Biologist Discovers What May Be World's 'Pickiest' Mates

Aug 03, 2005
Photo of male California fiddler crab (Credit: Catherine deRivera)

California fiddler crabs may be among the world’s pickiest animal when it comes to selecting a mate.
A study conducted by a biologist at the University of California, San Diego that appears in the August issue of the journal Animal Behaviour found that females of the species Uca crenulata may check out 100 or more male fiddler crabs and their burrows before finally deciding on a mate.

“As far as I know, no other species has been observed sampling nearly as many candidates as the California fiddler crab,” said Catherine deRivera, who conducted the study while a doctoral student and a lecturer at UCSD. She is now a research biologist at the Aquatic Bioinvasions Research and Policy Institute, a joint entity of the Smithsonian Environmental Research Center and Portland State University.

deRivera and a group of UCSD students who assisted her conducted their observations in the Sweetwater River estuary in Chula Vista, south of San Diego, near the Mexico-U.S. border. She said previous studies of mate selection in other animals, such as birds and the natterjack toad, found that females of most species typically sampled only a handful of potential mates before making a final selection.

“Most animals sample just a few mates, presumably because search costs override the benefits of lengthy searches,” she said in her paper. But female California fiddler crabs are much pickier, she discovered in her study, checking out male suitors and their bachelor pads an average of 23 times before making a final selection. One particularly choosy crab visited 106 male burrows, fully entering 15 of them, during her one hour and six minute search.

Why are female fiddler crabs so picky? The survival of their offspring, deRivera found in her experiments, appears to be strongly linked to the size of their mate and, more importantly, his corresponding abode.

“The size of the male’s burrow affects the development time of his larvae,” she said. “A burrow of just the right size allows larvae to hatch at the safest time, the peak outward nighttime flow of the biweekly tidal cycle.”

“Wide burrows speed incubation, so they cause the larvae to hatch too early and miss the peak tides. This research provides one of the first examples of how choosy resource selection can help offspring survivorship.”

Male fiddler crabs attract suitors by standing in front of their burrows and waving their enlarged claws at prospective female passers by, much as humans motions “come here” with their arms and hands

“The California fiddler crabs use a lateral wave that looks much like a human beckoning 'come here’,” deRivera said. “It also seems to serve as a 'come hither' signal, as a male waves, standing at his burrow entrance, and interested females come over.”

Interested females initially eye the males, who select their burrows based upon their body size, and if they’re interested, partially or fully enter a burrow to size it up.

“The burrow openings, which are circular, are just big enough for the owners to get in,” deRivera said. “Crabs enter burrows sideways so have to fit in front to back and top to bottom.”

When a female has found a mate and burrow to her liking, typically one that is about the same size as she, either she or the male will plug up the opening of the burrow and the couple will mate and incubate their eggs, which later hatch and release tiny crab larvae that are quickly flushed from the estuary by high night tides.

deRivera found that larger female crabs couldn’t be as picky about choosing mates as their smaller counterparts. They took less time, she noted, because they entered fewer burrows, primarily because many of the burrows they passed were too small to accommodate them and successfully incubate their eggs and release their larvae.

“Larvae were successfully released during high-amplitude nocturnal tides only when females incubated in burrows that allowed the larvae to exit the estuary swiftly and thus reduce predation risk, but not when females incubated in burrows that were too wide or narrow,” deRivera writes in her paper. “The effect of burrow aperture on incubation duration may explain why females sampled many male burrows as they searched for a mate and why females of different size classes selected and sampled differently.”

Source: UCSD

Explore further: Cassini: Return to Rhea

Related Stories

Isolated boodies repopulate the mainland

Mar 09, 2015

Two populations of translocated boodies (Bettongia lesueur) which were set up to re-establish locally extinct species at Lorna Glen in the Murchison have created a thriving population made up of fertile hybrid ...

The winter-to-spring cankerworm cycle

Feb 10, 2015

It is the time of the year when you might be thinking of snuggling up with hot chocolate and your favorite book, but female cankerworm moths are hard at work – laying the foundation for an invasion that ...

Exclusion fencing vital to relocation success

Oct 03, 2014

The successful reintroduction of brushtail possums to the Wheatbelt has been attributed to a habitat free from foxes, feral cats and other possums, with plenty of tree hollows and rock crevices.

Review: Ambitious 'Destiny' lacks imagination

Sep 18, 2014

Midway through "Destiny," the new science fiction epic from "Halo" creators Bungie, a smug prince is musing on the hero's desire to visit a mysterious site on Mars.

Recommended for you

Cassini: Return to Rhea

1 hour ago

After a couple of years in high-inclination orbits that limited its ability to encounter Saturn's moons, NASA's Cassini spacecraft returned to Saturn's equatorial plane in March 2015.

Comet dust—planet Mercury's 'invisible paint'

8 hours ago

A team of scientists has a new explanation for the planet Mercury's dark, barely reflective surface. In a paper published in Nature Geoscience, the researchers suggest that a steady dusting of carbon from p ...

It's 'full spin ahead' for NASA soil moisture mapper

11 hours ago

The 20-foot (6-meter) "golden lasso" reflector antenna atop NASA's new Soil Moisture Active Passive (SMAP) observatory is now ready to wrangle up high-resolution global soil moisture data, following the successful ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.