Research

Ecological and coevolutionary networks driving biosphere dynamics

Ongoing global warming has become one of the most serious environmental issues, which destabilize and threaten agriculture, human health, economics and politics on a global scale. Each year, the amount of green house gas circulating between the atmosphere and soil biosphere is much more than that emitted through human activities. This fact suggests that the basic understanding of the structure and dynamics of terrestrial ecosystems is indispensable for finding fundamental solutions for global warming and the related environmental issues.

Our aim in this project is to develop a series of new methodologies for understanding the diversity and community structure of belowground organisms and thereby construct theoretical and empirical bases for restoring forest ecosystems or designing efficient agricultural ecosystems. We are trying to integrate ecology, evolutionary biology, genomics and computer sciences in order to elucidate the “coevolutionary” interactions of belowground organisms.

Escalation of coevolutionary arms races

Organisms are surrounded by their predators, parasites, hosts, and mutualists, being involved in reciprocal adaptation processes with such ‘‘biotic environment’’. The concept of ‘‘coevolution’’, therefore, provides a basis for the comprehensive understanding of evolutionary and ecological dynamics in biological communities and ecosystems.

We have studied the arms race coevolution involving a seed-eating weevil (Curculio camelliae) with a long snout and its camellia plant (Camellia japonica) host with a thick fruit coat (pericarp) throughout the marked climatic gradient observed across the Japanese islands. A series of experimental and field studies demonstrated that female weevils, which bored holes through camellia pericarps to lay eggs into seeds, had evolved much longer snouts than males, especially in areas in which Japanese camellia pericarps were very thick. The thickness of the plant pericarp was heritable, and the camellia plant evolved a significantly thicker pericarp on islands with the weevil than on islands without it. Across populations with weevils, resource allocation to plant defense increased with increasing annual mean temperature or annual precipitation, thereby geographically differentiating the evolutionary and ecological interactions between the two species. Given that the coevolutionary relationship exhibited appreciable variation across a relatively small range of annual mean temperatures, ongoing global climatic change can dramatically alter the coevolutionary process, thereby changing the ecological interaction between these species. A population genetic study further showed that the populations of the weevil had diverged rapidly after the last glacial maximum, indicating that the geographic differentiation of the weevil-camellia coevolutionary processes occurred during the last postglacial period, being affected by changes in local climate.

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