Costs of dispersal

Patterns of sex-biased dispersal are consistent with social and ecological constraints in a group-living cichlid fish

BACKGROUND

Sex-biased dispersal is a common and widespread phenomenon that can fundamentally shape the genetic structure of the social environments in which animals live. For animals that live in and move between social groups, sex-biased dispersal can result in an asymmetry in the degree of relatedness among cohabiting males and females, which can have strong implications for their social evolution. In this study, we measured the relatedness structure within and across groups of a wild population of Neolamprologus multifasciatus, a highly-social, shell-dwelling cichlid fish endemic to Lake Tanganyika, East Africa. In total, we genotyped 812 fish from 128 social groups at 20 microsatellite loci. Neolamprologus multifasciatus live at high densities, and also experience strong ecological constraints on free movement throughout their habitat. At the same time, they exhibit sex differences in the degree of reproductive competition within their groups and this makes them an excellent model system for studying the factors associated with sex-biased dispersal.

RESULTS

Social groups of N. multifasciatus consist of multiple males and females living together. We found that cohabiting females were unrelated to one another (Lynch-Ritland estimates of relatedness = 0.045 ± 0.15, average ± SD), while males shared much higher, albeit variable, levels of relatedness to other males in their groups (0.23 ± 0.27). We uncovered a pronounced decline in relatedness between males living in separate groups as the spatial separation between them increased, a pattern that was not evident in females. Female dispersal was also markedly constrained by the distribution and availability of nearby territories to which they could emigrate.

CONCLUSIONS

Our results indicate female-biased dispersal in N. multifasciatus. Our study also highlights how the spatial distribution of suitable dispersal destinations can influence the movement decisions of animals. We also emphasize how sex-biased dispersal can influence the relatedness structure of the social environment in which individuals interact and compete with one another.

Habitat isolation reduces intra- and interspecific biodiversity and stability

Fragmentation is predicted to reduce biodiversity and stability by increasing habitat isolation and impeding dispersal among patches. These effects may manifest at both the interspecific and intraspecific levels, yet few studies have simultaneously explored dispersal effects across levels of organization. We used field mesocosm experiments to examine how habitat isolation (in the form of dispersal rate) alters inter- and intraspecific stability and diversity in local zooplankton communities. We observed effects of increasing dispersal rate at both the intra- and interspecific levels. Increasing dispersal increased local species diversity and reduced mean temporal variability of populations. At the intraspecific level, Daphnia pulex clonal diversity was enhanced by dispersal and mean temporal variability of clone abundances through time was reduced.

Aggregations reduce winter metabolic rates in the diapausing ladybeetle Hippodamia convergens

Energy conservation is linked to survival and fitness of overwintering ectotherms, and is particularly critical in winter. Although many insects overwinter individually, some form aggregations with conspecifics. Aggregations cause metabolic suppression in some insects, but the effect of aggregations on metabolic rates and energy use in overwintering aggregations remains underexplored. The convergent ladybeetle (Hippodamia convergens) overwinters in massive aggregations, making it an ideal system for testing the effect of aggregation size on metabolic rates in overwintering insects. We measured metabolic rates of beetle aggregations of 1, 10, 25, and 50 individuals using stop-flow respirometry across two ecologically relevant temperatures, and measured locomotor activity as one possible driver of group effects on metabolic rate. Metabolic rates per beetle decreased with increasing aggregation size at both temperatures, but was more pronounced at low temperatures. Metabolic rates scaled hypometrically with mass, with deeper response at cool temperatures. Activity decreased with aggregation size, but only at low temperatures. These results suggest that individuals within aggregations enter a deeper metabolically inactive state that single individual beetles cannot achieve, which is partly but not completely explained by a reduction in locomotor activity. This group strategy for energy conservation may provide an additional selective advantage for the evolution of large overwintering aggregations.

Staging to join non-kin groups in a classical cooperative breeder, the Florida scrub-jay

1. Why unrelated members form groups in animal societies remains a pertinent topic in evolutionary biology because benefits for group members often are not obvious. We studied subordinates that disperse to join unrelated social groups in the Florida scrub-jay Aphelocoma coerulescens, a cooperative breeding species mainly composed of kin-based groups. 2. We evaluated potential adaptive benefits of dispersing to become an unrelated helper (staging) versus remaining home and dispersing only to pair and breed (direct dispersal) to understand why non-kin-based groups form. 3. Using 35 years of demographic data, we quantified life history aspects of staging individuals and tested associations between social and ecological factors on the natal and staging territories. We compared fitness outcomes between dispersal strategies by analyzing survival, breeding recruitment, and direct reproductive output. We tested for sexual asymmetry potentially driven by differences in territory acquisition patterns and female-biased dispersal for this species. 4. Of birds that reached one-year-old, 28% staged at a non-natal territory before breeding or disappearing. Staging dispersers departed at younger ages and moved greater distances than direct dispersers. When looking at proximate factors on the natal territory associated with staging, males left groups with many same-sex helpers, while females often left when their father disappeared. For both sexes, staging individuals more likely came from high-quality territories and joined groups with fewer same-sex helpers than in their natal group. While staging and direct dispersers did not differ in survival or likelihood of becoming a breeder, staging males became breeders later and had lower lifetime reproductive success than direct dispersers. 5. In Florida scrub-jays, staging appears to be an alternative strategy for female helpers, but a best-of-a-bad-situation for males. This sexual asymmetry is consistent with males having more options than females to achieve higher reproductive success by breeding near home. Tradeoffs in cost-benefits of departing the natal territory and joining unrelated groups as a helper seem to best explain alternative dispersal patterns, with optimal social queues primarily driving the benefits. This research highlights plasticity in dispersal behavior in response to social and environmental conditions and offers a new perspective in our understanding of non-kin-based social groups.

