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A professorial cowboy--aesthete--the combination seems incongruous yet he was utterly of a piece--taught me how to think about evolution, which is to say about almost everything. (Armand Marie Leroi on [...]

Wood Frogs (Rana sylvatica LeConte, 1825 = Lithobates sylvaticus (LeConte, 1825)) exhibit one of the most extreme freeze tolerance responses found in vertebrates. While extensive work is continuing to resolve the physiological mechanisms involved, few have studied the effects of freezing on locomotor performance. The ability to mount an appropriate locomotor response is vital, as locomotion can affect both survivorship and reproductive success. To investigate how the biomechanical processes during locomotion are altered following freezing, stroke cycle timings and kinematic performance were measured prior to and immediately following a freeze--thaw cycle. Additionally, the effects of cooling rate (0.3 versus 0.8 [degrees]C/h) were also assessed. While jumping and swimming performance were both reduced post-freeze, the effects were more pronounced during swimming, with observed reductions in velocity and distance travelled. Interestingly, these changes occurred largely independent of cooling rate. Altered stroke cycle timings and highly variable muscle activation/deactivation patterns suggest an impairment in muscle function as frogs continued to recover from the effects of freezing. This was supported by the physiology of frogs post-freeze, specifically, the persistence of elevated glucose levels in muscles important during locomotion. Collectively, these findings suggest that reductions in locomotor performance observed immediately following a freeze--thaw cycle are driven by alterations in muscle function. Key words: Wood Frog, Rana sylvatica, freeze tolerance, cryoprotectants, cooling rate, biomechanics, locomotion. R?sum?: Les grenouilles des bois (Rana sylvatica LeConte, 1825 = Lithobates sylvaticus (LeConte, 1825)) pr?sentent une des r?actions de tol?rance au gel les plus importantes observ?es chez les vert?br?s. Si des efforts consid?rables visent ? ?lucider les m?-canismes physiologiques qui interviennent dans cette r?action, les effets du gel sur la performance locomotrice n'ont pas re?u beaucoup d'attention. La capacit? de produire une r?action locomotrice convenable est cruciale puisque la locomotion peut avoir une incidence tant sur la survie que sur le succ?s de reproduction. Pour examiner l'influence du gel sur les processus biom?caniques durant la locomotion, la chronologie et la performance cin?matique des cycles de battement des pattes ont ?t? mesur?es avant et imm?diatement apr?s un cycle de gel-d?gel. Les effets du taux de refroidissement (0,3 et 0,8[degrees] C/h) ont ?galement ?t? ?valu?s. Si les performances de saut et de nage ?taient toutes deux r?duites apr?s le gel, les effets ?taient plus prononc?s durant la nage, des baisses de la vitesse et de la distance parcourue ?tant observ?es. Fait ? noter, ces changements sont en bonne partie ind?pendants du taux de refroidissement. La modification de la chronologie des cycles de battement et les motifs tr?s variables d'activation et de d?sactivation des muscles indiqueraient une d?gradation de la fonction musculaire pendant que les grenouilles se remettent des effets du gel. Ces observations sont appuy?es par la physiologie des grenouilles apr?s le gel, plus pr?cis?ment la persistance de teneurs ?lev?es en glucose dans les muscles importants durant la locomotion. Collectivement, ces constatations donnent ? penser que les r?ductions de la performance locomotrice observ?es imm?diatement apr?s un cycle de gel--d?gel d?coulent de modifications de la fonction musculaire. [Traduit par la R?daction] Mots-cl?s: grenouille des bois, Rana sylvatica, tol?rance au gel, cryoprotecteurs, taux de refroidissement, biom?canique, locomotion., Introduction Many animals cope with seasonally subzero ( Certain species can tolerate freezing (Storey and Storey 1987, 1988), relying largely on amassing high levels of cryoprotectants in tissues to discourage [...]

The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was coupled with the origin of terrestrial locomotion and the evolution of supporting limbs. Polypterus is a member of thebasal- most group of ray - finned fish (actinopterygians) and has many plesiomorphic morphologies that are comparable to elpistostegid fishes, which are stem tetrapods. Polypterus therefore serves as an extant analogue of stem tetrapods, allowing us to examine how developmental plasticity affects the 'terrestrialization' of fish. We measured the developmental plasticity of anatomical and biomechanical responses in Polypterus reared on land. Here we show the remarkable correspondence between the environmentally induced phenotypes of terrestrialized Polypterus and the ancient anatomical changes in stem tetrapods, and we provide insight into stem tetrapod behavioural evolution. Our results raise the possibility that environmentally induced developmental plasticity facilitated the origin of the terrestrial traits that led to tetrapods., The evolution of terrestrial locomotion in vertebrates required the appearance of new behaviours and supporting appendicular structures (1-8). The skeletal changes included the origin of supporting limbs, the decoupling of [...]

