Trade-offs may constrain the evolution of defense against insect herbivores and other natural enemies such as plant pathogens that attack plants. Unfortunately, little data exist that definitively address this question. We conducted a greenhouse experiment to determine if there were trade-offs in defense against insect herbivores and plant viruses in the yellow monkeyflower, Mimulus guttatus (Scrophulariaceae). We conducted a 2 x 2 factorial experiment to quantify the effects of spittlebug infestation (Philaenus spumarius) and virus inoculation ( Cucumber mosaic virus, CMV) on the fitness of 26 maternal families of yellow monkeyflower. We found strong evidence of trade-offs in defense against these two natural enemies. On average, plants had high tolerance and resistance to one of the natural enemies, but not the other. There was, however, significant genetic variation in the trade-off. Maternal families varied in the intensity and direction of the trade-off. For example, some maternal families were very tolerant of spittlebug attack, but suffered dramatic reductions in fitness when inoculated with CMV, while other families responded in the opposite direction. This is one of the first studies to demonstrate genetic variation in trade-offs in defense against insect herbivores and plant pathogens.
Species 1: Homoptera Cercopidae Philaenus spumarius (meadow spittlebug)
Keywords: plant defense
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