Abstract
BackgroundThe observation that many alien species become invasive despite low genetic diversity has long been considered the ‘genetic paradox’ in invasion biology. This paradox is often resolved through the temporal buildup genetic diversity through multiple introduction events. These temporal dynamics in genetic diversity are especially important for annual invasive plants that lack a persistent seed bank, for which population persistence is strongly dependent on consecutive seed ‘re-establishment’ in each growing season. Theory predicts that the number of seeds during re-establishment, and the levels of among-population gene flow can strongly affect recolonization dynamics, resulting in either an erosion or build-up of population genetic diversity through time. This study focuses on temporal changes in the population genetic structure of the annual invasive plant Impatiens glandulifera across Europe. We resampled 13 populations in 6 regions along a 1600 km long latitudinal gradient from northern France to central Norway after 5 years, and assessed population genetic diversity with 9 microsatellite markers.ResultsOur study suggests sufficiently high numbers of genetically diverse founders during population re-establishment, which prevent the erosion of local genetic diversity. We furthermore observe that I. glandulifera experiences significant among-population gene flow, gradually resulting in higher genetic diversity and lower overall genetic differentiation through time. Nonetheless, moderate founder effects concerning population genetic composition (allele frequencies) were evident, especially for smaller populations.Despite the initially low genetic diversity, this species seems to be successful at persisting across its invaded range, and will likely continue to build up higher genetic diversity at the local scale.
Highlights
The observation that many alien species become invasive despite low genetic diversity has long been considered the ‘genetic paradox’ in invasion biology
In sum, we observed a small temporal increase in genetic diversity and decrease in among-population genetic differentiation between 2011 and 2016, for several I. glandulifera populations across Europe, despite a seemingly overall decrease in their population sizes. These results suggest that annual population re-establishment is following the ‘migrant pool’ colonization model [23], preventing the erosion of local genetic diversity and inflation of among-population genetic differentiation through the combined action of genetic bottlenecks and drift [9, 24]
Our results do suggest moderate founder effects concerning population genetic composition, especially for smaller populations, which is in agreement with the results of Walker et al [17]
Summary
The observation that many alien species become invasive despite low genetic diversity has long been considered the ‘genetic paradox’ in invasion biology This paradox is often resolved through the temporal buildup genetic diversity through multiple introduction events. Several chronosequence-based studies have, shown that the genetic paradox is often ‘resolved’ through the buildup of higher genetic diversity following multiple introduction events from the native range [6, 10, 13, 14] This clearly illustrates how temporal dynamics affect genetic diversity patterns of invasive aliens species after initial invasion, which can, in turn, determine the long-term success of these species in their invaded range [3]. We know very little about the temporal dynamics of population genetic diversity of invasive species, and repeated sampling of the same populations has rarely been done ([16], see [17,18,19,20])
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