Body size and the adoption of a migratory tactic in brook charr

The presence of a conditional strategy based on size attained before migration and a sex-ratio at migration biased towards females were explored in a population of brook charr Salvelinus fontinalis in the Sainte-Marguerite River, Quebec Province, Canada, where anadromous and resident forms live sympatrically. Seaward migration in the system occurred at 1 and 2 years old. Comparisons between backcalculated size-at-age of migrant and resident fish revealed that smaller fish at age 1 year delay migration to the following year and that bigger fish either migrated at age 1 year or remained resident for the rest of their life-cycle. Slow growth was associated with migration later in life (age 2 years) at a bigger size, which is consistent with the hypothesis of a threshold size for migration. No difference in size at age 1 year between migrant and resident fish suggests that other factors, such as growth efficiency and the presence of heritability of the tactics, are involved. Overall the sex ratio was equal for migrant and resident fish, while an age-specific bias was found: more males migrated at age 1 year and more females at age 2 years. These differences suggest that different tactics are adopted by different sexes.     

Reduction of Supercritical Multiregional Stochastic Models with Fast Migration

In this work we study the behavior of a time discrete multiregional stochastic model for a population structured in age classes and spread out in different spatial patches between which individuals can migrate. The dynamics of the population is controlled both by reproduction-survival and by migration. These processes take place at different time scales in the sense of the latter being much faster than the former. We incorporate the effect of demographic stochasticity into the population, which results in both dynamics being modelled by multitype Bienaymé–Galton–Watson branching processes. We present a multitype global model that incorporates the effect of both processes and, making use of the existence of different time scales for demography and migration, build a reduced model in which the variables correspond to the total population in each age class. We extend previous results that relate the behavior of the original and the reduced model showing that, given a large enough separation of time scales between demography and migration, we can obtain information about the behavior of the multitype global model through the study of the simpler reduced model. We concentrate on the case where the two systems are supercritical and therefore the expected number of individuals grows to infinity, and show that we can approximate the asymptotic structure of the population vector and the asymptotic population size of the original system through the study of the reduced model.     

Gulls can change their migratory behavior during lifetime

Migration is a widespread phenomenon among birds and is likely to be subject to strong selective pressures. Birds' annual routines and behaviors might be expected to change during their different life history stages, resulting in different, age‐related migration patterns. However, although migration has been the subject of many publications, age‐related differences in migration have received little attention. The present study examined age‐related changes in individual migration habits in lesser black‐backed gulls, Larus fuscus. We analyzed data from 10‐year (1998–2007) color‐ringing project in NW England, comprising more than 10 000 ringed individuals. Our results showed a latitudinal cline in age structure across the wintering range, with adults and gulls in their first breeding year wintering closer to the breeding grounds. Supporting this result we observed that individuals, as they get older, changed the migration behavior and winter closer to the breeding areas. Interestingly, we found no differences in survival rates across the wintering grounds. Thus differences in survival rates can not account for the latitudinal cline in age structure, and the observed findings seem to be best explained by the arrival time hypothesis, based on a mechanism whereby individuals are able to change their migratory behavior as result of the onset of sexual maturity and associated mating pressures.     

A network aware approach for the scheduling of virtual machine migration during peak loads

Live virtual machine migration can have a major impact on how a cloud system performs, as it consumes significant amounts of network resources such as bandwidth. Migration contributes to an increase in consumption of network resources which leads to longer migration times and ultimately has a detrimental effect on the performance of a cloud computing system. Most industrial approaches use ad-hoc manual policies to migrate virtual machines. In this paper, we propose an autonomous network aware live migration strategy that observes the current demand level of a network and performs appropriate actions based on what it is experiencing. The Artificial Intelligence technique known as Reinforcement Learning acts as a decision support system, enabling an agent to learn optimal scheduling times for live migration while analysing current network traffic demand. We demonstrate that an autonomous agent can learn to utilise available resources when peak loads saturate the cloud network.     

Evolution of migration in a metapopulation

In this paper a general deterministic discrete-time metapopulation model with a finite number of habitat patches is analysed within the framework of adaptive dynamics. We study a general model and prove analytically that (i) if the resident populations state is a fixed point, then the resident strategy with no migration is an evolutionarily stable strategy, (ii) a mutant population with no migration can invade any resident population in a fixed point state, (iii) in the uniform migration case the strategy not to migrate is attractive under small mutational steps so that selection favours low migration. Some of these results have been previously observed in simulations, but here they are proved analytically in a general case. If the resident population is in a two-cyclic orbit, then the situation is different. In the uniform migration case the invasion behaviour depends both on the type of the residents attractor and the survival probability during migration. If the survival probability during migration is low, then the system evolves towards low migration. If the survival probability is high enough, then evolutionary branching can happen and the system evolves to a situation with several coexisting types. In the case of out-of-phase attractor, evolutionary branching can happen with significantly lower survival probabilities than in the in-phase attractor case. Most results in the two-cyclic case are obtained by numerical simulations. Also, when migration is not uniform we observe in numerical simulations in the two-cyclic orbit case selection for low migration or evolutionary branching depending on the survival probability during migration.     

Banding data reveal bias in age‐class sampling of songbirds during spring migration

Population age structure and vital statistics are important for understanding songbird demography and for developing conservation strategies. Field‐based estimates of survival rates based on mark–recapture methods are conservative because they are constrained by problems associated with detection probabilities and emigration. However, data collected at bird‐banding stations during spring and fall migration can potentially provide useful demographic information. I used banding data collected over a 6‐yr period (2005–2010) at Long Point Bird Observatory on the north shore of Lake Erie in Ontario, Canada, and Powdermill Avian Research Center in southeastern Pennsylvania, U.S.A., to determine if banding records could be used to estimate vital statistics for several species of songbirds. As reported in previous studies, I found the proportion of juveniles captured during fall migration to be unrealistically high to be representative of true proportions, especially at Long Point. The proportion of juvenile songbirds captured remained implausibly high during spring migration, with related estimates of longevity and generation time implausibly low and of fecundity implausibly high. Based on apparent adult survival estimates from the literature that suggest an average age structure for songbirds of >55% adults and <45% juveniles, I found that capture rates for juveniles during spring migration were at least twice as high as that for adults. A slower pace of spring migration by juveniles likely accounts for some of this bias. Because the data cannot be assumed to represent unbiased samples with respect to the age structure of populations, my results indicate that banding data collected at bird‐banding stations during migration are not suitable for use in demographic studies.     

Population assessment and movement patterns of lake sturgeon (Acipenser fulvescens) in the Manistee River, Michigan, USA

Lake sturgeon (Acipenser fulvescens) population characteristics and migration patterns were evaluated in the Manistee River system, Michigan. Sturgeon (n = 102) were captured using gillnets, tagged and released in the system between 2001 and 2005. Biological data (weight, length, age, sex and spawning status) were collected to calculate length–weight relationships and relative condition factor (K_n), determine age structure, and estimate the annual spawning population size. Sturgeon were also implanted with radio and sonic transmitters, and migration patterns of 22 sturgeon were determined. The weight–length equation for sturgeon in the Manistee River system was log₁₀ W = 3.17log₁₀TL?5.52 and did not differ by sex. K_n equaled 0.72 and did not differ by sex or spawning status. Ages ranged from age 5 to age 54. Sexually mature male and female sturgeon were captured over the course of the study, and the size of the spawning population ranged from 21 to 66 spawners. Sturgeon migration movements up and down the Manistee River varied with date, water temperature, and discharge. The sturgeon appeared to use two different spawning sites in the Manistee River. The Manistee River system supports a remnant lake sturgeon population; the presence of a wide range of age classes and availability of a limited number of suitable spawning sites suggest continued recruitment to the population.     

Selling transracial adoption: families,markets, and the colour line

This short review looks at the implications of the title of The Age of Migration. It argues that most ages, not specifically our own time, could be defined as ‘ages of migration’. It argues that the specific characteristics of our particular age are those of internal more than international migrations and a dramatic rise in a series of forms of non-permanent population movements that can better be captured under the term ‘mobility’. In terms of longer-term forms of migration, it is also deceptive to assume that they will necessarily continue to increase. The piece focuses on forms of internal migration and on mobility.     

