Data from: Social complexity affects cognitive abilities but not brain structure in a Poecilid fish

Some cognitive abilities are suggested to be the result of a complex
social life, allowing individuals to achieve higher fitness through
advanced strategies. However, most evidence is correlative. Here, we
provide an experimental investigation of how group size and composition
affect brain and cognitive development in the guppy (Poecilia reticulata).
For six months, we reared sexually mature females in one of three social
treatments: a small conspecific group of three guppies, a large
heterospecific group of three guppies and three splash tetras (Copella
arnoldi) – a species that co-occurs with the guppy in the wild, and a
large conspecific group of six guppies. We then tested the guppies’
performance in self-control (inhibitory control), operant conditioning
(associative learning), and cognitive flexibility (reversal learning)
tasks. Using X-ray imaging, we measured their brain size and major brain
regions. Larger groups of six individuals, both conspecific and
heterospecific groups, showed better cognitive flexibility than smaller
groups, but no difference in self-control and operant conditioning tests.
Interestingly, while social manipulation had no significant effect on
brain morphology, relatively larger telencephalons were associated with
better cognitive flexibility. This suggests alternative mechanisms beyond
brain region size enabled greater cognitive flexibility in individuals
from larger groups. Although there is no clear evidence for the impact on
brain morphology, our research shows that living in larger social groups
can enhance cognitive flexibility. This indicates that the social
environment plays a role in the cognitive development of guppies.