Fitness costs refer to the negative impacts or disadvantages that an organism may experience as a result of maintaining a particular trait or behavior that is beneficial in certain environments. In evolutionary biology, fitness costs play a key role in understanding the trade-offs involved in the evolution and maintenance of various traits. These costs can manifest in various forms, such as reduced reproductive success, decreased survival rates, increased energy expenditure, or decreased overall health and longevity. By studying fitness costs, researchers can gain insights into the adaptive value of different traits and behaviors, as well as the constraints and limitations that organisms face in their evolutionary journey.