'Desperate larvae' revisited:: age, energy and experience affect sensitivity to settlement cues in larvae of the gastropod Alderia sp.
'Desperate larvae' revisited:: age, energy and experience affect sensitivity to settlement cues in larvae of the gastropod Alderia sp.
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DOI：
10.3354/meps312149
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发表时间：
2006-01-01
影响因子：
2.5
通讯作者：
Krug, Patrick J.
中科院分区：
文献类型：
--
作者：
Botello, Gilberto;Krug, Patrick J.
20世纪50年代提出的“绝望幼虫”假说认为，随着时间的推移，由于能量储备的耗尽，食电性幼虫对定居需求的辨别能力下降。它的预测在一些幼虫群居或对生物膜有反应的分类群中得到了证实，但这一假设尚未在幼虫对猎物或宿主来源的定居线索表现出严格要求的情况下得到验证。我们使用蛇科Alderia sp.，测试了年龄、营养状况和先前经历如何影响幼虫对寄主藻类长水蛭（Vaucheria longicaulis）定居线索的反应。虽然Alderia sp.的幼虫能够在不进食的情况下变形，但如果有浮游植物，它们是兼性浮游营养的，这使我们能够测试能量限制对剂量反应的影响。随着年龄的增长，未饲喂的幼虫对溶解沉降线索的反应越来越敏感，而饲喂的幼虫对溶解沉降线索的敏感性不随时间变化；因此，随着能量储备的减少，幼虫对栖息地线索的反应更强烈。随着年龄的增长，变态速度加快；初始沉降后，4 d龄幼虫比1 d龄幼虫提前12 ~ 24 h完成变态。幼虫可能定居下来，然后继续通过感知化学线索来评估环境，年龄较大的幼虫开始变态的速度更快。先前暴露于低于阈值剂量的自然提示触发了初始无反应者随后暴露的更高反应。一些家庭表现出比其他家庭更低的阈值剂量，这表明线索敏感性可能具有遗传成分。因此，栖息地的选择取决于特定幼虫的遗传背景、先前经验和能量含量之间的相互作用。我们的研究结果支持了一种适用于非群居物种的原始绝望幼虫假说的修正版本，即能量耗尽的幼虫在栖息地选择过程中接受较弱的信号并做出更快的反应。
Formulated in the 1950s, the 'desperate larva' hypothesis postulated that lecithotrophic larvae become less discriminating in their settlement requirements over time, due to depletion of energy reserves. Its predictions have been confirmed for some taxa in which larvae settle gregariously or in response to biofilms, but the hypothesis has not been tested with larvae that exhibit a stringent requirement for prey- or host-derived settlement cues. Using the opisthobranch Alderia sp., we tested how age, nutritional status and prior experience affected larval response to settlement cues from the host alga Vaucheria longicaulis. Although able to metamorphose without feeding, larvae of Alderia sp. were facultatively planktotrophic if phytoplankton were available, allowing us to test the effects of energy limitation on dose-response. Unfed larvae became increasingly responsive to dissolved settlement cues with age, whereas the sensitivity of fed larvae did not change over time; larvae thus responded more strongly to habitat cues as energy reserves diminished. Rate of metamorphosis also accelerated with age; following initial settlement, 4 d old larvae completed metamorphosis 12 to 24 h faster than 1 d old larvae. Larvae may settle and then continue to evaluate their environment via perception of chemical cues, with older larvae initiating metamorphosis more rapidly. Prior exposure to a subthreshold dose of the natural cue triggered a higher response to a subsequent exposure in initial non-responders. Some families exhibited a lower threshold dose than others, suggesting that cue sensitivity may have a heritable component. Habitat choice thus depends on interactions between the genetic background, prior experience and energy content of a given larva. Our results support a modified version of the original desperate-larva hypothesis applicable to nongregarious species, in which energy-depleted larvae accept weaker cues and respond more quickly during habitat selection.