How fish got onto land, and stayed there

Date:
June 17, 2020
Source:
British Ecological Society
Summary:
Research on blennies, a family of fish that have repeatedly left
the sea for land, suggests that being a 'jack of all trades'
allows species to make the dramatic transition onto land but
adapting into a 'master of one' allows them to stay there.



FULL STORY ========================================================================== Research on blennies, a family of fish that have repeatedly left the
sea for land, suggests that being a 'jack of all trades' allows species
to make the dramatic transition onto land but adapting into a 'master
of one' allows them to stay there. The findings are published in the
British Ecological Society journal Functional Ecology.


========================================================================== Researchers from University of New South Wales and the University of
Minnesota pooled data on hundreds of species of blennies, a diverse
family of fish where some are aquatic and others have left the water completely. They found that a flexible diet and behaviour were likely
to be instrumental in the transition to land.

However, once out of the water, restrictions on the type of food available triggered major evolutionary changes, particularly to their teeth, as
land dwelling blennies have become specialists in scraping algae and
detritus from rocks.

Dr Terry Ord, lead author of the research, said: "The implications
of our findings are that having a broad diet or being behaviourally
flexible can help you move into a new habitat. But once there, this
flexibility becomes eroded by natural selection. This presumably means
those highly specialised species are less likely to be able to make
further transitions, or cope with abrupt environment changes in their
existing habitat." The scenario of fish colonising land has obvious
parallels with the origin of all land vertebrates. "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 Dr Ord.

Blennies are a remarkable family of fish with different species occupying strikingly different environments. Some are aquatic. Others spend time in
and out of the water in the intertidal zone, an extreme environment with fluctuating water levels and pools that can rapidly change in temperature
and oxygen levels.

Some species of blenny are terrestrial and spend almost their entire
lives out of the water in the splash zone and must keep moist in order
to breathe through their skin and gills. Despite these challenges,
blennies have been incredibly successful in repeatedly making these
dramatic transitions.

Because of this diversity, different blenny fish species represent clearly defined stages of the invasion process between two completely different environments. This makes them a unique group of animals to study.

Dr Ord explained the origin of the study with his co-author Dr Peter
Hundt: "We both had extensive data collected on many different species
of blenny from across the world. Peter had detailed information on diet
and teeth morphology, while I had lots of data on behaviour and frequency
of different species emerging from water for brief or extended periods
on land.

"We threw a set of complex evolutionary statistical models at this
combined data and we were able to reveal the sequence of events that
likely allowed aquatic marine fishes to ultimately evolve into fishes
that could leave water and then colonise land. Our study also showed
how those species on land adaptively changed to better suit the
specialised diet needed to survive on land." The authors caution
that although the observational data suggests a flexible diet and
behaviour allows a transition to new environments to occur, it cannot
confirm causality. "Ideally we would perform some type of experimental investigation to try to establish casualty. What this experimental study
might be is hard to imagine at this stage, but we're working on it." Said
Dr Ord.

The authors are also looking to further investigate how the invasion
of land has impacted other aspects of blenny fish behaviour, ecology
and bodies.

"Terrestrial blennies are really agile out of water, and I suspect
they've adapted their body shape to allow them to hop about the rocks so freely. Which in turn implies they might not be able to go back to the
water" said Dr Ord, "It would also be exciting to know how their sensory systems might have adapted out of the water as well, given vision and
smell would probably work quite differently in these environments."

========================================================================== Story Source: Materials provided by British_Ecological_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Terry J. Ord, Peter J. Hundt. Crossing extreme habitat boundaries:
Jack‐of‐all‐trades facilitates invasion but is
eroded by adaptation to a master‐of‐one. Functional
Ecology, 2020; DOI: 10.1111/1365-2435.13600 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617091011.htm

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