The chemical basis of a signal of individual identity: shell pigment concentrations track the unique appearance of Common Murre eggs

In group-living species with parental care, the accurate recognition of one's own young is critical to fitness. Because discriminating offspring within a large colonial group may be challenging, progeny of colonial breeders often display familial or individual identity signals to elicit and receive parental provisions from their own parents. For instance, the common murre (or common guillemot: Uria aalge ) is a colonially breeding seabird that does not build a nest and lays and incubates an egg with an individually unique appearance. How the shell's physical and chemical properties generate this individual variability in coloration and maculation has not been studied in detail. Here, we quantified two characteristics of the avian-visible appearance of murre eggshells collected from the wild: background coloration spectra and maculation density. As predicted by the individual identity hypothesis, there was no statistical relationship between avian-perceivable shell background coloration and maculation density within the same eggs. In turn, variation in both sets of traits was statistically related to some of their physico-chemical properties, including shell thickness and concentrations of the eggshell pigments biliverdin and protoporphyrin IX. These results illustrate how individually unique eggshell appearances, suitable for identity signalling, can be generated by a small number of structural mechanisms.

Tracing Symbolic Behaviour Across the Southern Arc

This chapter traces early expressions of symbolic behaviour:—rock art, personal ornaments, occurrences of ochre, notational pieces, and mortuary practices—across the southern arc dispersal route of modern humans out of Africa to Sahul, from some 70–60,000 years ago. These aspects of symbolic behaviour do not display a consistent pattern of appearance along the southern arc, and dates for their appearance/preservation do not become progressively more recent as modern humans moved east out of Africa. These results are explained using the demographic, social, and symbolic framework proposed to account for geographical and chronological patterning observed in the ‘package’ of traits reflecting modern human behaviour. In this model, the appearance of symbolic behaviour is determined by levels of local/regional population pressure necessitating (or not) the need for identity signalling, ‘bonding’ behaviour/open social networks, and ‘bounding’ or emblemic behaviour/closed social networks.

Odorant receptors can mediate axonal identity and gene choice via cAMP-independent mechanisms

Odorant receptors (ORs) control several aspects of cell fate in olfactory sensory neurons (OSNs), including singular gene choice and axonal identity. The mechanisms of OR-induced axon guidance have been suggested to principally rely on G-protein signalling. Here, we report that for a subset of OSNs, deleting G proteins or altering their levels of signalling does not affect axonal identity. Signalling-deficient ORs or surrogate receptors that are unable to couple to Gs/Golf still provide axons with distinct identities and the anterior–posterior targeting of axons does not correlate with the levels of cAMP produced by genetic modifications. In addition, we refine the models of negative feedback by showing that ectopic ORs can be robustly expressed without suppressing endogenous gene choice. In conclusion, our results uncover a new feature of ORs, showing that they can instruct axonal identity and regulate olfactory map formation independent of canonical G-protein signalling and cAMP production.

Social influences on eating: implications for nutritional interventions

We review recent research on the effect of social context on food intake and food choice and assess the implications for nutritional interventions. We focus on studies of modelling of eating behaviour and the impact of perceived eating norms on the amounts and types of food that individuals eat. We suggest that social context influences eating via multiple mechanisms, including identity signalling and self-presentation concerns. However, building on existing theoretical models, we propose that social factors may be particularly influential on nutrition because following the behaviour of others is adaptive and social norms inform individuals about behaviours that are likely to be optimal (‘if everyone else is doing it, I probably should be’). Guided by understanding of the potential underlying mechanisms, we discuss how social norms might be used to promote healthier nutrition.