"Nice building you have there. I want it." Patrick Green from the University of Exeter filmed this battle between Mantis Shrimp.
Size is important to the small but mighty mantis shrimp, who have a distinct preference for burrows in remnants of coral with volumes that are close to their own size or just a little larger – in other words, large enough to fit their bodies but small enough that they can defend the entrance. Sometimes, a mantis shrimp will compromise, according to a new article in Animal Behavior magazine. If a burrow is already occupied and close to the ideal size or slightly smaller, the Mantis Shrimp will fight longer and harder for that burrow – and are more likely to win the competition.
As we previously reported, mantis shrimp come in many different varieties: there are around 450 known species. But they can generally be divided into two types: those who stab their prey with spear-like appendages ("spears"), and those who smash their prey ("smashers") with large, rounded, hammer-like claws ("raptorial appendages") "). These strikes are so fast – up to 23 meters per second, or 51 miles per hour – and powerful that they often create cavitation bubbles in the water and create a shock wave that can serve as a follow-up strike that stuns and sometimes kills prey. Sometimes A blow can even generate sonoluminescence, with the cavitation bubbles generating a brief flash of light when they collapse.
A 2018 study found that the secret of this powerful punch doesn't seem to lie in bulky muscles, but in the spring-loaded anatomical structure of the shrimp's arms, which resembles a bow and arrow. The shrimp's muscles pull on a saddle-shaped structure in the arm, causing it to bend and store potential energy that is released when the club-like claw swings. And earlier this year, scientists discovered that the mantis shrimp intuitively beats into the air at half its speed, suggesting that the animal can precisely control its beating behavior depending on the surrounding medium.
"Assessment of the resource value"
Patrick Green from the University of Exeter and J.S. Harrison of Duke University – authors of the new article on animal behavior – was interested in investigating what is known as the "resource valuation" in mantis shrimp of the beating variety (Neogonodactylus bredini). Both male and female mantis shrimp of this species are known to compete for coral scraps that provide shelter from predators and a safe space for egg mating and hatching. If a preferred build is already occupied, it can spark a dispute over who gets the build. These competitions typically involve a ritualized exchange of high-powered blows (Mantis Shrimp SMASH!), With the defending Mantis Shrimp also using its armored endplate to block the entrance of the den from intruders.
This type of animal competition is widespread in nature, and animals appear to be able to assess the value of such "controversial resources" and adjust their behavior accordingly. Such encounters are typically described as linear or categorical valuation, in which, for example, men fight more aggressively in the presence of women. Similarly, female parasitoid wasps compete for the most desirable hosts to lay their eggs in. The larger the host, the more food is available to the offspring, for example when hatching. Previous studies have shown that a woman's express charge appears to be a factor (or a selective force) in how aggressively they fight for a potential host and how likely she is to win such a competition.
Enlarge /. An intruder who may be assessing a burrow.
Previous studies have shown that mantid shrimp pluck burrows that are sized (volume) that matches their own height (mass) well, as do hermit crabs. For hermit crabs, there seems to be a tradeoff in resource valuation: hauling around a larger shell requires more energy, but provides more protection from predators, while the opposite is true for smaller shells. Green and Harrison suggest that when competing for a desired shell, hermit crabs prefer shells that are the preferred size or slightly larger, while placing less emphasis on shells that are much larger or smaller.
This would be an example of a quadratic resource value rating, where resources are rated highest at a certain peak value. This value decreases in both directions from this peak. In other words, there is an optimal sweet spot or "goldilocks zone" where an asset is classified as "just right" and the animal adjusts its behavior accordingly – e.g. B. by fighting more aggressively when such a desirable asset is challenged. Green and Harrison believed that a similar quadratic rating of resource value could apply to mantis shrimp – namely, that mantis shrimp value caves with an ideal volume, are more aggressive, and are more likely to win when around the Control fight such caves.
To test their hypothesis, the researchers conducted two series of experiments: "selection trials" in which mantis shrimp were free to choose unoccupied burrows of various sizes, and "staged competitions" in which "defending" and "invading" mantis shrimp randomly meet each other a competition for a preferred building was voted on. Green and Harrison predicted that their experiments would show that competitors would fight longer, harder, and more likely to win if their body length closely matched the volume of the contested den – and that the further the match from ideal, the further these factors would decrease deviates in both directions.
"This study is an example of maximum effort reserved for something that is 'just right'."
The researchers built dummy caves out of clear plastic tubing with a single opening wrapped in black vinyl with a clear area on top so they could observe what was going on inside. The mantis shrimp were collected from caves in seagrass beds along Panama's Caribbean coast. The researchers also videotaped the staged competitions (36 in total) and intervened if it appeared that one of the fighting shrimp was in danger of being seriously injured or dying.
Overall, they found that the occupying mantis shrimp successfully defended their burrows from intruders in 69 percent of the fights. However, those chances changed dramatically in cases where the invading mantid shrimp competed for burrows slightly smaller than their ideal size. Intruders won 67 percent of the fights in these circumstances, usually by striking first and more often.
"We know animals can evaluate a variety of factors, including the size of the opponent and the value of the prize, in deciding whether to fight and how hard," Green said of the results. "In this case, since a smaller den is likely occupied by a smaller adversary, mantid shrimp appear to compromise the size of the house if that means an easier battle. Animals might be considered to be the hardest fighters for the greatest wealth , but this study is an example of maximum effort reserved for something that is & # 39; just right & # 39; "."
There were some limitations, particularly limitations on sample size. Green and Harrison also acknowledged that the false caves were standardized and had fixed lengths and diameters, as opposed to naturally occurring caves, which usually have more variable dimensions. And the smooth hose is clearly different from the natural caves made of rock and rubble.
"Mantis shrimp are skillful modifiers to natural caves, using contagious blows to widen caves that are too narrow and using rocks and sand to fill caves that are too large," they wrote. "While the people we tested could not expand the dummy caves by strike, perhaps with more time to set up a residence, the people would have filled larger dummy caves."
DOI: Animal Behavior, 2020. 10.1016 / j.anbehav.2020.09.014 (About DOIs).
Listing picture by Roy Caldwell