Study: Male crabs corner their mates to coerce sex

CANBERRA, Australia, June 15 (UPI) -- For banana fiddler crabs, Uca mjoebergi, coerced copulation is a fact of life. New research shows some male crabs ensure offspring by cornering mates in small burrows.

Not all fiddler crab sex is non-consensual. Males court and compete for females, pitting their size, coloration and claw-waving abilities against one another in hopes of winning a would-be mate's affection. A female might consider as many as 20 males before making a decision.

Sometimes, however, a female's hand -- or claw -- is forced.

Scientists first realized females might be coerced into mating after noticing males often step aside as a potential pair enter a burrow, allowing the female to go first. This often backfires, as females sometimes walk away.

So why take the risk?

As researchers found out, the payoff is a greater chance of reproduction. Females that enter burrows first were more likely to mate with a male and lay eggs than those that entered second. Researchers say this suggests some females are forced into sex.

Researchers published their findings in the journal PLOS ONE.

"Mate-searching female fiddler crabs are fussy about the quality of a male's burrow, so they enter it to check its suitability as an incubation site before selecting the male as a mate," study co-author Patricia Backwell, a researcher at the The Australian National University, said in a news release. "Some males trap the female inside the burrow, coercing them to mate."