The present study assessed the aerial and aquatic visual abilities of juvenile grey bichir Polypterus senegalus, fish capable of terrestrial locomotion, by measuring the optokinetic response to stimuli of varying speed and spatial frequency. In water, fish tracked slow‐moving (2° s−1) stimuli moderately well and fast‐moving stimuli very poorly. Spatial acuity was very low compared with many other species, with maximum response observed at 0.05–0.075 stimulus cycles per degree of visual arc; however, it should be noted that adult fish, with their larger eyes, are likely to have somewhat improved spatial acuity. Low spatial acuity and limited stimulus tracking ability might be expected in a nocturnal ambush predator such as P. senegalus, where gaze stabilization may be less crucial and other sensory inputs may have greater importance in perception of the environment. In air, spatial and temporal acuity were both poorer by every measure, but some visual ability persisted. As the eye shows no anatomical specialization for aerial vision, poor vision was expected; however, the large decrease in saccade velocity observed in air trials was unexpected. Stimulus parameters typically have little effect on the characteristics of the saccade, so this finding may suggest that the function of the reflex system itself could be compromised in the aerial vision of some fishes capable of terrestrial locomotion. [ABSTRACT FROM AUTHOR]

The ability to modulate the function of muscle is integral to an animal's ability to function effectively in the face of widely disparate challenges. This modulation of function can manifest through short-term changes in neuromuscular control, but also through long-term changes in force profiles, fatigability, and architecture. However, the relative extent to which shorter-term modulation and longer-term plasticity govern locomotor flexibility remains unclear. Here, we obtain simultaneously-recorded kinematic and muscle activity data of fin and body musculature of an amphibious fish, Polypterus senegalus. After examining swimming and walking behaviour in aquatically-raised individuals, we show that walking behaviour is characterized by greater absolute duration of muscle activity in most muscles when compared with swimming, but that the magnitude of recruitment during walking is only increased in the secondary bursts of fin muscle and in the primary burst of the mid-body point. This localized increase in intensity suggests that walking in P. senegalus is powered in a few key locations on the fish, contrasting with the more distributed, low intensity muscle force that characterizes the stroke cycle during swimming. Finally, the increased intensity in secondary, but not primary, bursts of the fin muscles when walking likely underscores the importance of antagonistic muscle activity to prevent fin collapse, add stabilization, and increase body support. Understanding the principles that underlie the flexibility of muscle function can provide key insights into the sources of animal functional and behavioural diversity. [ABSTRACT FROM AUTHOR]

The ability of bones to sense and respond to mechanical loading is a central feature of vertebrate skeletons. However, the functional demands imposed on terrestrial and aquatic animals differ vastly. The pectoral girdle of the basal actinopterygian fish Polypterus senegalus was previously shown to exhibit plasticity following terrestrial acclimation, but the pectoral fin itself has yet to be examined. We investigated skeletal plasticity in the pectoral fins of P. senegalus after exposure to terrestrial loading. Juvenile fish were divided into three groups: a control group was kept under aquatic conditions without intervention, an exercised group was also kept in water but received daily exercise on land, and a terrestrial group was kept in a chronic semi-terrestrial condition. After 5 weeks, the pectoral fins were cleared and stained with Alcian Blue and Alizarin Red to visualize cartilage and bone, allowing measurements of bone length, bone width, ossification and curvature to be taken for the endochondral radial bones. Polypterus senegalus fin bones responded most strongly to chronic loading in the terrestrial condition. Fish that were reared in a terrestrial environment had significantly longer bones compared with those of aquatic controls, wider propterygia and metapterygia, and more ossified metapterygia and medial radials, and they showed changes in propterygial curvature. Exercised fish also had longer and more ossified medial radials compared with those of controls. Polypterus senegalus fin bones exhibit plasticity in response to novel terrestrial loading. Such plasticity could be relevant for transitions between water and land on evolutionary scales, but key differences between fish and tetrapod bone make direct comparisons challenging., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)