How Do Male Amphipods Get Partners? It's All In The Claw

A left clawed Dulichiella appendiculata. Believe it or not, when the right claw is dominant it is even larger. Bernardo J. O'Connor, University of Adelaide

Dulichiella appendiculata, a type of small amphipod crustacean, has evolved two different strategies when it comes to males winning mates. Which strategy a male adopts depends on whether he is right or left clawed, creating personality differences that are unusually easy to study. One researcher has taken advantage of this opportunity, and shed light on the way competing strategies replicate.

Male appendiculata have a single large claw, which they use to fight off rivals for mates. Females deposit their eggs in a pouch, rather like that of marsupials, where the males fertilize them. Males will guard a female when she is approaching this phase to make sure he is the one who gets to do the fertilizing, but a stronger-clawed competitor can displace him.

“While it’s common for males to have large structures of various kinds to attract females – think elk horns or peacock tails – there are very few species in nature with such asymmetry. The only other species are also crustaceans, such as male fiddler crabs, which also have one large claw,” said Dr. Pablo Munguia of the University of Adelaide in a statement

Among appendiculata equal numbers of males are right-clawed and left-clawed, but the right-clawed individuals take things to much greater extremes, wielding weapons that can be 20 percent of their body weight. Munguia told IFLScience that this can represent a considerable hindrance to free movement. Left claws tend to be smaller, although Mungia added that there is some overlap in size.

As a result, males behave very differently depending on which side their claw is on. When Mungia created a set of artificial reefs for the 5 to 6-milimeter-long crustaceans to live in, he found that right-clawed males were “more gregarious, hanging out with other males as well as attracting more females.”

Lefties, knowing they could not compete with their better-endowed rivals, are more entrepreneurial, boldly going where no amphipod has gone before, in the hope of finding not just a new reef, but females without a guarding male. Right-clawed males stay at home, possibly, Munguia told IFLScience, because it is too hard to lug that giant appendage to a new reef, but also possibly because, “If you're doing well, why shift?”


It may not look like much, but this reef is one of those that many Dulichiella appendiculata called home in the experiment. Pablo Munguia

The fact that the population remains roughly evenly balanced suggests each strategy works approximately equally well.

Munguia has published his findings in the Journal of Crustacean Biology.

Munguia doubts that there is much to learn about handedness in humans from appendiculata, but he told IFLScience that his work “helps us understand how different mating strategies and behavior preferences are formed.” Munguia plans to expand his studies from appendiculata, a species native to Florida, and examine Australian relatives to see how they manage the whole matter of getting dates.

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