Mechanisms of dispersal and colonisation in a wind-borne cereal pest, the haplodiploid wheat curl mite

Dispersal and colonisation determine the survival and success of organisms, and influence the structure and dynamics of communities and ecosystems in space and time. Both affect the gene flow between populations, ensuring sufficient level of genetic variation and improving adaptation abilities. In haplodiploids, such as Aceria tosichella (wheat curl mite, WCM), a population may be founded even by a single unfertilised female, so there is a risk of heterozygosity loss (i.e. founder effect). It may lead to adverse outcomes, such as inbreeding depression. Yet, the strength of the founder effect partly depends on the genetic variation of the parental population. WCM is an economically important pest with a great invasive potential, but its dispersal and colonisation mechanisms were poorly studied before. Therefore, here we assessed WCM dispersal and colonisation potential in relation to the genetic variation of the parental population. We checked whether this potential may be linked to specific pre-dispersal actions (e.g. mating before dispersal and collective behaviour). Our study confirms that dispersal strategies of WCM are not dependent on heterozygosity in the parental population, and the efficient dispersal of this species depends on collective movement of fertilised females.

Slow expanders invade by forming dented fronts in microbial colonies

Living organisms never cease to evolve, so there is a significant interest in predicting and controlling evolution in all branches of life sciences. The most basic question is whether a trait should increase or decrease in a given environment. The answer seems to be trivial for traits such as the growth rate in a bioreactor or the expansion rate of a tumor. Yet, it has been suggested that such traits can decrease, rather than increase, during evolution. Here, we report a mutant that outcompeted the ancestor despite having a slower expansion velocity when in isolation. To explain this observation, we developed and validated a theory that describes spatial competition between organisms with different expansion rates and arbitrary competitive interactions.

Most organisms grow in space, whether they are viruses spreading within a host tissue or invasive species colonizing a new continent. Evolution typically selects for higher expansion rates during spatial growth, but it has been suggested that slower expanders can take over under certain conditions. Here, we report an experimental observation of such population dynamics. We demonstrate that mutants that grow slower in isolation nevertheless win in competition, not only when the two types are intermixed, but also when they are spatially segregated into sectors. The latter was thought to be impossible because previous studies focused exclusively on the global competitions mediated by expansion velocities, but overlooked the local competitions at sector boundaries. Local competition, however, can enhance the velocity of either type at the sector boundary and thus alter expansion dynamics. We developed a theory that accounts for both local and global competitions and describes all possible sector shapes. In particular, the theory predicted that a slower on its own, but more competitive, mutant forms a dented V-shaped sector as it takes over the expansion front. Such sectors were indeed observed experimentally, and their shapes matched quantitatively with the theory. In simulations, we further explored several mechanisms that could provide slow expanders with a local competitive advantage and showed that they are all well-described by our theory. Taken together, our results shed light on previously unexplored outcomes of spatial competition and establish a universal framework to understand evolutionary and ecological dynamics in expanding populations.

Philomatry in plants: why do so many species have limited seed dispersal?

Many have noted limited seed dispersal of plants in diverse environments and attempted evolutionary explanations for it. Although philopatric ("love of fatherland") is used by zoologists to describe organisms that remain near their place of origin, philomatric ("love of motherland") is proposed as more appropriate for plants because seeds develop on the maternal parent, fecundity and dispersal are maternally influenced characteristics, and the term dovetails with the mother-site hypothesis (MSH) for the evolution of restricted dispersal. Proximate reasons for philomatry include intrinsic drivers such as morphological features of diaspores and where on the maternal parent they are produced. Extrinsic drivers include local environmental conditions, surrounding vegetation, and ineffective dispersal agents. The MSH proposes that selection should favor philomatry in a population adapted to a particular habitat because offspring will likewise be adapted to that same habitat. Several studies show philomatry can mitigate distance-dependent costs of dispersing into surrounding inhospitable areas. Undispersed diaspores can eliminate energetic costs of accessory structures or biochemicals needed by dispersible diaspores, but it is unclear whether these costs are significant to the evolution of philomatry. Disadvantages of limited dispersal are inability to escape deteriorating habitat conditions, inability to colonize new habitats, and inbreeding among offspring. Heterocarpic species offset these disadvantages by producing dispersed plus undispersed diaspores. A conceptual framework is presented relating dispersal distance to the probability of seedling establishment. Future research should recognize dispersal as a covarying syndrome of multiple life history traits and focus on ecological selection agents that favor philomatry.

Early-life experience shapes patterns of senescence in a food-caching passerine

For many species, breeding performance increases through early adulthood followed by declines later in life. Although patterns of age-specific decline have been shown to vary between individuals, the factors that lead to this individual variation in the intensity of reproductive senescence are yet to be fully understood. We investigated whether early-life social status influenced age-related trends in the breeding performance of male Canada jays (Perisoreus canadensis), year-round residents of North America's boreal and sub-alpine forests. Shortly after young become nutritionally independent, intra-brood dominance struggles lead to one juvenile (Dominant Juvenile) remaining on the natal territory after expelling its subordinate siblings (Ejectees). First, we show via radio tracking that in our declining range-edge population Ejectees either join an unrelated pair (67%), form a breeding pair with another bird (28%) or occupy a territory alone (5%). Second, using 39 years of breeding data, we demonstrate that Ejectee males advanced laying dates and increased the annual number of nestlings until 6 years of age before declining, whereas Dominant Juvenile males advanced laying dates until 11 years and increased annual number of nestlings until 12 years of age before declining. This study documents clear variation in ageing patterns between dominant and expelled young, with implications for the role of early-life experiences and phenotypic quality in determining patterns of ageing.

