Behavioural synchronization of large-scale animal movements - disperse alone, but migrate together?

Individual and ecological heterogeneity promote complex communication in social vertebrate group decisions

To receive the benefits of social living, individuals must make effective group decisions that enable them to achieve behavioural coordination and maintain cohesion. However, heterogeneity in the physical and social environments surrounding group decision-making contexts can increase the level of difficulty social organisms face in making decisions. Groups that live in variable physical environments (high ecological heterogeneity) can experience barriers to information transfer and increased levels of ecological uncertainty. In addition, in groups with large phenotypic variation (high individual heterogeneity), individuals can have substantial conflicts of interest regarding the timing and nature of activities, making it difficult for them to coordinate their behaviours or reach a consensus. In such cases, active communication can increase individuals' abilities to achieve coordination, such as by facilitating the transfer and aggregation of information about the environment or individual behavioural preferences. Here, we review the role of communication in vertebrate group decision-making and its relationship to heterogeneity in the ecological and social environment surrounding group decision-making contexts. We propose that complex communication has evolved to facilitate decision-making in specific socio-ecological contexts, and we provide a framework for studying this topic and testing related hypotheses as part of future research in this area. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Migrating mule deer compensate en route for phenological mismatches

Billions of animals migrate to track seasonal pulses in resources. Optimally timing migration is a key strategy, yet the ability of animals to compensate for phenological mismatches en route is largely unknown. Using GPS movement data collected from 72 adult female deer over a 10-year duration, we study a population of mule deer (Odocoileus hemionus) in Wyoming that lack reliable cues on their desert winter range, causing them to start migration 70 days ahead to 52 days behind the wave of spring green-up. We show that individual deer arrive at their summer range within an average 6-day window by adjusting movement speed and stopover use. Late migrants move 2.5 times faster and spend 72% less time on stopovers than early migrants, which allows them to catch the green wave. Our findings suggest that ungulates, and potentially other migratory species, possess cognitive abilities to recognize where they are in space and time relative to key resources. Such behavioral capacity may allow migratory taxa to maintain foraging benefits amid rapidly changing phenology.

Timing and distance of natal dispersal in Asian black bears

Dispersal has important implications for population ecology and genetics of a species through redistribution of individuals. In most mammals, males leave their natal area before they reach sexual maturity, whereas females are commonly philopatric. Here, we investigate the patterns of natal dispersal in the Asian black bear (Ursus thibetanus) based on data from 550 bears (378 males, 172 females) captured or removed in Gunma and Tochigi prefectures on central Honshu Island, Japan in 2003–2018. We used genetic data and parentage analysis to investigate sex-biased differences in the distance of natal dispersal. We further investigated the age of dispersal using spatial autocorrelation analysis, that is, the change in the correlation between genetic and geographic distances in each sex and age group. Our results revealed that male dispersal distances (mean ± SE = 17.4 ± 3.5 km) were significantly farther than female distances (4.8 ± 1.7 km), and the results were not affected by years of mast failures, a prominent forage source for this population. Based on an average adult female home range radius of 1.8 km, 96% of the males and 50% of the females dispersed. In the spatial autocorrelation analysis, the changes in the relationship between genetic and geographic distances were more pronounced in males compared to females. Males seem to mostly disperse at age 3 regardless of mast productivity, and they gradually disperse far from their home range, but young and inexperienced males may return to their natal home range in years with poor food conditions. The results suggest that factors driving the dispersal process seem to be population structure-based instead of forage availability-based. In females, a significant genetic relationship was observed among all individuals in the group with a minimum age of 6 years within a distance of 2 km, which resulted in the formation of matrilineal assemblages.

Long-term satellite tracking reveals patterns of long-distance dispersal in juvenile and adult Arctic foxes (Vulpes lagopus)

Long-distance dispersal plays a key role in species distribution and persistence. However, its movement metrics and ecological implications may differ whether it is undertaken by juveniles (natal dispersal) or adults (breeding dispersal). We investigated the influence of life stage on long-distance dispersal in the Arctic fox, an important tundra predator. We fitted 170 individuals with satellite collars during a 13-year study on Bylot Island (Nunavut, Canada), and analysed the tracks of 10 juveniles and 27 adults engaging in long-distance dispersal across the Canadian High Arctic. This behaviour was much more common than expected, especially in juveniles (62.5%, adults: 19.4%). Emigration of juveniles occurred mainly at the end of summer while departure of adults was not synchronized. Juveniles travelled for longer periods and over longer cumulative distances than adults, but spent similar proportions of their time travelling on sea ice versus land. Successful immigration occurred mostly in late spring and was similar for juveniles and adults (30% versus 37%). Our results reveal how life stage influences key aspects of long-distance dispersal in a highly mobile canid. This new knowledge is critical to understand the circumpolar genetic structure of the species, and how Arctic foxes can spread zoonoses across vast geographical areas.

