Lifespan behavioural and neural resilience in a social insect

Analyses of senescence in social species are important to understanding how group living influences the evolution of ageing in society members. Social insects exhibit remarkable lifespan polyphenisms and division of labour, presenting excellent opportunities to test hypotheses concerning ageing and behaviour. Senescence patterns in other taxa suggest that behavioural per- formance in ageing workers would decrease in association with declining brain functions. Using the ant Pheidole dentata as a model, we found that 120-day-old minor workers, having completed 86% of their laboratory lifespan, showed no decrease in sensorimotor functions underscoring complex tasks such as alloparenting and foraging. Collaterally, we found no age-associated increases in apoptosis in functionally specialized brain compartments or decreases in synaptic densities in the mushroom bodies, regions associa- ted with integrative processing. Furthermore, brain titres of serotonin and dopamine—neuromodulators that could negatively impact behaviour through age-related declines—increased in old workers. Unimpaired task performance appears to be based on the maintenance of brain functions supporting olfaction and motor coordination independent of age. Our study is the first to comprehensively assess lifespan task performance and its neurobiological correlates and identify constancy in behavioural performance and the absence of significant age-related neural declines

Brood care acts

Brood care act

Brood care time

Brood care tim

Predation

Predation was classified into 4 categories: 1= no aggression, 2= mandible flaring, 3= latent attack (delayed or not sustained for the duration the assay), 4= attack

Trail following

Annulus half width indicates the half width of the area around the pheromone trail where ants were tracked

Amines

DA and 5HT are raw values for the 20 ul sampled of homogenate sampled. Corr 5HT and Corr DA are whole brain titers

Microglomeruli

Lateral and medial refer to lateral and medial calyces. Distal and proximal refer to circles used for sampling. Details are provided in methods

Activity

Activit

Apoptosis

MB= mushroom bodies, AL= antennal lobes, OL = optic lobes, CC= central complex, SEZ= subesophageal zone RCB= remainder of the central brain. Brain region cells reflects the number of cells per brain region based on a subset of sampled brains (see methods for details). Proportion X (followed by brain region) reflects the amount of that brain region available for counting. Brain region prop indicates the proportion of apoptotic cells of each region scaled by the number of cells per region and the proportion of that region sampled. Brain region prop + 0.001 adds a constant for non-zero values. Log brain region prop are the log transformed values of brain region prop +0.001

Phototaxis

Phototaxi