Parasite abundance contributes to condition‐dependent dispersal in a wild population of large herbivore

Parasite abundance has been shown to have major consequences for host fitness components such as survival and reproduction. However, although natal dispersal is a key life history trait, whether an individual's decision to disperse or not is influenced by the abundance of parasites it carries remains mostly unknown. Current and opposing hypotheses suggest that infected individuals should either be philopatric to avoid the energetic costs of dispersal (condition dependence) or disperse to escape from heavily parasitised habitats. From intensive monitoring of a roe deer population inhabiting a multi‐use and spatially heterogeneous agricultural landscape, we evaluated the link between an individual's parasite abundance and its propensity to disperse, while accounting for confounding effects of body mass. Dispersal propensity generally decreased with both increasing nematode abundance and with decreasing body mass. Within the dispersing segment of the population, individuals with high nematode abundance left their natal home range later in the season than less parasitised deer. These results clearly show that parasite abundance is an important component of condition‐dependent dispersal in large herbivores. However, unexpectedly, three individuals that were both heavily parasitised and of low body mass dispersed. We suggest that this ‘leave it’ response to high parasite levels in the natal habitat could represent a last ditch attempt to improve reproductive prospects, constituting a form of emergency life history strategy.     

Sex‐specific life history responses to nymphal diet quality and immune status in a field cricket

Individual fitness is expected to benefit from earlier maturation at a larger body size and higher body condition. However, poor nutritional quality or high prevalence of disease make this difficult because individuals either cannot acquire sufficient resources or must divert resources to other fitness‐related traits such as immunity. Under such conditions, individuals are expected to mature later at a smaller body size and in poorer body condition. Moreover, the juvenile environment can also produce longer‐term effects on adult fitness by causing shifts in resource allocation strategies that could alter investment in immune function and affect adult lifespan. We manipulated diet quality and immune status of juvenile Texas field crickets, Gryllus texensis, to investigate how poor developmental conditions affect sex‐specific investment in fitness‐related traits. As predicted, a poor juvenile diet was related to smaller mass and body size at eclosion in both sexes. However, our results also reveal sexually dimorphic responses to different facets of the rearing environment: female life history decisions are affected more by diet quality, whereas males are affected more by immune status. We suggest that females respond to decreased nutritional income because this threatens their ability to achieve a large adult body size, whereas male fitness is more dependent on reaching adulthood and so they invest in immunity and survival to eclosion.     

Evolution of condition-dependent dispersal under kin competition

Dispersers often differ in body condition from non-dispersers. The social dominance hypothesis explains dispersal of weak individuals, but it is not yet well understood why strong individuals, which could easily retain their natal site, are sometimes exposed to risky dispersal. Based on the model for dispersal under kin competition by Hamilton and May, we construct a model where dispersal propensity depends on body condition. We consider an annual species that inhabits a patchy environment with varying patch qualities. Offspring body condition corresponds to the quality of the natal patch and competitive ability increases with body condition. Our main general result balances the fitness benefit from not dispersing and retaining the natal patch and the benefit from dispersing and establishing somewhere else. We present four different examples for competition, which all hint that dispersal of strong individuals may be a common outcome under the assumptions of the present model. In three of the examples, the evolutionarily stable dispersal probability is an increasing function of body condition. However, we found an example where, counterintuitively, the evolutionarily stable dispersal probability is a non-monotone function of body condition such that both very weak and very strong individuals disperse with high probability but individuals of intermediate body condition do not disperse at all.     

DISPERSAL PROPENSITY IN TETRAHYMENA THERMOPHILA CILIATES—A REACTION NORM PERSPECTIVE

Dispersal and phenotypic plasticity are two main ways for species to deal with rapid changes of their environments. Understanding how genotypes (G), environments (E), and their interaction (genotype and environment; G × E) each affects dispersal propensity is therefore instrumental for predicting the ecological and evolutionary responses of species under global change. Here we used an actively dispersing ciliate to quantify the contributions of G, E, and G × E on dispersal propensity, exposing 44 different genotypes to three different environmental contexts (densities in isogenotype populations). Moreover, we assessed the condition dependence of dispersal, that is, whether dispersal is related to morphological, physiological, or behavioral traits. We found that genotypes showed marked differences in dispersal propensity and that dispersal is plastically adjusted to density, with the overall trend for genotypes to exhibit negative density‐dependent dispersal. A small, but significant G × E interaction indicates genetic variability in plasticity and therefore some potential for dispersal plasticity to evolve. We also show evidence consistent with condition‐dependent dispersal suggesting that genotypes also vary in how individual condition is linked to dispersal under different environmental contexts thereby generating complex dispersal behavior due to only three variables (genes, environment, and individual condition).     

