Cohesion depends on kinship but no permanent leadership in larval societies of a Neotropical butterfly

In gregarious species, coordinated responses to environmental stimuli are important for a successful habitat and/or food selection. In this sense, maintenance of group cohesion after stochastic disturbances and during collective movements is expected to be advantageous, as is the existence of group leaders. Through laboratory experiments, we examined whether clusters of early instars of Mechanitis polymnia casabranca have both leaders and followers, as well as whether larvae are able to reaggregate depending on neighbors' degree of kinship. In the leadership experiment, clusters of second and third instars were placed in a trail arena having a stimulus leaf at its ending point. Every larva moving ahead from the group was recorded as a leader, and the remaining ones were followers. We also examined whether leaders were temporary or permanent. Of the 195 larvae tested, 22 were permanent leaders (11.28%), 71 larvae were assigned as temporary leaders (36.41%), and 102 larvae never behaved as leaders (52.31%). In the larval cohesion experiment, three treatments were assigned: (i) sibling larvae reared and tested together, (ii) sibling larvae separated after eclosion and tested together, and (iii) non-sibling larvae reared separated and tested together. Sibling larvae reaggregated significantly more compared to non-siblings, regardless of whether they were reared together or separately. Our results show that early instars of M. polymnia casabranca from the same egg cluster are able to recompose aggregations after disrupting disturbances and that group decision-making is mostly dependent on transient leaders.

Nestmate discrimination based on familiarity but not relatedness in eastern carpenter bees

How animals recognize conspecific individuals has important outcomes in many contexts, but interactions among group members are particularly important. Two recognition criteria are often implicated in these interactions: kin recognition is based on relatedness cues and nestmate recognition is based on familiarity. For social insects, both types of recognition are possible, as many nestmates are close kin and familiarity can develop among individuals that encounter each other repeatedly. To discern whether social insects use kin or nestmate recognition, it is necessary to simultaneously assess how relatedness and familiarity influence behaviour. The facultatively social eastern carpenter bee, Xylocopa virginica, offers an excellent opportunity to study how either nestmate or kin recognition (or both) may influence interactions among nestmates, as many females disperse from their natal nests in spring, and often attempt to join new colonies that may contain unrelated individuals. This leads to frequent behavioural interactions among females that may be related or unrelated, and familiar or unfamiliar. We used observation nests and microsatellite loci to assess the influence of familiarity and relatedness on behavioural interactions during the early phase of colony development, when females establish reproductive queues prior to brood production. Females were more likely to feed and were less aggressive to familiar rather than related nestmates, regardless of their relatedness. This suggests that eastern carpenter bees primarily use learned cues to discriminate among nestmates. Interactions with nestmates were also context-dependent, as females returning to the nest without food were the recipients of more aggression than those returning with food. If spring dispersal leads to reduced relatedness in X. virginica colonies, then nestmate recognition based on familiarity would be an important factor in maintaining group cohesion.