Marine pelagic larvae use a hierarchy of environmental cues to identify a suitable benthic habitat on which to settle and metamorphose into the adult phase of the life cycle. Most larvae are induced to settle by biochemical cues and many species have long been known to preferentially settle in the dark. Combined, these data suggest that larval responses to light and biochemical cues may be linked, but this has yet to be explored at the molecular level. Here, we track the vertical position of larvae of the sponge Amphimedon queenslandica to show that they descend to the benthos at twilight, by which time they are competent to respond to biochemical cues, consistent with them naturally settling in the dark. We use larval settlement assays under three different light regimes, combined with transcriptomics on individual larvae, to identify candidate molecular pathways underlying larval settlement. We find that larvae do not settle in response to biochemical cues if maintained in constant light. Our transcriptome data suggest that constant light actively represses settlement via the sustained up-regulation of two putative inactivators of chemotransduction in constant light only. Our data suggest that photo- and chemosensory systems interact to regulate larval settlement via nitric oxide and cyclic guanosine monophosphate signalling in this sponge, which belongs to one of the earliest-branching animal phyla.

中文翻译：

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相互依赖的光化学感应系统调节海洋海绵中幼虫沉降的分子和行为证据。

海洋中上层幼虫利用环境线索的层次结构来识别合适的底栖生境，在其上定居并变质为生命周期的成年阶段。大多数幼虫是通过生化线索诱导沉降的，早就知道许多物种会优先在黑暗中沉降。综合起来，这些数据表明，幼虫对光和生化线索的反应可能是相关的，但这尚未在分子水平上进行探索。在这里，我们追踪昆士兰两栖幼虫的幼虫的垂直位置，以显示它们在黄昏时下降到底栖动物，这时它们有能力对生化线索做出反应，这与它们自然地在黑暗中安顿下来是一致的。我们在三种不同的光照条件下使用幼虫沉降测定法，结合单个幼虫的转录组学，以确定潜在的幼虫沉降分子途径。我们发现，如果保持恒定的光照，幼虫不会响应生化线索而沉降。我们的转录组数据表明，恒定光照通过仅在恒定光照下通过持续持续上调两种假定的化学转导灭活剂来积极抑制沉降。我们的数据表明，光和化学感应系统相互作用，通过该海绵中的一氧化氮和环状鸟苷单磷酸信号传导调节幼虫的沉降，该海绵属于最早分支的动物门之一。我们的转录组数据表明，恒定光照通过仅在恒定光照下通过持续持续上调两个化学推定的灭活剂来积极抑制沉降。我们的数据表明，光和化学感应系统相互作用，通过该海绵中的一氧化氮和环状鸟苷单磷酸信号传导调节幼虫的沉降，该海绵属于最早分支的动物门之一。我们的转录组数据表明，恒定光照通过仅在恒定光照下通过持续持续上调两个化学推定的灭活剂来积极抑制沉降。我们的数据表明，光和化学感应系统相互作用，通过该海绵中的一氧化氮和环状鸟苷单磷酸信号传导调节幼虫的沉降，该海绵属于最早分支的动物门之一。