Evolution Of Dispersal Research Articles

Evolutionary conservatism and convergence both lead to striking similarity in ecology, morphology and performance across continents in frogs

Many clades contain ecologically and phenotypically similar species across continents, yet the processes generating this similarity are largely unstudied, leaving fundamental questions unanswered. Is similarity in morphology and performance across assemblages caused by evolutionary convergence or by biogeographic dispersal of evolutionarily conserved ecotypes? Does convergence to new ecological conditions erase evidence of past adaptation? Here, we analyse ecology, morphology and performance in frog assemblages from three continents (Asia, Australia and South America), assessing the importance of dispersal and convergent evolution in explaining similarity across regions. We find three striking results. First, species using the same microhabitat type are highly similar in morphology and performance across both clades and continents. Second, some species on different continents owe their similarity to dispersal and evolutionary conservatism (rather than evolutionary convergence), even over vast temporal and spatial scales. Third, in one case, an ecologically specialized ancestor radiated into diverse ecotypes that have converged with those on other continents, largely erasing traces of past adaptation to their ancestral ecology. Overall, our study highlights the roles of both evolutionary conservatism and convergence in explaining similarity in species traits over large spatial and temporal scales and demonstrates a statistical framework for addressing these questions in other systems.

Group tolerance, dispersal evolution, and the maintenance of polymorphism in recognition cues

In some systems, organisms form or join groups mediated by certain recognition cues. However, it is predicted that variability in such cues cannot be maintained as positive, frequency-dependent selection favors the dominant cue (Crozier’s paradox). We utilize a simple analytical model of 2 groups as well as computer simulations to find conditions where the coexistence (polymorphism) of 2 distinct recognition cues is maintained. We assume a species that forms reproductive groups and the adoption of a newborn individual into a group depends on that individual’s genotype (recognition cue) in relation to the group’s profile. We investigate the role of 2 factors affecting the level of isolation between groups, namely group tolerance toward deviant genotypes and dispersal between groups. Results from the analytical model show that high tolerance or high dispersal lead to the global fixation of a single genotype, whereas low group tolerance and low dispersal promote the globally stable coexistence of different genotypes. Interestingly, coexistence can only be global, with a different genotype dominating each group, or local, with 2 genotypes coexisting in one group, depending on the degree of tolerance and dispersal. Local coexistence, however, does not persist, when dispersal is allowed to evolve. In this case, low dispersal evolves, which stabilizes global coexistence but reduces local coexistence. If we expand the number of groups and assume spatially limited dispersal, global coexistence becomes a more likely outcome even under conditions where it was impossible in the 2-group system.

An empiricist's guide to theoretical predictions on the evolution of dispersal

Dispersal, the tendency for organisms to reproduce away from their parents, influences many evolutionary and ecological processes, from speciation and extinction events, to the coexistence of genotypes within species or biological invasions. Understanding how dispersal evolves is crucial to predict how global changes might affect species persistence and geographical distribution. The factors driving the evolution of dispersal have been well characterized from a theoretical standpoint, and predictions have been made about their respective influence on, for example, dispersal polymorphism or the emergence of dispersal syndromes. However, the experimental tests of some theories remain scarce partly because a synthetic view of theoretical advances is still lacking. Here, we review the different ingredients of models of dispersal evolution, from selective pressures and types of predictions, through mathematical and ecological assumptions, to the methods used to obtain predictions. We provide perspectives as to which predictions are easiest to test, how theories could be better exploited to provide testable predictions, what theoretical developments are needed to tackle this topic, and we place the question of the evolution of dispersal within the larger interdisciplinary framework of eco-evolutionary dynamics.

Parasite infection drives the evolution of state-dependent dispersal of the host

Dispersal plays a fundamental role in shaping the ecological processes such as host–parasite interactions, and the understanding of host dispersal tendency leads to that of parasites. Here, we present the result of our study on how the evolutionarily stable dispersal of a host would depend on parasite infection, considering kin competition among neighbours. We show that the evolving dispersal rate might be higher for susceptible than for infected individuals (S-biased dispersal) or vice versa (I-biased dispersal). S-biased dispersal is favoured by strong virulence affecting competitive ability, by high rate of parasite release during dispersal, and by low virulence for infected emigrants (i.e. low virulence affecting dispersal ability), whereas I-biased dispersal is favoured in the opposite situation. We also discuss population structure or between-deme genetic differentiation of the host measured with Wright’s FST. In I-biased dispersal, between-deme genetic differentiation decreases with the infection rate, while in S-biased dispersal, genetic differentiation increases with infection rate.