Cold winters have morph-specific effects on natal dispersal distance in a wild raptor

Dispersal is a key process with crucial implications in spatial distribution, density, and genetic structure of species’ populations. Dispersal strategies can vary according to both individual and environmental features, but putative phenotype-by-environment interactions have rarely been accounted for. Melanin-based color polymorphism is a phenotypic trait associated with specific behavioral and physiological profiles and is, therefore, a good candidate trait to study dispersal tactics in different environments. Here, using a 40 years dataset of a population of color polymorphic tawny owls (Strix aluco), we investigated natal dispersal distance of recruiting gray and pheomelanic reddish-brown (hereafter brown) color morphs in relation to post-fledging winter temperature and individual characteristics. Because morphs are differently sensitive to cold winters, we predicted that morphs’ natal dispersal distances vary according to winter conditions. Winter temperature did not affect the proportion of brown (or gray) among recruits. We found that dispersal distances correlate with winter temperature in an opposite manner in the two morphs. Although the gray morph undertakes larger movements in harsher conditions, likely because it copes better with winter severity, the brown morph disperses shorter distances when winters are harsher. We discuss this morph-specific natal dispersal pattern in the context of competition for territories between morphs and in terms of costs and benefits of these alternative strategies. Our results stress the importance of considering the interaction between phenotype and environment to fully disentangle dispersal movement patterns and provide further evidence that climate affects the behavior and local distribution of this species.

Strong spatial population structure shapes the temporal coevolutionary dynamics of costly female preference and male display

Female mating preferences for exaggerated male display traits are commonplace. Yet, comprehensive understanding of the evolution and persistence of costly female preference through indirect (Fisherian) selection in finite populations requires some explanation for the persistence of additive genetic variance (V_a) underlying sexual traits, given that directional preference is expected to deplete V_a in display and hence halt preference evolution. However, the degree to which V_a, and hence preference‐display coevolution, may be prolonged by spatially variable sexual selection arising solely from limited gene flow and genetic drift within spatially structured populations has not been examined. Our genetically and spatially explicit model shows that spatial population structure arising in an ecologically homogeneous environment can facilitate evolution and long‐term persistence of costly preference given small subpopulations and low dispersal probabilities. Here, genetic drift initially creates spatial variation in female preference, leading to persistence of V_a in display through “migration‐bias” of genotypes maladapted to emerging local sexual selection, thus fueling coevolution of costly preference and display. However, costs of sexual selection increased the probability of subpopulation extinction, limiting persistence of high preference‐display genotypes. Understanding long‐term dynamics of sexual selection systems therefore requires joint consideration of coevolution of sexual traits and metapopulation dynamics.

Host Plant Availability and Nest-Site Selection of the Social Spider Stegodyphus dumicola Pocock, 1898 (Eresidae)

An animals' habitat defines the resources that are available for its use, such as host plants or food sources, and the use of these resources are critical for optimizing fitness. Spiders are abundant in all terrestrial habitats and are often associated with vegetation, which may provide structure for anchoring capture webs, attract insect prey, or provide protective function. Social spiders construct sedentary communal silk nests on host plants, but we know little about whether and how they make nest-site decisions. We examined host plant use in relation to host plant availability in the social spider Stegodyphus dumicola Pocock, 1898 (Eresidae) across different arid biomes in Namibia and analysed the role of host plant characteristics (height, spines, scent, sturdiness) on nest occurrence. Host plant communities and densities differed between locations. Spider nests were relatively more abundant on Acacia spp., Boscia foetida, Combretum spp., Dichrostachys cinerea, Parkinsonia africana, Tarchonanthus camphoratus, and Ziziphus mucronatus, and nests survived longer on preferred plant genera Acacia, Boscia and Combretum. Spider nests were relatively more abundant on plants higher than 2 m, and on plants with thorns and with a rigid structure. Our results suggest that spiders display differential use of host plant species, and that characteristics such as rigidity and thorns confer benefits such as protection from browsing animals.

Dispersal syndromes can link intraspecific trait variability and meta-ecosystem functioning

Dispersal mediates the flow of organisms in meta-communities and subsequently energy and material flows in meta-ecosystems. Individuals within species often vary in dispersal tendency depending on their phenotypic traits (i.e., dispersal syndromes), but the implications of dispersal syndromes for meta-ecosystems have been rarely studied. Using empirical examples on vertebrates, arthropods, and microbes, we highlight that key functional traits can be linked to dispersal. We argue that this coupling between dispersal and functional traits can have consequences for meta-ecosystem functioning, mediating flows of functional traits and thus the spatial heterogeneity of ecosystem functions. As dispersal syndromes may be genetically determined, the spatial heterogeneity of functional traits may be further carried over across generations and link meta-ecosystem functioning to evolutionary dynamics.

Research Highlight: Social dispersal in giraffes

Research Highlight: Bond, M. L., Lee, D. E., Ozgul, A., Farine, D. R., & König, B. (2021). Leaving by staying: Social dispersal in giraffes. Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.13582. Dispersal is a key ecological and evolutionary process, which shows marked variability between and within species. The social and kinship structure of species fundamentally affects the patterns and types of dispersal, but information on how animals with fission-fusion group dynamics disperse is missing. Bond et al. provide novel data on natal dispersal of giraffe calves in relation to their dynamic multilayered social system, showing that individuals from both sexes can disperse socially, by switching association with different social groups, without leaving their natal area. The results highlight that traditional spatial-only measures of dispersal, such as dispersal distance, may be inadequate for social species with overlapping social units.

