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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Publications at this Location » Publication #265278
Title: No evolution of reduced resistance and compensation for psyllid herbivory by the invasive Genista monspessulana

Author
item Reddy, Angelica
item CARRUTHERS, RAYMOND - Former ARS Employee
item MILLS, NICHOLAS - University Of California

Submitted to: Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2015
Publication Date: 11/5/2015
Citation: Reddy, A.M., Carruthers, R., Mills, N.J. 2015. No evolution of reduced resistance and compensation for psyllid herbivory by the invasive Genista monspessulana. Plant Ecology. 216:1457-1468.

Interpretive Summary: Some introduced non-native plant species become invasive in their new environments. Many hypotheses have been proposed to explain this observation. One of them is the evolution of increased competitive ability hypothesis (EICA), which predicts that because invasive plants lack their natural insect herbivores in their new habitats, this results in the selection of faster-growing genotypes that reduce their allocation of resources for defense against insect herbivores. Understanding the defense strategy of an invasive plants may also help forecast the likely impact of herbivory by potential biological control agents. We tested the prediction of reduced defense (i.e. resistance) in French broom (Genista monspessulana), a plant targeted for biological control, measured indirectly as the performance of a psyllid herbivore (a potential biological control agent), by comparing native (France, Spain) and introduced (California, U.S.) plant populations. We also examined the ability of French broom to compensate for psyllid herbivory. Plant origin (native or introduced) did not influence the psyllid’s abundance and population growth rate, suggesting no change in resistance to herbivory for introduced plants. Similarly, we found no overall difference in plant performance between individuals in the presence and absence of psyllid herbivory, suggesting that French broom was able to fully compensate for herbivory. Damaged plants compensated by changing the pattern of branching, which also resulted in greater dry leaf biomass. We conclude that evolution of reduced defenses does not explain the success of French broom as an invader and that compensation for herbivory may limit the efficacy of the psyllid as a biological control agent.

Technical Abstract: The evolution of redirecting resources from plant defense to growth or reproduction may explain why some exotic species are successful invaders in new environments. For example, the evolution of increased competitive ability hypothesis (EICA) posits that escape from herbivores by invasive plants results in the selection of more vigorous genotypes that reduce their allocation of resources to defense. In addition, understanding the defense strategy of an invasive plant may help forecast the likely impact of herbivory. We tested the prediction of reduced defense (i.e. resistance) in Genista monspessulana, measured indirectly as the performance of a specialist psyllid herbivore, by comparing five native and introduced plant populations. We also examined the ability of G. monspessulana to compensate for herbivory in the presence and absence of psyllids for a single plant population from the native and introduced regions. Plant origin (native or introduced) did not influence the psyllid’s abundance and population growth rate, suggesting no change in resistance to herbivory for introduced plants. Similarly, we found no overall difference in plant performance between individuals in the presence and absence of psyllid herbivory, suggesting that G. monspessulana was able to fully compensate for herbivory. Damaged plants compensated by changing the pattern of branching, which also resulted in greater dry leaf biomass. We conclude that evolution of reduced defenses does not explain the success of G. monspessulana as an invader and that compensation for herbivory may limit the efficacy of the psyllid as a biological control agent.