Makoto Kato

Makoto KATO

  • Born in 1957
  • Field of specialization : Ecology
  • Completed doctoral program, Graduate School of Agriculture, Kyoto University
  • D.Agr., Kyoto University
  • Professor, Graduate School of Global Environmental Studies, Kyoto University
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It is the network of mutualistic relations among living organisms that supports biological diversity. Protecting this network is vital in order to conserve the natural environment.

Prof. Kato has been an avid collector of insects and shells ever since he was a child, and his dream was to become a researcher in the field of entomology. Thus he entered the Faculty of Agriculture at Kyoto University.

On entering as an undergraduate, he immediately began to mix with graduate students, helping out in field studies which dealt with the laborious investigation and analysis of insects. This was his initiation into the real world of research. At the time, there was a strong image of ecology as a field which was concerned mainly with population figures, but Prof. Kato’s interest is more focused on individual organisms.

From the time of his doctoral studies, he began research into the relationships between flowers and insects, looking into how co-evolution was achieved as the organisms maintained their various mutualistic relationships, such as pollination mutualism and defense mutualism. Recently, he discovered one to one obligate pollination mutualism, which exists between the Glochidion tree and the gracillariid moth. This is the third example of this mutualism known so far throughout the world, and is all the more valuable for being the first such discovery in the last hundred years.

"I was able to make this discovery because having studied both plants and insects, I was able to look at nature from a wide perspective. I am proud to say that with plants, I am the second most knowledgeable person in the University," laughs Prof. Kato. He also encourages his students to collect specimens and observe them, and understand their natural history and how they live, and use that to grasp how nature works from a wide perspective, rather than just picking up information from the internet and claiming they understand.

Given his research and publications over a wide range of environments, including forests, river and tidal wetlands, Prof. Kato is regularly invited to give lectures on conserving nature. People tend to look on nature conservation as protecting individual organisms such as beeches or eagles, but actually it is important to know about the mutualistic relations between organisms and to protect those networks, he insists. And the number of supporters of his ideas is steadily growing.

Biodiversity created by mutualism: From the sea and the forests of the Amami Islands

Networks of mutualism

There are many cases of different organisms living closely together,where their relationship, which must have originally been one of conflicting interests, has developed over time into a mutualistic one. The same kind of symbiosis often develops between parasites and their hosts. This is clear evidence that this sort of mutualistic relationship plays an extremely important role in stabilizing the ecosystem and in creating biodiversity. This article describes the astonishing networks of mutualism which can be found in the rich marine and land ecosystems of Amami Oshima, an island in southern Japan.

Marine mutualism

The sea is the habitat of organisms known as pelagic microalgae, filter feeders and detritus feeders, which have patterns of life that cannot be found in the terrestrial ecosystems. Two characteristic features of marine ecosystems are photosynthesis symbiosis, which allows algae to live inside a body, and inhabitation chains, in which a variety of organisms live both inside and on the surface of filter feeders and detritus

The beaches in Japan have been ruined as a result of human interference along the shoreline, but the Amami Islands still have some superb mud flats, coral reefs,mangroves and beds of sea grass. There are many sea cucumbers to be found under the rocks on the beaches which lie between the sea and the forest, and a new species of bivalve has been discovered living in their alimentary tracts. In general,bivalves are filter feeders,but this type of bivalve lives inside the bodies of sea cucumbers. They are also the first known example of a bivalve which lives together as a pair, with one large female and one small male. The pallium protrudes out of the shell and wraps round it, while the legs and the gonads also protrude out of the shell. Living inside another organism in this way is a remarkable example of biological diversity.

Fig.1. An untouched beach on Kakeromajima island

Fig.2. Holothuria pardalis and its oesophagus, together with the bivalve (Entovalva lessonothuriae) which lives inside the oesophagus.

Mutualism in the forest

Fig.3. The new species of tree
(Nothapodites amamianus) discovered on Amami Oshima.

At the same time,terrestrial ecosystems bring plants together with a variety of animals and fungi in 4types of mutualistic relations:pollination mutualism,seed dispersal mutualism,mycorrhizal mutualism and defense mutualism. For example, most angiosperms are pollinated by animals such as bees, and their seeds are dispersed by birds or monkeys. Many plants form mycorrhizae, and are helped in the absorption of nutrients by mycorrhizal fungi. They also use ants to eliminate herbivores. This type of mutualistic network is a main feature of the terrestrial ecosystem.

So what kind of mutualistic systems can we see in the forests of Amami? Amami has many indigenous species such as the Amami rabbit (Pentalagus furnessi) and Amami jay (Garrulus lidthi), which also doubtless form part of the distinctive mutualistic system of these forests. Recently, a new species of tree (of the family Icacinaceae, genus Nothapodites,which is known to include constituents with anticancer properties) has been discovered in the forest of Amami Oshima. The particular characteristics of the biota of the Amami Islands, and their value, are immeasurable.

A third case of obligate pollination mutualism

In this forest, there is known to be a tree of the Glochidion genus, which bears an inconspicuous flower whose system of pollination is beyond our imagination. This plant bears male and female flowers,neither of which have petals, and which no animal comes to during the day time.What is special about it was that the ripe fruit it bears is always fed on by gracillariid moths, and it thereby loses a part of its seeds. We thought that this might perhaps be another example of obligate pollination mutualism, known to operate in the fig and the yucca.

One night in May of the 7th year of our study, we checked that moth alighted on that flower, pollinated it, and it had laid its eggs there. The gracillariid moth collected pollen from the male flower and pollinated the female flower with it when it settled there. It then immediately laid eggs on the pistils. When they hatch, the moth larvae grow by feeding on the seeds as they develop, but they never fail to leave one part of the seeds uneaten.

Later on in the study, it was established that Glochidion plants of every species were pairing up with specific gracillariid moths in mutualistic relations for pollination purposes. Just as in the cases of fig–fig wasp mutualism and yucca–yucca moth mutualism, the relation between the Glochidion plants and the gracillariid moths is a third case of obligate pollination mutualism, with synergistic diversification among the plants and the pollinators. How and when did obligate pollination mutualism come about? How could the evolution from parasitism to mutualism have occurred? How did plants and pollinators coevolve, and how did their cospeciation happen? Why has the evolution of behavior which would circumvent the need for a mutualistic partner, such as multiple oviposition, been suppressed? Does obligate pollination mutualism lead to synergistic diversification? This model system is helping us to find the answers to questions such as these.

The nature of the Amami Islands, both in the sea and the forests, is woven into a network of mutualism. The complexity of these networks not only reflects the long history of the relationships between species, but without doubt also contributes in itself to the creation of diversity. With the biological diversity of both the marine and forest environments being lost at an alarming rate, the importance of mutualistic systems is becoming ever greater.

 Fig.4. The obligate pollination mutualism of the Glochidion plant and gracillariid moth.
A, male flower;
B, female flower;
C, pollinating female moth;
D, adult moth;
E, moth’s proboscis;
F, pollen attached to the proboscis;
G, pollinated female flower;
H, female moth ovipositting;
I, cross section of female flower with oviposition on it arrow pointing at eggs ;
J, ripe fruit;
K, fruit a part of whose seeds have been eaten by a moth larva.