Question

Every year, Christmas Island in the Pacific is overrun with over 120 million red crabs (Gecarcoidea natalis) moving across land between their breeding ground and habitat and towards the water to spawn.

Write and explain at least two alternate hypotheses for each of the following questions, and propose research to test your hypothesis. For your proposed research for each section, explain whether your work will be experimental, correlational, or conceptual and be sure to note what the strengths and weaknesses of your approach might be. Make sure that you explain you logic well.

a. What might be the adaptive benefits of everyone migrating at the same time?  (think about what happens to individuals that miss the event, or travel separately)

b. In this species males leave their burrows and arrive at the beach a couple of days before the females. Why might they do this?

c. How do they coordinate such that they migrate at the same time? (what type of cues might say it is time to leave, what physiological mechanisms might be at play?)

d. How do the crabs know where to go? (think about navigation and whether components might be learned or inherited).

Answer 1

Group migration in Fiddler's crab can be attributed to safety and competition. Red crab migrate to sea shore so that males can copulate with females. While moving in large group ensure that each male has higher chances of copulating with females which will be less if it would have been a secluded event. Another aspect of group migration is safety and exact navigation.

Red crab migration is triggered by advent of rainy season. Males crabs reach before female crabs to dig burrow and attract females for the mating. To ensure that male crabs get chance to mate they reach on the beach early to ensure they dig a burrow. After the mating the males leave the burrows allowing feamles to brood their fertilised eggs.

Fiddler crab's have a circadian clock, which is an internal 24- hours clock. This clock is an integral part of the nervous system. It is highly dependent on earth's magnetic field. With changes in activity of the sun, earths gravitational force is changed which results in lower and higher tides and all these signal are captured by this circadian clock. This circadian clock results in a rythmic behavior in animals termed as cirannual rhythms. Migration of Fiddler's crab is the result of this cirannual rhythm.

Fiddler crab's habitat forest vegetation. Although they have evolved form their ancestors which have originated in marine ecosystem. As part of evolutionary connects, Fiddler's crab has a prerequisite of keeping their lungs wet and moist. If exposed to high sunlight, these crabs will die soon due to dry lungs. While these crab's migrate, oceans high salinity and moist breeze guide these crabs to navigate toward the sea.