Exploring the Neurobiology of Larval Swimming, Settlement, and Metamorphosis in the Sea.

BACKGROUND:

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Marine invertebrate larvae come in all shapes and sizes. In some species, the larvae begin as a tiny version of a fully developed adult, but for most, the larvae go through several life stage transitions, each stage bringing dynamic changes in appearance and behaviour. As an animal develops, it must swim away from their parents and explore new habitats to settle on before their final metamorphosis into a sea-floor-dwelling adult. My research will focus on these behaviours where I ask questions like: How do larvae swim? How do they know when to settle? What drives metamorphosis? To answer these questions, I will aim to investigate the neurobiology at play during early life stages and wonder what internal signals (neurotransmitters, such as proteins and small chemicals) control larval behaviour and how the environment might influence those signals.

I hope that my research will push at the boundaries of marine biology and influence research in neurobiology. By studying the neurobiology underpinning marine larval behaviour, we can gain insight into how the earliest brains and nervous systems evolved and functioned. We could then apply our knowledge of how marine larvae sense and respond to their environment to improve larval rearing practices in aquaculture, inform and design marine protected areas and fisheries strategies, and predict how climate change could impact larval behaviour and the health of marine ecosystems such as coral reefs.

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METHODOLOGY:

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Throughout my project, I will integrate larval swimming and exploratory behaviours with advanced molecular and microscopy techniques. I will use 3D tracking of worm and mollusc larvae to characterise their different pre-settlement behaviours. Recording larval behaviour in the lab is difficult because they are so small, usually less than half a millimetre in size! To do this, I have built a behavioural arena that will let me light up and video these tiny animals. I would then explore how environmental cues, such as food, might alter their swimming behaviour. Then, to unpick how the animals’ nervous systems control swimming, settlement, and cue detection, I will record their behaviour after dosing the animals with different neurotransmitters. I will also visualise the cells responsible for controlling settlement by fluorescently tagging them and imaging the nerve cells under the microscope.

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RESULTS:

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Like many first-year PhD students I don’t have many results to show, but I can try to paint a picture of what I expect to find (see below). By exposing the larvae to different neurotransmitters, I can observe changes in their swimming speed, swimming direction, and surface exploration behaviours. Some neurotransmitters might increase or decrease the beat frequency of its ciliary band (a band of hair-like structures the larva uses for locomotion). Certain environmental cues might lead to directed swimming or sinking to the sea floor. There may be neurotransmitters that help or inhibit cue detection.

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