托福口语 Task 3

In biology, the concept of 'phenotypic plasticity' refers to the ability of a single genotype to produce different phenotypes in response to environmental conditions. This means that organisms with the same genetic makeup can exhibit variations in physical traits, behavior, or physiology depending on the environment they experience. Phenotypic plasticity allows species to adapt rapidly to changing environments without genetic changes, enhancing their survival and reproductive success in diverse habitats.

Professor: Let me give you a classic example from a study on water fleas, specifically Daphnia. When Daphnia are exposed to water containing chemicals from predators, like fish, they develop a defensive trait—they grow a spiny helmet and longer tail spine. These physical changes make them harder for fish to swallow. Interestingly, if the same Daphnia clones are raised in water without predator cues, they remain small and round without these spines. So, genetically identical offspring from the same mother can look very different depending on whether predators are present. This rapid adjustment in body shape is a perfect illustration of phenotypic plasticity—it’s not a genetic change but an environmental response that boosts their chances of survival.