Evolution in the dark
In the limestone massifs of Picos de Europa National Park, a real-time evolutionary process is unfolding. The fire salamander, Salamandra salamandra, a species typically known for its bright black and yellow warning coloration, has found its way into the deep, lightless cave systems. Specifically, populations of the local subspecies, Salamandra salamandra bernardezi, have become isolated in these subterranean habitats. This separation from the surface world has triggered a series of remarkable adaptations to a life of perpetual darkness.
These karst environments present a consistent, challenging habitat. The temperature remains stable and cool, and the humidity is near 100 percent. In the absence of light, the selective pressures that shaped their surface-dwelling relatives have vanished. The salamanders' bright, aposematic coloring, which warns predators of their toxic skin secretions, is useless here. Similarly, functional eyes, which are metabolically expensive to develop and maintain, offer no advantage. As a result, these cave-dwelling populations are exhibiting troglomorphism—the evolution of traits specific to cave life. This includes a gradual loss of skin pigmentation and the slow regression of their eyes, which become smaller and less functional with each passing generation. It is an example of regressive evolution, where complex features are lost when they no longer provide a survival advantage.