Abstract
AbstractAimThis study investigates how founder size may affect local genetic diversity and spatial genetic structure of the invasive American eastern grey squirrel (Sciurus carolinensis) in European areas. It also examines whether dispersal propensity and invasion rate may be related to founder size, genetic diversity and structure.LocationPiedmont, Italy; Northern Ireland, Northumberland and East Anglia, UK.MethodsAcross the invaded range in Europe, 315 squirrels from 14 locations, grouped in four areas, were sampled and examined at 12 highly polymorphic microsatellite loci. We estimated both genetic variation and population structure using AMOVA, Mantel tests and Bayesian analysis. We also estimated migration rates and range expansion rates.ResultsGenetic diversity varied in accordance with numbers of founders across populations. For instance, the Italian population had the smallest founder size and lowest genetic variability, whereas Northumberland had high values for both. Significant levels of genetic differentiation were observed in all the examined regions. Gene flow, migration and population range expansion rate were also higher in England and Ireland than in Italy.Main conclusionsPopulations descending from human‐mediated releases of few individuals were more genetically depauperate and more differentiated than populations established from a greater number of founders. Propagule pressure is therefore a significant factor in squirrel invasions. There is a trend whereby larger founder sizes were associated with greater genetic diversity, more dispersal, less local genetic differentiation and faster range expansion rate in squirrels. These findings have important management implications for controlling spread rate of squirrels and other invasive species: good practice should prioritize preventing further releases and the merging of genetically distinct populations as these events can augment genetic diversity.
Highlights
A major question of invasion biology is why some invasions tend to be more successful and harmful than others
Genetic diversity varied in accordance with numbers of founders across populations
Main conclusions Populations descending from human-mediated releases of few individuals were more genetically depauperate and more differentiated than populations established from a greater number of founders
Summary
A major question of invasion biology is why some invasions tend to be more successful and harmful than others. Genetic bottlenecks at introduction can reduce genetic diversity, cause inbreeding depression and reduce adaptability to the new environment, limiting chances of successful invasion (Frankham et al, 2002). Multiple introductions occurred in England, and populations arrived in Northumberland and East Anglia via an expanding population range. 30 individuals from Woburn Abbey were culled as pests and sampled and used as a surrogate source population for East Anglia. Eleven Woburn Abbey skin fragments dating back to 1921–1922 and stored at the Natural History Museum in London were sampled, representing the historical population from Woburn Abbey, and were used as a surrogate source for Northumberland and Ireland
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