|Budget Amount *help
¥3,700,000 (Direct Cost : ¥3,700,000)
Fiscal Year 2005 : ¥1,700,000 (Direct Cost : ¥1,700,000)
Fiscal Year 2004 : ¥2,000,000 (Direct Cost : ¥2,000,000)
The main purpose of the present project is to investigate experimentally and theoretically the relationship between genetic diversity and system stability. This is based on our previous findings that, in the experimental prey-predator system consisting of the azuki bean weevil (Callosobruchus chinensis) and its larval parasitic wasp (Heterospilus prosopidis), the system with the hybrid strain of the azuki bean weevil could coexist with parasitic wasps significantly longer than the system with either of the pure strains. Based on this finding, we concentrated our effort to generalize the importance of the genetic diversity on the system stability, and also to find the mechanisms promoting such relationships.
In our experimental study, we employed two species of bean weevils, Callosobruchus maculates and Acanthoscelides obtectus, and three species of parasitic wasps, H.prosopidis, Anisopteromalus calandrae, and Dinarmus basalis. A.obtectus has a unique characteristics among the bean weevi
ls, in that it lays eggs not attaching its eggs on the surface of the beans. This particular oviposition method necessitates the hatched larvae to find beans and borrow the entrance. There are two kinds of larvae, one (which we call pioneer) which actively borrow the entrance hole on the bean, and the other (which we call follower) which use the entrance hole made by pioneer. As the initial mortality of the pioneer is rather high, it is better for the hatched larvae to be a follower. Thus, the parent must decide the optimal proportion of the two types of larvae for her highest fitness. At the same time, offspring (eggs) must have some optimal proportion of the two types for their survival. Thus, there are possible parent-offspring conflicts. We carried out the experimental and theoretical studies for their optimal solution.
In one strain of C.maculatus, we observed two strategies of larval competition (contest and scramble) in different lines. By careful observation of the larval behavior in the beans, we found that the larvae of the line with scramble type competition construct the wall in the bean, which restricted the direct contact with other larvae and eventually allowed multiple larvae emerge as adults, whereas, the larvae of the contest type competition constructed no wall, and eventually contacted each other in the bean, and only one larva could emerge as adult. This shows that even within one strain of C.maculatus, the competition strategy can be flexible, and can be selected for by the quality (especially size) of beans on which they feed. Less