What likely caused the disappearance of body armor in sticklebacks in several lakes?

The decline of body armor in sticklebacks across various lakes can be attributed to independent mutations that were favored by natural selection. This phenomenon often occurs when different populations of a species adapt to similar environmental pressures, leading to similar traits emerging independently in different locations.

In the context of sticklebacks, natural selection can favor reduced body armor in environments where predation pressures are lower, thereby allowing individuals with less armor to thrive and reproduce more effectively. Since these lakes may have different characteristics (like varying predator compositions), mutations that lead to reduced armor can arise independently in each population of sticklebacks. As a result, the presence of advantageous traits in different populations can enhance survival and reproductive success under specific local conditions, demonstrating the role of natural selection in driving evolutionary change.

While common mutations spreading across all populations or environmental pressures from predators could play a role, the emphasis on independent mutations highlights the importance of localized adaptation rather than a unifying factor affecting all populations uniformly. Reproductive isolation would imply that populations cannot interbreed, which is not directly linked to changes in body armor in the evolutionary context provided. Thus, the correct choice underscores the significant impact of localized adaptive mutations in response to environmental conditions.