Age‐ and subcaste‐related patterns of serotonergic immunoreactivity in the optic lobes of the ant Pheidole dentata

Abstract

Serotonin, a biogenic amine known to be a neuromodulator of insect behavior, has recently been associated with age-related patterns of task performance in the ant Pheidole dentata. We identified worker age- and subcaste-related patterns of serotonergic activity within the optic lobes of the P. dentata brain to further examine its relationship to polyethism. We found strong immunoreactivity in the optic lobes of the brains of both minor and major workers. Serotonergic cell bodies in the optic lobes increased significantly in number as major and minor workers matured. Old major workers had greater numbers of serotonergic cell bodies than minors of a similar age. This age-related increase in serotonergic immunoreactivity, as well as the presence of diffuse serotonin networks in the mushroom bodies, antennal lobes, and central complex, occurs concomitantly with an increase in the size of worker task repertoires. Our results suggest that serotonin is associated with the development of the visual system, enabling the detection of task-related stimuli outside the nest, thus playing a significant role in worker behavioral development and colony-wide division of labor.

Polymorphism and division of labour in a socially complex ant: neuromodulation of aggression in the Australian weaver ant,Oecophylla smaragdina

“…The association of serotonergic circuitry with subcaste behavioural differentiation in the dimorphic ant Pheidole dentata supports this model. In comparison to minor workers, defensive majors have more 5-HT-immunoreactive cells in primary visual regions, more extensive serotonergic varicosities in sensory and integrative brain regions [67], and more elaborate axonal arborization in a serotonergic neuron integral to sensory integration [27]. Although relationships between neuromodulators and circuit development have been described in other taxa [68,69], the influence of neuroanatomical differences in 5-HT circuitry on 5-HT signalling and behaviour remains to be studied in ants.…”

Social dominance and reproductive differentiation mediated by dopaminergic signaling in a queenless ant

“…For example, brain octopamine levels are elevated in old honeybee workers to trigger foraging behavior (Shultz and Robinson, 2001). The age-dependent changes in brain amine levels are also observed in ants, implying that age-dependent transition of amine levels commonly occur in social Hymenoptera (Seid and Traniello, 2005;Seid et al, 2008;Wnuk et al, 2011).…”

“…Age-dependent increases of brain amine levels have been reported in workers of various social insects, implying strong links between biogenic amine and age-dependent worker polyethism (Schultz andRobinson, 1999, 2001;Seid and Traniello, 2005;Seid et al, 2008; but see Wnuk et al, 2011). In Diacamma, workers specialize in insidenest tasks for 1-2 months after eclosion (Nakata, 1995); thus, day-7 workers are still nurses.…”

“…Another difficulty comes from the pleiotropic functions of biogenic amines. Brain amine levels are also associated with worker division of labor and amine levels tend to be age dependent (Schultz andRobinson, 1999, 2001;Seid and Traniello, 2005;Seid et al, 2008;Wnuk et al, 2011). As age is also a major determinant of dominance rank (Strassmann and Meyer, 1983;Higashi et al, 1994;Monnin and Ratnieks, 1999;Tsuji and Tsuji, 2005), brain amine levels may be under complex regulation by age and dominance rank (Cuvillier-Hot and Lenoir, 2006).…”

Lifespan behavioural and neural resilience in a social insect

“…Minor workers expand their task repertoires from eclosion to approximately three weeks of age [23] while their brains undergo synaptic remodelling [28] and serotonergic systems that influence behavioural development and task performance mature [25,[29][30][31]. How do workers age behaviourally, and do age-related and brainbased neuroanatomical and neurochemical changes occur that could negatively impact lifespan task performance?…”