Blenny fish made a dramatic transition from water to land

A new study from the University of New South Wales (UNSW) has investigated the ability of blenny fish to make a successful transition onto land. The researchers report that a liberal diet and versatile lifestyle empowered blenny fish to convert, but they had to make major changes to adapt to terrestrial life.

Study lead author Professor Terry Ord is an evolutionary ecologist at UNSW.

“Some species of blennies never emerge from water and others stay on land full-time as adults – so they present a unique opportunity to study fish evolution in action and explore the transition from water to the land in a living animal,” said Professor Ord.

“In this study, we found that having a flexible diet has likely allowed blennies to make a successful leap onto land – but once out of the water, these remarkable land fish have faced restrictions on the type of food available to them.”

“These restrictions have triggered major evolutionary changes in their morphology, specifically dramatic changes in their teeth, as they have been forced to become specialist scrappers of the rocks to forage on algae and detritus.”

According to the researchers, analyzing blenny fish before and after they moved onto land could shed new light on how this type of transition is possible.

“There is ample evidence that transitions from one environment into another are responsible for the evolution of many of the species we see today, as well as the diversity in morphology and behavior we see across different species,” said Professor Ord. “But little is known about the mechanisms behind what drives those transitions in the first place.”

By combining a set of evolutionary statistical models with their data, the experts were able to identify the sequence of events that likely allowed blennies to leave water and colonize land. The team was also able to gain a better understanding of how blenny fish responded to their new habitat.

“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. 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,” explained Professor Ord.

“Our findings suggest that being a jack-of-all trade – for example, being flexible in the types of foods you can eat and being flexible in leaving water for very brief periods of time – can open the door to making what would seem to be a really dramatic change in habitat.”

“The flipside of our study suggests that some species that are already uniquely specialized to their existing environment are probably less able to make further transitions in habitat, or might not cope well if abrupt changes occur to their environment, for example as a consequence of the current climate crisis.”

The scientists noted that their research has limitations and said that further research is needed.

“This study is essentially observation, or what we call a correlational study. The data is suggestive that diet and behavioural flexibility is important for making major transitions in habitat, and that once those transitions have occurred, that flexibility is eroded by adaptation,” said Professor Ord.

“But ideally we would want to perform some type of experimental investigation to try to establish causality – that it is flexibility in diet and behavior specifically and not something else that allows such transitions to occur.” 

“It’s possible that diet or behavioral flexibility are not responsible, and that some other currently unknown factor is. What this experimental study might be is hard to imagine at this stage, but we’re working on it.”

The study is published in the in the British Ecological Society journal Functional Ecology.

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By Chrissy Sexton, Earth.com Staff Writer