Stress and body condition as prenatal and postnatal determinants of dispersal in the common lizard (Lacerta vivipara)

Dispersal is a complex phenomenon affected by multiple factors. Among the factors that influence dispersal in the common lizard (Lacerta vivipara), poor maternal body condition and stress are known to decrease dispersal propensity of juveniles. But the effect of individual factors on dispersal could change when several of them act concurrently or at different developmental stages. Prenatal factors can affect clutch and/or juvenile characteristics that later affect dispersal. Postnatal influences are mainly exerted on juvenile dispersal behavior. We investigated the role of body condition and stress on dispersal at a prenatal and a postnatal stage. Stress was mimicked by experimentally increasing corticosterone levels in pregnant females and recently born juveniles. We considered (1). the influence of maternal body condition and prenatal corticosterone treatment on clutch, juvenile characteristics and on dispersal behavior and (2). the influence of juvenile body condition and postnatal corticosterone treatment on juvenile dispersal behavior. There was an interaction between maternal condition and prenatal corticosterone treatment on juvenile dispersal. Dispersal decreased with maternal corticosterone increase only in juveniles from the more corpulent females, while it increased with juvenile body condition. Good maternal body condition affected clutch and juvenile characteristics favoring dispersal, while elevation of corticosterone level (stress) exerted the opposite effect. Juvenile body condition favored dispersal, while there was no effect of postnatal corticosterone treatment on juvenile dispersal propensity.     

Body condition dependent dispersal in a heterogeneous environment

We find the evolutionarily stable dispersal behaviour of a population that inhabits a heterogeneous environment where patches differ in safety (the probability that a juvenile individual survives until reproduction) and productivity (the total competitive weight of offspring produced by the local individual), assuming that these characteristics do not change over time. The body condition of clonally produced offspring varies within and between families. Offspring compete for patches in a weighted lottery, and dispersal is driven by kin competition. Survival during dispersal may depend on body condition, and competitive ability increases with increasing body condition. The evolutionarily stable strategy predicts that families abandon patches which are too unsafe or do not produce enough successful dispersers. From families that invest in retaining their natal patches, individuals stay in the patch that are less suitable for dispersal whereas the better dispersers disperse. However, this clear within-family pattern is often not reflected in the population-wide body condition distribution of dispersers or non-dispersers. This may be an explanation why empirical data do not show any general relationship between body condition and dispersal. When all individuals are equally good dispersers, then there exist equivalence classes defined by the competitive weight that remains in a patch. An equivalence class consists of infinitely many dispersal strategies that are selectively neutral. This provides an explanation why very diverse patterns found in body condition dependent dispersal data can all be equally evolutionarily stable.     

Evolution of body condition‐dependent dispersal in metapopulations

Body condition‐dependent dispersal strategies are common in nature. Although it is obvious that environmental constraints may induce a positive relationship between body condition and dispersal, it is not clear whether positive body conditional dispersal strategies may evolve as a strategy in metapopulations. We have developed an individual‐based simulation model to investigate how body condition–dispersal reaction norms evolve in metapopulations that are characterized by different levels of environmental stochasticity and dispersal mortality. In the model, body condition is related to fecundity and determined either by environmental conditions during juvenile development (adult dispersal) or by those experienced by the mother (natal dispersal). Evolutionarily stable reaction norms strongly depend on metapopulation conditions: positive body condition dependency of dispersal evolved in metapopulation conditions with low levels of dispersal mortality and high levels of environmental stochasticity. Negative body condition‐dependent dispersal evolved in metapopulations with high dispersal mortality and low environmental stochasticity. The latter strategy is responsible for higher dispersal rates under kin competition when dispersal decisions are based on body condition reached at the adult life stage. The evolution of both positive and negative body condition‐dependent dispersal strategies is consequently likely in metapopulations and depends on the prevalent environmental conditions.     

