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Lecture 10

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Department
Psychology
Course
PSY397H1
Professor
Martin Ralph
Semester
Winter

Description
Lecture 10: Orientation Roles of Melatonin Lesions to the pineal gland eliminates circannual rhythmicity Melatonin affects rhythm generation by the SCN Melatonin has been shown to synchronize rhythms in pups. Synchrony of Pups Circadian rhythms of fetal and neonatal rodents are entrained by their mothers which depends upon the material SCN. Administering melatonin to SCN lesioned hamsters entrains activity rhythm of pups Lesions to SCN disrupt melatonin, removing this source of time of day information. Hence mothers with SCN lesions produce desynchrony observed in litters born to SCN lesions. Sun Compass Orientation Amphipods (beach hoppers) are intertidal crustaceans with worldwide distribution. Numerous experiments have been performed that look at sun compass orientation in the escape behavior of amphipods. There is a little confusion in the literature, but in general I has been found that the animals use local cues if they are available, and celestial cues (the Sun) if local cues are not readily detectable. We will use the Hartwick, 1976 article along with the hypothetical beach shown here to illustrate the general concepts. As an example, we will use a population that lives on a beach that faces SW. Individuals may move along the beach, and very quickly learn the direction of water. When disturbed they will escape either toward the water or toward land, before burrowing into the sand. If we dig up some animals at the X, and release them, they will head preferentially either toward the water or away from it. In this experiment, animals released near the water (lower beach zone) on the same beach where they were collected head toward land. Animals that are collected on one beach and released on another near the water, will head toward land. This suggests that the animals are using local landmarks. Here, animals are released on the same beach from which they were collected. However, this time they are released on the upper beach, and they head toward the water. Orientations: 1. Landward Beach Orientation 2. Seaward Breach Orientation 3. Beach Orientation with local Cues 4. Clock-shifted Beach Orientation 5. Visual Orientation 6. Non-visual Orientation If we dig up some animals at the X, and release them, they will head toward the water preferentially (Y1) or land (Y2) depending on where they were released. Conclusion from these experiments: O. corniculata uses local cues to orient AND the direction of movement (escape) has something to do with survival Question: Would the animals use celestial cues if there were no visible landmarks? These animals were collected on one beach and released on another where there were no visible cues. Animals are expected to move away from the water if there are landmarks, but this time they move in the direction of land on their home beach, not the that of the release site. If we dig them up at X and release them out of sight of the water (Y), they will preferentially escape in the seaward direction on the home beach. To summarize these ideas, if we release them at Y in the lower zone, they will move toward land if there are landmarks, and along the beach if there are not. If we let them go on a cloudy day, they will initially escape in random directions. If we dig them up, then put them in a light cycle that is phase shifted (advanced) by 3 hours, they will assume that the day is three hours later than it really is. They will calculate the direction to escape based on their assumption that the sun is in a later position in the sky. As in a previous experiment, animals are collected at Del Mar Beach and released at North Island Beach (no landmarks). The animals continue to move landward according to the direction on their home beach (controls). However, if you delay their circadian clock by 6 hours, their preferred escape direction is deflected 90 degrees clockwise. This is because the animals’ clocks tell them that it is 6 hours earlier than it really is. If we dig them up, then put them in a light cycle that is phase shifted (advanced) by 3 hours, they will assume that the day is three hours later than it really is. They will calculate the direction to escape based on their assumption that the sun is in a later position in the sky. If we dig them up, then put them in a light cycle that is phase shifted (delayed) by 6 hours, they will assume that the day is six hours earlier than it really is. They will calculate
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