Data from: Post-metamorphic carryover 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 carryover 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 carryover effects of intraspecific larval competition. In particular, we assessed larval gut plasticity and determined if carryover effects could persist given the extensive gut remodeling 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 if any organ size plasticity contributed to metabolic carryover 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 carryover 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 two-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，幼虫栖息环境中的条件可产生持续至变态后的重要影响。这类遗留效应（carryover effects）可能会影响幼体生长可塑性，并对适合度产生重要后果。小型红眼树蛙（Agalychnis callidryas）幼体的生长速度快于体型更大的个体。我们探究了该生长模式在多大程度上源于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可塑性，并明确在植食性幼虫向肉食性幼体转变过程中发生的大规模肠道重塑情况下，这类遗留效应是否仍可存续。我们在低、中、高密度的中型实验生态系统（mesocosms）中饲养幼虫，并测定了幼虫期与幼体期的肠道、肝脏及脂肪体的大小。我们还监测了变态完成后幼体开始摄食的时间节点，并在摄食开始后测定了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，以探究是否存在由器官大小可塑性介导的代谢遗留效应。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。这类可塑性带来的效应可延续至变态完成后阶段。高幼虫密度组培育出的幼体体型更小，肠道相对更长，而肝脏与脂肪体则显著萎缩。体型特异性代谢速率未出现显著的遗留效应。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在变态尚未完全完成时就已开始摄食，而来自低幼虫密度组的大型幼体则出现了长达两周的显著摄食延迟。尽管不同实验组间幼体体重差异可达三倍，但在摄食开始后，摄食量与平均食物滞留时间均未随体型大小发生缩放。总体而言，高幼虫密度组产生的幼体体型偏小且脂质储备极低，相较于大型幼体，这可能诱发了它们的过度摄食行为。源自幼虫阶段的更长肠道可延续至幼体阶段，这能帮助小型幼体在不降低食物滞留时间的前提下提升摄食量。摄食模式与摄食起始时间的差异，可解释此前在该物种及其他物种中报道的体型依赖性生长模式。