Abstract
Existing theory for invasive nonnative species emphasizes the role of escaping specialist enemies. A useful approach is to reciprocally transplant enemies in a controlled and common experiment to quantify the interaction specificity of enemies from plant's native and nonnative ranges. Quantitative measures of interaction specificity, from two experiments with three host genotypes (Belgium, Louisiana, and Pennsylvania) and 37Pythiumisolates (10 Europe and 27 USA), revealed thatPythiumpathogens from populations ofPrunus serotinain its native range were not host genotype specific whilePythiumpathogens from its nonnative range vary with host genotype. This study provides empirical evidence suggesting thatPythiumfrom the nonnative range are either preadapted to or are actively adapting to this host. Although only for a single pathosystem, this study illustrates the importance of understanding enemy impact and host-specificity to assess whether an invader has escaped its natural enemies.
Highlights
Pathogens drive both genetic (e.g., [1]) and species diversity (e.g., [2]) by a shared mechanism—negative frequencydependent disease dynamics which causes more negative effects on the fitness of common species and genotypes than rare forms
Quantitative measures of interaction specificity, from two experiments with three host genotypes (Belgium, Louisiana, and Pennsylvania) and 37 Pythium isolates (10 Europe and 27 USA), revealed that Pythium pathogens from populations of Prunus serotina in its native range were not host genotype specific while Pythium pathogens from its nonnative range vary with host genotype
We show that a pool of Pythium isolates from the nonnative range of an invasive tree (P. serotina) is more host-genotype specific than two pools from its native range
Summary
Pathogens drive both genetic (e.g., [1]) and species diversity (e.g., [2]) by a shared mechanism—negative frequencydependent disease dynamics which causes more negative effects on the fitness of common species and genotypes than rare forms (reviewed in [1]). Most studies related to ERH have focused on species-level specialization by enemies (e.g., [4]), but the need exists to better understand forms of genotypic specialization (e.g., [5,6,7]). Biological control practitioners have long acknowledged the importance of genotypic forms of specialization and the need for control agents to affect all weed genotypes (e.g., [8]). A positive correlation has been detected between the number of associated pathogens and the outcrossing rate of the host [9]. These examples of genotype specificity help to explain why outcrossing weeds are harder to control with insect biocontrols than selfing plants [10]
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