Disease persistence in epidemiological models: the interplay between vaccination and migration

We consider the interplay of vaccination and migration rates on disease persistence in epidemiological systems. We show that short-term and long-term migration can inhibit disease persistence. As a result, we show how migration changes how vaccination rates should be chosen to maintain herd immunity. In a system of coupled SIR models, we analyze how disease eradication depends explicitly on vaccine distribution and migration connectivity. The analysis suggests potentially novel vaccination policies that underscore the importance of optimal placement of finite resources.     

Age structure in predator-prey systems: Intraspecific carnivore interaction,passive diffusion,and the paradox of enrichment

An existing arthropod predator-prey model incorporating age structure in the carnivore through the use of the von Foerster equation is extended to include the effects of intraspecific carnivore interaction and passive diffusion or migration. A linear stability analysis of the community equilibrium point of that differential-integral equation system is performed and the resulting secular equation analyzed by the method of D-partitions. These stability results are then compared to those obtained by employing an analogous differential equation model without age structure, in particular as they relate to the so-called paradox of enrichment. In the absence of passive diffusion, it is shown that, unlike for a differential equation model, the paradox of enrichment can occur even with a carnivore which exhibits intraspecific competition. This destabilizing effect of age structure is seen to occur most dramatically when interspecific interactions are large, while the effect of passive diffusion is to offset that tendency and restabilize the system. These predictions are in accordance with relevant experimental evidence involving mites.     

Mechanotransduction in endothelial cell migration

The migration of endothelial cells (ECs) plays an important role in vascular remodeling and regeneration. EC migration can be regulated by different mechanisms such as chemotaxis, haptotaxis, and mechanotaxis. This review will focus on fluid shear stress-induced mechanotransduction during EC migration. EC migration and mechanotransduction can be modulated by cytoskeleton, cell surface receptors such as integrins and proteoglycans, the chemical and physical properties of extracellular matrix (ECM) and cell-cell adhesions. The shear stress applied on the luminal surface of ECs can be sensed by cell membrane and associated receptor and transmitted throughout the cell to cell-ECM adhesions and cell-cell adhesions. As a result, shear stress induces directional migration of ECs by promoting lamellipodial protrusion and the formation of focal adhesions (FAs) at the front in the flow direction and the disassembly of FAs at the rear. Persistent EC migration in the flow direction can be driven by polarized activation of signaling molecules and the positive feedback loops constituted by Rho GTPases, cytoskeleton, and FAs at the leading edge. Furthermore, shear stress-induced EC migration can overcome the haptotaxis of ECs. Given the hemodynamic environment of the vascular system, mechanotransduction during EC migration has a significant impact on vascular development, angiogenesis, and vascular wound healing.     

A Stochastic Model for Reproductive Isolation Under Asymmetrical Mating Preferences

More and more evidence shows that mating preference is a mechanism that may lead to a reproductive isolation event. In this paper, a haploid population living on two patches linked by migration is considered. Individuals are ecologically and demographically neutral on the space and differ only on a trait, a or A, affecting both mating success and migration rate. The special feature of this paper is to assume that the strengths of the mating preference and the migration depend on the trait carried. Indeed, patterns of mating preferences are generally asymmetrical between the subspecies of a population. I prove that mating preference interacting with frequency-dependent migration behavior can lead to a reproductive isolation. Then, I describe the time before reproductive isolation occurs. To reach this result, I use an original method to study the limiting dynamical system, analyzing first the system without migration and adding migration with a perturbation method. Finally, I study how the time before reproductive isolation is influenced by the parameters of migration and of mating preferences, highlighting that large migration rates tend to favor types with weak mating preferences.     

Mathematical modeling of cascading migration in a tri-trophic food-chain system

Diel vertical migration is a behavioral antipredator defense that is shaped by a trade-off between higher predation risk in surface waters and reduced growth in deeper waters. The strength of migration of zooplankton increases with a rise in the abundance of predators and their exudates (kairomone). Recent studies span multiple trophic levels, which lead to the concept of coupled vertical migration. The migrations that occur at one trophic level can affect the vertical migration of the next lower trophic level, and so on, throughout the food chain. This is called cascading migration. In this paper, we introduce cascading migration in a well-known model (Hastings and Powell, Ecology 73:896–903, 1991). We represent the dynamics of the system as proposed by Hastings and Powell as a phytoplankton–zooplankton–fish (prey–middle predator–top predator) model where fish affect the migrations of zooplankton, which in turn affect the migrations of motile phytoplankton. The system under cascading migration enhances system stability and population coexistence. It is also observed that for a higher rate of cascading migration, the system shows chaotic behavior. We conclude that the observations of Hastings and Powell remain true if the cascading migration rate is high enough.     

Multilocus selection in subdivided populations I. Convergence properties for weak or strong migration

The dynamics and equilibrium structure of a deterministic population-genetic model of migration and selection acting on multiple multiallelic loci is studied. A large population of diploid individuals is distributed over finitely many demes connected by migration. Generations are discrete and nonoverlapping, migration is irreducible and aperiodic, all pairwise recombination rates are positive, and selection may vary across demes. It is proved that, in the absence of selection, all trajectories converge at a geometric rate to a manifold on which global linkage equilibrium holds and allele frequencies are identical across demes. Various limiting cases are derived in which one or more of the three evolutionary forces, selection, migration, and recombination, are weak relative to the others. Two are particularly interesting. If migration and recombination are strong relative to selection, the dynamics can be conceived as a perturbation of the so-called weak-selection limit, a simple dynamical system for suitably averaged allele frequencies. Under nondegeneracy assumptions on this weak-selection limit which are generic, every equilibrium of the full dynamics is a perturbation of an equilibrium of the weak-selection limit and has the same stability properties. The number of equilibria is the same in both systems, equilibria in the full (perturbed) system are in quasi-linkage equilibrium, and differences among allele frequencies across demes are small. If migration is weak relative to recombination and epistasis is also weak, then every equilibrium is a perturbation of an equilibrium of the corresponding system without migration, has the same stability properties, and is in quasi-linkage equilibrium. In both cases, every trajectory converges to an equilibrium, thus no cycling or complicated dynamics can occur.      

The effects of hatching date on timing of autumn migration in partial migrants – an individual approach

Timing of spring migration and breeding and their interaction with climate change has been widely studied in recent years, but the possible changes in timing of autumn migration have gained less attention. This work focuses on autumn migration and provides the first multi‐species individual‐based study of how hatching date affects the autumn migration date and migration age by using nestling ring data and re‐trappings of the same individuals during the autumn migration at the Hanko Bird Observatory, Finland. We studied three potentially multibrooded passerines (great tit, blue tit and coal tit) and two single‐brooded birds of prey (goshawk, sparrowhawk), all partially migratory short‐distance migrants. Individuals from late broods migrated at a younger age in all tit species and also in hawks the late hatched individuals tended to migrate at a younger age than the early‐hatched individuals. Late‐hatched individuals migrated later than early‐hatched individuals in blue and coal tits, where the latest hatchers represented second brood individuals. Based on our results, the time from hatching to autumn migration is not constant even among individuals of the same population. Our study indicates that climate warming induced advancement of avian breeding may cause changes in the timing of autumn migration through the frequency of second broods.     

Discrete and continuous mathematical models of DNA branch migration

DNA junctions, known as Holliday junctions, are intermediates in genetic recombination between DNAs. In this structure, two double-stranded DNA helices with similar sequence are joined at a branch point. The branch point can move along these helices when strands with the same sequence are exchanged. Such branch migration is modeled as a random walk. First, we model this process discretely, such that the motion of the branch is represented as transfer between discrete compartments. This is useful in analysing the results of DNA branch migration on junction comprised of synthetic oligonucleotides. The limit in which larger numbers of smaller steps go to continuous motion of the branch is also considered. We show that the behavior of the continuous system is very similar to that of the discrete system when there are more than just a few compartments. Thus, even branch migration on oligonucleotides can be viewed as a continuous process. One consequence of this is that a step size must be assumed when determining rate constants of branch migration.We compare migration where forward and backward movements of the branch are equally probable to biased migration where one direction is favored over the other. In the latter case larger differences between the discrete and continuous cases are predicted, but the differences are still small relative to the experimental error associated with experiments to measure branch migration in oligonucleotides.     

