Caste- and stage-dependent sensory brain plasticity in a subterranean termite

Abstract The sensory centres of insect brains reflect their capabilities to perceive and respond to olfactory and visual environments, along with other sensory stimuli. As neural tissues are metabolically costly to maintain, investment in these regions may shift with changing sensory demands across life stages. Termites live in eusocial colonies composed of morphologically and behaviourally distinct castes produced through developmental plasticity. Reproductive individuals also alter their sensory tasks during development. However, few studies have examined whether sensory brain plasticity underlies these changes. Here, we examined the brain morphology and sensory lobes across castes and reproductive stages in the invasive Formosan subterranean termite, Coptotermes formosanus. Dispersal alates exhibited the largest brain with expanded antennal and optic lobes, consistent with their multisensory activities above ground. Eyeless workers and soldiers both lacked fully developed optic lobes, and soldiers showed the most reduced antennal lobes, reflecting their subterranean lifestyle and differential behavioural repertoires. Sensory regions also restructured as alates transitioned into mature queens and kings, with fewer glomeruli and degenerated optic lobes. Our findings demonstrate strong links between sensory brain investment and caste- and stage-specific tasks, highlighting termite brain plasticity as an energy-saving strategy and an adaptation convergent with ants and bees.