Hitchhiking or hang gliding? Dispersal strategies of two cereal-feeding eriophyoid mite species

Dispersal shapes the dynamics of populations, their genetic structure and species distribution; therefore, knowledge of an organisms' dispersal abilities is crucial, especially in economically important and invasive species. In this study, we investigated dispersal strategies of two phytophagous eriophyoid mite species: Aceria tosichella (wheat curl mite, WCM) and Abacarus hystrix (cereal rust mite, CRM). Both species are obligatory plant parasites that infest cereals and are of economic significance. We investigated their dispersal success using different dispersal agents: wind and vectors. We hypothesised that in both mite species the main mode of dispersal is moving via wind, whereas phoretic dispersal is rather accidental, as the majority of eriophyoid mite species do not possess clear morphological or behavioural adaptations for phoresy. Results confirmed our predictions that both species dispersed mainly with wind currents. Additionally, WCM was found to have a higher dispersal success than CRM. Thus, this study contributes to our understanding of the high invasive potential of WCM.

Reproductive benefits associated with dispersal in headwater populations of Trinidadian guppies (Poecilia reticulata)

Theory suggests that the evolution of dispersal is balanced by its fitness costs and benefits, yet empirical evidence is sparse due to the difficulties of measuring dispersal and fitness in natural populations. Here, we use spatially explicit data from a multi-generational capture-mark-recapture study of two populations of Trinidadian guppies (Poecilia reticulata) along with pedigrees to test whether there are fitness benefits correlated with dispersal. Combining these ecological and molecular data sets allows us to directly measure the relationship between movement and reproduction. Individual dispersal was measured as the total distance moved by a fish during its lifetime. We analysed the effects of dispersal propensity and distance on a variety of reproductive metrics. We found that number of mates and number of offspring were positively correlated to dispersal, especially for males. Our results also reveal individual and environmental variation in dispersal, with sex, size, season, and stream acting as determining factors.

Experimental evidence that host choice by parasites is age-dependent in a fish-monogenean system

Host age is known to influence the risk of parasite infection, but there is very little experimental evidence on whether parasites show preference towards potential hosts of a specific age. To investigate how host age affects host choice by parasites, we used the Nile tilapia (Oreochromis niloticus) as a fish parasite model and manipulated its gill ectoparasitic monogeneans in mesocosm experiments. Our experimental setting combined three age classes (juvenile, subadult, and adult) of both infected donor hosts and uninfected potential target hosts assigned to each treatment. We predicted that adult target hosts would be more susceptible to parasites than juveniles and adults because they represent high-quality habitat patches. Contrary to our prediction, we found that subadults were more susceptible to parasites than juvenile and adult target hosts. Our models confirmed that variation in target host age influenced parasite choice, suggesting that subadults might represent the most favourable option for parasites regarding a balance between host quality and susceptibility. We provide experimental evidence that host choice by parasites is age-dependent, and that this life-history trait can play a major role in structuring parasite populations.

Prospecting and informed dispersal: Understanding and predicting their joint eco-evolutionary dynamics

The ability of individuals to leave a current breeding area and select a future one is important, because such decisions can have multiple consequences for individual fitness, but also for metapopulation dynamics, structure, and long-term persistence through non-random dispersal patterns. In the wild, many colonial and territorial animal species display informed dispersal strategies, where individuals use information, such as conspecific breeding success gathered during prospecting, to decide whether and where to disperse. Understanding informed dispersal strategies is essential for relating individual behavior to subsequent movements and then determining how emigration and settlement decisions affect individual fitness and demography. Although numerous theoretical studies have explored the eco-evolutionary dynamics of dispersal, very few have integrated prospecting and public information use in both emigration and settlement phases. Here, we develop an individual-based model that fills this gap and use it to explore the eco-evolutionary dynamics of informed dispersal. In a first experiment, in which only prospecting evolves, we demonstrate that selection always favors informed dispersal based on a low number of prospected patches relative to random dispersal or fully informed dispersal, except when individuals fail to discriminate better patches from worse ones. In a second experiment, which allows the concomitant evolution of both emigration probability and prospecting, we show the same prospecting strategy evolving. However, a plastic emigration strategy evolves, where individuals that breed successfully are always philopatric, while failed breeders are more likely to emigrate, especially when conspecific breeding success is low. Embedding information use and prospecting behavior in eco-evolutionary models will provide new fundamental understanding of informed dispersal and its consequences for spatial population dynamics.

Long-Distance Movements of Feral Cats in Semi-Arid South Australia and Implications for Conservation Management

Simple Summary

To efficiently control invasive animals, it is vital to have knowledge about their behaviour, their movements and how they use the landscape. Unusual behaviour is normally excluded from datasets, as it is considered to be an outlier that may distort analyses. In our study, we present movement data from feral cats in the arid and semi-arid zones of Australia. Feral cats are a serious problem to the native wildlife of Australia and in many parts of the world. Cats are known to show fidelity to geographic areas and may defend them against other cats. Until now, research has focused on these areas, home ranges or territories, that feral cats need to survive and reproduce. We argue that a part of their movement behaviour, large journeys away from the area they normally use, has been overlooked and has been considered to be unusual behaviour. We explain why we think that this is the case and present examples from other studies additional to our data set to show that these long-distance movements are a regular occurrence. To achieve a better protection of native wildlife from predation by feral cats, we believe that these long-distance movements should be considered as part of the normal behaviour of feral cats when planning cat control operations.

