Early olfactory environment influences social behaviour in adult Octodon degus

The importance of distinguishing individual differences in 'social impact' versus 'social responsiveness' when quantifying indirect genetic effects on the evolution of social plasticity

Social evolution and the dynamics of social interactions have previously been studied under the frameworks of quantitative genetics and behavioural ecology. In quantitative genetics, indirect genetic effects of social partners on the socially plastic phenotypes of focal individuals typically lack crucial detail already included in treatments of social plasticity in behavioural ecology. Specifically, whilst focal individuals (e.g. receivers) may show variation in their 'responsiveness' to the social environment, individual social partners (e.g. signallers) may have a differential 'impact' on focal phenotypes. Here we propose an integrative framework, that highlights the distinction between responsiveness versus impact in indirect genetic effects for a range of behavioural traits. We describe impact and responsiveness using a reaction norm approach and provide statistical models for the assessment of these effects of focal and social partner identity in different types of social interactions. By providing such a framework, we hope to stimulate future quantitative research investigating the causes and consequences of social interactions on phenotypic evolution.

Octodon degus: a natural model of multimorbidity for ageing research

Integrating the multifactorial processes co-occurring in both physiological and pathological human conditions still remains one of the main challenges in translational investigation. Moreover, the impact of age-associated disorders has increased, which underlines the urgent need to find a feasible model that could help in the development of successful therapies. In this sense, the Octodon degus has been indicated as a 'natural' model in many biomedical areas, especially in ageing. This rodent shows complex social interactions and high sensitiveness to early-stressful events, which have been used to investigate neurodevelopmental processes. Interestingly, a high genetic similarity with some key proteins implicated in human diseases, such as apolipoprotein-E, β-amyloid or insulin, has been demonstrated. On the other hand, the fact that this animal is diurnal has provided important contribution in the field of circadian biology. Concerning age-related diseases, this rodent could be a good model of multimorbidity since it naturally develops cognitive decline, neurodegenerative histopathological hallmarks, visual degeneration, type II diabetes, endocrinological and metabolic dysfunctions, neoplasias and kidneys alterations. In this review we have collected and summarized the studies performed on the Octodon degus through the years that support its use as a model for biomedical research, with a special focus on ageing.

Contribution of individual olfactory receptors to odor-induced attractive or aversive behavior in mice

Odorants are recognized by multiple olfactory receptors (ORs) and induce innate behaviors like attraction or aversion via olfactory system in mice. However, a role of an individual OR is unclear. Muscone is recognized by a few ORs including MOR215–1 and MOR214–3, and attracts male mice. Odor preference tests using MOR215–1 knockout mice revealed that MOR215–1 and other OR(s), possibly including MOR214–3, are involved in the attraction. (Z)-5-tetradecen-1-ol (Z5–14:OH) activates ~3 ORs, including Olfr288, and evokes attraction at low levels but aversion at higher levels. Olfr288 knockout mice show no attraction but aversion, suggesting Olfr288 is involved in preference for Z5–14:OH, whereas activation of other low-affinity Z5–14:OH receptors evokes aversion. Each OR appears to send a signal to a neural circuit that possesses distinct valence, leading to a certain behavior. The final output behavior with multiple ORs stimulation is determined by summation (addition or competition) of valences coded by activated ORs.

Recent evidence suggests that some olfactory receptor types (OR) may be indispensable to elicit certain innate odor-evoked behaviors. Here, the authors report that eliminating a single OR from the odor-activated ensemble leads to significant changes in odor perception and the evoked behavioral response.

Ligand Specificity and Evolution of Mammalian Musk Odor Receptors: Effect of Single Receptor Deletion on Odor Detection

Musk odors have been used widely for fragrance and medicine for >2000 years because of their fascinating scent and physiological effects. Therefore, fragrance manufacturers have been eager to develop high-quality musk compounds that are safe and easily synthesized. We recently identified muscone-responsive olfactory receptors (ORs) MOR215-1 and OR5AN1 in mice and humans, respectively (Shirasu et al., 2014). In this study, we identified musk ORs that are evolutionarily closely related to MOR215-1 or OR5AN1 in various primates and investigated structure-activity relationships for various musk odorants and related compounds. We found that each species has one or two functional musk ORs that exhibit specific ligand spectra to musk compounds. Some of them, including the human OR5AN1, responded to nitro musks with chemical properties distinct from muscone. The ligand specificity of OR5AN1 reflects the perception of musk odors in humans. Genetic deletion of MOR215-1 in mice resulted in drastic reduction of sensitivity to muscone, suggesting that MOR215-1 plays a critical role in muscone perception. Therefore, the current study reveals a clear link between the identified OR and muscone perception. Moreover, the strategy established for screening ligands for the muscone OR may facilitate the development of novel and commercially useful musk odors.

SIGNIFICANCE STATEMENT

The long-sought musk odor receptor family in mammals was discovered and found to be well conserved and narrowly tuned to musk odors. In mice, deletion of the most sensitive musk receptor resulted in drastic reduction in sensitivity to muscone, demonstrating a strong link between receptor and odor perception. In humans, we found one musk receptor that recognized both macrocyclic and nitro musks that had distinct chemical structures. The structure-activity relationships were in a good agreement with human sensory perception and therefore may be used to develop novel musk aroma in fragrance fields. Finally, identification of a natural ligand(s) for musk receptors in mammals other than musk deer would reveal an evolutionarily pivotal role in each species in the future.