Male fiddler crabs have an enlarger claw that they use in sexual displays to attract females and in assessing competing males. There have been some really cool studies done on Uca mjoebergi by Backwell and Jennions (and a load of other researchers too). These interesting crustaceans have lent themselves well to field experiments through the use of 'Robo-crab', a robot that the researchers have been able to use to investigate female preferences and male behaviours. Below are some abstracts from some of their work and links to the papers themselves.
Callander, Hayes, Jennions & Backwell (2013) Experimental evidence that immediate neighbors affect male attractiveness. Behavioral Ecology, 24:730-733
If female mate choice is based on comparison of locally available mates rather than absolute, fixed criteria, a male’s attractiveness might depend on the attractiveness of his immediate competitors. We use robotic models to test whether the number of females that a male fiddler crab, Uca mjoebergi, attracts depends on his immediate neighbors’ size. Larger males are, on average, more attractive to females and are also more likely to win male–male fights. Larger males can partially influence who their territorial neighbors are because they assist smaller neighbors to repel intruders that attempt to acquire the neighbor’s burrow (defence coalitions). This assistance might allow a male to avoid the costs of renegotiating territorial boundaries with new neighbors, who will also tend to be larger than the previous neighbor. In this study, we show that males are more likely to attract females if they court immediately alongside smaller males. This represents an additional potential benefit of defence coalitions, by ensuring that large males compete against smaller neighbors when courting.
http://beheco.oxfordjournals.org/content/24/3/730.short
Lailvaux, Reaney & Backwell (2009) Dishonest signalling of fighting ability and multiple performance traits in the fiddler crab Uca mjoebergi. Functional Ecology, 23:359-366
1. Signals used during male combat are expected to be honest indicators of fighting ability. However, recent studies show that dishonesty in male signalling is more prevalent than previously believed.
2. Here we show that regenerated (leptochelous) claws in male Uca mjoebergi fiddler crabs are not only dishonest signals of two types of whole-organism performance capacities that are likely to be useful during fights (claw closing force and pull-resisting force), but they are also less effective as weapons in situations where males are unable to bluff.
3. Original (brachychelous) male claws are statistically significant predictors (independent of body size) of both closing force and the force required to pull a male out of a tunnel. By contrast, leptochelous claw size does not convey information on those performance capacities following control for body size.
4. Furthermore, claw size affects fighting ability such that leptochelous residents are at a significant competitive disadvantage to brachychelous residents, although claw type does not affect the ability of non-resident males to win fights.
5. This study is among the first to show that male armaments can dishonestly signal performance traits that are likely important for winning fights, and is the first to show evidence for dishonest signalling of multiple components of fighting ability.
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2008.01501.x/full
Callander, Hayes, Jennions & Backwell (2013) Experimental evidence that immediate neighbors affect male attractiveness. Behavioral Ecology, 24:730-733
If female mate choice is based on comparison of locally available mates rather than absolute, fixed criteria, a male’s attractiveness might depend on the attractiveness of his immediate competitors. We use robotic models to test whether the number of females that a male fiddler crab, Uca mjoebergi, attracts depends on his immediate neighbors’ size. Larger males are, on average, more attractive to females and are also more likely to win male–male fights. Larger males can partially influence who their territorial neighbors are because they assist smaller neighbors to repel intruders that attempt to acquire the neighbor’s burrow (defence coalitions). This assistance might allow a male to avoid the costs of renegotiating territorial boundaries with new neighbors, who will also tend to be larger than the previous neighbor. In this study, we show that males are more likely to attract females if they court immediately alongside smaller males. This represents an additional potential benefit of defence coalitions, by ensuring that large males compete against smaller neighbors when courting.
http://beheco.oxfordjournals.org/content/24/3/730.short
Lailvaux, Reaney & Backwell (2009) Dishonest signalling of fighting ability and multiple performance traits in the fiddler crab Uca mjoebergi. Functional Ecology, 23:359-366
1. Signals used during male combat are expected to be honest indicators of fighting ability. However, recent studies show that dishonesty in male signalling is more prevalent than previously believed.
2. Here we show that regenerated (leptochelous) claws in male Uca mjoebergi fiddler crabs are not only dishonest signals of two types of whole-organism performance capacities that are likely to be useful during fights (claw closing force and pull-resisting force), but they are also less effective as weapons in situations where males are unable to bluff.
3. Original (brachychelous) male claws are statistically significant predictors (independent of body size) of both closing force and the force required to pull a male out of a tunnel. By contrast, leptochelous claw size does not convey information on those performance capacities following control for body size.
4. Furthermore, claw size affects fighting ability such that leptochelous residents are at a significant competitive disadvantage to brachychelous residents, although claw type does not affect the ability of non-resident males to win fights.
5. This study is among the first to show that male armaments can dishonestly signal performance traits that are likely important for winning fights, and is the first to show evidence for dishonest signalling of multiple components of fighting ability.
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2435.2008.01501.x/full
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