Abstract

Individuals within groups benefit when they are phenotypically
and behaviourally similar. Despite this, mixed-species aggregations
are found among a wide range of animal taxa and
are known to provide advantages in terms of enhanced foraging
efficiency and predator avoidance. However, little is
known about individual level interactions within these groups
or the mechanisms mediating their structure. Diet-derived
chemical cues can mediate within-species associations in fish,
but it is not known whether they serve a similar function
across species. To investigate this, we created mixed-species
groups of sympatric three-spined (Gasterosteus aculeatus)
and nine-spined (Pungitius pungitius) sticklebacks and manipulated
the diet of the constituent group members.We found
that three-spined sticklebacks did not associate more frequently
with conspecifics over heterospecifics when all animals
received the same diet, suggesting that species-specific cues
did not influence association patterns. However, when group
members were fed different diets, they interacted with
heterospecifics fed on the same diet more than with conspecifics
from a different diet treatment. This study demonstrates
the importance of chemical cues as a possible mechanism for
establishing familiarity, and thereby mediating within-group
structure even between individuals in mixed-species
aggregations. Understanding these underlying mechanisms
has significant implications for our understanding of other
social dynamics, including social learning and information
transfer.