托福听力

🎧 听力原文

Narrator: Listen to part of a lecture in a biology class. Professor: Today we're going to talk about a fascinating adaptation in some fish species: the ability to change sex. This phenomenon, called sequential hermaphroditism, occurs in many reef fish. For example, clownfish live in groups with a dominant female, a breeding male, and several non-breeding males. When the female dies, the breeding male changes into a female, and the largest non-breeding male becomes the new breeding male. In contrast, some species like the bluehead wrasse are protogynous, meaning they start as females and change to males. This often happens when a dominant male disappears, prompting the largest female to transform. This change is not just behavioral; it involves hormonal shifts and even changes in the gonads. The trigger is usually social, not age-related. So, these fish have a remarkable plasticity, allowing them to maximize reproductive success in dynamic environments.