Artificial selection for increased dispersal results in lower fitness

Dispersal often covaries with other traits, and this covariation was shown to have a genetic basis. Here, we wanted to explore to what extent genetic constraints and correlational selection can explain patterns of covariation between dispersal and key life‐history traits—lifespan and reproduction. A prediction from the fitness‐associated dispersal hypothesis was that lower genetic quality is associated with higher dispersal propensity as driven by the benefits of genetic mixing. We wanted to contrast it with a prediction from a different model that individuals putting more emphasis on current rather than future reproduction disperse more, as they are expected to be more risk‐prone and exploratory. However, if dispersal has inherent costs, this will also result in a negative genetic correlation between higher rates of dispersal and some aspects of performance. To explore this issue, we used the dioecious nematode Caenorhabditis remanei and selected for increased and decreased dispersal propensity for 10 generations, followed by five generations of relaxed selection. Dispersal propensity responded to selection, and females from high‐dispersal lines dispersed more than females from low‐dispersal lines. Females selected for increased dispersal propensity produced fewer offspring and were more likely to die from matricide, which is associated with a low physiological condition in Caenorhabditis nematodes. There was no evidence for differences in age‐specific reproductive effort between high‐ and low‐dispersal females. Rather, reproductive output of high‐dispersal females was consistently reduced. We argue that our data provide support for the fitness‐associated dispersal hypothesis.     

Condition‐dependence,pleiotropy and the handicap principle of sexual selection in melanin‐based colouration

The signalling function of melanin‐based colouration is debated. Sexual selection theory states that ornaments should be costly to produce, maintain, wear or display to signal quality honestly to potential mates or competitors. An increasing number of studies supports the hypothesis that the degree of melanism covaries with aspects of body condition (e.g. body mass or immunity), which has contributed to change the initial perception that melanin‐based colour ornaments entail no costs. Indeed, the expression of many (but not all) melanin‐based colour traits is weakly sensitive to the environment but strongly heritable suggesting that these colour traits are relatively cheap to produce and maintain, thus raising the question of how such colour traits could signal quality honestly. Here I review the production, maintenance and wearing/displaying costs that can generate a correlation between melanin‐based colouration and body condition, and consider other evolutionary mechanisms that can also lead to covariation between colour and body condition. Because genes controlling melanic traits can affect numerous phenotypic traits, pleiotropy could also explain a linkage between body condition and colouration. Pleiotropy may result in differently coloured individuals signalling different aspects of quality that are maintained by frequency‐dependent selection or local adaptation. Colouration may therefore not signal absolute quality to potential mates or competitors (e.g. dark males may not achieve a higher fitness than pale males); otherwise genetic variation would be rapidly depleted by directional selection. As a consequence, selection on heritable melanin‐based colouration may not always be directional, but mate choice may be conditional to environmental conditions (i.e. context‐dependent sexual selection). Despite the interest of evolutionary biologists in the adaptive value of melanin‐based colouration, its actual role in sexual selection is still poorly understood.     

Sex-biased and body condition dependent dispersal capacity in the endangered saproxylic beetle <Emphasis Type="Italic">Osmoderma eremita</Emphasis> (Coleoptera: Cetoniidae)

The dispersal capacity of rare and endangered insect species has rarely been estimated even though it is essential for their management. For these species, laboratory based experiments are considered more appropriate for determining dispersal capacity as well as the factors influencing it. We aimed to characterize dispersal capacity of the endangered saproxylic beetle Osmoderma eremita (Scopoli, 1763) (Coleoptera: Cetoniidae). We studied the influence of sex and body condition on several parameters of dispersal (seven parameters of flight capacity measured in laboratory and pre-flight behaviour observed in the wild). Tethered flight experiments, conducted on 30 individuals collected in several regions of France, revealed: (1) maximal single flight distance of 1,454 m and maximal total flight distance of 2,361 m; (2) higher flight capacity in females than males; (3) flight speed and take-off completion decreasing with increasing body condition only for females. Additionally, 32 individuals displaying pre-flight behaviour in the wild showed similar interacting influences of sex and body condition: females initiating pre-flight behaviour had lower body condition than males. Thus, males and females have different dispersal strategies. We propose that body condition influences on dispersal capacity should be considered for species conservation by, for instance, managing adult food resources at the landscape scale and need to be taken into account in introduction programmes.     

