Abstract
Understanding the factors that influence the success of ecologically and economically damaging biological invasions is of prime importance. Recent studies have shown that invasive populations typically exhibit minimal, if any, reductions in genetic diversity, suggesting that large founding populations and/or multiple introductions are required for the success of biological invasions, consistent with predictions of the propagule pressure hypothesis. Through population genetic analysis of neutral microsatellite markers and a gene experiencing balancing selection, we demonstrate that the solitary bee Lasioglossum leucozonium experienced a single and severe bottleneck during its introduction from Europe. Paradoxically, the success of L. leucozonium in its introduced range occurred despite the severe genetic load caused by single-locus complementary sex-determination that still turns 30% of female-destined eggs into sterile diploid males, thereby substantially limiting the growth potential of the introduced population. Using stochastic modeling, we show that L. leucozonium invaded North America through the introduction of a very small number of propagules, most likely a singly-mated female. Our results suggest that chance events and ecological traits of invaders are more important than propagule pressure in determining invasion success, and that the vigilance required to prevent invasions may be considerably greater than has been previously considered.
Highlights
Invasive species are a serious threat to biodiversity conservation [1,2,3] and the global economy [4], and understanding the patterns and processes governing the establishment and spread of exotic organisms is of primary importance
We did not observe more than 3 alleles per locus in North America (NA), and average allelic richness was reduced by 76% when compared to the French population (Table 1), a higher reduction in allelic richness than found in any other introduced animal surveyed for that parameter [10]
Highly reduced levels of genetic variation in introduced L. leucozonium populations along with significant bottleneck tests and lack of population structure suggest that this bee experienced a single and severe founder event during its introduction to North America
Summary
Invasive species are a serious threat to biodiversity conservation [1,2,3] and the global economy [4], and understanding the patterns and processes governing the establishment and spread of exotic organisms is of primary importance. Biogeographic and phylogenetic evidence show that L. leucozonium was introduced to North America (NA) from Europe [15] and museum collections suggest that this occurred at least a century ago [14]. Until recently, this bee was commonly considered native to NA [15], where it can be found in large numbers throughout its range [16,17]. Modeling analyses suggest that the founder population consisted of a very small number of propagules, most likely a singly-mated female
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