Abstract
Studying antagonistic coevolution between host plants and herbivores is particularly relevant for polyphagous species that can experience a great diversity of host plants with a large range of defenses. Here, we performed experimental evolution with the polyphagous spider mite Tetranychus urticae to detect how mites can exploit host plants. We thus compared on a same host the performance of replicated populations from an ancestral one reared for hundreds of generations on cucumber plants that were shifted to either tomato or cucumber plants. We controlled for maternal effects by rearing females from all replicated populations on either tomato or cucumber leaves, crossing this factor with the host plant in a factorial design. About 24 generations after the host shift and for all individual mites, we measured the following fitness components on tomato leaf fragments: survival at all stages, acceptance of the host plant by juvenile and adult mites, longevity, and female fecundity. The host plant on which mite populations had evolved did not affect the performance of the mites, but only affected their sex ratio. Females that lived on tomato plants for circa 24 generations produced a higher proportion of daughters than did females that lived on cucumber plants. In contrast, maternal effects influenced juvenile survival, acceptance of the host plant by adult mites and female fecundity. Independently of the host plant species on which their population had evolved, females reared on the tomato maternal environment produced offspring that survived better on tomato as juveniles, but accepted less this host plant as adults and had a lower fecundity than did females reared on the cucumber maternal environment. We also found that temporal blocks affected mite dispersal and both female longevity and fecundity. Taken together, our results show that the host plant species can affect critical parameters of population dynamics, and most importantly that maternal and environmental conditions can facilitate colonization and exploitation of a novel host in the polyphagous T. urticae, by affecting dispersal behavior (host acceptance) and female fecundity.
Highlights
Plants and herbivores exert strong selective pressures upon each other (Schoonhoven et al 2005), resulting in a coevolutionary arms race (Ehrlich and Raven 1964; Kant et al 2008)
Our results show that the host plant species can affect critical parameters of population dynamics, and most importantly that maternal and environmental conditions can facilitate colonization and exploitation of a novel host in the polyphagous T. urticae, by affecting dispersal behavior and female fecundity
We investigated the responses of T. urticae to a host shift, using mite populations maintained on entire plants and tested on detached leaves
Summary
Plants and herbivores exert strong selective pressures upon each other (Schoonhoven et al 2005), resulting in a coevolutionary arms race (Ehrlich and Raven 1964; Kant et al 2008). The herbivore ability to get around host plant defenses is important for polyphagous species, which can feed and reproduce on several plant families (Schoonhoven et al 2005), relative to monophagous species, which are specialized on a few closely related plant species expected to carry similar defenses. A related question is how and by which mechanisms can populations of polyphagous herbivores adapt and exploit many host plant species. Addressing this question is exciting from an evolutionary perspective, for example, to understand local adaptation processes, but can provide crucial information for the management of crop pests
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