Effect of neck collars on the body condition of migrating Greater Snow Geese

Markers are widely used to study behavior, migration, and the life history traits of birds such as survival, dispersal, and reproductive success. The presence of neck collars has been shown to impact the breeding propensity of adult female Greater Snow Geese (Chen caerulescens atlantica), but not their survival rates. We evaluated the hypothesis that the reduction in breeding propensity in neck‐collared birds was due to a reduction in the body condition of these long‐distance migrants that rely on a partial capital breeding strategy. Our study was conducted during 4 consecutive years along the St. Lawrence estuary in Quebec, Canada, a major spring staging area for these geese. We captured and marked 2552 geese with collars and 34 were recaptured in subsequent years at the same site. After controlling for confounding variables such as year and date of capture, we found that the presence of a neck collar reduced body condition of females during spring staging. Female Greater Snow Geese lost an average of 105.5 ± 39.1 (SE) g (4% of body mass) after carrying a collar for 1 yr and an average of 81.9 ± 43.6 g compared to original mass when recaptured 2 or 3 yr later. Our results suggest that the previously reported reduction in breeding propensity of neck‐collared geese may be due to a reduction in body condition during spring staging. Neck collars could negatively affect the body condition of female Greater Snow Geese by increasing their energy expenditure (due to increased drag during flight or to chronic stress) or reducing their foraging efficiency.     

Condition‐dependent movement and dispersal in experimental metacommunities

Dispersal and the underlying movement behaviour are processes of pivotal importance for understanding and predicting metapopulation and metacommunity dynamics. Generally, dispersal decisions are condition‐dependent and rely on information in the broad sense, like the presence of conspecifics. However, studies on metacommunities that include interspecific interactions generally disregard condition‐dependence. Therefore, it remains unclear whether and how dispersal in metacommunities is condition‐dependent and whether rules derived from single‐species contexts can be scaled up to (meta)communities. Using experimental protist metacommunities, we show how dispersal and movement depend on and are adjusted by the strength of interspecific interactions. We found that the predicting movement and dispersal in metacommunities requires knowledge on behavioural responses to intra‐ and interspecific interaction strengths. Consequently, metacommunity dynamics inferred directly from single‐species metapopulations without taking interspecific interactions into account are likely flawed. Our work identifies the significance of condition‐dependence for understanding metacommunity dynamics, stability and the coexistence and distribution of species.     

Alleles underlying larval foraging behaviour influence adult dispersal in nature

The dispersal and migration of organisms have resulted in the colonisation of nearly every possible habitat and ultimately the extraordinary diversity of life. Animal dispersal tendencies are commonly heterogeneous (e.g. long vs. short) and non‐random suggesting that phenotypic and genotypic variability between individuals can contribute to population‐level heterogeneity in dispersal. Using laboratory and field experiments, we demonstrate that natural allelic variation in a gene underlying a foraging polymorphism in larval fruit flies (for), also influences their dispersal tendencies as adults. Rover flies (for^R; higher foraging activity) have consistently greater dispersal tendencies and are more likely to disperse longer distances than sitter flies (for^s; lower foraging activity). Increasing for expression in the brain and nervous system increases dispersal in sitter flies. Our study supports the notion that variation in dispersal can be driven by intrinsic variation in food‐dependent search behaviours and confirms that single gene pleiotropic effects can contribute to population‐level heterogeneity in dispersal.     

Mechanistic modelling of animal dispersal offers new insights into range expansion dynamics across fragmented landscapes

Understanding and predicting the dynamics of range expansion is a major topic in ecology both for invasive species extending their ranges into non‐native regions and for species shifting their natural distributions as a consequence of climate change. In an increasingly modified landscape, a key question is ‘how do populations spread across patchy landscapes?‘ Dispersal is a central process in range expansion and while there is a considerable theory on how the shape of a dispersal kernel influences the rate of spread, we know much less about the relationships between emigration, movement and settlement rules, and invasion rates. Here, we use a simple, single species individual‐based model that explicitly simulates animal dispersal to establish how density‐dependent emigration and settlement rules interact with landscape characteristics to determine spread rates. We show that depending on the dispersal behaviour and on the risk of mortality in the matrix, increasing the number of patches does not necessarily maximise the spread rate. This is due to two effects: first, individuals dispersing at the expanding front are likely to exhibit lower net‐displacement as they typically do not travel far before finding a patch; secondly, with increasing availability of high quality habitat, density‐dependence in emigration and settlement can decrease the number of emigrants and their net‐displacement. The rate of spread is ultimately determined by the balance between net travelled distance, the dispersal mortality and the number of dispersing individuals, which in turn depend on the interaction between the landscape and the species’ dispersal behaviour. These results highlight that predicting spread rates in heterogeneous landscapes is a complex task and requires better understanding of the rules that individuals use in emigration, transfer and settlement decisions.     