Evolution of dispersal and mating systems along geographic gradients: implications for shifting ranges

SummaryDispersal affects species' ability to move or adapt in response to environmental change. Successful long‐distance dispersal also requires reproduction in areas with few mates, thus mating systems, especially the capacity for self‐fertilization, may influence the speed and success of range shifts.Here, we review: the theoretical predictions regarding dispersal and mating‐system evolution at equilibrium, expanding and contracting range limits; the empirical support for these predictions; and how these geographic patterns may influence future range evolution.Equilibrium range limits can arise from environmental gradients in habitat quality, temporal variation or habitat heterogeneity. Dispersal has been predicted to increase or decrease towards range edges, depending on which life‐history traits respond to the ecological gradient(s). In general, spatial habitat isolation selects against dispersal, whereas temporal stochasticity favours dispersal.At expanding range fronts, dispersal should increase due to spatial sorting for dispersive individuals and the benefits of colonizing vacant habitat. Dispersal evolution is likely more constrained during native range shifts than invasions. Models of expansion across environmental gradients and during climate‐tracking range shifts are lacking.Little theory considers evolution at contracting range margins. We suggest that increased dispersal should be selected if there is local adaptation to climate, as dispersers from warmer areas will out‐compete nondispersers no longer adapted to new climatic conditions. Dispersal increases should be more pronounced in regions where local adaptation is stronger.Self fertilization may be favoured at equilibrium, expanding or contracting range margins by providing reproductive assurance. However, this benefit depends on how inbreeding depression is influenced by genetic load, the severity of the abiotic environment, and the competitive milieu in edge populations. Models for the joint evolution of mating and dispersal in plants suggest that although selfing may evolve at range limits, it will not necessarily be associated with high dispersal.Empirical evidence to test these predictions is scarce. Geographic surveys of dispersal traits, mating‐system traits and relevant selective factors are needed, especially studies of: (i) stable range limits that identify underlying environmental gradients; (ii) moving range limits that compare traits across space and time; and (iii) contracting limits that assess variation in local adaptation towards the range edge.

Evolution of dispersal in open advective environments

We consider a two-species competition model in a one-dimensional advective environment, where individuals are exposed to unidirectional flow. The two species follow the same population dynamics but have different random dispersal rates and are subject to a net loss of individuals from the habitat at the downstream end. In the case of non-advective environments, it is well known that lower diffusion rates are favored by selection in spatially varying but temporally constant environments, with or without net loss at the boundary. We consider several different biological scenarios that give rise to different boundary conditions, in particular hostile and "free-flow" conditions. We establish the existence of a critical advection speed for the persistence of a single species. We derive a formula for the invasion exponent and perform a linear stability analysis of the semi-trivial steady state under free-flow boundary conditions for constant and linear growth rate. For homogeneous advective environments with free-flow boundary conditions, we show that populations with higher dispersal rate will always displace populations with slower dispersal rate. In contrast, our analysis of a spatially implicit model suggest that for hostile boundary conditions, there is a unique dispersal rate that is evolutionarily stable. Nevertheless, both scenarios show that unidirectional flow can put slow dispersers at a disadvantage and higher dispersal rate can evolve.

The social evolution of dispersal with public goods cooperation

Selection can favour the evolution of individually costly dispersal if this alleviates competition between relatives. However, conditions that favour altruistic dispersal also mediate selection for other social behaviours, such as public goods cooperation, which in turn is likely to mediate dispersal evolution. Here, we investigate - both experimentally (using bacteria) and theoretically - how social habitat heterogeneity (i.e. the distribution of public goods cooperators and cheats) affects the evolution of dispersal. In addition to recovering the well-known theoretical result that the optimal level of dispersal increases with genetic relatedness of patch mates, we find both mathematically and experimentally that dispersal is always favoured when average patch occupancy is low, but when average patch occupancy is high, the presence of public goods cheats greatly alters selection for dispersal. Specifically, when public goods cheats are localized to the home patch, higher dispersal rates are favoured, but when cheats are present throughout available patches, lower dispersal rates are favoured. These results highlight the importance of other social traits in driving dispersal evolution.

