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Abstract Over the last decade, a large effort has been made to understand how extreme climate events disrupt species interactions. Yet, it is unclear how these events affect plants and herbivores directly, via metabolic changes, and indirectly, via their subsequent altered interaction. We exposed common milkweed (Asclepias syriaca) and monarch caterpillars (Danaus plexippus) to control (26:14°C, day:night) or heat wave (HW) conditions (36:24°C, day:night) for 4 days and then moved each organism to a new control or HW partner to disentangle the direct and indirect effects of heat exposure on each organism. We found that the HW directly benefited plants in terms of growth and defence expression (increased latex exudation and total cardenolides) and insect her'bivores through faster larval development. Conversely, indirect HW effects caused both plant latex and total cardenolides to decrease after subsequent herbivory. Nonetheless, increasing trends of more toxic cardenolides and lower leaf nutritional quality after herbivory by HW caterpillars likely led to reduced plant damage compared to controls. Our findings reveal that indirect impacts of HWs may play a greater role in shaping plant‐herbivore interactions via changes in key physiological traits, providing valuable understanding of how ecological interactions may proceed in a changing world.
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Complementary effects of two plant defence traits on behaviour and performance of monarch butterfly caterpillars
Abstract Plants have evolved multiple defensive traits in response to herbivory; in turn, herbivore specialists evolved adaptive behaviours to avoid or tolerate such defences. Here, we employ milkweeds (Asclepiasspp.) to test two defences, latex and trichomes, for their independent and interactive effects on behaviour and performance of monarch caterpillars (Danaus plexippus).Latex exuded upon damage and the density of leaf trichomes positively correlate across milkweed species, suggesting they may have evolved together as synergistic defences. Nonetheless, the complementary roles of these two traits have been little‐studied. We focus on two behaviours: shaving, or the removal of trichomes, and chewing, which encompasses both deactivation of latex and leaf consumption.In an experiment with seven milkweed species, with and without manipulated latex flow, we found latex to be the primary determinant of reducing chewing, while both defences positively predicted shaving behaviour in the first instar. Next, we conducted a factorial experiment throughout the first three instars, manipulating latex and trichomes on a high‐latex, high‐trichome species, the woolly milkweedAsclepias vestita. On plants with latex and trichomes intact, caterpillars spent the most time shaving and least time chewing of all treatment groups, suggesting a possible synergism. These defence‐driven behavioural effects decreased later in larval development.Latex and trichomes both impacted monarch performance, additively increasing mortality and reducing growth of survivors. Thus, latex and trichomes represent two important plant defences with effects on specialist herbivore behaviour and implications for insect fitness.
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- Award ID(s):
- 2209762
- PAR ID:
- 10576988
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Ecological Entomology
- Volume:
- 50
- Issue:
- 2
- ISSN:
- 0307-6946
- Format(s):
- Medium: X Size: p. 329-339
- Size(s):
- p. 329-339
- Sponsoring Org:
- National Science Foundation
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