Long-term satellite tracking reveals patterns of long-distance dispersal in juvenile and adult Arctic foxes (Vulpes lagopus)

Long-distance dispersal plays a key role in species distribution and persistence. However, its movement metrics and ecological implications may differ whether it is undertaken by juveniles (natal dispersal) or adults (breeding dispersal). We investigated the influence of life stage on long-distance dispersal in the Arctic fox, an important tundra predator. We fitted 170 individuals with satellite collars during a 13-year study on Bylot Island (Nunavut, Canada), and analysed the tracks of 10 juveniles and 27 adults engaging in long-distance dispersal across the Canadian High Arctic. This behaviour was much more common than expected, especially in juveniles (62.5%, adults: 19.4%). Emigration of juveniles occurred mainly at the end of summer while departure of adults was not synchronized. Juveniles travelled for longer periods and over longer cumulative distances than adults, but spent similar proportions of their time travelling on sea ice versus land. Successful immigration occurred mostly in late spring and was similar for juveniles and adults (30% versus 37%). Our results reveal how life stage influences key aspects of long-distance dispersal in a highly mobile canid. This new knowledge is critical to understand the circumpolar genetic structure of the species, and how Arctic foxes can spread zoonoses across vast geographical areas.

Long-term satellite tracking reveals patterns of long-distance dispersal in juvenile and adult Arctic foxes (Vulpes lagopus)

Long-distance dispersal plays a key role in species distribution and persistence. However, its movement metrics and ecological implications may differ whether it is undertaken by juveniles (natal dispersal) or adults (breeding dispersal). We investigated the influence of life stage on long-distance dispersal in the Arctic fox, an important tundra predator. We fitted 170 individuals with satellite collars during a 13-year study on Bylot Island (Nunavut, Canada), and analysed the tracks of 10 juveniles and 27 adults engaging in long-distance dispersal across the Canadian High Arctic. This behaviour was much more common than expected, especially in juveniles (62.5%, adults: 19.4%). Emigration of juveniles occurred mainly at the end of summer while departure of adults was not synchronized. Juveniles travelled for longer periods and over longer cumulative distances than adults, but spent similar proportions of their time travelling on sea ice versus land. Successful immigration occurred mostly in late spring and was similar for juveniles and adults (30% versus 37%). Our results reveal how life stage influences key aspects of long-distance dispersal in a highly mobile canid. This new knowledge is critical to understand the circumpolar genetic structure of the species, and how Arctic foxes can spread zoonoses across vast geographical areas.

Kinship and similarity drive coordination of breeding-group choice in male spotted hyenas

When and where animals reproduce influences the social, demographic and genetic properties of the groups and populations they live in. We examined the extent to which male spotted hyenas (Crocuta crocuta) coordinate their breeding-group choice. We tested whether their propensity to settle in the same group is shaped by passive processes driven by similarities in their socio-ecological background and genotype or by an adaptive process driven by kin selection. We compared the choices of 148 pairs of same-cohort males that varied in similarity and kinship. We found strong support for both processes. Coordination was highest (70% of pairs) for littermates, who share most cumulative similarity, lower (36%) among peers born in the same group to different mothers, and lowest (7%) among strangers originating from different groups and mothers. Consistent with the kin selection hypothesis, the propensity to choose the same group was density dependent for full siblings and close kin, but not distant kin. Coordination increased as the number of breeding females and male competitors in social groups increased, i.e. when costs of kin competition over mates decreased and benefits of kin cooperation increased. Our results contrast with the traditional view that breeding-group choice and dispersal are predominantly solitary processes.

