Abstract
Herbivory induces plant defenses. These responses are often costly, yet enable plants under attack to reach a higher fitness than they would have reached without these defenses. Spider mites (Tetranychus ssp.) are polyphagous plant-pests. While most strains of the species Tetranychus urticae induce defenses at the expense of their performance, the species Tetranychus evansi suppresses plant defenses and thereby maintains a high performance. Most data indicate that suppression is a mite-adaptive trait. Suppression is characterized by a massive down-regulation of plant gene-expression compared to plants infested with defense-inducing mites as well as compared to control plants, albeit to a lesser extent. Therefore, we hypothesized that suppression may also benefit a plant since the resources saved during down-regulation could be used to increase reproduction. To test this hypothesis, we compared fruit and viable seed production of uninfested tomato plants with that of plants infested with defense-inducing or defense-suppressing mites. Mite-infested plants produced fruits faster than control plants albeit in lower total amounts. The T. evansi-infested plants produced the lowest number of fruits. However, the number of viable seeds was equal across treatments at the end of the experiment. Nonetheless, at this stage control plants were still alive and productive and therefore reach a higher lifetime fitness than mite-infested plants. Our results indicate that plants have plastic control over reproduction and can speed up fruit- and seed production when conditions are unfavorable. Moreover, we showed that although suppressed plants are less productive in terms of fruit production than induced plants, their lifetime fitness was equal under laboratory conditions. However, under natural conditions the fitness of plants such as tomato will also depend on the efficiency of seed dispersal by animals. Hence, we argue that the fitness of induced plants in the field may be promoted more by their higher fruit production relative to that of their suppressed counterparts.
Highlights
Plants have evolved multilayered defenses under pressure from pathogens and herbivores
T. urticae Santpoort-2 significantly upregulated the PI-IIc and PR-1a expression in Micro-Tom compared to uninfected control leaflets at 7 dpi (Figure 1; F2,11 = 18.56, P < 0.001; F2,12 = 14.56, P < 0.001), In contrast, T. evansi did not upregulate the expression of PI-IIc or PR-1a above control levels significantly in Micro-Tom (Figure 1; F2,11 = 18.56, P = 0.68; F2,12 = 14.56, P = 0.49)
We observed that mite-infested plants produced fruits faster than control plants albeit in lower total amounts
Summary
Plants have evolved multilayered defenses under pressure from pathogens and herbivores. These defenses determine the extent to which plants can escape being eaten depending on the level of susceptibility of the attacker (Schuman and Baldwin, 2016). Plant defenses may be produced constitutively or be induced upon attack (Walling, 2000). Plant Defenses and Fitness Costs characterized by the establishment of structural reinforcements; the accumulation of toxins and inhibitors of an attacker’s digestive proteases (Kessler and Baldwin, 2002) and can include the attraction of foraging natural enemies of herbivores, e.g., via the release of distinct odors (Sabelis et al, 2001). SA- and JA-dependent responses act often antagonistically and this may reflect an adaptive tailoring of distinct defenses against distinct attackers (Thaler et al, 2012)
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