Understanding how species have evolved in the past is extraordinarily difficult. Typically, we only have small fragments of information available to study immensely complicated processes, such as why some fish transitioned to land 380 million years ago. However, on a small island located in the South Pacific, four species of blenny fishes are living out a scene from history. These fish live in the intertidal pools that dominate the rocky beach front. As high tide comes in, the blennies leave the water for land, and scientists want to know why.

To test the hypothesis that predators drove fish from sea to land, scientists placed blenny mimics both in the intertidal pools and on non-submerged surfaces. Researchers then measured the frequency of attacks on the blenny mimics. Surprisingly, the predators normally located in deeper waters used high tide to creep into the pools. The water mimics were attacked by predatory fish more frequently than their on-land counterparts were by birds or other organisms. This is the first study to show fish becoming amphibious to avoid predators. These results could be extrapolated to the first amphibious fish, who may have left the water to inhabit safer locales as well.

Predators are not the only reason these blennies or other fish might have left the sea for land. Increasing water temperatures and decreasing oxygen concentrations might also spur the blennies to seek the oxygen-rich air. It is also possible a lack of aquatic food makes water less desirable. Researchers could use the blennies to test these other hypotheses. Additionally, these fish could help us discover how physiological adaptations occur during the water-to-land transition by comparing them to non-transitioning blenny species.

Acknowledgements: Many thanks to Valentina Di Santo, a post-doc in the Lauder Lab at Harvard University. Val is currently studying the energetics of skates and their physiological response to climate change.

Managing Correspondent: Zane Wolf

Original Article: Ecological Release from Aquatic Predation Is Associated with the Emergence of Marine Blenny Fishes onto Land – The American Naturalist

Other Media Coverage: These Fish Have Been Caught Evolved to Survive on Land – ScienceAlert; Blennies In Rarotonga Prefer To Stay Out Of The Water In Order To Survive – Science Times

Image Credit: Image by Courtney Morgans

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