The 3rd IFB Seminar

The 3rd IFB Seminar took place in the conference room of the Institute of Freshwater Biology.

Title: Chaotic dynamics in a three-species system of beetles and parasitoids, switching predation, and learning regulators

Lecturer: Masakazu Shimada

Affiliation: Professor Emeritus, Graduate School of Arts and Sciences, The University of Tokyo Project Researcher, Department of Global Systems Science, The University of Tokyo Research Promotion Director, Headquarters, ERATO Fukatsu Symbiotic Evolution Institute, Bioprocess Research Division, National Institute of Advanced Industrial Science and Technology

Abstract: The three-species predator-prey system of bean weevils and parasitoid wasps, although simple in structure, exhibits complex dynamics due to non-equilibrium interactions. In this talk, we will present the dynamics of the “top-heavy three-species system” (two predators) and the “wide-toothed three-species system” (two prey) as three-species food web structures. These three-species systems show long-term coexistence due to non-equilibrium competitive exclusion, which is a central issue in ecology, long-term chaotic dynamics, oscillations of switching predation, and the effect of learning regulators.

(1) “Chaotic dynamics of the top-heavy three-species system”: The predatory actions of the two parasitoid wasps are diametrically opposed. Braconid wasps have a high host discovery efficiency but lay few eggs. On the other hand, the host discovery efficiency of the Japanese dung bean wasp depends on the host density in the bean, and when the host density is low, the host discovery efficiency is low. When host density is high, the Japanese dung bean wasp creates a tube with an ovipositor to suck sap, and by foraging, it produces a large number of eggs at once and parasitizes many hosts. The three-species system of these two species and the host bean weevil, the azuki bean weevil, shows complex dynamics over a period of 1000 days, with a Lyapunov exponent greater than 1.0, indicating chaotic dynamics. Furthermore, the spatial structure of individual bean populations is predicted to exert a memory effect on the non-equilibrium spatiotemporal dynamics, strongly stabilizing the unstable host-parasitoid dynamics that would otherwise tend to diverge.

(2) “Switching predation dynamics of a divergent three-species system”: Pteromalaspa quinqueradiata exhibits a Type III functional response, relying on the odors of two host bean weevils (Azuki bean weevil and C. bruchida) for parasitism and oviposition. This demonstrates density-dependent odor learning predatory behavior, and during a survey of the population dynamics of the three-species system, we detected antiphase oscillations in predation pressure on the two host species. As a result, the three-species system showed a long duration of 100 generations, with a two-week time-lag antiphase oscillation associated with the growth of the two host species within the beans. In addition, the substances that regulate the odor learning of the two bean weevil hosts were chemically analyzed by GC-MS, and a bioassay in which chemically synthesized substances were applied to the surface of hostless beans was performed, and it was possible to induce parasitic behavior of Pteroma punctata similar to that in the three-species experimental system.