Seasonal migratory animals can evolve residency through adaptation. The threshold model of quantitative genetics predicts that residency evolves from migrants when genetic variation for lower liability, or a latent state underlying migratory propensity, is positively selected. However, it is unknown what cellular and molecular regulations underlie this process. The hypothalamus, which regulates physiology and behaviour of vertebrates by integrating internal and environmental conditions, is a strong candidate structure where migratory propensity may be regulated. To understand the hypothalamic molecular regulation underlying the evolutionary change to residency, we use the Eurasian blackcap system comprising ancestral migratory and derived resident populations. By combining a common-garden experiment with single-cell epigenetics, we compare genomic regions with open chromatin between migratory and resident populations and seasons. We find that the seasonal change in chromatin accessibility is reduced in residents across major cell types. This suggests that the evolutionary transition to residency involves a reduction in the amplitude of seasonal change in epigenetic states in multiple hypothalamic cell types, which may collectively represent migratory liability. Environmental shifts, such as deglaciation for blackcaps, may play an important role in exposing and selecting variation in the seasonal reaction norm of liability underlying the evolution of seasonal plastic traits.This article is part of the theme issue 'Ecological epigenetics at the intersection of behaviour and life history variation in non-model animals'.
Deep sleep (N3) and rapid eye movement (REM) sleep are critical for memory and emotional regulation and are often disrupted in neurological and psychiatric disorders. Recent work suggests that focal limbic slow oscillations may provide a target for transcranial electrical stimulation (TES). This study evaluated the feasibility of low-intensity, limbic-targeted TES during sleep and its effects on sleep architecture in healthy adults. A total of 17 healthy participants completed a sham-controlled intervention using an at-home TES device. Stimulation was synchronized with N2 onset, and an overnight electroencephalogram (EEG) was recorded. Sleep stage durations and proportions were compared between TES and off conditions. Limbic-targeted TES was associated with longer total sleep time than the off condition. A repeated-measures ANOVA demonstrated a significant main effect of condition without a significant condition & times; sleep-stage interaction. Planned pairwise comparisons showed longer absolute N3 and REM sleep durations during TES, whereas only REM increased as a proportion of total sleep time. Participants tolerated the device well, and blinding was maintained. Limbic-targeted TES was feasible to administer during sleep in a natural home environment and was associated with increased total sleep time. These findings provide preliminary evidence of sleep-architecture modulation and support further investigation in larger studies and clinical populations.This article is part of the discussion meeting issue 'Digital healthcare for the management of functional neurological disorders'.
Abstract Seabirds cue into other birds and marine mammals to amplify their foraging success. Consequently, changes to the community (e.g. as the climate warms) can impact foraging success and potentially fitness. For example, flying birds that use groups of seals or penguins as cues might decline if the seal or penguin population declines, owing to fewer opportunities for positive foraging associations with one another. To test this idea, we leveraged data from transect surveys spanning 38 years (data collected in 1985, 1991, 1993 and 2023) in waters surrounding the subantarctic island South Georgia. We asked: ‘Has the frequency with which seabirds form statistically significant pairings with other species declined over time?’ We found such changes have occurred: network connectivity (the percentage of species pairings out of all possible pairs) decreased from approximately 40 to 7%, although the overall impact of warming on the community in 2023 was complicated by the arrival of a 100 km iceberg from the Weddell Sea. Possible fitness impacts from reduced associations could have broad-ranging consequences as the ocean continues to warm and the community changes. The results presented here represent one of just a handful of at-sea surveys documenting the winter seabird community at South Georgia. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.
Abstract Marine predators frequently form ephemeral multi-predator feeding aggregations around dense prey patches, yet the mechanisms and outcomes of these dynamic events remain poorly resolved. We quantified how California sea lion (Zalophus californianus) presence influenced humpback whale (Megaptera novaeangliae) foraging using 46 multi-sensor video tags (mean duration: 7.4 ± 7.1 h) deployed on fish-feeding whales in Monterey Bay, California, USA (2014–2023). Across 1808 lunge-feeding events, whales foraging with sea lions exhibited a 23% higher feeding rate and a 16% shorter inter-lunge interval, while the overall percentage of time spent foraging did not change. Across deployments, humpback whale lunge speeds, manoeuvring metrics, and energetic proxies (overall dynamic body acceleration) did not differ with sea lion presence, indicating no detectable increase in per-lunge locomotor cost. When body size was accounted for in a lunge-level linear mixed-effects analysis, sea lion presence was associated with a 35% reduction in approach duration, an 8% increase in approach mean speed and a 25% shorter total lunge duration. Collectively, these results support the interpretation that sea lion-associated bait ball foraging increases humpback whale feeding frequency primarily by compressing search and approach time rather than altering engulfment mechanics or increasing per-lunge energetic expenditure, indicating a potential contribution of sea lions to prey concentration. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.
Abstract Multi-predatory feeding aggregations (MPFAs) occur when several predator species concurrently exploit shared, spatially and temporally aggregated prey. Although MPFAs are well described in some marine ecosystems, their prevalence in the Norwegian Sea has historically been underestimated. Here, we synthesize existing biological, acoustic, visual and behavioural evidence to reinterpret classical predator–prey observations through the lens of MPFAs. Our reassessment revealed that numerous events previously described as single-predator interactions actually represent multi-species feeding assemblages involving marine mammals, large predatory fishes and seabirds. These MPFAs primarily target highly abundant pelagic schooling fishes, such as Norwegian spring-spawning herring, northeast Atlantic (NEA) mackerel, blue whiting and capelin. We compiled, to our knowledge, the first region-wide overview of documented and inferred MPFAs in the Norwegian Sea, characterizing species assemblages, ecological settings and behavioural mechanisms. We further discussed how predator physiology, group foraging strategies, prey schooling dynamics and oceanographic features interact to create conditions favourable for MPFAs. Recognizing MPFAs as common and ecologically influential phenomena has important implications for understanding food webs and ecosystem-based fisheries management. Therefore, we recommend that future research in the region explicitly incorporate MPFAs through multi-sensor observational approaches, behavioural analyses and integration into ecosystem models to better represent the functional role of predators in the NEA. This article is part of the theme issue ‘Multi-predator feeding aggregations in pelagic waters’.
