Sucrose acceptance threshold and feeding behaviour in nectivorous ants: starvation and serotonin effects

FALIBENE, A; JOSENS, R

Copenhagen

Congreso; XVI Congress of the International Union for the Study of Social Insects; 2010

International Union for the Study of Social Insects

 Feeding is a complex behaviour and its regulation involves the integration of a wide range of external and internal factors. Such is  also  the case  for the ant Camponotus mus, which modifies its feeding behaviour depending on the nectar quality but also on its internal state, determined by the colony’s sugar requirements. Physiologically, the biogenic amine serotonin (5-HT) is involved in numerous processes related with feeding behaviour. We  examined the effects of serotonin on feeding related behaviour and its relationship with starvation in C. mus ants. Feeding behaviour and electrical activity of the sucking pump were recorded in ants that received different concentrations of orally administered serotonin. This was  compared with the effects produced by starvation. In addition, we developed a novel protocol to analyse the sucrose acceptance threshold  in ants. Our results have shown that 5-HT promoted a decrease in sucrose feeding in a dose-dependent manner. Intake rate of 5-HT-treated ants was lower than that of control ants, similar to the decrease observed for non starved ants. Our recordings lead us to discern that intake rate reduction by serotonin was mainly due to a decrease in the volume of solution ingested per pump contraction while intake rate reduction by satiation was due to a decrease in pumping frequency. Sucrose acceptance threshold changed with the level of carbohydrate starvation: the higher the starvation level, the lower the solution concentration that elicited a response. On the other hand, oral-administered 5-HT did not modify sucrose acceptance threshold under our experimental conditions. Our results show that both 5-HT and satiation promote a depressant effect on sucking pump activity, however, they act by different mechanisms. These findings are discussed in the frame of feeding control and the role of biogenic amines in insect behaviour.