Abstract

Movements that extend beyond the usual space use of an animal have been documented in a range of species and are particularly prevalent in arid areas. We present long-distance movement data on five feral cats (Felis catus) GPS/VHF-collared during two different research projects in arid and semi-arid Australia. We compare these movements with data from other feral cat studies. Over a study period of three months in the Ikara-Flinders Ranges National Park, 4 out of 19 collared cats moved to sites that were 31, 41, 53 and 86 km away. Three of the cats were males, one female; their weight was between 2.1 and 4.1 kg. Two of the cats returned to the area of capture after three and six weeks. During the other study at Arid Recovery, one collared male cat (2.5 kg) was relocated after two years at a distance of 369 km from the area of collar deployment to the relocation area. The movements occurred following three years of record low rainfall. Our results build on the knowledge base of long-distance movements of feral cats reported at arid study sites and support the assertion that landscape-scale cat control programs in arid and semi-arid areas need to be of a sufficiently large scale to avoid rapid reinvasion and to effectively reduce cat density. Locally, cat control strategies need to be adjusted to improve coverage of areas highly used by cats to increase the efficiency of control operations.

Sex-Specific Routes to Independent Breeding in a Polygynous Cooperative Breeder

How can individuals obtain a breeding position and what are the benefits associated with philopatry compared to dispersal? These questions are particularly intriguing in polygamous cooperative breeders, where dispersal strategies reflect major life history decisions, and routes to independent breeding may utterly differ between the sexes. We scrutinized sex-dependent life-history routes by investigating dispersal patterns, growth rates and mortality in a wild colony of the cooperatively breeding cichlid Neolamprologus savoryi. Our data reveal that female helpers typically obtain dominant breeding positions immediately after reaching sexual maturity, which is associated with strongly reduced growth. In contrast, males obtain breeder status only at twice the age of females. After reaching sexual maturity, males follow one of two strategies: (i) they may retain their subordinate status within the harem of a dominant male, which may provide protection against predators but involves costs by helping in territory maintenance, defence and brood care; or (ii) they may disperse and adopt a solitary status, which diminishes survival chances and apparently reflects a best-of-a-bad-job strategy, as there are no obvious compensating future fitness benefits associated with this pathway. Our study illustrates that sex-dependent life history strategies strongly relate to specific social structures and mating patterns, with important implications for growth rates, the age at which breeding status is obtained, and survival.

Dispersal patterns in black howler monkeys (Alouatta pigra): Integrating multiyear demographic and molecular data

Dispersal is a fundamental process in the functioning of animal societies as it regulates the degree to which closely related individuals are spatially concentrated. A species' dispersal pattern can be complex as it emerges from individuals' decisions shaped by the cost-benefit tradeoffs associated with either remaining in the natal group or dispersing. Given the potential complexity, combining long-term demographic information with molecular data can provide important insights into dispersal patterns of a species. Based on a 15-year study that integrates multiyear demographic data on six groups with longitudinal and cross-sectional genetic sampling of 20 groups (N = 169 individuals, N = 21 polymorphic microsatellite loci), we describe the various dispersal strategies of male and female black howler monkeys (Alouatta pigra) inhabiting Palenque National Park, Mexico. Genetically confirmed dispersal events (N = 21 of 59 males; N = 6 of 65 females) together with spatial autocorrelation analyses revealed that the dispersal pattern of black howlers is bisexual with strong sex-biases in both dispersal rate (males disperse more often than females) and dispersal distance (females disperse farther than males). Observational and genetic data confirm that both males and females can successfully immigrate into established groups, as well as form new groups with other dispersing individuals. Additionally, both males and females may disperse singly, as well as in pairs, and both may also disperse secondarily. Overall, our findings suggest multiple dispersal trajectories for black howler males and females, and longer multiyear studies are needed to unravel which demographic, ecological and social factors underlie individuals' decisions about whether to disperse and which dispersal options to take.

Should dispersers be fast learners? Modeling the role of cognition in dispersal syndromes

Both cognitive abilities and dispersal tendencies can vary strongly between individuals. Since cognitive abilities may help dealing with unknown circumstances, it is conceivable that dispersers may rely more heavily on learning abilities than residents. However, cognitive abilities are costly and leaving a familiar place might result in losing the advantage of having learned to deal with local conditions. Thus, individuals which invested in learning to cope with local conditions may be better off staying at their natal place. In order to disentangle the complex relationship between dispersal and learning abilities, we implemented individual-based simulations. By allowing for developmental plasticity, individuals could either become a 'resident' or 'dispersal' cognitive phenotype. The model showed that in general residents have higher learning abilities than dispersers. Dispersers evolve higher learning ability than residents when dispersers have long life spans and when dispersal occurs either early or late in life, thereby maximizing the time in one habitat patch. Time is crucial here, because the longer an individual resides in a location where it can use its learned knowledge or behavior, the more often it profits from it and thus eventually obtains a net benefit from its investment into learning. Both, longevity and the timing of dispersal within lifecycles determine the time individuals have to recoup that investment and thus crucially influence this correlation. We therefore suggest that species' life history will strongly impact the expected cognitive abilities of dispersers, relative to their resident conspecifics, and that cognitive abilities might be an integral part of dispersal syndromes.

Floral Resources Enhance Fecundity, but Not Flight Activity, in a Specialized Aphid Predator, Hippodamia convergens (Coleoptera: Coccinellidae)

Adult aphid predators disperse across the landscape seasonally in search of prey aggregations that are patchily distributed and temporally variable. However, flight is energetically costly and consumes resources that could be invested in reproduction. Hippodamia convergens is an important aphid predator in North American cereal crops and other agricultural systems. Consumption of floral resources can enhance adult survival during periods of low prey availability and may improve reproductive success. We tested how an omnivorous adult diet containing floral resources (diluted honey and pulverized bee pollen) interacts with body size to influence reproduction and flight behavior compared to a prey-only diet. Two sizes of beetles were produced by controlling larval access to food—3 h daily access produced small beetles; ad libitum access produced large beetles with faster development. Reproductive performance was tracked for 18 days, and female flight activity was assayed via 3 h bouts of tethered flight. Diet composition and body size interacted to influence preoviposition period, with large females in prey-only treatments delaying oviposition the longest. The omnivorous adult diet improved 18-day fecundity relative to a prey-only diet, but egg fertility was unaffected. Adult size affected oviposition pattern, with small beetles laying smaller, but more numerous, clutches. Females flew up to 7 km in 6 h, but neither body size nor adult diet influenced flight distance, suggesting that all diet treatments generated energy reserves sufficient to power flights of short duration. However, pre-reproductive females flew > 60% further than they did post-reproduction, likely due to the energetic costs of oviposition. Thus, access to pollen and nectar increased reproductive success and altered oviposition patterns in H. convergens, indicating the importance of floral resources in the agricultural landscape to conservation of this predator and its biological control services.

High frequency of prospecting for informed dispersal and colonisation in a social species at large spatial scale

Animals explore and prospect space searching for resources and individuals may disperse, targeting suitable patches to increase fitness. Nevertheless, dispersal is costly because it implies leaving the patch where the individual has gathered information and reduced uncertainty. In social species, information gathered during the prospection process for deciding whether and where to disperse is not only personal but also public, i.e. conspecific density and breeding performance. In empty patches, public information is not available and dispersal for colonisation would be more challenging. Here we study the prospecting in a metapopulation of colonial Audouin's gulls using PTT platform terminal transmitters tagging for up to 4 years and GPS tagging during the incubation period. A large percentage of birds (65%) prospected occupied patches; strikingly, 62% of prospectors also visited empty patches that were colonised in later years. Frequency and intensity of prospecting were higher for failed breeders, who dispersed more than successful breeders. Prospecting and dispersal also occurred mostly to neighbouring patches where population density was higher. GPSs revealed that many breeders (59%) prospected while actively incubating, which suggests that they gathered information before knowing the fate of their reproduction. Prospecting may be enhanced in species adapted to breed in ephemeral habitats, such as Audouin's gulls. Interestingly, none of the tracked individuals colonised an empty patch despite having prospected over a period of up to three consecutive years. Lack of public information in empty patches may drive extended prospecting, long time delays in colonisation and non-linear transient phenomena in metapopulation dynamics and species range expansion.

Consistent signatures of urban adaptation in a native, urban invader ant Tapinoma sessile

Biological invasions are becoming more prevalent due to the rise of global trade and expansion of urban areas. Ants are among the most prolific invaders with many exhibiting a multiqueen colony structure, dependent colony foundation and reduced internest aggression. Although these characteristics are generally associated with the invasions of exotic ants, they may also facilitate the spread of native ants into novel habitats. Native to diverse habitats across North America, the odorous house ant Tapinoma sessile has become abundant in urban environments throughout the United States. Natural colonies typically have a small workforce, inhabit a single nest, and are headed by a single queen, whereas urban colonies tend to be several orders of magnitude larger, inhabit multiple nests (i.e., polydomy) and are headed by multiple queens (i.e., polygyny). Here, we explore and compare the population genetic and breeding structure of T. sessile within and between urban and natural environments in several localities across its distribution range. We found the social structure of a colony to be a plastic trait in both habitats, although extreme polygyny was confined to urban habitats. Additionally, polydomous colonies were only present in urban habitats, suggesting T. sessile can only achieve supercoloniality within urbanized areas. Finally, we identified strong differentiation between urban and natural populations in each locality and continent-wide, indicating cities may restrict gene flow and exert intense selection pressure. Overall, our study highlights urbanization's influence in charting the evolutionary course for species.

Conditional natal dispersal provides a mechanism for populations tracking resource pulses after fire

Animals that persist in spatially structured populations face the challenge of tracking the rise and fall of resources across space and time. To combat these challenges, theory predicts that species should use conditional dispersal strategies that allow them to emigrate from patches with declining resources and colonize new resource patches as they appear. We studied natal dispersal movements in the black-backed woodpecker (Picoides arcticus), a species known for its strong association with recent post-fire forests in western North America. We radio-tracked juveniles originating from seven burned areas and tested hypotheses that environmental and individual factors influence dispersal distance and emigration rates—investigating emigration while additionally accounting for imperfect detection with a novel Bayesian model. We found that juveniles were more likely to leave natal areas and disperse longer distances if they were heavier or hatched in older burned areas where resources are increasingly scarce. Juveniles were also more likely to leave their natal burn if they hatched in a nest closer to the fire perimeter. While dispersing across the landscape, black-backed woodpeckers selected for burned forest relative to unburned available habitat. Together, these results strongly support the hypothesis that black-backed woodpecker populations track resource pulses across fire-prone landscapes, with conditional natal dispersal acting as a mechanism for locating and colonizing newly burned areas. Lending empirical support to theoretical predictions, our findings suggest that changes in resource distribution may shape dispersal patterns and, consequently, the distribution and persistence of spatially structured populations.

