It is not because of their antisocial behavior that spiders that reach adulthood leave their family groups, as we thought until today, but it is rather the resulting isolation that makes them intolerant to their kind.
According to the animal cognition expert Raphael Jeanson and his colleagues at Toulouse III – Paul Sabatier University in France, this new knowledge makes it possible to better understand the evolution of sociability in arthropods.
Most of the 50,000 species of spiders are solitary, and interactions between adults are limited to the mating period. Outside of the mating season, they are generally aggressive towards their own kind, even going as far as cannibalism.
In the vast majority of these species, however, young spiders have a phase in which they exhibit a high degree of tolerance among themselves.
Then, the “adolescent” spiders progressively move away from the social group and lead a solitary life.
The researchers studied the mechanisms responsible for social cohesion in the spider Agelena labyrinthica, a species widely distributed in France. To achieve this, they combined experimental and theoretical approaches.
Their main conclusion: the dissociation of social groups is not the result of a change in the nature of social interactions, but an increase in the mobility associated with processes of maturation.
Thus, neither the decline of the mutual attraction nor the increase of the aggressive behaviors are at the origin of the dispersion, this moment when the spiders leave the family cell to populate their ecosystem.
Why do they become intolerant?
To answer this question, the researchers maintained young spiders alone or in groups for 20 days. They then observed that:
- The twinning of two spiders kept in isolation led to violent aggression and cannibalism.
- The spiders kept in groups showed no aggressive behavior.
These results suggest that social isolation leads to an alteration in the response of spiders to stimuli emitted by congeners.
Thus, the appearance of aggression is the consequence, and not the cause, of dispersion.
According to the authors of this work published in the journal PLoS Biology, this new knowledge could help to understand the processes involved in the dispersal of solitary spiders and provide clues to the mechanisms that led to the development of forms of sustainable social life.