Dispersal depends on body condition and predation risk in the semi‐aquatic insect,Notonecta undulata

Dispersal is the movement of organisms across space, which has important implications for ecological and evolutionary processes, including community composition and gene flow. Previous studies have demonstrated that dispersal is influenced by body condition; however, few studies have been able to separate the effects of body condition from correlated variables such as body size. Moreover, the results of these studies have been inconsistent with respect to the direction of the relationship between condition and dispersal. We examined whether body condition influences dispersal in backswimmers (Notonecta undulata). We also tested whether an interaction between body condition and predation risk (another proximate factor that influences dispersal) could contribute to the previously observed inconsistent relationship between condition and dispersal. We imposed diet treatments on backswimmers in the laboratory, and measured the effects of food availability on body condition and dispersal in the field. We found that dispersal was a positive function of body condition, which may have important consequences for population characteristics such as the rate of gene flow and population growth. However, the effects of body condition and predation risk were additive, not interactive, and therefore, our data do not support the hypothesis that the interaction between condition and predation risk contributes to the inconsistency in the results of previous condition‐dependent dispersal studies.     

Mechanisms and reproductive consequences of breeding dispersal in a specialist predator under temporally varying food conditions

Individual variation in breeding dispersal has extensive ecological and evolutionary consequences, but the factors driving individual dispersal behaviour and their fitness consequences remain poorly understood. Our data on dispersal events of a rodent‐specialist predator, the Eurasian kestrel Falco tinnunculus, over 20 years in western Finland offers a unique opportunity to explore the mechanisms underlying breeding dispersal behaviour and its reproductive consequences in a wild bird population. Sex, age, body condition and previous breeding success affected breeding dispersal. Dispersal distances were longer in females than in males as well as longer in yearlings than in older individuals. Body condition was positively correlated to breeding dispersal distances, particularly for females. The lowest dispersal distances were recorded for intermediate brood sizes in the year preceding dispersal. Our results highlight sex‐ and environment‐specific consequences of breeding dispersal on reproductive performance. During increase phases of the three‐year vole cycles, males dispersing further had lower reproductive performance after dispersal, whereas in females, long breeding dispersal distances were associated with increased breeding success under all environmental conditions. These results suggest benefits associated to breeding dispersal in females, potentially related to large spatio‐temporal variation in main food abundance and intensity of intra‐specific competition. Breeding dispersal of males was costly during increasing food abundance, indicating the potential fitness benefits of environmental familiarity in this migratory species. Overall, our results indicate that both individual traits and environmental factors interact to shape breeding dispersal strategies in wide‐ranging predator populations under fluctuating food conditions.     

Dispersal and diversity – unifying scale‐dependent relationships within the neutral theory

The response of species diversity to dispersal capability is inherently scale‐dependent: increasing dispersal capability is expected to increase diversity at the local scale, while decreasing diversity at the metacommunity scale. However, these expectations are based on model formulations that neglect dispersal limitation and species segregation at the local scale. We developed a unifying framework of dispersal–diversity relationships and tested the generality of these expectations. For this purpose we used a spatially‐explicit neutral model with various combinations of survey area (local scale) and landscape size (metacommunity scale). Simulations were conducted using landscapes of finite and of conceptually infinite size. We analyzed the scale‐dependence of dispersal‐diversity relationships for exponentially‐bounded versus fat‐tailed dispersal kernels, several levels of speciation rate and contrasting assumptions on recruitment at short dispersal distances. We found that the ratio of survey area to landscape size is a major determinant of dispersal–diversity relationships. With increasing survey‐to‐landscape area ratio the dispersal–diversity relationship switches from monotonically increasing through a U‐shaped pattern (with a local minimum) to a monotonically decreasing pattern. Therefore, we provide a continuous set of dispersal–diversity relationships, which contains the response shapes reported previously as extreme cases. We suggest the mean dispersal distance with the minimum of species diversity (minimizing dispersal distance) for a certain scenario as a key characteristic of dispersal–diversity relationships. We show that not only increasing mean dispersal distances, but also increasing variances of dispersal can enhance diversity at the local scale, given a diverse species pool at the metacommunity scale. In conclusion, the response of diversity to variations of dispersal capability at spatial scales of interest, e.g. conservation areas, can differ more widely than expected previously. Therefore, land use and conservation activities, which manipulate dispersal capability, need to consider the landscape context and potential species pools carefully.     

