Female Aggression in the Snapping Shrimp

Differences between sexes, known as sexual dimorphism, are a common result of an evolutionary process called sexual selection. In males, sexual dimorphism is commonly seen in weaponry and aggression as these features are utilised when competing with other males in order to secure mating opportunities with females.

An example of sexual dimorphism is well known in the snapping shrimp. Both sexes possess a deadly snapping claw that is primarily used as a weapon to defend their territory.  Should a snap from the claw come into contact with an opponent, it can cause dismemberment or even death.

The shrimp’s claw is remarkably hardy. Should the shrimp lose it in battle, the smaller claw can then go on to transform into a new snapping claw.

Research into the differences between male and female snapping shrimp left the US researchers surprised at the results as, despite having a smaller snapping claw, females were found to be far more aggressive than males.

The new study, published in the journal Ethology, determined aggressive behaviour on the amount of claw snaps that the shrimps took at one another. The shrimps were allocated a burrow and given time to become residents in the burrow before being presented with an ‘intruding’ shrimp. It was found that the female shrimps were far more aggressive to other females than males were to either sex.

The surprising results have posed more questions for the researchers to answer, namely why the females are so much more aggressive than the males. Female aggression has not been as thoroughly studied as that in males although current lines of thought believe that males are central to the aggression observed. It could be that the females are directly fighting over males or may be defending territories. Larger territories mean that it will not be as easy for males to travel between multiple females and in this way the female is ensuring she has exclusive access to him.

Picture reference:
Hkchan123, Alpheus heterochaelis [ONLINE]. Available at:http://en.wikipedia.org/wiki/Alpheus_heterochaelis#mediaviewer/File:Alpheus_heterochaelis.jpg [Accessed 09 July 14].

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Amy Moore

Amy is currently studying for a Masters in Science Communication. Follow her on twitter @_Amy_Moore91

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