Development of locomotion in low water exposure using sturgeon

Abstract

The evolution of early land vertebrates from aquatic forms of life was a biological 32 milestone. The transition to land was accompanied with expectedly challenging physiological 33 and morphological evolutionary hurdles. So far, fossil records have provided substantial 34 information on the origin of quadrupedal locomotion. However, fossil evidence alone is 35 insufficient to understand how the soft-tissue-dependent motor functions and locomotion were 36 acquired and developed. In the present study, we focus on locomotion of the sturgeon, an extant 37 primitive fish, as a new experimental model, to investigate behavioural plasticity. Their 38 locomotion in low-water-level conditions was similar to an escape response in water, the 39 C-start escape response, which is used by most fish and amphibian juveniles to avoid predation. 40Sturgeons were also found to have mastered rolling-over in response to low water levels, 41 resulting in the improvement of their trunk-twisting action. Sturgeons acquired an efficient shift 42 in their centroid, thereby improving their mobility. We hypothesise that the escape response 43 triggered by environmental hazards drove the development of locomotion, which was 44 accompanied by a variety of behaviours. 45 46 47Animal locomotion is any of a variety of ways that animals use to move from one place to 48 another. Forms of locomotion include, walking, running, jumping, swimming, and flying. 49About 20,000 species of fish live in the hydrosphere, including the sea, rivers, and lakes. In 50 general, fish live a lifetime in the water, but some fish live in intertidal zones and tidal flats. 51These fish are constantly exposed to environmental changes compared to underwater. 52 Therefore, these fishes have modified their behaviour and physiological functions suitable for 53 the habitat (Nelson, 2006) In the Devonian period, 400 million years ago, the pectoral and 54 pelvic fins of fish evolved into appendicular structures, enabling terrestrial locomotion. 55 However, it remains unclear what kind of environment provoked the evolution of these 56 appendicular structures and what kind of mechanisms contributed to the development of 57 terrestrial locomotion (Goetz et al., 2015; Grande and Bemis, 1991; Gregory and Raven, 1941; 58 Niedźwiedzki et al., 2010). Recent studies have reported some interesting results in 59 morphological and behavioural approaches to understanding the origins of quadrupedal 60 locomotion. King et al. (King et al., 2011) observed the underwater behaviour of lungfish, one 61 of the few species of extant finned sarcopterygians, which showed locomotion similar to 62 terrestrial walking. Other studies demonstrated that Polypterus, the extant fish closest to the 63 common ancestor of actinopterygians and sarcopterygians, exhibited developmental and 64 phenotypic plasticity when exposed to low water levels (Standen et al., 2014; Standen et al., 65 2016) Lungfish and Polypterus are both capable of spontaneously moving onto land in search 66 for water and food and, thus...