The yellow gene regulates behavioral plasticity by repressing male courtship in Bicyclus anynana butterflies

Seasonal plasticity in male courtship in Bicyclus anynana butterflies is due to variation in levels of the steroid hormone 20E (20-hydroxyecdysone) during pupation. Wet season (WS) males have high levels of 20E and become active courters. Dry season (DS) males, have lower levels of 20E and reduced courtship rates, although WS courtship rates can be achieved if DS male pupae are injected with 20E at 30% of pupation. Here we investigated the genes involved in male courtship plasticity and examine whether 20E plays an organizational role in the pupal brain that later influences the sexual behaviour of adults. We show that DS pupal brains have a 7-fold upregulation of the yellow gene relative to the WS and that knocking out yellow leads to increased male courtship. We find that injecting 20E into DS pupa reduced yellow expression although not significantly. Our results show that yellow is a repressor of the neural circuity for male courtship behaviour in B. anynana. 20E levels experienced d...