by Amanda Franklin
There is a huge diversity of colors and patterns throughout the animal kingdom. Animals commonly use these colors and patterns to communicate with other animals. They may signal to a predator that potential prey is toxic, tell females about whether a courting male is a good mating partner or provide important information about an opponent’s fighting ability. The purpose of these signals, and their interplay with other types of signals (e.g. chemical, acoustic) is a fascinating object of current research.
Stomatopods (mantis shrimp) are bright and colorful marine crustaceans. They are well known for possessing the most complex visual system with a mind boggling 16 photoreceptor types! In comparison, humans have only three, birds do slightly better with four or five, and butterflies are stomatopods’ closest rival with up to twelve. With all these photoreceptors, stomatopods have the ability to see human-visible light, ultraviolet (UV) light, and polarized light.
But what are stomatopods using this vision for? It looks as if they might be using color to communicate during fights. Stomatopods are highly aggressive animals and can punch so hard that they can break glass (or your thumb!). Both males and females compete over burrows that they live in. Before escalating to punching one another , they generally perform a threat display , called the meral spread, which displays UV reflective patches on their punching arms. Do these patches communicate information to opponents during fights?
Our recently published research shows that the UV reflective patches are assessed by opponents in contests. In order to figure this out, we removed UV reflectance of some animals’ patches by painting these patches with sunscreen. It turned out that stomatopods fighting opponents with no UV reflectance behaved more aggressively and fights were shorter in length. We think that the UV reflective patches could be making the threat display flashier by drawing an opponent’s attention to the punching arms.
Stomatopods are also known to use chemical cues in these contests. Research by the Caldwell Lab in California has shown that chemical cues can help a stomatopod detect the size of an opponent that is partially concealed in its burrow. Stomatopods also use chemical cues to determine whether they have recently fought an opponent. If they recently fought and lost, they are less likely to fight the opponent again!
Our research demonstrates that the UV patches are giving the opponent different information to chemicals cues. We investigated this by removing some opponents’ ability to detect chemical cues by dipping their antennae in freshwater. When they could not detect chemical cues, we observed different behavioral changes than what was observed when UV reflectance was removed. This indicates that chemical cues and UV reflectance comprise a multimodal signal, with each component conveying different information to the sparring stomatopods.
Gaining information about opponents before exchanging punches could allow stomatopods to avoid injuries from entering fights that they will be unable to win. Stomatopods probably gain additional information about their opponents by assessing more than one type of signal. It appears that stomatopod ‘language’ is more complex than it might seem at first glance!
For more information, see the full research article published in Royal Society Open Science.
Amanda Franklin is a 2012 fellow of the Fulbright Science and Technology Award, from Australia, and is a doctoral candidate at Tufts University in Boston, USA. She is currently one of the editors for The Global Scientist.
This post was guest edited by Charles de Bourcy, a 2012 fellow of the Fulbright Science & Technology Award, from Luxemburg, and a doctoral candidate at Stanford University.