Primed and cued: long-term acoustic telemetry links interannual and seasonal variations in freshwater flows to the spawning migrations of Common Snook in the Florida Everglades

BACKGROUND

Spawning migrations are a widespread phenomenon among fishes, often occurring in response to environmental conditions prompting movement into reproductive habitats (migratory cues). However, for many species, individual fish may choose not to migrate, and research suggests that conditions preceding the spawning season (migratory primers) may influence this decision. Few studies have provided empirical descriptions of these prior conditions, partly due to a lack of long-term data allowing for robust multi-year comparisons. To investigate how primers and cues interact to shape the spawning migrations of coastal fishes, we use acoustic telemetry data from Common Snook (Centropomus undecimalis) in Everglades National Park, Florida, USA. A contingent of Snook migrate between rivers and coastal spawning sites, varying annually in both the proportion of the population that migrates and the timing of migration within the spawning season. However, the specific environmental factors that serve as migratory primers and cues remain unknown.

METHODS

We used eight years of acoustic telemetry data (2012-2019) from 173 tagged Common Snook to investigate how primers and cues influence migratory patterns at different temporal scales. We hypothesize that (1) interannual differences in hydrologic conditions preceding the spawning season contribute to the number of individuals migrating each year, and (2) specific environmental cues trigger the timing of migrations during the spawning season. We used GLMMs to model both the annual and seasonal migratory response in relation to flow characteristics (water level, rate of change in water level), other hydrologic/abiotic conditions (temperature, salinity), fish size, and phenological cues independent of riverine conditions (photoperiod, lunar cycle).

RESULTS

We found that the extent of minimum marsh water level prior to migration and fish size influence the proportion of Snook migrating each year, and that high river water level and daily rates of change serve as primary cues triggering migration timing.

CONCLUSION

Our findings illustrate how spawning migrations are shaped by environmental factors acting at different temporal scales and emphasize the importance of long-term movement data in understanding these patterns. Research providing mechanistic descriptions of conditions that promote migration and reproduction can help inform management decisions aimed at conserving ecologically and economically important species.

Viewing animal migration through a social lens

Evidence of social learning is growing across the animal kingdom. Researchers have long hypothesized that social interactions play a key role in many animal migrations, but strong empirical support is scarce except in a few unique systems and species. In this review, we aim to catalyze advances in the study of social migrations by synthesizing research across disciplines and providing a framework for understanding when, how, and why social influences shape the decisions animals make during migration. Integrating research across the fields of social learning and migration ecology will advance our understanding of the complex behavioral phenomena of animal migration and help to inform conservation of animal migrations in a changing world.

Social environment influences termination of nomadic migration

The final stage of migration, when animals terminate migratory movements and transition to a more sedentary state, remains the least understood phase of migration. Whereas migrants that return to the same locations each year may use mechanisms associated with locating a specific destination, migrants with low site fidelity, such as nomadic migrants, may rely on local environmental cues to determine when to cease migratory movements. Using an experiment with captive birds, we tested whether the presence of a conspecific influences the termination of migration, indicated by changes in behaviour and physiology, in a nomadic migrant (the pine siskin, Spinus pinus). We paired migratory birds with a non-migratory individual or left migratory and non-migratory individuals unpaired. Migratory paired birds had a significant decline in nocturnal activity immediately after pairing and activity levels remained lower two weeks later, with significant declines in energetic reserves and flight muscle size also observed. By contrast, migratory unpaired birds maintained high levels of activity and energetic reserves. These results provide evidence for a role of the social environment in migratory termination decisions. Social cues may be particularly useful in nomadic migrants, such as pine siskins, to facilitate settling in high quality, but unfamiliar, habitats.

Long-distance, synchronized and directional fall movements suggest migration in Arctic hares on Ellesmere Island (Canada)

Animal migration contributes largely to the seasonal dynamics of High Arctic ecosystems, linking distant habitats and impacting ecosystem structure and function. In polar deserts, Arctic hares are abundant herbivores and important components of food webs. Their annual migrations have long been suspected, but never confirmed. We tracked 25 individuals with Argos satellite telemetry to investigate the existence of migration in a population living at Alert (Ellesmere Island, Nunavut, Canada). During fall, 21 hares undertook directional, long-distance movements in a southwestern direction towards Lake Hazen. Daily movement rates averaged 1.3 ± 0.5 km, 4.3 ± 1.6 km, and 1.7 ± 0.9 km before, during, and after relocation, respectively. Straight-line and minimum cumulative distances traveled averaged 98 ± 18 km (range: 72-148 km) and 198 ± 62 km (range: 113-388 km), respectively. This is the first report of large-scale seasonal movements in Arctic hares and, surprisingly, in any lagomorph species. These movements may be part of an annual migratory pattern. Our results redefine our understanding of the spatial ecology of Arctic hares, demonstrate unsuspected mobility capacities in lagomorphs, and open new perspectives regarding the ecological dynamics of the northern polar deserts.

Seasonal strategies differ between tropical and extratropical herbivores

Seasonal diet shifts and migration are key components of large herbivore population dynamics, but we lack a systematic understanding of how these behaviors are distributed on a macroecological scale. The prevalence of seasonal strategies is likely related to herbivore body size and feeding guild, and may also be influenced by properties of the environment, such as soil nutrient availability and climate seasonality. We evaluated the distribution of seasonal dietary shifts and migration across large-bodied mammalian herbivores and determined how these behaviors related to diet, body size, and environment. We found that herbivore strategies were consistently correlated with their traits: seasonal diet shifts were most prevalent among mixed feeding herbivores and migration among grazers and larger herbivores. Seasonality also played a role, particularly for migration, which was more common at higher latitudes. Both dietary shifts and migration were more widespread among extratropical herbivores, which also exhibited more intermediate diets and body sizes. Our findings suggest that strong seasonality in extratropical systems imposes pressure on herbivores, necessitating widespread behavioral responses to navigate seasonal resource bottlenecks. It follows that tropical and extratropical herbivores may have divergent responses to global change, with intensifying herbivore pressure in extratropical systems contrasting with diminishing herbivore pressure in tropical systems.

The Potential for Physiological Performance Curves to Shape Environmental Effects on Social Behavior

As individual animals are exposed to varying environmental conditions, phenotypic plasticity will occur in a vast array of physiological traits. For example, shifts in factors such as temperature and oxygen availability can affect the energy demand, cardiovascular system, and neuromuscular function of animals that in turn impact individual behavior. Here, we argue that nonlinear changes in the physiological traits and performance of animals across environmental gradients—known as physiological performance curves—may have wide-ranging effects on the behavior of individual social group members and the functioning of animal social groups as a whole. Previous work has demonstrated how variation between individuals can have profound implications for socially living animals, as well as how environmental conditions affect social behavior. However, the importance of variation between individuals in how they respond to changing environmental conditions has so far been largely overlooked in the context of animal social behavior. First, we consider the broad effects that individual variation in performance curves may have on the behavior of socially living animals, including: (1) changes in the rank order of performance capacity among group mates across environments; (2) environment-dependent changes in the amount of among- and within-individual variation, and (3) differences among group members in terms of the environmental optima, the critical environmental limits, and the peak capacity and breadth of performance. We then consider the ecological implications of these effects for a range of socially mediated phenomena, including within-group conflict, within- and among group assortment, collective movement, social foraging, predator-prey interactions and disease and parasite transfer. We end by outlining the type of empirical work required to test the implications for physiological performance curves in social behavior.

Anticipated effects of abiotic environmental change on intraspecific social interactions

Social interactions are ubiquitous across the animal kingdom. A variety of ecological and evolutionary processes are dependent on social interactions, such as movement, disease spread, information transmission, and density-dependent reproduction and survival. Social interactions, like any behaviour, are context dependent, varying with environmental conditions. Currently, environments are changing rapidly across multiple dimensions, becoming warmer and more variable, while habitats are increasingly fragmented and contaminated with pollutants. Social interactions are expected to change in response to these stressors and to continue to change into the future. However, a comprehensive understanding of the form and magnitude of the effects of these environmental changes on social interactions is currently lacking. Focusing on four major forms of rapid environmental change currently occurring, we review how these changing environmental gradients are expected to have immediate effects on social interactions such as communication, agonistic behaviours, and group formation, which will thereby induce changes in social organisation including mating systems, dominance hierarchies, and collective behaviour. Our review covers intraspecific variation in social interactions across environments, including studies in both the wild and in laboratory settings, and across a range of taxa. The expected responses of social behaviour to environmental change are diverse, but we identify several general themes. First, very dry, variable, fragmented, or polluted environments are likely to destabilise existing social systems. This occurs as these conditions limit the energy available for complex social interactions and affect dissimilar phenotypes differently. Second, a given environmental change can lead to opposite responses in social behaviour, and the direction of the response often hinges on the natural history of the organism in question. Third, our review highlights the fact that changes in environmental factors are not occurring in isolation: multiple factors are changing simultaneously, which may have antagonistic or synergistic effects, and more work should be done to understand these combined effects. We close by identifying methodological and analytical techniques that might help to study the response of social interactions to changing environments, highlight consistent patterns among taxa, and predict subsequent evolutionary change. We expect that the changes in social interactions that we document here will have consequences for individuals, groups, and for the ecology and evolution of populations, and therefore warrant a central place in the study of animal populations, particularly in an era of rapid environmental change.

Migration trajectories of the diamondback moth Plutella xylostella in China inferred from population genomic variation

BACKGROUND

The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), is a notorious pest of cruciferous plants. In temperate areas, annual populations of DBM originate from adult migrants. However, the source populations and migration trajectories of immigrants remain unclear. Here, we investigated migration trajectories of DBM in China using genome-wide single nucleotide polymorphisms (SNPs) genotyped using double-digest RAD (ddRAD) sequencing. We first analyzed patterns of spatial and temporal genetic structure among southern source and northern recipient populations, then inferred migration trajectories into northern regions using discriminant analysis of principal components (DAPC), assignment tests, and spatial kinship patterns.

RESULTS

Temporal genetic differentiation among populations was low, indicating that sources of recipient populations and migration trajectories are stable. Spatial genetic structure indicated three genetic clusters in the southern source populations. Assignment tests linked northern populations to the Sichuan cluster, and central-eastern populations to the southern and Yunnan clusters, indicating that Sichuan populations are sources of northern immigrants and southern and Yunnan populations are sources of central-eastern populations. First-order (full-sib) and second-order (half-sib) kin pairs were always found within populations, but ~ 35-40% of third-order (cousin) pairs were found in different populations. Closely related individuals in different populations were found at distances of 900-1500 km in ~ 35-40% of cases, while some were separated by > 2000 km.

CONCLUSION

This study unravels seasonal migration patterns in the DBM. We demonstrate how careful sampling and population genomic analyses can be combined to help understand cryptic migration patterns in insects. © 2020 Society of Chemical Industry.

Ecological markers to monitor migratory bird populations: Integrating citizen science and transboundary management for conservation purposes

Countries share responsibility for the management and conservation of migratory bird species. However, a limited understanding of population dynamics hampers the implementation of harvest and transboundary management. Age-ratios and population density can be useful indicators to assess population dynamics to improve management and conservation actions. Here, the dynamics of an Atlantic population of Common quail Coturnix coturnix, using 32,508 quail samples and 4814 hunter questionnaires over a 20-year period (1996-2016) served as a comparative study for examining age-ratio patterns related to different geographic zones, population density and weather parameters. Results show that age-ratios varied over zones and years, specifically age-ratio 1 (AR1), used as an index of late breeding attempts, varied from 0.1 to 0.21. Age-ratio 2 (AR2), a surrogate of central recruitment, varied from 0.16 to 0.66. Finally, age-ratio 3 (AR3), used as an indicator of the population's annual breeding success, varied from 3.69 to 6.68. Age-ratio is linked to internal and external factors (i.e. effect of rainfall, variations over time and density-dependent relationships) depicting how quail age groups make segregated migration in time and space. Quail age groups perform a complex pattern of migration because of entwined changes in abundance, migration routes and timing, influencing population connectivity and dynamics. Our findings highlight the relevance of citizen science and transboundary agreements to improve management and conservation measures of migrant species. Administrations and policy-makers in developed and developing countries must coordinate efforts to engage hunters in a participatory management systems to achieve sustainability.

An initial record of a long-distance dispersal route of a male sika deer in central Japan

We conducted a global positioning system (GPS) tracking of a male sika deer (Cervus nippon) and his mother in the eastern foothills of the northern Japanese Alps, central Japan. Sika deer exhibited similar seasonal movement patterns; however, the male deer left his natal group at 11 months of age. At 15 months of age, the male deer settled in the neighboring mountain, which was 74 km away from his natal range. This is the first record of long-distance (>50 km) natal dispersal of the sika deer. Our findings might help to explain the expanding distribution of the sika deer.

