Rest-activity rhythms characteristics and seasonal changes in seasonal affective disorder

ABSTRACT

Identifying objectively measurable seasonal changes in 24-h activity patterns (rest-activity rhythms or RARs) that occur in seasonal affective disorder (SAD) could help guide research and practice towards new monitoring tools or prevention targets. We quantified RARs from actigraphy data using non-parametric and extended cosine based approaches, then compared RARs between people with SAD and healthy controls in the summer (n = 70) and winter seasons (n = 84). We also characterized the within-person seasonal RAR changes that occurred in the SAD (n = 19) and control (n = 26) participants who contributed repeated measures. Only controls had significant winter increases in RAR fragmentation (intra-daily variability; in controls mean winter-summer changes (log scale) = 0.05, 0.21 standard deviation, p = 0.03). In SAD participants only, estimated evening settling times (down-mesor) were an average of 30 min earlier in the winter compared with the summer (1-h standard deviation, p = 0.045). These RAR characteristics correlated with greater fatigue (Spearman r = 0.36) but not depression symptom severity. Additional research is needed to ascertain why healthy controls, but not people with SAD, appear to have increased RAR fragmentation in the winter. People with SAD lacked this increase in RAR fragmentation, and instead had earlier evening setting in the winter. Prospective and intervention studies with greater temporal resolution are warranted to ascertain how these seasonal behavioral differences relate to fatigue pathophysiology in SAD. Future research is needed to determine whether extending the winter active period, even in relatively fragmented bouts, could help reduce the fatigue symptoms common in SAD.     

Maternal survival costs in an asocial mammal

Maternal characteristics, social dynamics, and environmental factors can all influence reproduction and survival and shape trade‐offs that might arise between these components of fitness. Short‐lived mammals like the golden‐mantled ground squirrel (GMGS; Callospermophilus lateralis) tend to maximize effort toward current reproduction at the expense of survival but may be complicated by other aspects of the species’ life history and environment. Here, we use 25 years of data (1995–2020) collected from a population of GMGS at the Rocky Mountain Biological Research Laboratory in Gothic, Colorado, to test the effect of several maternal characteristics (e.g., age, experience, and timing of litter emergence), social context (e.g., litter sex ratio and kin density), and environmental context (e.g., date of bare ground and length of vegetative growing season) on survival of reproductive female GMGS using Cox proportional hazard models. Our results indicated that social dynamics (i.e., density) and environmental conditions (i.e., standardized first day of permanent snow cover and length of growing season) explained significant variation in annual maternal survival, while maternal characteristics did not. A higher density of related breeding females and the total number of females (both related and unrelated to the focal mother) were associated with an increase in the mortality hazard. A later standardized date of the first day of permanent snow cover and a shorter growing season both reduced the maternal mortality hazard. Together, our results suggest that factors extrinsic to the squirrels affect maternal survival and thus may also influence local population growth and dynamics in GMGS and other short‐lived, territorial mammal species.     

Innate and Learned Predator Recognition Mediated by Chemical Signals in Eurycea nana

Effective and efficient predator recognition and avoidance are essential for the persistence of prey populations, especially in habitats where non-native predators have been introduced. Predator recognition studies are commonly couched within a learned or innate dichotomous framework; however, characteristics of some systems or species could favor innate recognition combined with the ability to alter avoidance responses based on experience with predators. Eurycea nana is a fully aquatic salamander inhabiting a system with a diverse, yet temporally stable, community of native and non-native opportunistically foraging fish predators. To examine predator recognition, we examined avoidance responses (decreased activity) of predator-naïve (first-generation, captive-reared) and predator-experienced (recently collected) E. nana to the chemical cues of a native predator, a non-native predator, a non-predator, and a blank control. Both predator-naïve and predator-experienced E. nana significantly lowered activity in response to the native fish predator when compared with a blank control. Interestingly, predator-naïve E. nana decreased activity in response to the non-native fish predator while predator-experienced E. nana did not. These results indicate that while there is an innate component to predator recognition in E. nana , experience and risk assessment may also be important.     

A metagenomic view of novel microbial and metabolic diversity found within the deep terrestrial biosphere at DeMMO: A microbial observatory in South Dakota,USA

The deep terrestrial subsurface is a large and diverse microbial habitat and vast repository of biomass. However, in relation to its size and physical heterogeneity we have limited understanding of taxonomic and metabolic diversity in this realm. Here we present a detailed metagenomic analysis of samples from the Deep Mine Microbial Observatory (DeMMO) spanning depths from the surface to 1.5 km into the crust. From eight geochemically and spatially distinct fluid samples we reconstructed ~600 partial to near-complete metagenome-assembled genomes (MAGs), representing 50 distinct phyla and including 18 candidate phyla. These novel clades include members of the candidate phyla radiation, two new MAGs from OLB16, a phylum originally identified in DeMMO fluids and for which only one other MAG is currently available, and new MAGs from the Eisenbacteria, Omnitrophota, and Edwardsbacteria. We find that microbes spanning this expansive phylogenetic diversity and physical subsurface space gain a competitive edge by maintaining a wide variety of functional pathways, are often capable of numerous dissimilatory energy metabolisms and poised to take advantage of nutrients as they become available in isolated fracture fluids. Our results support and expand on emerging themes of tight nutrient cycling and genomic plasticity in deep subsurface biosphere taxa.