This week's paper is by Maya deVries, a postdoc at the Scripps Institute for Oceanography, and is in Biology Letters. deVries has examined how stomatopod (the mantis shrimps) diet diverges with their hunting appendages. Some stomatopods have spearing arms that allow them to stab prey. Other stomatopods have amazing smashing appendages. These smashers are some of the fastest moving animal parts on earth, moving so fast (20 meters per second!) through the water that they cause the water to vaporize (called cavitating). The vapor bubble then implodes with heat, light and sound. A smashing mantis shrimp therefore breaks a snail shell with both it's own strike and the implosion of vaporized water! Much of this research was done by Sheila Patek, and you can watch her give a TED talk about it.
In this week's paper deVries examined the diet of two small stomatopods, a spearer and a smasher, that live in the same habitat in French Polynesia. deVries hypothesized that they would have very different diets in accordance with their different morphologies. The spearer would be eating more soft-bodied prey and the smasher more snails and other hard prey.
What she did
deVries determined the diets of these two stomatopods using stable isotope analysis. She collected the stomatopods as well as eight potential prey including shrimp, crabs, hermit crabs, clams, fish, and worms. Different animals (and plants for that matter) have different ratios of carbon to nitrogen in their tissues. After measuring the ratios in the prey species de Vries can then plot the ratios of the two stomatopods on top of the prey isotope ratios, and where the stomatopod ratios fall is indicative of which prey they are eating.
What she found
deVries found that the spearing stomatopods had been eating lots of fish, and the smashing species were eating a lot of clams, but both species consumed all of the prey (they were eating about 70% fish and clams respectively). This was less specialization than deVries expected to see in these species given that they have to compete with each other when they eat the same diets, and their very different weapons.
deVries proposes that the evolution of the amazing smashing appendages in stomatopods rather than causing them to specialize on hard-bodied prey, thereby narrowing their diet, just broadens their current diet by allowing them to add lots of clams to a fish diet. Rather than dividing up the available food using their different weapons the two species eat a lot of the same things but are able to expand their diet in slightly different directions with different weapons.
Stomatopods are amazing animals for lots of reasons. They also have unique color vision (there's a good RadioLab on this) which I guess is not a surprise when they can look like this: