The story of Mexican cave fish, Astyanax mexicanus, an intriguing example of how environmental stressors play a role in development, adaptability, and diversification of an organism. Shown in image is mexicanus species, noticeably different from its surface counterpart in that it does not have developed eyes and lacks pigmentation.
Recent findings support idea that cave species arose when surface fish were trapped in cave waters, raising levels of stress in animals. As thinking goes, triggering stress pathways destabilize a network of proteins that normally works to stabilize phenotype, leading to altered gene expression. Such conditions will lead to increased phenotypic variation, including development of eyes in subsequent generations.
Which of following choices is a feasible explanation for selective advantage of individuals with diminished or no sight?