…and this is a 
This is quite possibly the most awesome biology photo ever taken. It is two blind-folded crayfish battling each other in clouds of fluorescent green urine. It's a good thing it's just a picture, because if it were a video, in 3D, with the Star Trek fight music playing in the background, every science nerd in the world would have to lie down and die in ecstasy. Don't click on the little arrow below it! I won't be responsible for the consequences! (Fortunately, I can't put it into 3D motion, so I won't be slaughtering my readership here.)
The premise of this work is a small dilemma in sexual selection theory. The theory predicts that females are generally the choosy, limiting sex, so they should invest less in courtship — they can simply lie back, look alluring, and let the males fight it out over them before picking a winner. Males are expected to invest the most in courtship, because after all, winning gets them the big payoff with little expense, while females get the big expense of egg laying/pregnancy. That boys are traditionally expected to ask girls out on dates, not vice versa, makes a lot of sense in the context of this theory.
A possible contradiction to the theory, though, is the production of female pheromones to invite courtship. Many arthropods in particular — consider moths that produce olfactory signals that males have evolved enormous antennae to detect — use female-initiated signals to initiate courtship behavior in males, as if every day were Sadie Hawkins Day.
One way to resolve the contradiction, though, is to discover that the signal evolved for some other purpose than triggering courtship. Perhaps ancestral female moths were flying about smelling generically mothy, and male moths are simply homing in on something the females can't help but produce.
Enter the crayfish, Pacifastacus leniusculus. Females in this species initiate courtship with a grand aromatic puff of urine, a kind of crustacean invitation to dance that I am quite glad our species does not emulate. In the photo above, it's been visualized by injecting the crayfish with a dye, fluorescein, that can be seen against a black background with the proper illumination. The crayfish have been blindfolded so that their behaviors aren't triggered by visual cues.
And the answer they discovered is that the copious urination is an aggression, not courting, signal. Males spew it out when they're fighting with other males, females do it at the start of courtship, and males actually reduce the amount of urine produced during courtship. So they're not saying, "I love you, come get me," they're saying "Grrr, fight, fight, fight" when they spray the tank with urine.
What's the advantage to the ladies here? It's the incitement. The crayfish live in high population densities, and stirring up a little trouble and getting the males to fight provides an opportunity to select a winner. It may also produce a local population of desirable contenders: a whiff of urine may encourage wimpy males to run away and avoid potential trouble, while the more aggressive males may home in on it.
Berry FC, Breithaupt T (2010) To signal or not to signal? Chemical communication by urine-borne signals mirrors sexual conflict in crayfish. BMC Biology 8:25.
Life Science
Comments
Posted by: Algernon, elle sans chapeau
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March 30, 2010 2:25 PM
Awww... they flirt like I do.
Posted by: Brownian, Most Vicious & Petty of Pharyngulites
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March 30, 2010 2:26 PM
You've obviously not been reading any of the comments wherein I describe my dating life.
Posted by: Moggie
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March 30, 2010 2:28 PM
I hate my job. I've just got home from a shitty day in the IT trenches, and here I find that some bastard has a job fitting blindfolds to fighting crayfish.
Posted by: Glen Davidson
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March 30, 2010 2:30 PM
With humans it's kind of muddled. True, boys ask the girls out (typically are expected to initiate courtship in the great majority of cultures), but the amount of female rivalry and competition (how much is spent on makeup, etc.?) seems about as great as in males--if usually with rather less violence and/or threat thereof.
Humans seem atypical (if hardly alone) in that respect, as in many other aspects. At least we're not big on pee fights.
Glen D
http://tinyurl.com/mxaa3p
Posted by: bart.mitchell
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March 30, 2010 2:31 PM
Damn, someone find a video of those crayfish fighting. I would play that video every morning with coffee to get my heart pumping.
Plus, I'd get hungry for crayfish. After I washed the urine off.
Posted by: 朴競花/박경화 (Gyeong Hwa)
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March 30, 2010 2:32 PM
Oh but we do PZ. Or at least a few members of ours species engage in it.
Posted by: Adamvs Maximvs
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March 30, 2010 2:32 PM
Hey PZ (+people)
There's a video of the crayfish battle too;
http://news.sciencemag.org/sciencenow/2010/03/video-crayfish-urine-sparks-a-lo.html
now just combine that with the music = nerdgasm?
Posted by: Hairhead
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March 30, 2010 2:34 PM
Animals are as sneaky, devious, and wacky as humans in their mating rituals.
For instance, you know a number of those deer species where the huge, studly stag with the great rack of antlers fights off other studly competitors from mating with his harem? Well, it seems that 50% of the fawns born to his harem are not his! What happens it that while Mr. Studly is risking life and limb fighting, the nerd stags who lack humungous racks sneak up on the harem and impregnate some of the female deer. This has been referred to by researchers as the "sneaky fucker" strategy, and it keeps the gene pool of the deer strongly various.
I'm sure it keeps the intelligence of the general deer population at a high enough level too!
