Abstract:

Interactions among co-evolved species has been assumed to operate in a symmetrical manner, resulting in stable equilibrium or evolutionary stable strategies for the observed species. However, recent observational and experimental data highlight the existence of asymmetrical interactions, which may lead to meta-populations or non-equilibrium states (e.g. chaos) between co-evolved species. Here, we explore the asymmetrical interaction in the classic ‘fig-fig wasp’ co-evolution model system and show how such asymmetric interactions may produce meta-populations. It is well known that there are two different kinds of fig wasps inhabiting fig fruits (i.e. pollinator wasps and non-pollinating exploiter wasps). Exploiter wasps have a fitness advantage over pollinator wasps because they do not pay the cooperative cost. However, figs can effectively restrict exploiter wasps, and reward the pollinator wasps, resulting in complex asymmetric interactions among species. Specifically, the discriminative restriction of paretic wasps by fig trees will cause drastic population decreases or even local extinction of the exploiter species in some fig trees, syconia, or associated habitats. In patches where populations of exploiters are low or extinct, pollinator wasps will immigrate leading to concomitant population size increases due to the high reward of fig trees. The prosperity of pollinator wasps will then attract more exploiters, and population increases of exploiter wasps will lead to the sanction by fig trees again. Over the long term, populations of different wasps will chaotically oscillate either temporally or evolutionary through asymmetric interactions.

Key words: metapopulation effect, pollinator wasp, exploiter wasp, mutualism, asymmetric interaction, sanction