Evidence for rapid evolutionary change in an invasive plant in response to biological control

Abstract

We present evidence that populations of an invasive plant species that have become re-associated with a specialist herbivore in the exotic range through biological control have rapidly evolved increased antiherbivore defences compared to populations not exposed to biocontrol. We grew half-sib families of the invasive plant Lythrum salicaria sourced from 17 populations near Ottawa, Canada, that differed in their history of exposure to a biocontrol agent, the specialist beetle Neogalerucella calmariensis. In a glasshouse experiment, we manipulated larval and adult herbivory to examine whether a population's history of biocontrol influenced plant defence and growth. Plants sourced from populations with a history of biocontrol suffered lower defoliation than naïve, previously unexposed populations, strongly suggesting they had evolved higher resistance. Plants from biocontrol-exposed populations were also larger and produced more branches in response to herbivory, regrew faster even in the absence of herbivory and were better at compensating for the impacts of herbivory on growth (i.e. they exhibited increased tolerance). Furthermore, resistance and tolerance were positively correlated among genotypes with a history of biocontrol but not among naïve genotypes. Our findings suggest that biocontrol can rapidly select for increased defences in an invasive plant and may favour a mixed defence strategy of resistance and tolerance without an obvious cost to plant vigour. Although rarely studied, such evolutionary responses in the target species have important implications for the long-term efficacy of biocontrol programmes.

Transpacific coalescent pathways of coconut rhinoceros beetle biotypes: Resistance to biological control catalyses resurgence of an old pest

“…While biological control agents have clear benefits, our results reveal the mechanism of a potential breakdown and emphasize the importance of continued quarantine against pests, even those already thought to be present in a region. Novel pest bio‐ and genotypes appear, with the potential to enhance outbreak damage in both invasive and native ranges (e.g., Delatte et al., ; Stastny & Sargent, ). In the case of O. rhinoceros , it is unclear whether OrNV resistance is the sole phenotypic factor contributing to biotype G's invasion success, but a new approach to monitoring ongoing changes in invasive pest genomics is essential as globalization rapidly facilitates the spread of novel, virulent biotypes.…”

Invasion history alters the behavioural consequences of immune system activation in cane toads

“…By contrast, at the range-core where pathogens are common, tolerance to an inevitable infection may be a more appropriate strategy. Although the role of selection on tolerance is well recognised in studies on invasive plants (Muller-Scharer, Schaffner, & Steinger, 2004;Stastny & Sargent, 2017;Zas, Moreira, & Sampedro, 2011), its role in shaping animal invasions is only now emerging (Brace, Sheikali, & Martin, 2015;Coon, Brace, McWilliams, McCue, & Martin, 2014;Martin, Hopkins, Mydlarz, & Rohr, 2010;Young, Parker, Gilbert, Guerra, & Nunn, 2017). If, however, resistance and tolerance strategies differ in their associated levels of sickness behaviour (Adelman & Hawley, 2017) which in turn impact the rate of dispersal, then these strategies may be important targets of selection at invasion fronts.…”

Bugs scaring bugs: enemy‐risk effects in biological control systems

“…Additionally, though we focus on arthropod pests, work on invasive plants suggests that invasive species facing no topdown pressure may evolve to devote fewer resources to anti-enemy responses and more to competitive ability (Blossey and Notzold, 1995). This process may be rapidly reversed upon the reintroduction of natural enemies through biological control programs, with invasive species rapidly developing anti-enemy responses that could drastically change the initial CE-NCE ratio (Stastny and Sargent, 2017). *Focal observations might reveal some NCEs related to the expression of anti-predator behaviours, although would be unlikely to quantify the costs of such behaviours.…”