out the relationship between snails and a kind of snake whose predation is specialized to snails. The report shows that the specialized snake predation drives prey (snail) speciation. Snail Eating Snake (Pareas iwasakii), which is specialized predator of snails, is distributed broadly from the Yaeyama Islands of Okinawa to southern China, India, and Southeast Asia. This snake has specialized its jaw to eat dextral (clockwise coiled) snails, because many snails are clockwise coiled. This speciation causes sinistral (counterclockwise coiled) snails survive predation by the snake: the snake tends to miss capture of the snails when the snake is given sinistral snails. This works as an advantage to sinistral snails, and as a result, many sinistral snails can be observed in regions where the Snail-Eating Snakes is distributed.

According to the Ministry of the Environment’s Red List, approximately 30% of terrestrial Molluscan species, including snails, are endangered due to human activities such as logging forests and developing land in their habitats, as their means of movement is crawling over the ground on their bellies and this is a barrier for their survival.

Pareas Snake Preying on a Snail

Successful predation of a right-coiled shell

Failed predation of a left-coiled shell

Source: Hoso, M., Kameda, Y., Wu, S. P., Asami, T., Kato, M. & Hori, M. (2010) A speciation gene for left-right reversal in snails results in anti-predator adaptation

Photographs provided by Masaki Hoso

The numbers of teeth differ between the left and right sides of the jaw.

# Section 2 Relationship between the Earth’s Environment and Living Organisms

In Section1 we looked at the close relationship between our everyday lives and biodiversity. Our everyday lives depend on biodiversity, and the biodiversity is dependent on keeping the living organisms and the ecosystems in good health and preserving the interaction between those ecosystems and living organisms.

Here focusing on dynamic migration of birds and fish and dispersal of animals, we will discuss the relationship between ecosystems and organisms in order to understand it.

### 1. The Relationship between Organisms and the Earth

## (1) The Flyway - Crossing in the Sky

In the Heian Period ( $ 8^{th} $ to $ 12^{th} $ Century), Sei Shonagon, who was a court lady to Empress around year 1000, wrote “The Pillow Book” (in Japanese “Makura no Sōshi”): “In autumn evenings...more charming still is a file of wild geese, like specks in the distant sky.” This expresses the sight of aquatic birds migrating over Japan before winter comes, which has an aesthetic of autumn. In recent years, the migrating route of some bird species has been coming clearly due to the development of bird banding surgery, and tracking study technology that uses satellites to ducks and hawks. For example, Wigeon and Pintail, which can be seen in large numbers across Japan from autumn to winter, breed in Russia’s Kamchatskaya Peninsula in the summer and then fly to Hokkaido in autumn. These ducks take a rest of their wings in lakes on their way to the south of Japan, feeding themselves. And they pass the winter in south regions of Japan.

Here we will look at this migration through the trend in number of Pintails that fly to wetlands in Japan. The number of Pintails in Hokkaido reaches a peak around December. After that they fly to the south, and there are hardly few Pintails in Hokkaido's Lake Furenko. Large number of Pintails pass the winter in Japan's southern areas. After they leave for the north before spring, they are no longer seen in the places where they passed the winter. In spring, reaching a peak around April for crossing Hokkaido again, almost none remain in Japan around May (Figure 2-2-1).

Aquatic birds thus use wetlands not by staying in a single place but instead use them like stepping stones.