The oxytocin/vasopressin signalling system comprises G protein-coupled receptors and their endogenous peptide ligands and appears to be important for water homeostasis, reproduction, learning, memory and behaviour [1]. To date, its biological function in insects has only been studied in the beetle Tribolium castaneum where it has been implicated in water retention in Malpighian tubules [2; 3]. The first evidence that an oxytocin/vasopressin-like signalling system exists in social insects came from ant genome sequencing [4] indicating the presence of one receptor and one neuropeptide precursors protein in all sequenced ant species [5]. For our study we have chosen two ant species of the genus Lasius that are closely related genetically, but significantly differ in their ecology and colony structure [6].
Following pharmacological characterization of the ligand-receptor pair in vitro, our aim was to determine the distribution and expression level of both the receptor and precursor in different parts of the body and developmental stages in ants using qPCR and immunostaining. Next we were able to generate a knock-down of the precursor in Lasius ants and performed in vivo behavioural experiments.
Our qPCR results indicate that this signalling system can be involved in male reproduction (high expression of receptor in male heads and reproductive organs) similar to other invertebrate species. On the other hand, the expression of receptor in Malpighian tubules is very low which contradict earlier findings in beetles [2]. Additionally, high expression of receptor in some parts of digestive system and fat body, differences in expression during circadian and seasonal rhythms and down-regulation of the precursor after starvation indicate that oxytocin/vasopressin signalling in ants may be involved in food uptake, digestion and maintenance of energy status.