Monday, September 27, 2010

Evolution of mimicry in octopuses

From BBC News & Wired

This fascinating creature was discovered in 1998 off the coast of Sulawesi in Indonesia, the mimic octopus is the first known species to take on the characteristics of multiple species.

This octopus is able to copy the physical likeness and movement of more than fifteen different species, including sea snakes, lionfish, flatfish, brittle stars, giant crabs, sea shells, stingrays, jellyfish, sea anemones, and mantis shrimp.

This animal is so intelligent that it is able to discern which dangerous sea creature to impersonate that will present the greatest threat to its current possible predator.

The Indonesian mimic octopus has the boldest defense strategy of any of its cephalopod cousins, and now scientists know how that strategy evolved.
Rather than blending into the scenery, the octopus mimics the swimming behavior and shape of a variety of toxic sea creatures — like flatfish and sea snakes — and displays bold color patterns that shock predators.

For the study, scientists focused on mimic’s ability to swim on the sea floor like a flatfish, of which there are several toxic varieties in the region where the octopus lives.

The analysis revealed that the behavior evolved in three key steps :
  • first, mimic octopus ancestors started switching on bold colors to shock predators when camouflage failed.
  • next, they learned to swim like sea-floor–dwelling fish and developed longer arms that facilitate the motion.
  • third, they combined the bold color patterns and flatfish swimming technique, and started doing it while out on daily forays and resting.
The Indonesian mimic octopus has the extraordinary ability to pass itself off as many of the toxic fishes or sea snakes that share its habitat.
Instead of blending into the background, the animal impersonator often uses a daredevil strategy of making itself more conspicuous to predators.
Scientists believe the behaviour evolved to scare other animals.
By flattening its head and arms, using a bold brown and white colour display and adopting an undulating swimming technique T. mimicus can fool predators that it is, in fact, a poisonous flatfish rather than a tasty meal.

Because this high risk defence strategy is quite rare, scientists from the California Academy of Sciences and Conservation International Indonesia were keen to understand how its abilities evolved and why they are used.

Dr Christine Huffard from Conservation International Indonesia is one of the authors of the study published in the Biological Journal of the Linnean Society.

"The close relatives of T. mimicus use drab colours and camouflage to successfully hide from predators." she said. "Why does T. mimicus instead draw attention to itself, and repeatedly abandon the camouflage abitilies it inherited from its ancestors in favour of a bold new pattern?"

By analysing its DNA the researchers established when different traits appeared in its ancestors' lineage from its brown-and-white colour displays to its ability to swim like a flatfish using its long arms.

The researchers believe its impersonation skills were advantageous because the mimic could fool predators into thinking it was a poisonous flatfish like the peacock or zebra sole which lives nearby.

Healy Hamilton is Director of the Center of applied Biodiversity Informatics at the California Academy of Sciences.

"While the mimic octopus's imitation of flatfish is far from perfect, it may be 'good enough' to fool predators where it lives... In the time it takes a predator to do a double take, the octopus may be able to get away," she said.

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