Regeneration of Mnemiopsis leidyi under different food quantities

Many marine invertebrate are known to be capable of extensive body regeneration in response to injury. However, little attention has been paid to individual variations in regenerative self-repair response among individuals under given environmental conditions. The invasive ctenophore Mnemiopsis leidyi has been shown to have plasticity in regenerative response, sometimes completely replacing all missing structures, and sometimes forming metastable and fully functional half animals. We manipulated food quantity to high and low levels to investigate to what extent internal energy resources drive the choice of regeneration response in bisected juveniles. Our results show that while undergoing whole-body regeneration is favored under high food supply, formation of stable half animals is strongly favored under low food supply when attempts of whole-body regeneration fail to be successful. When food uptake is impaired, tissues of the gastro-vascular system seem to serve as main energy resource and, hence, start to shrink and to be gradually resorbed. Tissue regeneration seems to be generally costly as regeneration of the apical organ can lead to complete gut resorption when maintained under low prey supply. Under both high and low food treatments, stable half animals show similar survivability as to regenerating whole animals which underlines their functional role as an energy-saving survival mode. In conclusion, regeneration plasticity has likely evolved as an adaptive trade-off between considerably high regeneration costs and rather low energy storage capacities, leading to higher population fitness under adverse conditions.

已知诸多海洋无脊椎动物（marine invertebrate）具备响应损伤的大规模躯体再生能力。然而，在既定环境条件下，学界对不同个体间再生自我修复响应的个体差异关注甚少。入侵性栉水母动物（ctenophore）Mnemiopsis leidyi的再生响应具有可塑性：有时可完全替换所有缺失的躯体结构，有时则会形成亚稳定且功能完整的半体个体。本研究通过将食物供应量设置为高、低两个水平，探究在对半切分的幼体中，体内能量储备在多大程度上驱动再生响应的选择。研究结果显示：在食物供应充足的条件下，个体更倾向于进行全躯体再生；而当全躯体再生尝试失败时，在食物匮乏的条件下，形成稳定半体个体的策略则会受到强烈偏好。当食物摄取受限时，胃肠血管系统（gastro-vascular system）的组织会作为主要的能量储备来源，进而开始萎缩并被逐渐吸收。组织再生通常存在较高的能量成本：在猎物供应匮乏的条件下，顶端器官（apical organ）的再生甚至会导致肠道完全被吸收。在高、低食物处理组中，稳定半体个体与正在进行全躯体再生的个体存活率相近，这印证了其作为一种节能生存策略的功能价值。综上，再生可塑性极有可能是在极高的再生成本与较低的能量储备能力之间演化出的一种适应性权衡策略，可在不利环境条件下提升种群适合度。