Posted by: vanharris
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March 30, 2010 2:37 PM
Just wait until PETA gets a whiff of this! Forget the crayfish, they'll probably piss themselves. To PETA, this must be as bad a a dog fight.
Posted by: blf
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March 30, 2010 2:44 PM
So if the urine is, for these crayfish, an aggressive signal, what about the moths's signals: Is that really an attraction signal (now), or something else?
And any idea what it started as? (I realize Pee Zed speculated about “smelling generically mothy”—and I presume that whatever it started as. it has changed over time.)
Not a biologist, so apologies if this is complete gibberish, well-known, whatevers…
Posted by: Brownian, Most Vicious & Petty of Pharyngulites
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March 30, 2010 2:44 PM
That's not uncommon in fish. Selection pressures cause males to tend to be very masculine, or at least enough so that they can fight off other suitors, or very feminine so they can sidle up to the female unmolested by competitive males. Those that fit some phenotypic average between the two extremes don't get to mate as often.
Posted by: Pierce R. Butler
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March 30, 2010 2:47 PM
The first rule of Piss Club is that we don't talk about pissing.
Posted by: Menyambal: Making sambal (it isn't dragon magic).
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March 30, 2010 2:50 PM
I was out on a bicycle trail after a heavy rain recently, and was threatened by crayfish several times. They may have thought that I was threatening them, but they came out with claws and head up, legs and tail spread, strutting and stancing, and looking horribly samurai.
I would not like to fight one.
Posted by: timrowledge, Ersatz Haderach
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March 30, 2010 2:53 PM
Possible value of an aggression signal - it attracts attention. Once she gets attention from excited male the mating signals can be deployed. If they are short range but aggression is long range that might be usable technique.
Posted by: M31
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March 30, 2010 2:56 PM
The mating habits of porcupines also involve urine, but it's usually males peeing on the females, who for the previous several days have been (both sexes) walking around rubbing their genitals on everything. The males also hike around on three legs rubbing their genitals with the fourth.
The males also have to be damn sure the female is receptive and ready because forcing it on a porcupine is not a good idea :-O
(This mammal happy to have a mate not covered in quills or urine.)
Posted by: Silič O'Nopolitanopoulos, Färschdbischuf Beesknees aus Ulm und Klein Elguth, Elector Pharynguline.
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March 30, 2010 2:58 PM
I may be a wimp.And, true, I'm not in to watersports.
But I don't think those two things are correlated.
Posted by: Brownian, Most Vicious & Petty of Pharyngulites
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March 30, 2010 3:00 PM
In light of this new information regarding the kinds of things that set crayfish off, I suggest that you either find a bike route equipped with public toilets or carry an empty bottle with you for hygiene's sake, Menyambal.
Posted by: JohnnieCanuck
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March 30, 2010 3:07 PM
Coho salmon, Oncorhynchus kisutch are one such species. Smaller males, called jacks, which return a year early from the ocean, wait until a female begins to spawn with her brawny, colourful mate. Then they quickly sneak in and out, adding their milt to his.
Amongst other things this spreads genes between their three chronologically isolated populations.
Posted by: nick
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March 30, 2010 3:26 PM
This reminds me of high school!
Posted by: https://me.yahoo.com/a/DhjBEuJ8pt63x6eBKuPx0Jv9_QE-#7c327
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March 30, 2010 3:29 PM
Or, they could just be old guys like me who rely on Depends undergarments and rarely think about sex.
Posted by: Noadi
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March 30, 2010 3:31 PM
Cuttlefish are even more devious. The smaller nerd cuttlefish actually disguise themselves as females and will mate with the female cuttlefish right under the tentacles of the big brawny males. Yet one more reason cephalopods are the coolest animals ever.
Posted by: blf
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March 30, 2010 3:34 PM
This makes me wonder about Cuttlefish, OM's, muse.
Posted by: Anodyne
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March 30, 2010 3:39 PM
Despite their close relation to crayfish, arboreal lobsters go about this in a totally different and much less horrific manner. This is a good thing--who wants to walk under a tree while a lobster relieves itself?? It's hard enough contending with those nefarious birds.
Thank goodness for the internet.
...though I still haven't figured out how one can type with such large claws.
Posted by: 'Tis Himself, OM
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March 30, 2010 3:53 PM
My brother and I used to do something similar. We'd go to the beach and while the bully was kicking sand on my brother I'd be with the bully's girl friend....
Posted by: ambook
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March 30, 2010 3:53 PM
Oh please, someone please do the video with music.
Posted by: 32bituser
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March 30, 2010 4:11 PM
Kudos for the Star Trek TOS reference in the post title
Posted by: Sven DiMilo
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March 30, 2010 4:13 PM
Right so and proximately, crayfish urine is excreted from glands the ducts of which open at the bases of the eyestalks, right up front. Urine is propelled by water currents that shoot forward from the gill chambers just lateral to the eyestalks. These water currents are created by undulating appendages, the other branches of which function as mouthparts.
Arthropods: Inside-out, backwards, and upside-down.
Posted by: cairne.morane
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March 30, 2010 4:15 PM
Lesbian cuttlefish!?!
