Feedback Effects Between the Food Chain and Induced Defense Strategies

Background Oviposition decisions are critical to the fitness of herbivorous insects and are often impacted by the availability and condition of host plants. Monarch butterflies (Danaus plexippus) rely on milkweeds (Asclepias spp.) for egg-laying and as food for larvae. Previous work has shown that monarchs prefer to oviposit on recently regrown plant tissues (after removal of above-ground biomass) while larvae grow poorly on plants previously damaged by insects. We hypothesized that these effects may depend on the life-history strategy of plants, as clonal and non-clonal milkweed species differ in resource allocation and defense strategies. Methodology/Principal Findings We first confirmed butterfly preference for regrown tissue in a field survey of paired mowed and unmowed plots of the common milkweed A. syriaca. We then experimentally studied the effects of plant damage (comparing undamaged controls to plants clipped and regrown, or damaged by insects) on oviposition choice, larval performance, and leaf quality of two closely related clonal and non-clonal species pairs: (1) A. syriaca and A. tuberosa, and (2) A. verticillata and A. incarnata. Clonal and non-clonal species displayed different responses to plant damage, impacting the proportions of eggs laid on plants. Clonal species had similar mean proportions of eggs on regrown and control plants (≈35–40% each), but fewer on insect-damaged plants (≈20%). Meanwhile non-clonal species had similar oviposition on insect-damaged and control plants (20–30% each) but more eggs on regrown plants (40–60%). Trait analyses showed reduced defenses in regrown plants and we found some evidence, although variable, for negative effects of insect damage on subsequent larval performance. Conclusions/Significance Overall, non-clonal species are more susceptible and preferred by monarch butterflies following clipping, while clonal species show tolerance to clipping and induced defense to insect herbivory. These results have implications for monarch conservation strategies that involve milkweed habitat management by mowing. More generally, plant life-history may mediate growth and defense strategies, explaining species-level variation in responses to different types of damage.

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The transition from a cyanobacterial to algal world and the emergence of animals

Emerging Topics in Life Sciences ◽

10.1042/etls20180039 ◽

2018 ◽

Vol 2 (2) ◽

pp. 181-190 ◽

Cited By ~ 17

Author(s):

Jochen J. Brocks

Keyword(s):

Food Chain ◽

Arms Race ◽

Trophic Levels ◽

Snowball Earth ◽

Particle Sizes ◽

Nutrient Transfer ◽

Marine Habitat ◽

Defense Strategies ◽

Molecular Fossils ◽

Maximum Particle

The Neoproterozoic, 1000–541 million years (Myr) ago, saw the transition from a largely bacterial world to the emergence of multicellular grazers, suspension feeders and predators. This article explores the hypothesis that the first appearance of large, multicellular heterotrophs was fueled by an elevated supply of nutrients and carbon from the bottom of the food chain to higher trophic levels. A refined record of molecular fossils of algal sterols reveals that the transition from dominantly bacterial to eukaryotic primary production in open marine habitat occurred between 659 and 645 Myr ago, in the hot interlude between two Snowball Earth glaciations. This bacterial–eukaryotic transition reveals three characteristics: it was rapid on geological timescales, it followed an extreme environmental catastrophe and it was permanent — hallmarks of an ecological hysteresis that shifted Earth's oceans between two self-stabilizing steady states. More than 50 million years of Snowball glaciations and their hot aftermath may have purged old-world bacterial phytoplankton, providing empty but nutrient-rich ecospace for recolonization by larger algae and transforming the base of the food web. Elevated average and maximum particle sizes at the base of the food chain may have provided more efficient energy and nutrient transfer to higher trophic levels, fueling an arms race toward larger grazers, predators and prey, and the development of increasingly complex feeding and defense strategies.

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Overgrazing-induced legacy effects may permit Leymus chinensis to cope with herbivory

PeerJ ◽

10.7717/peerj.10116 ◽

2020 ◽

Vol 8 ◽

pp. e10116

Author(s):

Fenghui Guo ◽

Xiliang Li ◽

Saheed Olaide Jimoh ◽

Yong Ding ◽

Yong Zhang ◽

...

Keyword(s):

Induced Defense ◽

Leymus Chinensis ◽

Leaf Angle ◽

Legacy Effects ◽

Defense Strategies ◽

Tolerance Strategy ◽

Herbivory Tolerance ◽

Below Ground ◽

Simulated Grazing ◽

Colonizing Ability

There is growing evidence that herbivory-induced legacy effects permit plants to cope with herbivory. However, herbivory-induced defense strategies in plants against grazing mammals have received little attention. To further understand the grazing-induced legacy effects on plants, we conducted a greenhouse experiment with Leymus chinensis experiencing different grazing histories. We focused on grazing-induced legacy effects on above-ground spatial avoidance and below-ground biomass allocation. Our results showed that L. chinensis collected from the continuous overgrazing plot (OG) exhibited higher performance under simulated grazing in terms of growth, cloning and colonizing ability than those collected from the 35-year no-grazing plot (NG). The enhanced adaptability of OG was attributed to increased above-ground spatial avoidance, which was mediated by larger leaf angle and shorter height (reduced vertical height and increased leaf angle contributed to the above-ground spatial avoidance at a lower herbivory stubble height, while reduced tiller natural height contributed to above-ground spatial avoidance at a higher herbivory stubble height). Contrary to our prediction, OG pre-allocated less biomass to the rhizome, which does not benefit the herbivory tolerance and avoidance of L. chinensis; however, this also may reflect a tolerance strategy where reduced allocation to rhizomes is associated with increased production of ramets.

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