Final answer:
True, different selective pressures in marine and pond environments have led to marine stickleback fishes retaining spines for defense, while pond-dwelling sticklebacks have evolved to lose their spines due to predation from dragonfly larvae and other factors.
Step-by-step explanation:
The statement regarding the three-spined stickleback fish indicates a scenario where the evolutionary process is influenced by environmental factors. It is true that stickleback fish that can migrate to the ocean possess spines, which likely serve as a defense against larger predators in marine environments. In contrast, stickleback populations that are land-locked in ponds have evolved to not have spines; this is a beneficial trait in their specific habitat, which includes threats from predatory dragonfly larvae. Spines can actually hinder the stickleback's survival in these pond environments because they make the fish more susceptible to predation by these larvae.
This interesting aspect of evolution reflects how changes in environmental conditions and different selective pressures can lead to significant physical changes in a species. Stickleback fish in different environments, such as oceans and land-locked ponds, face varying challenges and threats, leading to the evolution of different physical traits that can aid in their survival and reproduction in their respective habitats. The existence of these different traits among populations underscores the principle of natural selection, as first outlined by Charles Darwin's theory of evolution. In these ecosystems, the evolution of species and the environmental conditions influence each other in a reciprocal relationship, as has been demonstrated in scientific studies.