Development of locomotion in low water exposure using sturgeon
The evolution of early land vertebrates from aquatic forms of life was a biological milestone. The transition to land was accompanied with expectedly challenging physiological and morphological evolutionary hurdles. So far, fossil records have provided substantial information on the origin of quadrupedal locomotion. However, fossil evidence alone is insufficient to understand how the soft-tissue-dependent motor functions and locomotion were acquired and developed. In the present study, we focus on locomotion of the sturgeon, an extant primitive fish, as a new experimental model, to investigate behavioural plasticity. Their locomotion in low-water-level conditions was similar to an escape response in water, the C-start escape response, which is used by most fish and amphibian juveniles to avoid predation. Sturgeons were also found to have mastered rolling-over in response to low water levels, resulting in the improvement of their trunk-twisting action. Sturgeons acquired an efficient shift in their centroid, thereby improving their mobility. We hypothesise that the escape response triggered by environmental hazards drove the development of locomotion, which was accompanied by a variety of behaviours.