The crustacean's tendency to coil its tail plate, or telson, and trade blows had been observed in several species before. But Green said little work had been done on how that behavior helps decide a winner when two mantis shrimp go head to head. [Image Gallery: Magnificent Mantis Shrimp]
"What we did that was novel was to look at how that behavior is used in the resolution of contests," Green said. "And describing it as 'telson sparring' in the paper relates to what we think is its use as an escalated method of assessment."
In the study, the researchers describe how the behavior could hold parallels to sparring in large mammals, such as elephants and deer. Those animals sometimes employ nonlethal use of weapons like antlers or tusks to assess a competitor.
While the researchers' current hypothesis is that the contests demonstrate which shrimp is the most aggressive or motivated fighter, Green said he hopes to investigate measures of strike performance other than peak force. This will help researchers see if different factors influence the outcome of contests, he said.
"The animal that bites harder or grabs harder is often the one that wins," Green said. "But we want to look a little more deeply into other metrics of performance and really get a bit more into the biomechanics of this exchange."
Mantis shrimp expert Roy Caldwell, a professor of integrative biology at the University of California, Berkeley, welcomed the study. "Most work in this area has been on tetrapods and it is nice to see parallels showing up in invertebrates that possess lethal weapons," he told Live Science.
But in the experiments, the lack of an advantage for the shrimp already occupying a burrow suggests their design was not that attractive to the shrimp or didn't provide them decent protection, he said, adding that his own experiments with size-matched individuals showed that burrow residents were more likely to win contests.
Caldwell also noted that most "telson sparring" contests are between shrimp unequally matched due to size, injury or stage in their molt cycle, and his studies have shown that any weakness in a shrimp's strike is quickly discovered and capitalized on.
Caldwell agrees that in contests over burrows, persistence appears to signal an intruder's motivation, and despite their advantage, the burrow residents will often flee under sustained attack. But, he believes telson sparring is likely just one of several aggressive tactics employed by mantis shrimp.
The detailed findings of the new study were published yesterday (Sept. 22) in the journal Biology Letters.
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