A stochastic differential game approach toward animal migration

A stochastic differential game model for animal migration between two habitats under uncertain environment, a new population dynamics model, is formulated. Its novelty is the use of an impulse control formalism to naturally describe migrations with different timings and magnitudes that the conventional models could not handle. Uncertainty of the environment that the population faces with is formulated in the context of the multiplier robust control. The optimal migration strategy to give the maximized minimal profit is found through a Hamilton-Jacobi-Bellman quasi-variational inequality (HJBQVI). A key message from HJBQVI is that its free boundary determines the optimal migration strategy. Solving the HJBQVI is carried out with a specialized stable and convergent finite difference scheme. This paper theoretically suggests that the sub-additivity of the performance index, the index to be optimized through the migration, critically affects the resulting strategy. The computational results with the established scheme are consistent with the theoretical predictions and support importance of the sub-additivity property. Social interaction to reduce the net mortality rate is also quantified, suggesting a linkage between the present and existing population dynamics models.

Beyond Migration: Causes and Consequences of Nomadic Animal Movements

Recent advances in animal tracking reveal that many species display irregular movements that do not fall into classical categories of movement patterns such as range residency or migration. Here, we develop a unifying framework that distinguishes these nomadic movements based on their patterns, drivers, and mechanisms. Though they occur in diverse taxa and geographic regions, nomadic movements are united by both their underlying environmental drivers, mainly environmental stochasticity, and the resulting irregular, far-ranging movement patterns. The framework further classifies types of nomadic movements, including full, seasonal, phase, irruptive, and partial nomadism. Nomadic movements can have unique effects on populations, communities, and ecosystems, most notably providing intermittent disturbances and novel introductions of propagules.

Brood parasitism, relatedness and sociality: a kinship role in female reproductive tactics

Conspecific brood parasitism (CBP) is a reproductive tactic in which parasitic females lay eggs in nests of other females of the same species that then raise the joint brood. Parasites benefit by increased reproduction, without costs of parental care for the parasitic eggs. CBP occurs in many egg-laying animals, among birds most often in species with large clutches and self-feeding young: two major factors facilitating successful parasitism. CBP is particularly common in waterfowl (Anatidae), a group with female-biased natal philopatry and locally related females. Theory suggests that relatedness between host and parasite can lead to inclusive fitness benefits for both, but if host costs are high, parasites should instead target unrelated females. Pairwise relatedness (r) in host-parasite (h-p) pairs of females has been estimated using molecular genetic methods in seven waterfowl (10 studies). In many h-p pairs, the two females were unrelated (with low r, near the local population mean). However, close relatives (r = 0.5) were over-represented in h-p pairs, which in all 10 studies had higher mean relatedness than other females. In one species where this was studied, h-p relatedness was higher than between nesting close neighbours, and hosts parasitized by non-relatives aggressively rejected other females. In another species, birth nest-mates (mother-daughters, sisters) associated in the breeding area as adults, and became h-p pairs more often than expected by chance. These and other results point to recognition of birth nest-mates and perhaps other close relatives. For small to medium host clutch sizes, addition of a few parasitic eggs need not reduce host offspring success. Estimates in two species suggest that hosts can then gain inclusive fitness if parasitized by relatives. Other evidence of female cooperation is incubation by old eider Somateria mollissima females of clutches laid by their relatives, and merging and joint care of broods of young. Merging females tended to be more closely related. Eiders associate with kin in many situations, and in some geese and swans, related females may associate over many years. Recent genetic evidence shows that also New World quails (Odontophoridae) have female-biased natal philopatry, CBP and brood merging, inviting further study and comparison with waterfowl. Kin-related parasitism also occurs in some insects, with revealing parallels and differences compared to birds. In hemipteran bugs, receiving extra eggs is beneficial for hosts by diluting offspring predation. In eggplant lace bugs Gargaphia solani, host and parasite are closely related, and kin selection favours egg donation to related females. Further studies of kinship in CBP, brood merging and other contexts can test if some of these species are socially more advanced than presently known.

