托福口语 Task 3

In biology, the term 'commensalism' refers to a symbiotic relationship between two species in which one species benefits while the other is neither helped nor harmed. The species that benefits is called the commensal, while the other is the host. This interaction is distinct from mutualism, where both species benefit, and parasitism, where one species benefits at the expense of the other. Commensalism often involves the commensal gaining food, shelter, or transportation from the host without causing any significant impact on the host's survival or reproduction.

Professor: To illustrate commensalism, let's consider a real-world example from marine biology. The remora, also known as the suckerfish, has a modified dorsal fin that acts as a suction cup on top of its head. This allows the remora to attach itself to larger marine animals, such as sharks or manta rays. When the shark feeds and scraps drop, the remora detaches briefly to eat the leftover food particles, then reattaches. The remora clearly benefits—it gets free transportation and access to food without expending much energy. Now, does the shark suffer? Not really. The shark doesn't seem to notice the remora, and its feeding or swimming is not impeded. The remora doesn't bite the shark or steal food directly from its mouth; it just picks up scraps that would otherwise be lost. So the shark is essentially unaffected. This relationship fits commensalism perfectly—one species benefits, the other is neutral.