of individuals can disrupt natural genetic structure by altering patterns of genetic differentiation or gene flow that may have previously a 2013 The Authors. Genetic Footprint of Introduction in Red Squirrels occurred Such an alteration of gene flow can have negative consequences including isolating sub-populations causing inbreeding, or joining separate locally adapted populations causing individuals to become less fit in the alternate environment. Conservation biologists have increasingly begun to use islands as refuges on which to “maroon” vulnerable wildlife populations (Cade and Temple 1995)
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