20,000 Leagues - Under the Pond
By her own admission, Professor Jennifer Basil occasionally gets lost. Since moving to New York City she has had to learn how to navigate the West Village and find her way around Manhattan, and in doing so has had to create for herself a new "internal map" of her environment and where she lives and works. But she still, occasionally, ends up in the wrong place.
How creatures find their way around their worlds has always fascinated Professor Basil, and her current research projects attempt to find out how they do it. Take crayfish, for example. These tasty crustaceans live in muddy ponds that they explore regularly for food, shelter, mates and fights. But at the end of the day, they have to be able to find their way back to their holes and safety.
For a small creature, navigating a pond that might enlarge after a flood of rain, shrink during a dry spell, or suddenly become a different shape because of a fallen branch, is no easy task. How does it know?
It all begins, Professor Basil says, with the senses that the crayfish use to explore and learn about their environment. They have eyes, but in muddy ponds these may be of little use; they can detect chemicals floating in the water using small appendages that don't look much like a nose; and they can feel their way around using what Professor Basil calls a "white cane" with which they tap, tap, tap their way along solid surfaces.
Using these senses they travel out from their holes or burrows, seeing, smelling and tapping their way around their pond and building up a "mental" picture of what they find. This internal memory map can save their lives. If danger suddenly threatens, they can scurry directly back to safety by the shortest route using their stored knowledge of where they are and where they need to be.
In Professor Basil's fish tanks, crayfish find themselves in a very different world to the one in which they normally live. However, when they are placed in their new home, millions of years of evolution take over, and the crayfish begin to explore. They tap and feel their way around the sides of the tank, measure its dimensions and make their internal maps of what they find.
Above them, video cameras record their every move and the tapes will later be analyzed for the extent and length of these exploratory trips. But after a while the crayfish become comfortable with their new surroundings and settle down for a rest. That is when Professor Basil changes things. The size or the tank may be changed, the dimensions may be changed, or new obstructions may be added.
Suddenly faced with a new "pond," the crayfish rush off to explore once more, and Professor Basil's cameras again record their every move. But what are they learning and how are they learning it? These are the next questions that can only be answered by a long series of trials in which the crayfish encounter situations not normally part of their lives.
For example, tiny blindfolds can be put over their eyes to find out how important it is for crayfish to see what they are exploring. Or their "white canes" can be tied to their back, making it impossible for them to feel their way around. Each of these restrictions has an effect on how and how long the crayfish spend re-examining their experimental pond, and all the while, the cameras record their efforts.
But even a perfect picture has to be remembered, so Professor Basil is trying to see what role memory plays in the life of a crayfish. Immediately after one of her crustaceans has explored its new world, it is placed on ice. This rapid cooling does not hurt the crayfish, but it does prevent it from processing its memories. Next time it is tested, it is clear at once that it has not remembered a single thing about its previous life. Short-term memory has not become long-term memory.
In another part of her research program Professor Basil goes much deeper. Away from the Louisiana ponds, and out in the very deepest parts of the ocean, lives a creature much, much older than humans or crayfish. These are the descendants of ancient shelled mollusks that were already old when the dinosaurs came and went — the Nautilus.
Peering from their pin-hole eyes is not the best way of finding food at ocean depths where light does not reach. So the Nautilus uses its refined sense of smell. Dead fish and other rotting organisms give off a plume of odor that drifts and twists through the water in swirling, complex patterns that the Nautilus must be able to follow if it is going to find its next meal.
Like trained, sniffing dogs looking for explosives or contraband, the Nautilus "sniffs" its way through the water constantly adjusting and readjusting its orientation according to the strength and direction of the odor plume. As Professor Basil is finding out, this is no easy task, and once again it is more than a pure, mechanical or automatic response; it too seems to involve memory.
Animals of all kinds have incredibly complex patterns of behavior, including finding their way around. Next time you get lost in a strange city, think of Professor Basil's crayfish and Nautilus and what is being learnt about the ways they avoid making the same mistake!