Key to fish family's land-walking abilities revealed in study of Asia's hillstream loaches

Date:
August 26, 2020
Source:
New Jersey Institute of Technology
Summary:
A new genetic and morphological study of South Asia's hillstream
loach (Balitoridae) family is shedding new light on the fishes'
unusual land- walking capabilities, including that of the family's
strangest relative - - Cryptotora thamicola -- a rare, blind
cavefish from Thailand with an uncanny ability to walk on land
and climb waterfalls using four limbs that move in salamander-like
fashion.



FULL STORY ==========================================================================
In a study published in the Journal of Morphology, a team of researchers
from New Jersey Institute of Technology (NJIT), Florida Museum of Natural History, Louisiana State University and Thailand's Maejo University
have successfully pieced together the ancestral relationships that make
up the family tree of hillstream loaches (Balitoridae), detailing for
the first time a range of unusual pelvic adaptations across the family
that have given some of its members an ability to crawl, or even walk
as salamanders do, to navigate terrestrial surfaces.


==========================================================================
The team's DNA-based comparative analysis of the fish family, known to currently encompass more than 100 species native to South and Southeast
Asia, is the first of its kind to include Cryptotora thamicola -- the only living species of fish known to walk on land in a step pattern similar
to tetrapods, or four-limbed vertebrates such as reptiles and amphibians.

The results have revealed that three dominant variations of pelvic anatomy
in the family, notably including key variations of a robust pelvic girdle
and elongated sacral rib among many loaches, which researchers expect
are central in explaining the different degrees of land-walking behavior exhibited by the fishes. The team says that the family's modified pelvic features enabling terrestrial locomotion, which were found most pronounced
in Cryptotora thamicola, may have been adapted to enhance their odds of survival in rivers and other fast-moving water environments that many Balitoridae inhabit today.

"The modified morphology of these Balitoridae, particularly the enlarged
sacral rib connecting the pelvic plate to the vertebral column, is
a big part of why studying this family is so exciting," said Callie
Crawford, the study's corresponding author and Ph.D. candidate at NJIT's Department of Biological Sciences. "These loaches have converged on a structural requirement to support terrestrial walking not seen in other
fishes. What we've discovered is three anatomical groupings that have
major implications for the biomechanics of terrestrial locomotion of these loaches, and the relationships among these fishes suggest that the ability
to adapt to fast-flowing rivers may be what was passed on genetically,
more than the specific morphology itself." "Now that we have revealed a spectrum of pelvic morphologies among these fishes, we can compare the
extent of skeletal support with the walking performance in a species,"
said Brooke Flammang, the study's lead principal investigator and
assistant professor of biology at NJIT. "This will allow us to measure
the mechanical contribution of robust hips to terrestrial locomotion."
Unlike most living fishes that feature pelvic fins located more anteriorly
and attached to the pectoral girdle, balitorids typically boast a
skeletal connection between the pelvic plate (basipterygium) and the
vertebral column via a modified sacral rib and its distal ligament. These modifications are understood to help generate force against the ground
useful for navigating land. The most extreme example emerged in 2016
with the discovery of Cryptotora thamicola in the fast-flowing aquatic conditions of the Tham Maelana and Tham Susa karst cave systems in
northern Thailand. NJIT researchers then first identified that the rare
species used a robust pelvic girdle attached to its vertebral column to
walk and climb waterfalls with a salamander-like gait.



========================================================================== "This trait is likely key to helping these fishes avoid being washed away
in the fast-flowing environment that they live in," said Zach Randall, co-author of the paper and biological scientist at Florida Museum of
Natural History.

"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." "The sacral ribs allow forces from the
fins pressing against the ground to be transferred to the body so that
every time the fin pushes down during a step, the body is pushed up
and forward," explained Flammang. "The increased surface area of the
more modified sacral ribs also offers more room for muscle attachment,
so fishes such as Cryptotora thamicola can rotate their hips during
walking, producing a salamander-like gait." River Loach Family Factions
To better understand the evolution of the river loach family, the team conducted a broad sampling of ?CT-scan data taken from 29 representative specimens, analyzing and comparing skeletal structures, muscle morphology
as well as sacral rib shape across 14 of the 16 balitorid genera. The
team also sampled genomic datasets of 72 loaches across seven families
to reconstruct the evolutionary relationships in the Ballitoridae tree
of life. "We were able to use a large survey of museum specimens and CT scanning to incorporate data even from specimens that didn't have tissue
or genetic data intact," noted Randall.

The results showed that the loaches fall into three distinct morphotypes,
which are expected to correlate to how well they are able to maneuver
on land: species with a long, narrow rib that meets the pelvic plate;
species with a thicker, slightly curved rib meeting the pelvic plate;
and species with a robust crested rib interlocking with the pelvic
plate. Of the species sampled, eleven fell into the third category with advanced land-walking abilities, such as Cryptotora thamicola, displaying
the most robust sacral rib connection between the basipterygium and
vertebral column.

"Our analysis showed that the morphotypes are not grouped by closely
related taxa, but instead appear spread out across the phylogeny. That indicates to us that the extent of the modification of these features is
less reflecting shared ancestry and more likely a product of adaptation
to the flow regimes of their environments," explained Crawford. "To better understand how and why these distinct morphotypes developed, we need more knowledge of the habitat of each species, including water flow rates,
substrate types and how the rivers and streams change between rainy and
dry seasons." Crawford and colleagues now aim to further investigate
the stability physics and muscular forces at play that allow certain
species to push their bodies off their ground as they walk. The team,
including a recent Rutgers University graduate, Amani Webber-Schultz,
recently completed fieldwork in Thailand earlier this year to collect
more balitorid specimens, which they are studying using high-speed videos
of the fishes walking.

"This will allow us to study details of their walking kinematics and
gain even more insight into how walking performance might change between species with different pelvic morphologies," said Crawford.

The study was supported by the National Science Foundation's Understanding
the Rules of Life Grant # 1839915 to BE Flammang, P Chakrabarty, and
LM Page.


========================================================================== Story Source: Materials provided by
New_Jersey_Institute_of_Technology. Original written by Jesse
Jenkins. 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/2020/08/200826131859.htm

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