Conservation Actions in Multi-Species Systems: Species Interactions and Dispersal Costs

We use the General Equilibrium Ecosystem Model (GEEM) parameterized to Wyoming sagebrush to explore the impact of two common simplifications in bio-economic policy frameworks on species conservation decisions. First, we compare conservation policies based on 2-species food web models to those based on a more complex food web. We find that using the simpler model can miss opportunities for more conservation benefits in the presence of species interactions. Second, we define the impact of species dispersal costs on population distributions in a heterogenous landscape and explore conservation policies to reduce those costs to enable species to move away from disturbed areas. Conservation actions that reduce dispersal costs for all species reflect species interactions and thresholds that determine which species disperse.

Exogenous corticosterone and melanin-based coloration explain variation in juvenile dispersal behaviour in the barn owl (Tyto alba)

Natal dispersal affects many processes such as population dynamics. So far, most studies have examined the intrinsic and extrinsic factors that determine the distance between the place of birth and of first breeding. In contrast, few researchers followed the first steps of dispersal soon after fledging. To study this gap, we radio-tracked 95 barn owl nestlings (Tyto alba) to locate their diurnal roost sites from the fledging stage until December. This was used to test whether the age of nest departure, post-fledging movements and dispersal distance were related to melanin-based coloration, which is correlated to fitness-related traits, as well as to corticosterone, a hormone that mediates a number of life history trade-offs and the physiological and behavioural responses to stressful situations. We found that the artificial administration of corticosterone delayed the age when juveniles left their parental home-range in females but not in males. During the first few months after fledging, longer dispersal distances were reached by females compared to males, by individuals marked with larger black feather spots compared to individuals with smaller spots, by larger individuals and by those experimentally treated with corticosterone. We conclude that the onset and magnitude of dispersal is sensitive to the stress hormone corticosterone, melanin-based coloration and body size.

Assortative mating for between-patch dispersal status in a wild bird population: Exploring the role of direct and indirect underlying mechanisms

Previous studies have reported functional integration between dispersal and other phenotypic traits allowing individuals to alleviate dispersal costs, and such associations can affect dispersal evolution in return. In sexually reproducing species, assortative mating according to dispersal can shape the maintenance of such trait associations. Despite the potentially crucial consequences of dispersal in natural populations, assortative mating for dispersal and its underlying mechanisms remain largely unexplored. Here, we assessed assortative mating for between-patch dispersal status in a fragmented population of a small passerine bird, the collared flycatcher, and explored whether such assortative mating could result from (i) direct mate choice based on dispersal-related behavioural (aggressiveness and boldness) and morphological traits (tarsus and wing length), (ii) biased mating due to spatio-temporal heterogeneity in the distribution of dispersal phenotypes and/or (iii) post-mating adjustment of dispersal phenotype or dispersal-related traits. We found intrinsic assortative mating (i.e. positive among-pair correlation) for current dispersal status (in the year of mating) but not for natal dispersal status, even though we could not exclude it due to limited power. We also found assortative mating for boldness and age category (yearlings vs. older adults), and the probability for pair members to be assorted for current dispersal status was higher when both pair members were of similar boldness score and of the same age compared with mixed-age pairs. Mate choice based on boldness and age thus appears as a possible mechanism underlying assortative mating for dispersal status. Our analyses however remained correlative, and only an experimental manipulation of these traits could allow inferring causal links. Non-random mating for dispersal-related traits may affect the evolution of dispersal syndromes in this population. More work is nevertheless needed to fully assess the evolutionary implications of age- and behaviour-based assortative mating for dispersal.

Flight efficiency explains differences in natal dispersal distances in birds

The factors responsible for variation in dispersal distances across species remain poorly understood. Previous comparative studies found differing results and equivocal support for theoretical predictions. Here I re-examine factors that influence natal dispersal distances in British birds while taking into account the cost of transport as estimated from proxies of long-distance flight efficiency. First, I show that flight efficiency, as estimated by the hand-wing index, the aspect ratio, or the lift-to-drag ratio, is a strong predictor of dispersal distances among resident species. Most migratory species showed a similar pattern, but a group of species with relatively low aerodynamic efficiency showed longer-than-expected dispersal distances, making the overall trend independent of flight efficiency. Ecological, behavioral, and life history factors had a small or nil influence on dispersal distances, with most of their influence likely mediated by adaptations for the use of space reflected in flight efficiency. This suggests that dispersal distances in birds are not determined by adaptive strategies for dispersal per se, but are predominantly influenced by the energetic cost of movement.

Plastic cell morphology changes during dispersal

Dispersal is the movement of organisms from one habitat to another that potentially results in gene flow. It is often plastic, allowing organisms to adjust dispersal movements depending on environmental conditions. A fundamental aim in ecology is to understand the determinants underlying dispersal and its plasticity. We utilized 22 strains of the ciliate Tetrahymena thermophila to determine if different phenotypic dispersal strategies co-exist within a species and which mechanisms underlie this variability. We quantified the cell morphologies impacting cell motility and dispersal. Distinct differences in innate cellular morphology and dispersal rates were detected, but no universally utilized combinations of morphological parameters correlate with dispersal. Rather, multiple distinct and plastic morphological changes impact cilia-dependent motility during dispersal, especially in proficient dispersing strains facing challenging environmental conditions. Combining ecology and cell biology experiments, we show that dispersal can be promoted through plastic motility-associated changes to cell morphology and motile cilia.

