July 31, 2013 report
Study shows some spiders have individualized personalities
(Phys.org) —Researchers studying the Stegodyphus sarasinorum spider in India have found that individual specimens have different personality traits from one another. In their paper published in Proceedings of the Royal Society B, the team report that some spiders in the field study exhibited more "boldness" than did others.
Scientists have known for many years that animals have distinct personalities—cats and dogs are prime examples. Less clear is whether smaller organisms with smaller less developed brains do as well. To find out, the researchers in India focused on Stegodyphus sarasinorum, one of the few spider species that live in colonies. Rather than focus on a range of different types of possible personalities, the team chose instead to focus on just one: boldness. With spiders, boldness is a characteristic that describes a tendency to rush out of the nest to see what sort of creature has become stuck in its web, rather than hanging behind watching to see what develops.
The researchers chose the spider colony because scientists suspect that the more social an organism type is the more likely there are to be differing personalities within a group.
To learn which spiders might have which personality traits, the researchers went out into the field and bagged several spider nests and brought them back to the lab. After dissecting the nests, 40 specimens were chosen from each to serve as objects of study—each had colored spots applied to their backs to denote the level of aggression they exhibited when stimulated and to help in identifying them. Next, all of the spiders from the original nests were placed in artificial nests which were then placed in trees near the research facility. There, the researchers simulated insects being captured in webs and studied the actions of the spiders that occurred as a result.
In analyzing the data, the researchers found that those spiders that had exhibited the most aggression in the first part of the study, were the very same ones that acted most boldly when insects became stuck in their webs—suggesting that individualized personality traits in the spiders tends to determine which sort of job they have—those that are bolder tend to be the ones that deal with captured prey, while those that are meeker wind up nurturing offspring or engaging in other less confrontational tasks.
Deciphering the mechanisms involved in shaping social structure is key to a deeper understanding of the evolutionary processes leading to sociality. Individual specialization within groups can increase colony efficiency and consequently productivity. Here, we test the hypothesis that within-group variation in individual personalities (i.e. boldness and aggression) can shape task differentiation. The social spider Stegodyphus sarasinorum (Eresidae) showed task differentiation (significant unequal participation) in simulated prey capture events across 10-day behavioural assays in the field, independent of developmental stage (level of maturation), eliminating age polyethism. Participation in prey capture was positively associated with level of boldness but not with aggression. Body size positively correlated with being the first spider to emerge from the colony as a response to prey capture but not with being the first to attack, and dispersal distance from experimental colonies correlated with attacking but not with emerging. This suggests that different behavioural responses to prey capture result from a complex set of individual characteristics. Boldness and aggression correlated positively, but neither was associated with body size, developmental stage or dispersal distance. Hence, we show that personalities shape task differentiation in a social spider independent of age and maturation. Our results suggest that personality measures obtained in solitary, standardized laboratory settings can be reliable predictors of behaviour in a social context in the field. Given the wealth of organisms that show consistent individual behavioural differences, animal personality could play a role in social organization in a diversity of animals.
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