Migratory plasticity is not ubiquitous among large herbivores

The migratory movements of wild animals can promote abundance and support ecosystem functioning. For large herbivores, mounting evidence suggests that migratory behaviour is an individually variable trait, where individuals can easily switch between migrant and resident tactics. The degree of migratory plasticity, including whether and where to migrate, has important implications for the ecology and conservation of large herbivores in a changing world. Mule deer (Odocoileus hemionus) are an iconic species of western North America, but are notably absent from the body of literature that suggests large herbivore migrations are highly plastic. We evaluated plasticity of migration in female mule deer using longitudinal GPS data collected from 312 individuals across nine populations in the western United States, including 882 animal-years (801 migrants and 81 residents). We followed both resident and migratory mule deer through time to determine whether individual animals switched migratory behaviours (i.e., whether to migrate) from migratory to residency or vice versa. Additionally, we examined the fidelity of individuals to their migration routes (i.e., where to migrate) to determine whether they used the same routes year after year. We also evaluated whether age and reproductive status affected propensity to migrate or fidelity to migratory routes. Our results indicate that mule deer, unlike other large herbivores, have little or no plasticity in terms of whether or where they migrate. Resident deer remained residents, and migrant deer remained migrants, regardless of age, reproductive status or number of years monitored. Further, migratory individuals showed strong fidelity (>80%) to their migration routes year after year. Our study clearly shows that migration plasticity is not ubiquitous among large herbivores. Because of their rigid migratory behaviour, mule deer may not adapt to changing environmental conditions as readily as large herbivores with more plastic migratory behaviour (e.g., elk). The fixed migratory behaviours of mule deer make clear that conservation efforts aimed at traditional seasonal ranges and migration routes are warranted for sustaining this iconic species that continues to decline across its range.

Single cell analysis reveals a biophysical aspect of collective cell-state transition in embryonic stem cell differentiation

In the stem cell research field, the molecular regulatory network used to define cellular states has been extensively studied, however, the general driving force guiding the collective state dynamics remains to be identified from biophysical aspects. Here we monitored the time-development of the cell-state transition at the single-cell and colony levels, simultaneously, during the early differentiation process in mouse embryonic stem cells. Our quantitative analyses revealed that cellular heterogeneity was a result of spontaneous fluctuation of cellular state and cell-cell cooperativity. We considered that the cell state is like a ball fluctuating on a potential landscape, and found that the cooperativity affects the fluctuation. Importantly, the cooperativity temporarily decreased and increased in the intermediate state of cell differentiation, leading to cell-state transition in unison. This process can be explained using the mathematical equation of flashing-ratchet behaviour, which suggests that a general mechanism is driving the collective decision-making of stem cells.

Population and evolutionary dynamics in spatially structured seasonally varying environments

Increasingly imperative objectives in ecology are to understand and forecast population dynamic and evolutionary responses to seasonal environmental variation and change. Such population and evolutionary dynamics result from immediate and lagged responses of all key life‐history traits, and resulting demographic rates that affect population growth rate, to seasonal environmental conditions and population density. However, existing population dynamic and eco‐evolutionary theory and models have not yet fully encompassed within‐individual and among‐individual variation, covariation, structure and heterogeneity, and ongoing evolution, in a critical life‐history trait that allows individuals to respond to seasonal environmental conditions: seasonal migration. Meanwhile, empirical studies aided by new animal‐tracking technologies are increasingly demonstrating substantial within‐population variation in the occurrence and form of migration versus year‐round residence, generating diverse forms of ‘partial migration’ spanning diverse species, habitats and spatial scales. Such partially migratory systems form a continuum between the extreme scenarios of full migration and full year‐round residence, and are commonplace in nature.

