Abstract
Plant fitness is often a result of both sexual and asexual reproductive success and, in perennial plants, over several years. Folivory can affect both modes of reproduction. However, little is known about the effects of folivory on resource allocation to the two modes of reproduction simultaneously and across years. In a 2‐year common garden experiment, we examined the effects of different levels of folivory by the strawberry leaf beetle, Galerucella tenella, on current growth, as well as current and future sexual and asexual reproduction (runners) of perennial woodland strawberry, Fragaria vesca. In addition, we measured the chlorophyll content in leaves in the year of experimental damage to determine whether there was increased photosynthetic activity, and, thus, a compensatory response to herbivory. Finally, we tested whether the previous year's folivory, as a result of its effect on plant fitness, affected the level of natural herbivory the plant experienced during the subsequent year. In the year of experimental damage, plants that were exposed to moderate and high levels of folivory (25% and 50% leaf area consumed, respectively) increased their photosynthetic activity compared to control plants. However, only plants exposed to high folivory exhibited negative effects, with a lower probability of flowering compared to control plants, indicating that plants exposed to low or moderate folivory were able to compensate for the damage. Negative effects of folivory were carried over to the subsequent year. Plants that were exposed to moderate folivory (25% leaf area consumed) during first year produced fewer flowers and fruits in the subsequent year. Runner production was consistently unaffected by folivory. The effects of experimental folivory on the level of natural herbivory were mediated via its effects on plant fitness. Our results show that the negative effects of folivory only influence sexual reproduction in woodland strawberry. Furthermore, even though woodland strawberry can tolerate moderate amounts of folivory in the short term, the negative effects on fitness appear later; this highlights the importance of studying the effects of herbivory over consecutive years in perennial plants.
Highlights
One strategy that plants use to cope with herbivore damage is tolerance, that is, mechanisms that enable compensation for damage (Strauss & Agrawal, 1999; Tiffin, 2000)
Most studies on tolerance have been conducted by concentrating on traits related to sexual fitness, such as number of flowers, fruits, or seeds (e.g., Carmona & Fornoni, 2013; Muola, Mutikainen, Laukkanen, Lilley, & Leimu, 2010; Puentes & Ågren, 2012); less information is available pertaining to long‐lived plants employing both sexual and asexual reproduction
TA B L E 1 The results of the analyses of covariance testing the effects of experimental damage, initial plant size, and block on plant size and chlorophyll content (SPAD value), and generalized linear models testing the effects of experimental damage, initial plant size, and block on the probability of flowering, setting fruits, and producing runners during the year of the experimental damage
Summary
One strategy that plants use to cope with herbivore damage is tolerance, that is, mechanisms that enable compensation for damage (Strauss & Agrawal, 1999; Tiffin, 2000). Even though the amount of herbivory that plants experience is affected by many other factors than plant vigor, herbivores’ preference to feed on vigorous plants is likely to add to the long‐term effects of herbivory and potentially to the plants’ ability to compensate for the herbivore damage. We measured the ability of woodland strawberry (Fragaria vesca) to tolerate leaf damage by the strawberry leaf beetle Galerucella tenella (Coleoptera: Chrysomelidae), hereafter strawberry leaf beetle (SLB) This was done by measuring the effects of different levels of leaf damage on survival, growth, and chlorophyll content, as well as sexual and asexual reproduction of woodland strawberry across two years. We were able to investigate whether damage in 1 year affects the level of natural herbivory that the plants experience the following year
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