Meta-analyses reveal support for the Social Intelligence Hypothesis

The Social Intelligence Hypothesis (SIH) is one of the leading explanations for the evolution of cognition. Since its inception a vast body of literature investigating the predictions of the SIH has accumulated, using a variety of methodologies and species. However, the generalisability of the hypothesis remains unclear. To gain an understanding of the robustness of the SIH as an explanation for the evolution of cognition, we systematically searched the literature for studies investigating the predictions of the SIH. Accordingly, we compiled 103 studies with 584 effect sizes from 17 taxonomic orders. We present the results of four meta-analyses which reveal support for the SIH across interspecific, intraspecific and developmental studies. However, effect sizes did not differ significantly between the cognitive or sociality metrics used, taxonomy or testing conditions. Thus, support for the SIH is similar across studies using neuroanatomy and cognitive performance, those using broad categories of sociality, group size and social interactions, across taxonomic groups, and for tests conducted in captivity or the wild. Overall, our meta-analyses support the SIH as an evolutionary and developmental explanation for cognitive variation.

Cytoarchitectural characteristics associated with cognitive flexibility in raccoons

With rates of psychiatric illnesses such as depression continuing to rise, additional preclinical models are needed to facilitate translational neuroscience research. In the current study, the raccoon (Procyon lotor) was investigated due to its similarities with primate brains, including comparable proportional neuronal densities, cortical magnification of the forepaw area, and cortical gyrification. Specifically, we report on the cytoarchitectural characteristics of raccoons profiled as high, intermediate, or low solvers in a multiaccess problem-solving task. Isotropic fractionation indicated that high-solvers had significantly more cells in the hippocampus (HC) than the other solving groups; further, a nonsignificant trend suggested that this increase in cell profile density was due to increased nonneuronal (e.g., glial) cells. Group differences were not observed in the cellular density of the somatosensory cortex. Thionin-based staining confirmed the presence of von Economo neurons (VENs) in the frontoinsular cortex, although no impact of solving ability on VEN cell profile density levels was observed. Elongated fusiform cells were quantified in the HC dentate gyrus where high-solvers were observed to have higher levels of this cell type than the other solving groups. In sum, the current findings suggest that varying cytoarchitectural phenotypes contribute to cognitive flexibility. Additional research is necessary to determine the translational value of cytoarchitectural distribution patterns on adaptive behavioral outcomes associated with cognitive performance and mental health.

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.

Female degus show high sociality but no preference for familiar peers

Group-living animals vary in social behavior across multiple dimensions, including in the selectivity of social interactions with familiar versus unfamiliar peers. Standardized behavioral tests can be used to tease apart different dimensions of behavior. These serve a dual function-on one hand, helping to isolate behavioral factors that may support collective behavior in natural habitats, and, on another, providing a basis for comparative approaches to understanding physiological mechanisms of behavior. Degus (Octodon degus) are South American caviomorph rodents that nest and forage in groups with relatively low genetic relatedness. Flexibility in group membership is likely supported by gregariousness toward strangers, but the relative preference for strangers compared with familiar individuals has not been systematically tested. We assessed the specificity of social preferences in female degus using a same-sex partner preference test. Degus huddled extensively with both familiar and unfamiliar peers, with no average preference for one over the other. Detailed analysis of social interactions demonstrated an effect of familiarity on social investigation and aggressive behaviors, indicating that degus distinguished between familiar and unfamiliar conspecifics, even though it did not impact huddling. This behavioral profile is thus far unique to degus; in similar tests, meadow and prairie voles exhibit strong partner preferences for known peers, while mice exhibit low social huddling and spend relatively less time in social chambers. Understanding how group-living species differ in specific aspects of social behavior such as familiarity/novelty preference and propensity for social contact will offer a foundation to interpret differences in neural systems supporting sociality.