Posted by: Sven DiMilo
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March 30, 2010 4:20 PM
oh, and they're smelling with those antennae.
Posted by: charley
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March 30, 2010 4:28 PM
When the kids were little, we kept an aquarium and threw in whatever was caught in a nearby stream, including crayfish. The mating crayfish were partial to missionary position with the male pinning the female's "wrists" to the ground with his claws. At first she'd be like, no way, and curl up her abdomen, but eventually she'd relent and unfurl.
Posted by: bevansdesign
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March 30, 2010 4:44 PM
There's not even a link to download that music on that site. Jeez.
Anyone find a way to download it yet?
Posted by: Hank Fox
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March 30, 2010 4:51 PM
And if you look real close and squint a bit, the shadows the two fighting crayfish make is the symbol from the Gamesters of Triskelion.
Twenty quatloos on the strapping gladiator on the left!
Posted by: cafink
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March 30, 2010 4:51 PM
Crawfish, guys. Crawfish.
Posted by: Anodyne
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March 30, 2010 4:56 PM
I think you mean crawdads
Posted by: Cuttlefish, OM, CR
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March 30, 2010 5:17 PM
I’d piss off a crayfish
I’d sneak with you, deer,
Or engage in behavior
From macho to queer
As long as it’s healthy
And no one objects;
Birds do it, bees do it
And fuck, I want sex!
We’ll do it like lions—
I’ll stop when you bite
Or peregrine falcons
Who couple in flight
Or lusty giraffes, we’ll
Entangle our necks
It’s springtime, or nearly,
And fuck, I want sex!
I’ll embrace you forever
Like anglerfish, maybe
Or else, like a seahorse,
I’ll carry the baby;
I’ll lasso you close,
Like an Argentine Duck
With its corkscrew-like penis,
But dammit, let’s fuck!
We’ll make like banana slugs,
Lusty and zealous
And do stuff to make
The bonobos all jealous;
The truth is, I’m married,
And thus, out of luck,
But the spirit is willing,
So pleeeease, can we fuck?
http://digitalcuttlefish.blogspot.com/2010/03/it-must-be-spring.html
Posted by: https://me.yahoo.com/a/x1CsKko.p.keyee5Rk.DLZd7ts9OdS.ilqZgGw--#2a28e
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March 30, 2010 5:21 PM
I'm surprised no one has discussed the threat of crustacean terrorists.
Posted by: Hairhead
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March 30, 2010 5:48 PM
Cuttlefish, bustin' a gut!
Jesus Christ, Cuttlefish, that is one of your BEST yet! And I've been reading you for four years or so now!
Posted by: Hairhead
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March 30, 2010 6:30 PM
Oh, and I must admit, without a bit of shame, I knew every single one of the mating tactics/protocols that Cuttlefish mentioned. If I have all that in my head, why can't I write like Cuttlefish?
Posted by: JamesTiberiusKirk
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March 31, 2010 12:20 AM
Which crustacean is me and which is Spock?
Oh, I know I the "hammier" acting one.
Posted by: Antiochus Epiphanes
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March 31, 2010 12:29 AM
*bows to Cuttlefish*
This study demonstrates clearly something that I have been saying for years, and which zoologists largely seem to ignore: Metazoans are gross.
Posted by: JamesTiberiusKirk
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March 31, 2010 12:35 AM
Uh oh! Looks like Spock has the Pon Far.
Where's Bones when I need him?
Posted by: jmelancon
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March 31, 2010 12:58 AM
They're crawfish.
And they're delicious.
Posted by: monado
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March 31, 2010 1:11 AM
Ha! Saw the video (no Star Trek music) on Daily Planet, "the only daily science news TV show." Great stuff, if a little gee-whiz sometimes.
Posted by: Menyambal: Making sambal (it isn't dragon magic).
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March 31, 2010 1:13 AM
They are crawdads around here, which may explain the fighting, but sure makes the mating a bit unsettling. For some.
Posted by: DLC
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March 31, 2010 1:33 AM
Live long and prosper, Crayfish!
Here comes a cajun with a cookpot, it appears I shall do neither.
Posted by: WCorvi
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March 31, 2010 5:45 AM
There's a program called Wave Repair that allows you to capture any sound your computer makes:
http://www.delback.co.uk/wavrep/
You can then do all sorts of editing, etc. It is shareware, so free for trial 30 days.
Posted by: Snoof
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March 31, 2010 8:48 AM
The sneaky fucker strategy works among vertebrates, too. I vaguely remember DNA testing done on one group of chimps a while back revealed that most babies were sired by, not the dominant male of the troupe, but his trusted second-in-command. Thankfully (for the second), nobody thought to inform the dominant male of what his wingman had been getting up to while he was busy defending his position.
Posted by: chuckgoecke
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March 31, 2010 10:15 AM
Mmmmmm crawfish! And I do suck the heads!
Posted by: phud
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March 31, 2010 1:32 PM
Pinch the tail, suck the head. Mmmmm. And we are in season