Model
Digital Document
Publisher
Florida Atlantic University
Description
Most marine organisms partition particular activities, such as growth, migration, reproduction, and
hatching, to particular seasons, times of the day or night, or phases of the lunar cycle. The result is
characterized as a “rhythm”. Scientists who study these rhythms generally ask two kinds of questions:
why do they occur when they do that is, what is their survival value, and how are they controlled,
physiologically? Hatchling marine turtles almost always emerge from their nests at night, then crawl
down the beach to the sea and migrate offshore. By doing so at night they avoid lethally warm beach
sands and diurnally active predators in the shallows. But these “survival value” explanations do not
account for how the turtles, digging their way upward inside the nest toward the beach surface, know
that it’s dark and time to emerge. The classic explanation for how they “know” is based upon surface
sand temperatures. During the day, these sands can be very warm 50° C. When hatchlings digging
upward encounter these heated sands, they stop digging until the sand cools, after sunset. But these
observations fail to explain why in most studies, hatchlings rarely emerge from their nests at dawn or in
the early morning, when the sand is still cool. To account for those observations, we hypothesize that
the turtles must also possess a time sense that inhibits emergence during inappropriate times, such as
shortly before or after sunrise.
hatching, to particular seasons, times of the day or night, or phases of the lunar cycle. The result is
characterized as a “rhythm”. Scientists who study these rhythms generally ask two kinds of questions:
why do they occur when they do that is, what is their survival value, and how are they controlled,
physiologically? Hatchling marine turtles almost always emerge from their nests at night, then crawl
down the beach to the sea and migrate offshore. By doing so at night they avoid lethally warm beach
sands and diurnally active predators in the shallows. But these “survival value” explanations do not
account for how the turtles, digging their way upward inside the nest toward the beach surface, know
that it’s dark and time to emerge. The classic explanation for how they “know” is based upon surface
sand temperatures. During the day, these sands can be very warm 50° C. When hatchlings digging
upward encounter these heated sands, they stop digging until the sand cools, after sunset. But these
observations fail to explain why in most studies, hatchlings rarely emerge from their nests at dawn or in
the early morning, when the sand is still cool. To account for those observations, we hypothesize that
the turtles must also possess a time sense that inhibits emergence during inappropriate times, such as
shortly before or after sunrise.
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