Testing the role of heat shock protein 90 as an evolutionary capacitor of behavioural variation in Tribolium castaneum

Evolutionary capacitance allows populations to ‘store’ cryptic genetic variation, revealing associated phenotypes only under stressful conditions. This process, which can accelerate evolutionary adaptation, has been linked to heat shock protein 90 (HSP90), a key molecular chaperone that plays a central role in buffering genetic variation. While HSP90’s function as a capacitor for morphological variation has been demonstrated in multiple species, its potential function in behavioural variation has only been explored in Drosophila melanogaster . Suppressing HSP90 led to variation in individual activity patterns. Here, we tested whether HSP90 reduction increases behavioural variation in the red flour beetle Tribolium castaneum , a new model for individual variation in diurnal activity patterns. We monitored adult beetle locomotor activity following pharmacological HSP90 impairment in larvae using 17-DMAG. We found increased variance in the activity peak phase of males as well as an increase in variance for occupying the lowest activity state, as inferred from hidden Markov models. Our study adds empirical evidence for HSP90-regulated behavioural variation that could have significant evolutionary consequences regarding temporal niche occupancy.