Abstract
The ability of invasive species to adapt to novel conditions depends on population size and environmental mismatch, but also on genetic variation. Away from their native range, invasive species confronted with novel selective pressures may display different levels of neutral versus functional genetic variation. However, the majority of invasion studies have only examined genetic variation at neutral markers, which may reveal little about how invaders adapt to novel environments. Salmonids are good model systems to examine adaptation to novel pressures because they have been translocated all over the world and represent major threats to freshwater biodiversity in the Southern Hemisphere, where they have become invasive. We examined patterns of genetic differentiation at seven putatively neutral (microsatellites) loci and one immune-related major histocompatibility complex (MHC class II-β) locus among introduced rainbow trout living in captivity (farmed) or under natural conditions (naturalized) in Chilean Patagonia. A significant positive association was found between differentiation at neutral and functional markers, highlighting the role of neutral evolutionary forces in shaping genetic variation at immune-related genes in salmonids. However, functional (MHC) genetic diversity (but not microsatellite diversity) decreased with time spent in the wild since introduction, suggesting that there was selection against alleles associated with captive rearing of donor populations that do not provide an advantage in the wild. Thus, although high genetic diversity may initially enhance fitness in translocated populations, it does not necessarily reflect invasion success, as adaptation to novel conditions may result in rapid loss of functional MHC diversity.
Highlights
Human-mediated global change is causing the local extinction of some species and the spread of others, resulting in novel species interactions and changes in ecosystem functioning
We examined patterns of genetic differentiation at seven putatively neutral loci and one immune-related major histocompatibility complex (MHC class II-b) locus among introduced rainbow trout living in captivity or under natural conditions in Chilean Patagonia
In order to gain a better understanding of the role of genetic variation in determining establishment success during biological invasions, we examined variability at neutral loci and at a functional, immune-related locus among translocated rainbow in Chilean Patagonia
Summary
Human-mediated global change is causing the local extinction of some species and the spread of others, resulting in novel species interactions and changes in ecosystem functioning. Invasive species can trigger dramatic changes in native biodiversity, both at community and ecosystem levels and represent one of the main threats to global biodiversity (Gurevitch and Padilla 2004; Carroll 2007; Randi 2008). Invaders are able to persist at small initial population sizes before expanding and becoming invasive (Novak 2007). The initial invasion phase represents a critical time for the adaptation of species to local conditions (Sakai et al 2001), and invaders may pass through demographic bottlenecks until suitable environmental conditions arise (Prentis et al 2008). The ability of founders to adapt to novel conditions may depend on population size and environmental mismatch, and on levels of genetic variation
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