The presence/absence of conspecifics modulates the circadian locomotor activity and body mass in spotted munia (Lonchura punctulata)

Biological clocks regulate the behavior and physiology of animals by tracking the local time using diverse time cues. Social cues are relevant in studying the behavior of gregarious animals, but these cues have not been widely studied in birds. Temporal information for circadian timekeeping is socially communicated through visual, physical, olfactory, and auditory means. We examined the efficacy of pulsatile social interactions on locomotor activity and its associated characteristics such as distribution profile of rest and activity, total counts, activity duration, phase shift in activity onset, and circadian periodicity in spotted munia. Besides, we analyzed the effect of such social interactions on their body mass. Spotted munia exhibited phase shift in the onset of activity when subjected to social isolation, but these cues could not affect their circadian periodicity. In Pair as well as in Group, social isolation led to increased activity and activity duration, and decreased body mass in guests relative to the host bird. Our results suggest that the circadian rhythm of locomotor activity in spotted munia is quite sensitive to socialization and isolation, and isolation is detrimental for the birds. Consistent with these observations, the decline in body mass revealed the physiological consequences of social isolation on spotted munia.

Physiological effects of food availability times in higher vertebrates

Food availability is a crucial ecological determinant of population size and community structure, and controls various life-history traits in most, if not all, species. Food availability is not constant; there are daily and seasonal differences in food abundance. When coupled to appetite (urge to eat), this is expressed as the eating schedule of a species. Food availability times affect daily and seasonal physiology and behaviour of organisms both directly (by affecting metabolic homeostasis) and indirectly (by altering synchronization of endogenous rhythms). Restricted food availability times may, for example, constrain reproductive output by limiting the number or quality of offspring or the number of reproductive attempts, as has been observed for nesting frequency in birds. Consuming food at the wrong time of day reduces the reproductive ability of a seasonal breeder, and can result in quality-quantity trade-offs of offspring. The food availability pattern serves as a conditioning environment, and can shape the activity of the genome by influencing chromatin activation/silencing; however, the functional linkage of food availability times with epigenetic control of physiology is only beginning to emerge. This Review gives insights into how food availability times, affected by changes in eating schedules and/or by alterations in feeding environment or lifestyle, could have hitherto unknown consequences on the physiology and reproductive fitness of seasonally breeding vertebrates and those that reproduce year round.

Comparative epigenetics in animal physiology: An emerging frontier

The unprecedented access to annotated genomes now facilitates the investigation of the molecular basis of epigenetic phenomena in phenotypically diverse animals. In this critical review, we describe the roles of molecular epigenetic mechanisms in regulating mitotically and meiotically stable spatiotemporal gene expression, phenomena that provide the molecular foundation for the intra-, inter-, and trans-generational emergence of physiological phenotypes. By focusing principally on emerging comparative epigenetic roles of DNA-level and transcriptome-level epigenetic mark dynamics in the emergence of phenotypes, we highlight the relationship between evolutionary conservation and innovation of specific epigenetic pathways, and their interplay as a priority for future study. This comparative approach is expected to significantly advance our understanding of epigenetic phenomena, as animals show a diverse array of strategies to epigenetically modify physiological responses. Additionally, we review recent technological advances in the field of molecular epigenetics (single-cell epigenomics and transcriptomics and editing of epigenetic marks) in order to (1) investigate environmental and endogenous factor dependent epigenetic mark dynamics in an integrative manner; (2) functionally test the contribution of specific epigenetic marks for animal phenotypes via genome and transcript-editing tools. Finally, we describe advantages and limitations of emerging animal models, which under the Krogh principle, may be particularly useful in the advancement of comparative epigenomics and its potential translational applications in animal science, ecotoxicology, ecophysiology, climate change science and wild-life conservation, as well as organismal health.

Effects of timed food availability on reproduction and metabolism in zebra finches: Molecular insights into homeostatic adaptation to food-restriction in diurnal vertebrates

Food availability affects metabolism and reproduction in higher vertebrates including birds. This study tested the idea of adaptive homeostasis to time-restricted feeding (TRF) in diurnal zebra finches by using multiple (behavioral, physiological and molecular) assays. Adult birds were subjected for 1 week or 3 weeks to food restriction for 4 h in the evening (hour 8-12) of the 12 h light-on period, with controls on ad lib feeding. Birds on TRF showed enhanced exploratory behavior and plasma triglycerides levels, but did not show differences from ad lib birds in the overall food intake, body mass, and plasma corticosterone and thyroxine levels. As compared to ad lib feeding, testis size and circulation testosterone were reduced after first but not after third week of TRF. The concomitant change in the mRNA expression of metabolic and reproductive genes was also found after week 1 of TRF. Particularly, TRF birds showed increased expression of genes coding for gonadotropin releasing hormone (GnRH) in hypothalamus, and for receptors of androgen (AR) and estrogen (ER-alpha) in both hypothalamus and testes. However, genes coding for the deiodinases (Dio2, Dio3) and gonadotropin inhibiting hormone (GnIH) showed no difference between feeding conditions in both hypothalamus and testes. Further, increased Sirt1, Fgf10 and Ppar-alpha, and decreased Egr1 expression in the liver suggested TRF-effects on the overall metabolism. Importantly, TRF-effects on gene expressions by week 1 seemed alleviated to a considerable extent by week 3. These results on TRF-induced reproductive and metabolic effects suggest homeostatic adaptation to food-restriction in diurnal vertebrates.