Skeletal study suggests at least 11 fish species are capable of walking


Date:
September 8, 2020
Source:
Florida Museum of Natural History
Summary:
An international team of scientists has identified at least 11
species of fish suspected to have land-walking abilities.



FULL STORY ==========================================================================
An international team of scientists has identified at least 11 species
of fish suspected to have land-walking abilities.


==========================================================================
The findings are based on CT scans and a new evolutionary map of the
hillstream loach family, which includes the only living fish species
caught in the act of walking: a rare, blind cavefish known as Cryptotora thamicola, or the cave angel fish. Pinpointing which species of hillstream loaches have walking capabilities can help scientists piece together
how the first land-walking vertebrates might have come to be.

In a new study, researchers from the Florida Museum of Natural History,
the New Jersey Institute of Technology, Louisiana State University and
Maejo University in Thailand analyzed the bone structure of nearly 30 hillstream loach species, describing for the first time three categories
of pelvic shapes. Based on the shape of the bone that connects some
loaches' spines to their pelvic fins, the team found that 10 other species
of loach shared the cave angel fish's unusually hefty pelvic girdle.

"Fishes don't usually have any connection between their spine and pelvic
fin," said biologist Zachary Randall, manager of the Florida Museum's
imaging lab and one of the study's co-authors. "But before, the idea
was that the cave angel fish was totally unique. What's really cool
about this paper is that it shows with high detail that robust pelvic
girdles are more common than we thought in the hillstream loach family."
But not all loaches are so gifted: Though more than 100 species of
hillstream loach are found throughout Southeast Asia, the cave angel
fish is the only one whose walking capabilities have been observed and
studied. Its salamander-like wiggle, powered by enlarged ribs bolstered
with stabilizing muscle attachments, was first described in Scientific
Reports in 2016 by Brooke Flammang, an assistant professor of biology
at NJIT and the study's lead principal investigator.

Randall said the cave angel fish's walk is a key adaptation for surviving
fast- flowing cave streams. It can grip rocky streambeds and move between habitats - - even up waterfalls -- as water levels fluctuate in the dry
season. The cave angel fish's increased mobility could help it access well-oxygenated stream regions with few or no occupants. Still, little
is known about the species, including what it eats.



========================================================================== "These loaches have converged on a structural requirement to support terrestrial walking not seen in other fishes," said study lead author and
NJIT Ph.D. candidate Callie Crawford in a statement. "The relationships
among these fishes suggest that the ability to adapt to fast-flowing
rivers may be what was passed on genetically," rather than a set of
specific physical characteristics.

The team used CT scanning and DNA analysis to trace the evolutionary
history of the hillstream loach family and found that, rather than
evolving from a single origin, a robust pelvic region appeared several
times across the hillstream loach family.

"Even though the cave angel fish was first described in 1988, this is
the first time it's been included in the hillstream loach family tree,"
Randall said.

"With our Thai collaborators and using DNA analysis, we were able to
use hundreds of genes to trace how pelvic shapes in these fish have
evolved over time. Now, we have a much more accurate tree that adds a
framework for studying how many species can walk and the extent to which they're able to." "This study brought together a team of researchers
with interests and levels of expertise that varied from those of us who
do fieldwork and study fishes in their natural habitats to geneticists
to comparative anatomists," added Lawrence Page, Florida Museum curator
of fishes and a co-principal investigator of the study. "The result is a greatly improved understanding of the evolution of an extremely uncommon
event -- the ability of a fish to walk on land." Randall and his team
most recently observed the cave angel fish on a 2019 cave excursion
in northwest Thailand. Given the rarity of spotting a cave angel fish
in the field, Randall said the team was surprised to find six of them
clinging to the bed of a fast-flowing shallow stream among glittering stalagmites in one of the cave's chambers. He added that the cave angel
fish's rarity meant that museum specimens and CT data were key to mapping
the family's evolution.

"The beauty of CT scanning is that you can capture different types of
high- resolution data without compromising the integrity of the specimen," Randall said. "For rare species like this one, it even allows you to
capture things that are hard to observe in the field, even what it eats."
The team published its work in the Journal of Morphology.


========================================================================== Story Source: Materials provided by
Florida_Museum_of_Natural_History. Original written by Halle
Marchese. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Callie H. Crawford, Zachary S. Randall, Pamela B. Hart, Lawrence
M. Page,
Prosanta Chakrabarty, Apinun Suvarnaraksha, Brooke
E. Flammang. Skeletal and muscular pelvic morphology of hillstream
loaches (Cypriniformes: Balitoridae). Journal of Morphology, 2020;
DOI: 10.1002/jmor.21247 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200908200522.htm

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