Experience influences shoal member preference in a species pair of sticklebacks

Recognition of suitable group members can be learned through experience or can be genetically based. To determine when learning may be important in social recognition, we compared the social recognition of juveniles and adults of 2 sympatric species of three-spined sticklebacks (Gasterosteus spp.). We altered the social environment of both species, rearing individuals with varying numbers of conspecifics and heterospecifics. We measured the effect of this social experience with heterospecifics on shoaling tendency and shoal member preferences. We also explored age effects by comparing juveniles and adults. Experience modified both the degree of sociality and the choice of social partners. We found that juveniles of both species had a stronger tendency to shoal than adults and that experience with heterospecifics influenced social tendency for juvenile benthics but not limnetics. Use of body size cues in selecting social partners by juveniles was also altered by experience. Only juveniles raised with conspecifics preferred conspecifics that were similar in size. Experience had a large effect for adults who preferred to associate with the species they had been raised with. Differences between juveniles and adults were more pronounced than differences between species. Our results suggest that individuals learn their species identity from the social environment and that this affects social preference. Learned social preferences may also have implications for the maintenance of reproductive isolation between these species.