Metapopulation dynamics of the bog fritillary butterfly: experimental changes in habitat quality induced negative density‐dependent dispersal

Habitat quality and habitat geometry are two crucial factors driving metapopulation dynamics. However, their intricacy has prevented so far a reliable test of their relative impact on local population dynamics and persistence. Here we report on a long‐term study in which we manipulated habitat quality within a butterfly metapopulation, whereas habitat geometry was kept constant. The treatment consisted in lowering the quality of certain habitat patches while others were kept untreated, using the same spatial design over years. The effect of the treatment on metapopulation dynamics was assessed by comparing residence probability and dispersal rates within the same habitat network on 11 and 6 independent butterfly generations before and after treatment, respectively. Results showed that the experimental decrease in habitat quality generated significantly higher emigration rates from treated patches. This increase was associated with a significant decrease in dispersal rates out of untreated patches, and a significant higher residence probability in these patches. The direct relation between lower habitat quality and higher dispersal propensity in treated patches was expected. However, the lower dispersal from untreated patches after treatment was opposite to the expectation of positive density dependent dispersal generally observed in butterflies. Such negative density‐dependent dispersal would allow a rapid fine‐tuning of dispersal rates to changes in habitat quality, particularly when the spatial autocorrelation of the environmental is low. Accordingly, dispersal would promote an ideal free distribution of individuals in the landscape according to their fitness expectation.     

Unpredictable perturbation reduces breeding propensity regardless of pre‐laying reproductive readiness in a partial capital breeder

Theoretically, individuals of migratory species should optimize reproductive investment based on a combination of timing of and body condition at arrival on the breeding grounds. A minimum threshold body mass is required to initiate reproduction, and the timing of reaching this threshold is critical because of the trade‐off between delaying breeding to gain in condition against the declining value of offspring with later reproductive timing. Long‐lived species have the flexibility within their life history to skip reproduction in a given year if they are unable to achieve this theoretical mass threshold. Although the decision to breed or not is an important parameter influencing population dynamics, the mechanisms underlying this decision are poorly understood. Here, we mimicked an unpredictable environmental perturbation that induced a reduction in body mass of Arctic pre‐breeding (before the laying period) female common eiders Somateria mollissima; a long‐lived migratory seaduck, while controlling for individual variation in the pre‐laying physiological reproductive readiness via vitellogenin (VTG) – a yolk‐targeted lipoprotein. Our aim was to causally determine the interaction between body condition and pre‐laying reproductive readiness (VTG) on breeding propensity by experimentally reducing body mass in treatment females. We first demonstrated that arrival body condition was a key driver of breeding propensity. Secondly, we found that treatment and VTG levels interacted to influence breeding propensity, indicating that our experimental manipulation, mimicking an unpredictable food shortage, reduced breeding propensity, regardless of the degree of pre‐laying physiological reproductive readiness (i.e. timing of ovarian follicles recruitment). Our experiment demonstrates that momentary environmental perturbations during the pre‐breeding period can strongly affect the decision to breed, a key parameter driving population dynamics.     

Heritability of dispersal in the great reed warbler

Dispersal is commonly considered to be a condition‐dependent behaviour with no or low heritability. Here, we show that dispersal in the great reed warbler (Acrocephalus arundinaceus) has a high heritability. Analyses of capture–recapture data of male great reed warblers gathered from the species’ whole Swedish breeding range revealed a remarkable offspring–parent resemblance in dispersal behaviour (philopatry vs. inter‐population dispersal). Also, the degree of dispersal differed between cohorts, which shows that dispersal was partly conditionally dependent. The offspring to mid‐parent estimate of heritability was 0.50. In a previous study of the same data set of male offspring, we did not detect associations between dispersal and several relevant environmental, parental and offspring condition factors. Thus, our results indicate that variation in dispersal partly has a genetic basis in great reed warblers.