Abstract
Oxytocin has a conserved role in regulating animal social behaviour including parental-offspring interactions. Recently an oxytocin-like neuropeptide, nematocin, and its cognate receptors have been identified in the nematode Caenorhabditis elegans. We provide evidence for a pheromone signal produced by C. elegans larvae that modifies the behaviour of adult animals in an oxytocin-dependent manner increasing their probability of leaving a food patch which the larvae are populating. This increase is positively correlated to the size of the larval population but cannot be explained by food depletion nor is it modulated by biogenic amines, which suggest it is not an aversive behaviour. Moreover, the food-leaving behaviour is conspecific and pheromone dependent: C. elegans adults respond more strongly to C. elegans larvae compared to other nematode species and this effect is absent in C. elegans daf-22 larvae which are pheromone deficient. Neurotransmitter receptors previously implicated in C. elegans foraging decisions NPR-1 and TYRA-3, for NPY-like neuropeptides and tyramine respectively, do not appear to be involved in oxytocin-dependent adult food-leaving. We conclude oxytocin signals within a novel neural circuit that regulates parental-offspring social behaviour in C. elegans and that this provides evidence for evolutionary conservation of molecular components of a parental decision making behaviour.
Highlights
Animals have evolved intricate mechanisms that enable them to optimally locate and utilise food in their environment to satisfy their nutritional requirements, a behaviour called foraging
Previous studies have identified the tendency of C. elegans to transiently leave a defined ‘worm naïve’ bacterial lawn is initially very low but shows a steady increase over time such that at the later time-points the number of worms off the food patch increases[2]
To test whether or not there was a significant change in the density of the bacterial lawn we measured bacterial growth curves for OP50 lawns that had been cultivated for 24 hours with 7 gravid worms; that is, the conditions under which there was a progressive increase in food-leaving (Fig. 1A)
Summary
Animals have evolved intricate mechanisms that enable them to optimally locate and utilise food in their environment to satisfy their nutritional requirements, a behaviour called foraging This is controlled by neural circuits which integrate conflicting sensory cues to drive behaviour appropriate to the specific current conditions. It has been found that both arrested L1 or dauer larvae, which are C. elegans life stages generated under starvation conditions, produce signals that trigger adult food-leaving[16] or dispersal This is reinforced by evidence that population density can trigger dispersal for wild-type[14] and it is enhanced in a chitin synthase mutant, chs-2, which is nutritionally compromised[9]. We provide evidence for an additional important modulator of adult C. elegans food-leaving behaviour, namely the specific impact of the presence of their larval progeny on their foraging response
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