Brain and Behavior


Individual Variation

hermaphroditic fish
domestic cats
crayfish aggression

Alzheimer's and other Pathologies

The Question of Gender

The Question of Sexuality



What's this about brain and behavior variation within a species???

Let's first look at a "simple" animal- the fish. In particular, let's look at a type of fish called "Thalassoma" . These fish can do an amazing thing-- they can switch genders! What does that mean and why do we care, you may ask? Let's look at the specifics:

Scientists have noticed that there are two types of males in this species: "supermales" and "initial phase (IP) males", and one type of females: "initial phase (IP) females". Supermales are more aggressive than the others, especially about mating, plus they have large bodies and distinctive iridescent coloring. Think of them as the "football jock" stereotype of the fish world. The IP males are much less aggressive and less colorful than the supermales; they are only able to spawn females' eggs on the sly, due to the aggressive and territorial nature of the supermales. However, if the supermale is taken out of the group, then the IP male quickly changes his behavior and appearance-- becoming more aggressive and changing color. In addition, any large IP females CHANGE SEX and begin all sexual behaviors of the supermale.

(image from "Sex Change in the Bluehead Wrasse") by J. Ford)

So, not only do the normal males turn into supermales, but the large females turn into normal males! How do we know that they've changed sex? By looking at behavior, of course! The researchers observed that the fish that originally acted like females began to be more aggressive towards other males. As this aggressiveness emerged so too did changes in their colorations, indicating that the female had completely become a supermale.

Let's recap: when a change occurs in this fish society, the normal males become supermales AND any large females become supermales as well. Two groups of fish have the ability to change their behavior such that their role in the social group shifts.

Hmmm . . . there is a change in behavior. Does that mean that their brain is changing as well? If we think the brain affects behavior, then theoretically one could assume that the fish's brains must be changing somehow. What do you think?

Do the females' brain change because her behavior has changed??