Sneaky cheaters!

Last week I explored the concept of animal communication through honest signalling, in which a signaller sends a signal of quality to a receiver. In order for an individual to be able to create and carry a costly trait, they must have a high fitness. Predators learn that they should try and go for a weaker individual instead, intraspecific competitors learn it would be futile to approach them for fights, and members of the opposite sex are honestly signalled that they would be a mate with a higher fitness.

This concept has been widely researched and discussed in the last few decades, and the accepted idea has gone from organisms displaying implicit honesty, to no honesty and no long-term communication at all, and finally to cost-reinforced honesty (which is the conventional explanation of today) (Rowell et al. 2006).

You see, as always, there are going to be some which manage to break the rules and sneak through the system. If they can do this without creating too much fuss whilst in the meantime increasing their fitness, then why not?

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Sourced from:http://flickrhivemind.net/User/BrentDPayne/Interesting
Photographer unknown

 These cheeky individuals can cheat by giving a dishonest signal. An example where deception in intraspecific fights is important is when stomatopods of the species Gonodactylus bredini fight over ownership of a cavity (Adams & Caldwell, 1990). This species exhibits a display called the meral spread, which involves leaning out (usually keeping their body in the burrow) to reveal the meral spot, a small, colourful depression on the underside of the appendage, and to make the individual appear large and threatening (Adams & Caldwell, 1990). Normally the size of this display provides accurate information about the aggressiveness of the signaller. This is used when defending homes, and also when females defend their eggs (Adams & Caldwell, 1990).

Peacock mantis shrimp (different species of mantis shrimp) engaging in the meral display
Photo by: Linda Cline

 However, research has shown that newly moulted individuals sometimes also exhibit this display to bluff to their components (Adams & Caldwell, 1990). These weakened individuals are left with a very vulnerable soft exoskeleton that cannot withstand blows, and so as they lack the ability to actually defend themselves in a fight, the display in this case can be interpreted as bluffs (Adams & Caldwell, 1990). The body is not seen and so competitors do not see that the individual is weakened.

Bluffing has also been seen in a species of Green Tree Frogs, Rana clamitans, where some small males exaggerate their quality by lowering their acoustic pitch to resemble that of larger males (Bee et al. 2000).

Male Green Tree Frogs Rana clamitans  calling to females
Sourced from: http://academics.skidmore.edu/wikis/NorthWoods/index.php/Rana_clamitans_melanota_-_Green_Frog

Photographer:  Unknown

 Dishonest advertisement is also seen in species of Fiddler crabs such as Uca lactea mjoebergi, which have been shown to lie about their fighting ability. Males have an enlarged major claw (which looks very impractical in my opinion) which is used both to attract females and fight rivals (Backwell et al. 2000, Lailvaux et al. 2009). Most often, those possessing larger claws win the fights, and so we expect larger claws to be an honest signal of increased fitness and fighting ability (Backwell et al. 2000, Lailvaux et al. 2009).

Male fiddler crab, Uca mjoebergi Photographer: Tanya Detto 

When a male crab loses a claw, it occasionally re-generates a new one. This new claw (termed a leptochelous) is about the same size as the original, however much weaker (Backwell et al. 2000, Lailvaux et al. 2009). However, what’s interesting is that rival crabs are unable to distinguish between the original and weaker claw and are still intimidated by its size and deterred from combat (Backwell et al. 2000, Lailvaux et al. 2009). As the crab with the regenerated claw would be unable to back up his ‘claims’ that he is a strong male if he ever actually got into a fight, this is seen also a prime example of a bluff.

Watch the video below to see two male Fiddler crabs battling it off:

So if escaping battles and predators and getting the ladies with minimal energy and cost is this easy, why doesn’t everyone do it?

Imagine a group of foraging birds, which signal a warning call to each other whenever predators are near. The receiver (predator) receives an honest signal that its prey are aware that it is there, and so gets the message that he/she should move on and try and find a group of unsuspecting birds instead. If cheats gave random false alarms, just in case a predator is nearby, then individuals would soon learn that there is no point in fleeing as it is probably a false alarm and it’s likely that there isn’t anything preying on them, just like the other 43 false alarms of that morning.

