Cricket Agression and Sexual Selection

Territoriality and Aggression in The Black Field Cricket Tetorgryllus commodus

Introduction

The Black Field Cricket Tetogryllus commodus displays both intra and inter sexual selection. Observations have shown that the male cricket will compete with other male crickets until an individual establishes dominance over the territory. The cricket who wins, will then defend his territory which contains valuable resources which the female cricket is attracted too.

A female only needs to mate with 1 male in order to fertilise her eggs. This means that the female will need to choose very carefully who she will mate with. She will choose a cricket she wishes to mate with dependent on his morphological characteristics. These desirable characteristics will then be passed onto her offspring and increase their chances of survival. The female being picky with her mate choice and the confrontation between males is what drives sexual dimorphism.

The purpose of this experiment is to test the hypothesis that a cricket who currently defends a territory has more chance of winning a fight between an intruding cricket. This hypothesis also predicts that the territory holder will show more aggression than the intruder.

The second hypothesis that is tested, is to confirm if a larger cricket is more likely to win in a fight, than a smaller cricket, thus increasing its fitness which will appear attractive to a female.

Materials and Methods

An ethogram of aggressive behaviours of crickets should be written up before beginning the experiment. These are a list of all the behaviours which will be counted during the experiment.

In order to test the first hypothesis that a territory holder is more likely to win a fight, 2 crickets were placed in 2 separate containers with breathable holes. One of the crickets had a small drop of paint dropped onto its thorax to clearly distinguish the difference between the 2 crickets. They were then given time to acclimatise to their new spaces which...