Here, we first review basic scenarios of partial migration and associated models designed to identify conditions that facilitate the maintenance of migratory polymorphism. We highlight that such models have been fundamental to the development of partial migration theory, but are spatially and demographically simplistic compared to the rich bodies of population dynamic theory and models that consider spatially structured populations with dispersal but no migration, or consider populations experiencing strong seasonality and full obligate migration. Second, to provide an overarching conceptual framework for spatio‐temporal population dynamics, we define a ‘partially migratory meta‐population’ system as a spatially structured set of locations that can be occupied by different sets of resident and migrant individuals in different seasons, and where locations that can support reproduction can also be linked by dispersal. We outline key forms of within‐individual and among‐individual variation and structure in migration that could arise within such systems and interact with variation in individual survival, reproduction and dispersal to create complex population dynamics and evolutionary responses across locations, seasons, years and generations. Third, we review approaches by which population dynamic and eco‐evolutionary models could be developed to test hypotheses regarding the dynamics and persistence of partially migratory meta‐populations given diverse forms of seasonal environmental variation and change, and to forecast system‐specific dynamics. To demonstrate one such approach, we use an evolutionary individual‐based model to illustrate that multiple forms of partial migration can readily co‐exist in a simple spatially structured landscape. Finally, we summarise recent empirical studies that demonstrate key components of demographic structure in partial migration, and demonstrate diverse associations with reproduction and survival. We thereby identify key theoretical and empirical knowledge gaps that remain, and consider multiple complementary approaches by which these gaps can be filled in order to elucidate population dynamic and eco‐evolutionary responses to spatio‐temporal seasonal environmental variation and change.

Coevolution of patch-type dependent emigration and patch-type dependent immigration

The three phases of dispersal - emigration, transfer and immigration - are affecting each other and the former and latter decisions may depend on patch types. Despite the inevitable fact of the complexity of the dispersal process, patch-type dependencies of dispersal decisions modelled as emigration and immigration are usually missing in theoretical dispersal models. Here, I investigate the coevolution of patch-type dependent emigration and patch-type dependent immigration in an extended Hamilton-May model. The dispersing population inhabits a landscape structured into many patches of two types and disperses during a continuous-time season. The trait under consideration is a four dimensional vector consisting of two values for emigration probability from the patches and two values for immigration probability into the patches of each type. Using the adaptive dynamics approach I show that four qualitatively different dispersal strategies may evolve in different parameter regions, including a counterintuitive strategy, where patches of one type are fully dispersed from (emigration probability is one) but individuals nevertheless always immigrate into them during the dispersal season (immigration probability is one). I present examples of evolutionary branching in a wide parameter range, when the patches with high local death rate during the dispersal season guarantee a high expected disperser output. I find that two dispersal strategies can coexist after evolutionary branching: a strategy with full immigration only into the patches with high expected disperser output coexists with a strategy that immigrates into any patch. Stochastic simulations agree with the numerical predictions. Since evolutionary branching is also found when immigration evolves alone, the present study is adding coevolutionary constraints on the emigration traits and hence finds that the coevolution of a higher dimensional trait sometimes hinders evolutionary diversification.

Genetics of dispersal

Dispersal is a process of central importance for the ecological and evolutionary dynamics of populations and communities, because of its diverse consequences for gene flow and demography. It is subject to evolutionary change, which begs the question, what is the genetic basis of this potentially complex trait? To address this question, we (i) review the empirical literature on the genetic basis of dispersal, (ii) explore how theoretical investigations of the evolution of dispersal have represented the genetics of dispersal, and (iii) discuss how the genetic basis of dispersal influences theoretical predictions of the evolution of dispersal and potential consequences.

Dispersal has a detectable genetic basis in many organisms, from bacteria to plants and animals. Generally, there is evidence for significant genetic variation for dispersal or dispersal‐related phenotypes or evidence for the micro‐evolution of dispersal in natural populations. Dispersal is typically the outcome of several interacting traits, and this complexity is reflected in its genetic architecture: while some genes of moderate to large effect can influence certain aspects of dispersal, dispersal traits are typically polygenic. Correlations among dispersal traits as well as between dispersal traits and other traits under selection are common, and the genetic basis of dispersal can be highly environment‐dependent.

By contrast, models have historically considered a highly simplified genetic architecture of dispersal. It is only recently that models have started to consider multiple loci influencing dispersal, as well as non‐additive effects such as dominance and epistasis, showing that the genetic basis of dispersal can influence evolutionary rates and outcomes, especially under non‐equilibrium conditions. For example, the number of loci controlling dispersal can influence projected rates of dispersal evolution during range shifts and corresponding demographic impacts. Incorporating more realism in the genetic architecture of dispersal is thus necessary to enable models to move beyond the purely theoretical towards making more useful predictions of evolutionary and ecological dynamics under current and future environmental conditions. To inform these advances, empirical studies need to answer outstanding questions concerning whether specific genes underlie dispersal variation, the genetic architecture of context‐dependent dispersal phenotypes and behaviours, and correlations among dispersal and other traits.