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Animal’s Agression More Important Than Size

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Big fish survive, but which one becomes big? Personality makes the difference.

fish, size, agression, personality, survive, strength, win, foodHow did this goldfish get so big? Probably because it won when fighting over food with other fish. But why did it win? Because it already was big? Or because it just acted more aggressive? A new study shows the last answer could be more important.

We already saw it last week in the video showing a goose chasing a gorilla: size isn’t everything in the animal kingdom. Researchers of the University of Exeter and the Texas A & M University found you can sometimes even better predict the outcome of a food fight with the personality-type of the competitors, than with their body size.

To test this, they put pairs of hungry sheepshead swordtail fishes in a tank with food and filmed their behaviour. The researchers found it’s quite easy to categorize the male fishes as agressive or shy, because the same fish often repeated the same behaviour. An important classification, it appeared, because this personality trait could significantly predict who would win the fight. Some small fish won, just by attacking their larger opponent.

The researchers talk about a Napoleon (or ‘small man) syndrome, in which smaller fish compensate for their size with aggresive behavior. They conclude that “personality can have far reaching implications for life and survival”. This phenomenon was more difficult to detect in females, however. The ladies rarely attacked their opponent to win food.

What happened after the fights is less suprising but gives more insight into the subject: the fish that won the fight over food eventually grew bigger. This shows the ‘chicken and egg problem’ we face by explaining the relationship between agression, body size and survival.

Photo: Flickr, philipevans
Source: Exeter University
Wilson, A., Grimmer, A., & Rosenthal, G. (2013). Causes and consequences of contest outcome: aggressiveness, dominance and growth in the sheepshead swordtail, Xiphophorus birchmanni Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-013-1540-7

agressive animals, animal research facts

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