Resource dependence of chemical defense and life-history patterns in oribatid mites

• Applicant: Professor Dr. Michael Heethoff
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 290419352

Organisms interact antagonistically with others in their environment and possess defensive strategies for protection against predators, parasites or competitors. Especially among terrestrial arthropods, chemical defensive secretions are of outmost importance for the dynamics of predator prey interactions. Oribatid mites are among the most speciose chelicerate groups, and most diverse and abundant in forest soil and litter, on lichens, mosses and bark in ecosystems all over the world, except the arctic region. About 10,000 species have been described, and abundances in temperate forest soil ecosystems reach hundreds of thousands of individuals per square meter. Most oribatid mite species (glandulate Oribatida) possess a pair of exocrine opisthosomal glands, producing complex blends of hydrocarbons, terpenes and aromatics (some species also produce alkaloids); these are stored in reservoirs for immediate availability. The interpretation of the biological function of oribatid oil gland secretions was quite speculative for a long time, but we have recently provided the first experimental evidence for their adaptive value as allomones. Based on quantitative regeneration data of defensive secretions and predator attack frequencies, we further developed a functional response model called "reducible defence", demonstrating that reservoir based chemical defence is a highly dynamic process. Here, the biosynthetic regeneration rate of defensive secretions shapes the dynamics of predator prey interactions and is responsible for stability or instability of the interaction and, in consequence, for the whole part of soil food webs that include reservoir based chemically defended prey species. The regeneration of defensive secretions has a high energetic cost which certainly also influences other life history parameters (growth, reproduction, development). However, the relation of resource quality and regeneration / life history remains to be elucidated. Hence, we want to address four scientific questions in the context of resource dependent chemical defense and life history parameters. Q1: How does nutritional composition affect the functional performance of oil gland chemistry (quality and quantity) and life history parameters (e.g. growth, reproduction)?Q2: Which nutrients are essential for oil gland secretion biosynthesis?Q3: How are the different chemical classes (especially aromatics) of oil gland compounds synthesized?Q4: Do oribatid mites execute optimal foraging when choosing resources and on which sensory mechanisms is this choice based on?

• DFG Programme: Research Grants