Data from: Post-metamorphic carry-over effects of larval digestive plasticity

For animals with complex life cycles, conditions in the larval environment can have important effects that persist after metamorphosis. These carry-over effects may influence juvenile growth plasticity and have important fitness consequences. Small juvenile red-eyed treefrogs, Agalychnis callidryas, grow faster than larger ones. We examined to what extent this growth pattern is due to carry-over effects of intraspecific larval competition. In particular, we assessed larval gut plasticity and determined whether carry-over effects could persist given the extensive gut remodelling that occurs when herbivorous larvae transition to carnivorous juveniles. We reared larvae in mesocosms at low, medium and high densities and measured the size of both larval and juvenile guts, livers and fat bodies. We also monitored the timing of the onset of juvenile feeding post-metamorphosis and, after the onset of feeding, we measured intake rate and mean diet retention time. Finally, we measured juvenile metabolic rates to determine whether any organ size plasticity contributed to metabolic carry-over effects. Larval density had strong effects on larval morphology with higher densities increasing gut length and decreasing liver and fat body sizes. The effects of this plasticity carried over post-metamorphosis. High larval densities produced smaller juveniles with proportionately longer guts and extremely small livers and fat bodies. There were no apparent carry-over effects on size-specific metabolic rate. Differences in larval density were also associated with differences in post-metamorphic feeding. Small juveniles from high larval densities began feeding even before metamorphosis was complete, whereas large juveniles from low larval densities experienced a significant 2-week delay. Although juvenile body mass varied over threefold across treatments, once feeding was initiated, neither intake nor mean diet retention time scaled with body size. Overall, high larval densities produced small juveniles with very low lipid reserves that may have stimulated hyperphagia relative to larger juveniles. Longer guts carried over from the larval stage could facilitate this by allowing small juveniles to elevate intake without sacrificing diet retention time. Patterns of intake coupled with differences in the onset of feeding explain the size-dependent growth pattern previously reported in this and other species.对于具有复杂生活史的动物而言，幼虫栖息环境的条件可产生能够延续至变态发育后的显著影响。这类遗留效应（carry-over effects）可能会影响幼体生长可塑性，并对个体适合度产生重要后果。 小型幼体红眼树蛙（Agalychnis callidryas）的生长速率快于体型更大的同类。本研究探究了该生长模式在多大程度上源自种内幼虫竞争所带来的遗留效应。具体而言，我们评估了幼虫肠道的可塑性，并明确了在植食性幼虫转变为肉食性幼体时发生的大规模肠道重塑过程中，遗留效应是否仍可持续存在。 我们在中型实验生态系统（mesocosms）中分别以低密度、中密度与高密度饲养幼虫，并测定了幼虫及幼体的肠道、肝脏与脂肪体的大小。我们还监测了变态完成后幼体开始进食的时间节点；在幼体启动进食后，我们测定了其摄食速率与平均食物滞留时间。最后，我们测定了幼体的代谢速率，以明确器官大小可塑性是否会对代谢遗留效应产生贡献。 幼虫密度对幼虫形态具有显著调控作用：更高的幼虫密度会延长肠道长度，同时缩小肝脏与脂肪体的体积。这类可塑性带来的影响会延续至变态发育后。高幼虫密度组培育出的幼体体型更小，肠道相对长度更长，而肝脏与脂肪体则极度萎缩。未观察到体型特异性代谢率存在明显的遗留效应。 幼虫密度的差异同样与变态后的摄食模式差异相关。来自高幼虫密度组的小型幼体甚至会在变态过程完全结束前就开始进食，而来自低幼虫密度组的大体型幼体则会经历显著的2周进食延迟。尽管不同实验组间幼体体重差异可达三倍，但在启动进食后，摄食量与平均食物滞留时间均未随体型发生缩放。 总体而言，高幼虫密度培育出的幼体体型更小且脂质储备极低，这可能会刺激其相较于大体型幼体产生过度摄食行为。从幼虫阶段遗留下来的更长肠道可通过允许小型幼体在不牺牲食物滞留时间的前提下提升摄食量，从而促进这一现象。摄食模式结合进食起始时间的差异，可解释此前在该物种及其他物种中观测到的体型依赖型生长模式。