A small, diverse species of fish with big eyes and slimy skin has evolved a special toolkit to survive – and thrive – both in the water and on land, a dramatic transition that may help explain how species are able to adapt to changing environmental conditions and habitats.
Blennies are known as a “jack of all trades” for their ability to live in marine, brackish, and freshwater environments around the world, some in extreme environments with fluctuating temperature and oxygen levels while others may be found in intertidal zones. Yet some species are primarily terrestrial, providing an ample opportunity to study how successful species are able to transition to new environments.
To determine the underlying mechanisms behind this transition, researchers at the University of New South Wales and the University of Minnesota pooled data on the diet and teeth morphology, behavior, and the frequency at which hundreds of species emerge from the water for either brief or extended periods of time. Statistical modeling revealed a sequence of events that “likely allowed aquatic marine species to ultimately evolve into fishes that could leave [the] water and colonize land,” according to the study published in Functional Ecology.
Successfully amphibious species of blennies had a flexible diet and behavior, allowing them to scrape algae and detritus from rocks. Even so, once on land restrictions of food type and availability triggered further evolutionary changes, especially in the teeth. Instead of promoting a greater diversification of species, the researchers write that the invasion of land appears to “only offer a limited niche for survival.” Though adapting to new environments through a “generalist strategy” may be optimal in the short-term, it may not help to successfully establish populations in the new environment and may offer fewer opportunities for diversification.
"The implications of our findings are that having a broad diet or being behaviorally flexible can help you move into a new habitat. But once there, this flexibility becomes eroded by natural selection,” said study author Terry Ord in a statement. “This presumably means those highly specialized species are less likely to be able to make further transitions or cope with abrupt environment changes in their existing habitat."
Blennies are a unique group of animals to study as they present different stages of evolution and adaptation between extreme environments. The fish’s colonization of land may help to better inform the origin of land vertebrates as they evolved from ocean- to land-lubbers.
"Fossils can give us important insights into how that transition might have unfolded, and the types of evolutionary adaptations it required or produced. But having a contemporary example of fish making similar ecological transitions can also help us understand the general challenges that are faced by fish out of the water,” said Ord.
Though it appears that blennies’ flexible diet and behavior make them better equipped to transition between environments, it doesn’t confirm causality but rather just finds a link between the characteristics and their habitat changes. Regardless, the findings may have broader implications for understanding how animals may respond to wider scale environmental changes.