Likewise, in the case of the mantis shrimp mentioned above, if mantis shrimp continuously bluffed opponents successfully every time, then all mantis shrimp would evolve to bluff by using the technique of meral spread display, and it would eventually no longer be effective and fall into disuse.

Over time every dishonest signal would weaken the integrity of the whole system (Adams & Mesterton-Gibbons, 1995; Johnstone & Grafen, 1993; Rowell et al. 2006). For this reason, in order to establish and maintain what is called an Evolutionary Stable strategy (ESS), the proportion of dishonest signals must be low. That is, bluffing with the display must only work for certain individuals (Adams & Mesterton-Gibbons, 1995; Johnstone & Grafen, 1993; Rowell et al. 2006).

In fact, at the ESS the very strongest and the very weakest members of the population threaten while animals of intermediate strength do not (Rowell et al. 2006). Think about the mantis shrimp again... When strong mantis shrimp display, they may deter the conspecific, however even if they don’t they are probably able to win the battle as their display is in fact honest of their superior fighting ability. When a newly molted mantis shrimp bluffs, it takes the risk that the conspecific might attack, and just hopes that it doesn’t actually have to get in a fight. This is disastrous if the bluff doesn’t work. For this reason, for individuals of mediocre strength the risk isn’t worth it and they are better off not using the technique to ward off competitors and investing their energy in something else (Adams & Mesterton-Gibbons, 1995; Johnstone & Grafen, 1993; Rowell et al. 2006). Hence we see a system where only the strongest and the weakest mantis shrimp benefit from bluffing and the bluffing technique will continue to ward off opposing conspecifics as long as this low frequency of individuals bluffing is maintained (Holden, 1995).

References:

• Adams E.S & Mesterton-Gibbons M 1995, "The cost of threat displays and the stability of deceptive communication", Journal of Theoretical Biology, vol. 175, no. 4, pp. 405-405.
• Adams, E.S. & Caldwell, R.L. 1990, "Deceptive communication in asymmetric fights of the stomatopod crustacean Gonodactylus bredini", Animal Behaviour, vol. 39, no. 4, pp. 706-716
• Backwell, P.R., Christy, J.H., Telford, S.R., Jennions, M.D. & Passmore, N.I. 2000, "Dishonest signalling in a fiddler crab", Proceedings. Biological sciences / The Royal Society, vol. 267, no. 1444, pp. 719-724.
• Bee, M.A., Perrill, S.A. & Owen, P.C. 2000, "Male green frogs lower the pitch of acoustic signals in defense of territories: A possible dishonest signal of size?", Behavioral Ecology, vol. 11, no. 2, pp. 169-177.
• http://academics.skidmore.edu/wikis/NorthWoods/index.php/Rana_clamitans_melanota_-_Green_Frog (3^rd May 2014)
• http://flickrhivemind.net/User/BrentDPayne/Interesting (3^rd May 2014)
• http://www.blueboard.com/mantis/pics/cline_meral.htm (3^rd May 2014)
• http://www.sciencedaily.com/releases/2008/11/081111203501.htm (3^rd May 2014)
• https://www.youtube.com/watch?v=vPIc8s-V8fM (3^rd May 2014)
• Johnstone, R.A. & Grafen, A. 1993, "Dishonesty and the handicap principle", Animal Behaviour, vol. 46, no. 4, pp. 759-764.
• Lailvaux, S.P., Reaney, L.T. & Backwell, P.R.Y. 2009, "Dishonest Signalling of Fighting Ability and Multiple Performance Traits in the Fiddler Crab Uca mjoebergi", Functional Ecology, vol. 23, no. 2, pp. 359-366.
• Rowell, J.T., Associate Editor: Peter D. Taylor, Editor: Michael C. Whitlock, Ellner, S.P. & Reeve, H.K. 2006, "Why Animals Lie: How Dishonesty and Belief Can Coexist in a Signaling System", The American Naturalist, vol. 168, no. 6, pp. E180-E204.