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Leaf fluctuating asymmetry (FA) is an important indicator of plant responses to various sources of stress, which range from poor nutritional and harsh environmental conditions to herbivory and parasitism. Mistletoes are important hemiparasites, which represent a source of stress for their host plants but, in spite of being common in all major biogeographical regions of the world, no study has measured the response of their hosts in terms of leaf FA. We addressed the effect of mistletoes on host–plant foliar FA by comparing parasitized and non-parasitized individuals of four host species in two sites in southeastern Brazil, Serra do Cipo and Serra do Rola Moca. In the four host species, parasitized individuals presented significantly higher levels of leaf FA than unattacked plants. The specialist mistletoe Phoradendron cf. amplexicaule induced higher levels of FA on its host Erythroxylum suberosum (Erythroxylaceae) than the generalist mistletoe Struthanthus flexicaulis did on either Mimosa calodendron (Fabaceae), Lychnophora pinaster (Asteraceae) or Stachytarpheta glabra (Verbenaceae). We hypothesized that specialized parasites could be more damaging to their hosts than generalist mistletoes, which could explain the higher FA levels observed. Significant differences in FA levels among parasitized individuals within species were found, which were significantly correlated with intensity of infection (number of mistletoes per host individual). The results indicate that mistletoes represent an important factor of stress for their host plants, and that FA can be an excellent instrument for evaluating the effects of infections by parasitic plants. |
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