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

Abstract

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.