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，幼虫所处环境的条件可在变态发育后仍产生持久影响。这类携带效应（carry-over effects）可能会影响幼体的生长可塑性，并对适合度产生重要影响。小型幼体红眼树蛙（Agalychnis callidryas）的生长速度快于体型较大的同类。本研究旨在探究该生长模式在多大程度上源于种内幼虫竞争所带来的携带效应。具体而言，我们评估了幼虫的肠道可塑性，并明确了在植食性幼虫转变为肉食性幼蛙的过程中发生的广泛肠道重塑情况下，携带效应是否仍能持续存在。

我们将幼虫置于低密度、中密度和高密度的中型实验生态系统（mesocosms）中饲养，并测量了幼虫和幼蛙的肠道、肝脏及脂肪体的大小。我们还监测了变态发育后幼体开始进食的时间；在幼体开始进食后，我们测定了其摄食速率和平均食物滞留时间。最后，我们测量了幼蛙的代谢率，以探究器官大小可塑性是否会对代谢携带效应产生影响。

幼虫密度对幼虫形态具有显著影响：密度越高，肠道长度越长，而肝脏和脂肪体的体积则越小。这种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蛙体型更小，肠道比例更长，肝脏和脂肪体则极度萎缩。未观察到携带效应对按体型标准化的代谢率存在显著影响。

幼虫密度的差异同样与变态发育后的摄食模式相关。来自高幼虫密度组的小型幼蛙甚至在变态发育完全完成前就开始进食，而来自低幼虫密度组的大型幼蛙则会经历显著的2周延迟。尽管各实验组间幼蛙的体重差异可达三倍，但一旦开始进食，摄食量和平均食物滞留时间均未随体型大小发生缩放。

总体而言，高幼虫密度组培育出的幼蛙体型更小、脂质储备极低，这相较于体型更大的幼蛙可能会刺激其出现暴食行为。从幼虫阶段延续而来的更长肠道，可通过允许小型幼蛙在不降低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，解释了此前在该物种及其他物种中观察到的体型依赖型生长模式。