Altitudinal migration of insects

A number of insects have been suggested to perform seasonal migration between low- and high-altitude areas. In these insects, support for the occurrence of migration mainly came from observations that focal insects disappeared from a certain range of altitudes but appeared at different altitudes with short time lags. In some insects, further support was obtained by mark–recapture studies, analyses of the seasonal change of age structure or reproductive conditions in individuals from different altitudes and studies on dormancy or temperature tolerance. Other means that can be used to assess the occurrence of altitudinal migration are briefly mentioned. Two types of migration, the dormancy-associated and dormancy-independent types, are discriminated. In the former type, insects usually breed in spring, migrate to high-altitude areas in late spring or early summer, usually for aestivation, and return to low-altitude areas in autumn. In this type, the same individuals perform upward and downward migration. In the latter type, insects also perform upward migration in late spring or early summer and downward migration in autumn, but they breed both in low- and high-altitude areas. The adaptive and evolutionary aspects of altitudinal migration are briefly mentioned.     

Age-related migration patterns in Larus fuscus spp.

Migration is a critical period in a bird’s life that can affect the fitness of individuals. Intra-population migratory patterns and the way different sex and/or age classes within a population differ in timing and/or distance of migration are not completely understood. The present study aims to observe inter- and intra-population migratory patterns in the western population of Lesser Black-backed Gulls (Larus fuscus spp.), shedding light on age-related differences of temporal patterns of occurrence in the Portuguese coastal areas during migration and winter. One thousand seven hundred and fifty-four colour ring records were analysed matching a 30-year period of observations on the Portuguese coast between 1975 and 2005. During migration, the graellsii population represents 90% of the migratory flow of L. fuscus through Portugal with the intermedius accounting for 9% and the fuscus population, being vestigial in this period, accounting for 1%. Nevertheless, interesting significant differences were observed between the age classes of the three populations during this period, the graellsii population having a large number of first winters (40% of the migratory contingent of this population) followed by immatures and adults whilst in the intermedius and fuscus populations, the largest age class is the adults. During winter, no inter-population differences were found. When comparing migration and winter periods, intra-population differences were found in the graellsii and fuscus populations regarding distribution and age classes. These results indicate different migratory routes amongst different populations suggesting a leapfrog migration in L. fuscus and also a differential age-related migration pattern that might result from first winters migrating further south in search of a wintering place since adults heavily occupy the closest wintering quarters in their attempt to arrive earlier at their breeding ground.     

Post-settlement migratory behaviour and growth-related costs in two diadromous fish species, Galaxias maculatus and Galaxias brevipinnis

The physiological challenges incurred during the transition from sea to fresh water and the constraints they place on the rate at which the common galaxiid Galaxias maculatus and the climbing galaxiid Galaxias brevipinnis can migrate from marine to freshwater habitats were examined. The duration of the marine to freshwater transition, the relationship between post-settlement age (PSA) and standard length ( L _S) as a proxy for energetic costs incurred during settlement and the potential effects of estuary geomorphology on migratory behaviour was investigated. Rate of upstream migration after settlement was not uniform. Upstream migration rate was slowest directly after settlement and increased with increasing PSA and distance from the river mouth, indicating a delay in upstream migration by newly recruited galaxiids. L _s did not increase with age, at least within the first 21 days post settlement. These patterns were consistent for both species, in spite of differences in their life histories, across the recruitment season, despite seasonal variation in recruit size, and among estuaries with different properties. The results suggest that the timing and speed of migratory behaviour primarily reflect physiological constraints. Given the duration of residency of these species in estuaries, this study indicates that estuaries are critical transitional habitats for diadromous fishes during their migration from marine to freshwater habitats.     

Using underdominance to bi-stably transform local populations

Underdominance refers to natural selection against individuals with a heterozygous genotype. Here, we analyze a single-locus underdominant system of two large local populations that exchange individuals at a certain migration rate. The system can be characterized by fixed points in the joint allele frequency space. We address the conditions under which underdominance can be applied to transform a local population that is receiving wildtype immigrants from another population. In a single population, underdominance has the benefit of complete removal of genetically modified alleles (reversibility) and coexistence is not stable. The two population system that exchanges migrants can result in internal stable states, where coexistence is maintained, but with additional release of wildtype individuals the system can be reversed to a fully wildtype state. This property is critically controlled by the migration rate. We approximate the critical minimum frequency required to result in a stable population transformation. We also concentrate on the destabilizing effects of fitness and migration rate asymmetry. Practical implications of our results are discussed in the context of utilizing underdominance to genetically modify wild populations. This is of importance especially for genetic pest management strategies, where locally stable and potentially reversible transformations of populations of disease vector species are of interest.