Why Be Fake? Because Honesty is Too Expensive ...

In earlier posts, we've talked about the life of a crab ... and about the predisposition for some crabs to fake how strong they are. At SICB in January, Candice presented a talk detailing why exactly it pays to be weak.

image by Dan Hancox

Here's my recap on Candice's talk ...
Crustaceans are violent types, posturing and fighting for territories, mating partners, and resources. Because claws are such excellent weapons, fights are often decided by the individuals merely checking each others' claws out. Bigger claws = dominance. This ameliorates the risks associated with claw-battle, while still deciding dominance.

But Candice has found that the size of the claw is not always indicative of its strength - namely, some individuals are fakers. You see, claw muscles - which are used to clamp and tear in a fight situation - are hidden inside the chitinous claw. So a big-clawed crustacean might just lack big muscles underneath, meaning it's more likely to lose if the interaction escalates into a fight.

So why wouldn't a crustacean just grow the muscle? This is what Candice wondered. She noticed that crabs with re-generated claws tended to have wimpy claws, relative to their claw size. So, she measured the energy needed to maintain claw muscles in fiddler crabs with strong, original claws as well as crabs with weak, regenerated claws.

 

Candice believes that dishonesty in fiddler crabs is related to metabolic costs - namely, how much energy is required to keep that muscle active. Crabs with strong, original claws spent ~22% of their metabolic energy budget on their claw muscle - pretty close to the amount of metabolic energy humans use to support our large glucose-hungry brains.

In contrast, crabs with weak, re-generated claws used only ~12% of their daily energy on claw muscle.

That constitutes a massive energetic savings for fakers, unless they get caught ...

CB in DC

At this precise moment, Candice is working at the Natural History Museum in Washington, D.C. - measuring crustacean claws as part of a study for her PhD.

Or, she might be sleeping. (I can never get those time-differences right ... )

At any rate, this is her lovely little brownstone ...

She's even famous now, in a "The Lost Symbol" kind of way, toiling away in the crustacean collections in Pod 5* at the Museum Support Centre (MSC), a high-security warehouse in the sketchy part of town.

*The same section of the warehouse featured in Dan Brown's book ... in case you haven't read it yet.
 

And how does Candice spend her days in DC? She's on the bus at 7:30, heading to the Natural History Museum in downtown DC, where she catches the shuttle to the warehouse facility where the crustacean collections are housed.

In to her little lab in the wet collections rooms by 8:30, she starts taking photos of crab claws and measuring the sizes of the shell and legs - for different specimens and different species. It sounds like quick work, but given she has to take 3 measurements of each crab leg (and each crab has 8 measurable legs), she may just be there ... all year.

Not really. But I'm sure that's how she feels sometimes. 10-15 minutes per crab x a warehouse full of crabs = significant porters needed at the end of the day.

Candice measures claws on her own, but has lunch with the other 10-15 researchers who work at the warehouse measuring, cataloging and sorting other types of invertebrates. They all chat and sometimes have science talks, so it's been a great way to meet everyone else.

Then it's back home again, to forget about claws for 12 hours or so.

And why is she doing all this? Candice is looking for tradeoffs between claw size and other morphology among different crustacean species - compensatory mechanisms (like we just learned about with geckoes). We'll talk more about the science after she gets back.

(all the pictures in this post were provided by Candice. Thanks!)

Animal Signalling

We're giving signals whether we know it or not. All the time - and without saying a word - we show others that we're bored or interested or infatuated or annoyed ... And this ability certainly isn't unique to humans.

Signalling is pretty much everywhere in the animal kingdom.

We know that some organisms use displays or calls or body structures to attract mates ... or ward off intruders ... or show how wonderfully strong and appealing they are. (Hmmm ... can you think of any examples?)

But what scientists are starting to figure out is that not all these signals are - shall we say - honest. Sometimes appearances aren't the same as reality. And there are times when it pays to show what you might be, rather than what you actually are. We're studying dishonesty in signalling in a number of different research systems, including crabs (who signal strength via their claws) and soccer players (who signal fouls via dives).

photo by Skye Cameron

You can read more about our signalling work here:
Cheating pays off for females but not males
How humans differ from crabs

Or here:
Walter G, Van Uietregt V, & Wilson RS. 2011. Social control of unreliable signals of strength in males but not females of the crayfish Cherax destructor. Journal of Experimental Biology. 214: 3294-3299.

Wilson RS & Angilletta MJ. In press. Dishonest signals of strength. In Ed. D. J. Irschick, M. Briffa, and J. Podos. Animal Signalling: a Functional Perspective. Ralph Wiley Press.

Wilson RS, Condon CH, David G, FitzGibbon SI, Niehaus AC & Pratt K. 2010. Females prefer athletes, males fear the disadvantaged: different signals used in female choice and male competition have varied consequences. Proceedings of the Royal Society of London Series B 277: 1923-1928. 
 
Wilson RS, James RS, Bywater C & Seebacher F. 2009. Costs and benefits of increased weapon size differ between sexes of the slender crayfish, Cherax dispar. Journal of Experimental Biology 212:853-858.

Bywater C, Angilletta MJ and Wilson RS. 2008. Weapon size is a reliable predictor of weapon strength and social dominance in females of the slender crayfish. Functional Ecology. 22:311-316.

Seebacher F & Wilson RS. 2007. Individual recognition in crayfish (Cherax dispar): the roles of strength and experience in deciding aggressive encounters. Biology Letters 3:471-474. 
 
Wilson RS, Angilletta MJ, James RS, Navas C & Seebacher F. 2007. Dishonest signals of strength in male slender crayfish (Cherax dispar) during agonistic interactions. The American Naturalist. 170:284-291