Jumping and swimming are key locomotor traits in frogs intimately linked to survival and dispersal. French populations of the frog Xenopus laevis from the invasion front are known to possess greater terrestrial locomotor endurance. Here, we tested whether individuals from the invasion front show differences in their muscle physiology that may underlie the observed whole-organism performance differences. We measured muscle contractile properties of the isolated gastrocnemius muscle in vitro, including isometric stress, activation and relaxation time, and work loop power output, both before and during a period of fatiguing contractions. We found that frogs from the centre of the range can produce tetanus force in their gastrocnemius muscle faster than animals from the periphery of the range, which could contribute to higher performance in one-off jumps. Yet, populations did not differ in muscle endurance. These results, coupled with previous work on this invasive population of Xenopus laevis, suggest that the greater stamina observed in individuals from the periphery may be more due to anatomical differences such as longer hind limbs and larger hearts along with potentially other as of yet untested physiological differences rather than differences in the mechanical properties of skeletal muscle.

中文翻译：

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在法国非洲爪蟾入侵种群中，肌肉收缩特性是否会导致运动表现的差异？

跳跃和游泳是青蛙的关键运动特征，与生存和传播密切相关。众所周知，来自入侵前沿的青蛙非洲爪蟾的法国种群具有更强的陆地运动耐力。在这里，我们测试了来自入侵前沿的个体是否表现出肌肉生理的差异，这可能是观察到的整个生物体表现差异的基础。我们在体外测量了离体腓肠肌的肌肉收缩特性，包括在疲劳收缩之前和期间的等长应力、激活和松弛时间以及工作循环功率输出。我们发现来自该区域中心的青蛙可以比来自该区域外围的动物更快地在腓肠肌中产生破伤风力，这可能有助于提高一次性跳跃的表现。然而，人群在肌肉耐力方面没有差异。这些结果，加上之前对非洲爪蟾这一侵入性种群的研究表明，在外周个体中观察到的更大的耐力可能更多是由于解剖学差异，例如更长的后肢和更大的心脏以及潜在的其他尚未经过测试的生理学骨骼肌的机械特性的差异而不是差异。