Data from: Cut your losses: self-amputation of injured limbs increases survival

Autotomy, self-induced limb loss, is an extreme trait observed throughout the animal kingdom; lizards drop their tails, crickets release their legs, and crabs drop their claws. These repeated evolutionary origins suggest that autotomy is adaptive. Yet, we do not have a firm understanding of the selective pressures that promote and maintain this extreme trait. Although multiple adaptive hypotheses exist, research has generally focused on autotomy’s adaptive value as a form of predator escape. However, autotomy could also be selected to reduce the cost of an injured limb, which we investigate here. Previously, this alternative hypothesis has been challenging to directly test because when an injury occurs on an autotomizable limb, that limb is almost always dropped (i.e., autotomy is behaviorally fixed within populations). Recently, however, we have identified a species, Narnia femorata (Insecta: Hemiptera: Coreidae), where some individuals autotomize limbs in response to injury, but some do not. This natural variation allowed us to investigate both the survival costs of retaining an injured limb and the benefits of autotomizing it. In this study, we find a positive association between autotomizing injured limbs and survival, thereby quantifying a new and likely widespread benefit of autotomy—reducing the cost of injury.自切（autotomy），即自主诱导的肢体断落行为，是广泛分布于动物界的一类极端性状：蜥蜴可断尾自保、蟋蟀可弃足逃生、螃蟹会脱落螯肢。这类反复独立演化出的起源表明，自切行为具有适应性优势。然而，目前学界对于推动并维持这一极端性状的选择压（selective pressure）仍缺乏清晰认知。尽管已提出多种适应性假说，但现有研究大多将自切的适应性价值聚焦于其作为反捕食策略的功能。不过，自切也可能因能够降低受伤肢体带来的生存成本而被选择保留，这正是本研究的探讨方向。此前，这一替代性假说难以直接验证，原因在于：当可发生自切的肢体遭遇损伤时，该肢体几乎总会被断落，即种群内的自切行为在行为学上具有固定性。近期我们发现了一种名为足壮异蝽（Narnia femorata，昆虫纲：半翅目：缘蝽科）的物种，其部分个体在肢体受伤时会发生自切，而另一部分个体则不会。这种自然存在的行为变异，使得我们得以同时探究保留受伤肢体的生存成本，以及实施自切行为所能带来的收益。本研究发现，对受伤肢体实施自切与个体存活率呈正相关，由此量化了自切行为一项全新且可能广泛存在的适应性收益——降低受伤带来的生存成本。