Distinct decision-making properties underlying the species specificity of group formation of flies.

Many animal species form groups. Group characteristics differ between species, suggesting that the decision-making of individuals for grouping varies across species. However, the actual decision-making properties that lead to interspecific differences in group characteristics remain unclear. Here, we compared the group formation processes of two Drosophilinae fly species, Colocasiomyia alocasiae and Drosophila melanogaster, which form dense and sparse groups, respectively. A high-throughput tracking system revealed that C. alocasiae flies formed groups faster than D. melanogaster flies, and the probability of C. alocasiae remaining in groups was far higher than that of D. melanogaster. C. alocasiae flies joined groups even when the group size was small, whereas D. melanogaster flies joined groups only when the group size was sufficiently large. C. alocasiae flies attenuated their walking speed when the inter-individual distance between flies became small, whereas such behavioural properties were not clearly observed in D. melanogaster. Furthermore, depriving C. alocasiae flies of visual input affected grouping behaviours, resulting in a severe reduction in group formation. These findings show that C. alocasiae decision-making regarding grouping, which greatly depends on vision, is significantly different from D. melanogaster, leading to species-specific group formation properties.

Regulation of Satiety Quiescence by Neuropeptide Signaling in Caenorhabditis elegans.

Sleep and metabolism are interconnected homeostatic states; the sleep cycle can be entrained by the feeding cycle, and perturbation of the sleep often results in dysregulation in metabolism. However, the neuro-molecular mechanism by which metabolism regulates sleep is not fully understood. We investigated how metabolism and feeding regulate sleep using satiety quiescence behavior as a readout in Caenorhabditis elegans, which shares certain key aspects of postprandial sleep in mammals. From an RNA interference-based screen of two neuropeptide families, RFamide-related peptides (FLPs) and insulin-like peptides (INSs), we identified flp-11, known to regulate other types of sleep-like behaviors in C. elegans, as a gene that plays the most significant role in satiety quiescence. A mutation in flp-11 significantly reduces quiescence, whereas over-expression of the gene enhances it. A genetic analysis shows that FLP-11 acts upstream of the cGMP signaling but downstream of the TGFß pathway, suggesting that TGFß released from a pair of head sensory neurons (ASI) activates FLP-11 in an interneuron (RIS). Then, cGMP signaling acting in downstream of RIS neurons induces satiety quiescence. Among the 28 INSs genes screened, ins-1, known to play a significant role in starvation-associated behavior working in AIA is inhibitory to satiety quiescence. Our study suggests that specific combinations of neuropeptides are released, and their signals are integrated in order for an animal to gauge its metabolic state and to control satiety quiescence, a feeding-induced sleep-like state in C. elegans.