Sex differences in morphology across an expanding range edge in the flightless ground beetle, Carabus hortensis

Species' ranges are dynamic, changing through range shifts, contractions, and expansions. Individuals at the edge of a species' shifting range often possess morphological traits that increase movement capacity, that are not observed in individuals farther back within the species' range. Although morphological traits that increase in proportion toward the range edge may differ between the sexes, such sex differences are rarely studied.Here, we test the hypotheses that body size and condition increase with proximity to an expanding range edge in the flightless ground beetle, Carabus hortensis, and that these trait changes differ between the sexes.Male, but not female, body size increased with proximity to the range edge. Body size was positively correlated with male front and mid tibia length and to female hind tibia length, indicating that body size is indicative of movement capacity in both sexes. Body condition (relative to body size) decreased with increasing population density in males but not females. Population density was lowest at the range edge.Our results indicate that sex is an important factor influencing patterns in trait distribution across species' ranges, and future studies should investigate changes in morphological traits across expanding range margins separately for males and females. We discuss the implications for sex differences in resource allocation and reproductive rates for trait differentiation across species' shifting ranges.

Social strategies used by dispersing males to integrate into a new group in Tibetan macaques (Macaca thibetana)

In group-living mammals, an individual's fitness depends, in part, on the quality of social relationships it has with others. Among species of nonhuman primates in which one sex is philopatric, individuals of that sex often develop strong social bonds and alliances with closely related kin. Less is known regarding the social processes used by dispersing adults to form stable bonds with nonkin in their new group. From May to December 2009, April to August 2010, September to December 2011, and February to May 2012, we collected data on grooming interactions in wild Tibetan macaques (Macaca thibetana), a female philopatric species, at Mt. Huangshan, China. Our goal was to compare social interactions and bond formation between resident males, recent immigrant males, and resident females. Our results indicate that recent immigrant males formed stable partner relationships with a small number of resident females and groomed these females more frequently or for longer than they received grooming. In contrast, resident males switched female grooming partners more frequently, received more grooming than they gave, and formed relationships with a greater number of female partners. We argue that the ability of recent immigrant male Tibetan macaques to maintain strong and persistent social bonds with a small set of resident adult females is a primary factor that enables them to establish residence in a new multimale-multifemale group. The present study provides new and important insights into the integrated social strategies used by dispersing males and resident females to maintain group stability.

Behavioural change during dispersal and its relationship to survival and reproduction in a cooperative breeder

The ability of dispersing individuals to adjust their behaviour to changing conditions is instrumental in overcoming challenges and reducing dispersal costs, consequently increasing overall dispersal success. Understanding how dispersers' behaviour and physiology change during the dispersal process, and how they differ from resident individuals, can shed light on the mechanisms by which dispersers increase survival and maximise reproduction.

By analysing individual behaviour and concentrations of faecal glucocorticoid metabolites (fGCM), a stress‐associated biomarker, we sought to identify the proximate causes behind differences in survival and reproduction between dispersing and resident meerkats Suricata suricatta.

We used data collected on 67 dispersing and 108 resident females to investigate (a) which individual, social and environmental factors are correlated to foraging and vigilance, and whether the role of such factors differs among dispersal phases, and between dispersers and residents; (b) how time allocated to either foraging or vigilance correlated to survival in dispersers and residents and (c) the link between aggression and change in fGCM concentration, and their relationship with reproductive rates in dispersing groups and resident groups with either long‐established or newly established dominant females.

Time allocated to foraging increased across dispersal phases, whereas time allocated to vigilance decreased. Time allocated to foraging and vigilance correlated positively and negatively, respectively, with dispersers' group size. We did not find a group size effect for residents. High proportions of time allocated to foraging correlated with high survival, and more so in dispersers, suggesting that maintaining good physical condition may reduce mortality during dispersal. Furthermore, while subordinate individuals rarely reproduced in resident groups, the conception rate of subordinates in newly formed dispersing groups was equal to that of their dominant individuals. Mirroring conception rates, in resident groups, fGCM concentrations were lower in subordinates than in dominants, whereas in disperser groups, fGCM concentrations did not differ between subordinates and dominants.

Our results, which highlight the relationship between behavioural and physiological factors and demographic rates, provide insights into some of the mechanisms that individuals of a cooperative species can use to increase overall dispersal success.

Digest: Dispersal reduction drives rapid diversification in alpine grasshoppers

Dispersal-associated traits -such as flight ability- influence how species move across the landscape, and can dramatically impact their distributions and patterns of genetic structure. Ortego et al. examine genomic data from two recently diverged alpine grasshopper lineages with distinct wing sizes to assess the demographic impacts of flight loss. The authors showed that flight loss may lead to asymmetric introgression during speciation, and can significantly increase rates of intraspecific diversification.

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.

Early life experience influences dispersal in coyotes (Canis latrans)

Natal dispersal plays an important role in connecting individual animal behavior with ecological processes at all levels of biological organization. As urban environments are rapidly increasing in extent and intensity, understanding how urbanization influences these long distance movements is critical for predicting the persistence of species and communities. There is considerable variation in the movement responses of individuals within a species, some of which is attributed to behavioral plasticity which interacts with experience to produce interindividual differences in behavior. For natal dispersers, much of this experience occurs in the natal home range. Using data collected from VHF collared coyotes (Canis latrans) in the Chicago Metropolitan Area we explored the relationship between early life experience with urbanization and departure, transience, and settlement behavior. Additionally, we looked at how early life experience with urbanization influenced survival to adulthood and the likelihood of experiencing a vehicle related mortality. We found that coyotes with more developed habitat in their natal home range were more likely to disperse and tended to disperse farther than individuals with more natural habitat in their natal home range. Interestingly, our analysis produced mixed results for the relationship between natal habitat and habitat selection during settlement. Finally, we found no evidence that early life experience with urbanization influenced survival to adulthood or the likelihood of experiencing vehicular mortality. Our study provides evidence that early life exposure influences dispersal behavior; however, it remains unclear how these differences ultimately affect fitness.