Adaptation to stressful environments : invasion success of the Colorado potato beetle (Leptinotarsa decemlineata)

Abstract

Biological invasions, specifically human-induced dispersals, are one of the major threats to our biodiversity and are predicted to increase. Invasive pests provide an opportunity to study whether adaptation to human-induced environments could promote invasions to other human-induced environments. One major anthropogenic selection pressure is created by pesticides, and pests can be exposed to various pesticides in their native, as well as introduced, ranges. I investigated whether exposure to anthropogenic selection (i.e. insecticides and herbicides) and exposure to multiple anthropogenic stressors selects for higher stress tolerance. I also tested whether parental prolonged diapause or insecticide exposure can increase larval stress tolerance, using an invasive pest (Leptinotarsa decemlineata) as a study species. First, I found that populations differ in their insecticide resistance, which could be due to their past invasion history, as well as past intensity of selection by insecticides. Differences in the resistance were due to both qualitative and quantitative changes in the insecticide target sites, but also due to higher antioxidant defence. These differences also lead to differences in stress tolerance when the individuals were exposed to other pesticides. Second, I found that exposure to both herbicide and insecticide can have interactive effects (both antagonistic and synergistic). Third, I found that prolonged diapause could be a strategy to skip environmental conditions the species is poorly adapted to, however, it carries a sex-specific fertility cost, which could be mitigated by higher offspring body mass. Last, I found that exposure to sublethal doses of insecticide had positive within- and transgenerational effects, by means of increased female body mass and survival. To conclude, exposure to anthropogenic stress could select in addition to pesticide resistance for higher stress tolerance and can induce changes in fitness-related traits and thus contribute to the invasion success of the Leptinotarsa decemlineata.