Natures wonders: blind walking cavefish (Introduction)

by David Turell , Monday, March 28, 2016, 14:34 (3160 days ago) @ David Turell

These tropical fish can climb waterfalls and are sown o have a pelvic girdle-like anatomy similar to tetrapods: - http://www.nature.com/articles/srep23711 - "Fishes have adapted a number of different behaviors to move out of the water, but none have been described as being able to walk on land with a tetrapod-like gait. Here we show that the blind cavefish Cryptotora thamicola walks and climbs waterfalls with a salamander-like diagonal-couplets lateral sequence gait and has evolved a robust pelvic girdle that shares morphological features associated with terrestrial vertebrates. In all other fishes, the pelvic bones are suspended in a muscular sling or loosely attached to the pectoral girdle anteriorly. In contrast, the pelvic girdle of Cryptotora is a large, broad puboischiadic plate that is joined to the iliac process of a hypertrophied sacral rib; fusion of these bones in tetrapods creates an acetabulum. The vertebral column in the sacral area has large anterior and posterior zygapophyses, transverse processes, and broad neural spines, all of which are associated with terrestrial organisms. The diagonal-couplet lateral sequence gait was accomplished by rotation of the pectoral and pelvic girdles creating a standing wave of the axial body. These findings are significant because they represent the first example of behavioural and morphological adaptation in an extant fish that converges on the tetrapodal walking behaviour and morphology. - *** - " Several extant fishes have a number of morphological and behavioural traits that facilitate moving out of water to escape predation, find food or new habitats, or lay eggs1,2,3. The most simplistic and least anatomically derived method to move across a dry horizontal surface is to undulate or flip the body by modifying the same motor programs that facilitate swimming and escape responses in water, as is seen in eels4, killifishes2,5, and sticklebacks6. Some fishes are able to walk underwater using their pectoral fins and pelvic fins (e.g. frogfish7); however, in submerged walking the bodyweight is supported by the fluid around the organism. Polypterus8, mudskippers9,10 and walking catfish11 move on land via crutching or lateral pushing by the posterior body and tail to rotate forward over their pectoral fins. Lungfish can walk on a horizontal surface using primarily pelvic driven alternating fin movements12. Fishes known for vertical climbing, such as Hawaiian waterfall climbing gobies, use either intermittent, rapid axial undulation (Awaous guamensis and Lentipes concolor) or oral and pelvic suction (Sicyopterus stimpsoni)13. Notably, none of these fishes walk with a diagonal-couplets lateral sequence gait on land, which has been described as a purely tetrapodal innovation. - *** - "While a study of the development of the pelvic girdle in this cavefish has not yet been possible, it appears that structurally, the pelvic girdle of Cryptotora converges on tetrapodal morphology that supports muscular attachment and transfer of forces for terrestrial walking16,21. In other fishes, including those that can walk by crutching or lunging, there is no bony connection between the pelvis and vertebral column and the pelvis is held in place by a muscular sling." - Comment: One might consider the point that in the evolution of fish a tendency to develop walking is built in. Pre-planning?