Wednesday, October 17, 2007

Smells like Home (repost)

So I just got back from a great meeting, and now that my brain is functional again, I wanted to share an interesting talk that I attended. Basically, for those who have never experienced it, when you got to a meeting you get to here a ton of research, most of which is not published yet or in progress. So several days of hearing really smart people doing really cool stuff! (although it can be a mixed bag…) My brain exploded. But now that the knowledge has begun to settle…
The following is a description of some work being done by several people in Australia.

Okay, some background. Most fish have a stage after thy hatch when they float around in the water, before they get big enough to settle out. This would lead to mixing of fish, as they could potentially end up anywhere. However, when they looked at the genetics of some of these fish found on near by reefs, they found that they were very different and not mixing. This means that the baby fish are finding away to keep themselves in the area, or coming back when they are big enough to swim. But how do they know which reef is the one they hatched from?
These researchers looked at larval fish just before they became big enough to settle and tried to see if the babies could ‘tell’ their home by the smell of the water. What they found was that babies found on one reef preferred the water of that reef to any others. They also found that when they kept the babies in the different water for a time to get them to adjust to the new water, they still preferred their ‘home’ water.

Since most of these fish were brooded as eggs on the reef, the researchers were also curious to see when this smell impression was made. Were they impressed while they were in the egg or at hatching? So they took some anemone fish eggs (clown fish), which were known to home not only to reefs, but also back to particular anemones, and ran some tests. Some eggs were kept in anemone water till just before they hatched, and others were only put in anemone water when they were hatching. What they found was that the fish imprinted on the anemone, smelling water immediately after hatching, but not while they were in the eggs.

What it means is that it is possible that some of the fishes on reefs smell the water after hatching, than use the odor to keep themselves from getting too far from their home. So when it comes time for them to settle, they settle on the same area they were born in!
Below is the original abstract with the names and the affiliations of the researchers working on this. I look forward to reading the paper when it gets published.

Boston University Marine Program, Marine Biological Laboratories, James Cook University

Olfactory imprinting in coral reef fish

Most marine organisms have a pelagic larval dispersal phase, leading to the question of how far larvae disperse. Larval behavior and odor preferences may play an important role in larval dispersal and settlement. Apogonid larvae prefer the odor of the reef on which they were caught over other reefs and ocean water. It is possible that this response is due to acclimatization to the odor of water the fish have been recently swimming instead of a long-term preference. We tested apogonid larvae settling on One Tree Island by catching them as they came onto the reef and testing their preference for water for One Tree vs. water from Heron Island in a flume preference test. We then held the fish in either One Tree or Heron water and tested them over a period of nine days. The preference for One Tree water declined in both groups over time; there was no significant difference between the animals held in One Tree or Heron water and both groups maintained a preference for One Tree throughout the testing period. Odor preferences remain stable over time despite exposure to other odors and it is possible they are the result of olfactory imprinting to the home reef odor. Olfactory imprinting has been shown in anemonefishes, but the sensitive period is unknown. Breeding pairs of Amphiprion melanopus were held either with or without an anemone. Eggs and larvae were exposed the anemone from egg laying through hatching (1), from egg laying to just prior to hatching (2), just previous to and 1 hour after hatching (3) or had no anemone exposure (4). At 15 days those larvae in groups 2 and 4 had no preference for the anemone while those in groups 1 and 3 showed a strong significant preference for anemone odor. In this species of reef fish larvae must be exposed to the imprinting odor after hatching in order to learn it.

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