Reaction-diffusion-advection models for the effects and evolution of dispersal

This review describes reaction-advection-diffusion models for the ecological effects and evolution of dispersal, and mathematical methods for analyzing those models. The topics covered include models for a single species, models for ecological interactions between species, and models for the evolution of dispersal strategies. The models are all set on bounded domains. The mathematical methods include spectral theory, specifically the theory of principal eigenvalues for elliptic operators, maximum principles and comparison theorems, bifurcation theory, and persistence theory.

Entropy/energy stable schemes for evolutionary dispersal models

In this paper we propose some entropy/energy stable finite difference schemes for the reaction–diffusion–advection equation arising in the evolution of biased dispersal of population dynamics. The peculiar feature of these active dispersal models is that the transient solution converges to the stable steady state when time goes to infinity. For the numerical method to capture the long-time pattern of persistence or extinction, we use the relative entropy when the resource potential is logarithmic, and explore the usual energy for other resource potentials. The present schemes are shown to satisfy three important properties of the continuous model for the population density: (i) positivity preserving, (ii) equilibrium preserving, and (iii) entropy or energy satisfying. These ensure that our schemes provide a satisfying long-time behavior, thus revealing the desired dispersal pattern. Moreover, we present several numerical results which confirm the second-order accuracy for various resource potentials and underline the efficiency to preserve the large time asymptotic.

Multiple waves of colonization by monarch flycatchers (Myiagra, Monarchidae) across the Indo‐Pacific and their implications for coexistence and speciation

AbstractAimIslands and archipelagos have played an important role in the development of ecological and evolutionary theories. Using a newly compiled molecular phylogeny we infer the biogeographical history of a monarch flycatcher genus, Myiagra, which is distributed across the Indo‐Pacific. We subsequently integrate biogeographical and ecomorphological data to examine the role of dispersal and trait evolution in the build‐up of avian assemblages.LocationAustralia, the Moluccas, New Guinea and Pacific islands.MethodsWe generated a taxonomically densely sampled mitochondrial DNA dataset that included almost all species and subspecies of the reciprocally monophyletic genera Myiagra and Arses. We then used maximum likelihoood and Bayesian inference to infer their phylogenetic relationships. To reconstruct their biogeographical history, we first dated the tree topology and then used Lagrange to infer ancestral geographical areas. Finally, we combined ancestral area reconstructions with information on ecomorphological traits to infer mechanisms underlying community assembly.ResultsWe provide the first comprehensive molecular phylogenetic reconstruction for Myiagra and Arses monarch flycatchers. Our phylogenetic reconstruction reveals a relatively recent diversification from the Miocene associated with several major dispersal events. Ancestral area reconstruction reveals several independent colonizations of the Moluccas, Melanesia, Fiji and the Micronesian islands. Ancestral state reconstruction of ecological traits suggests that the diversity of traits in co‐occurring species of monarch flycatchers results from independent colonization events and ecological niche conservatism rather than in situ diversification.Main conclusionsThree waves of colonization, non‐overlapping in time, led to independent speciation events in the Bismarcks, Fiji and the Moluccas, in addition to in situ speciation events on remote islands of Micronesia, the Solomons, Vanuatu and Samoa. Few of these colonizations have led to the co‐occurrence of congenerics or species with similar ecomorphological profiles on the same island. Thus, we suggest that priority effects might prevent new colonizers from establishing themselves if they share high levels of ecological similarity with resident species. We conclude that historical dispersal to and colonization of new islands, combined with ecologically deterministic priority effects, drove the assembly of insular monarch flycatcher communities across the Indo‐Pacific.

Genetic integration of local dispersal and exploratory behaviour in a wild bird

Dispersal is a major determinant of the ecological and evolutionary dynamics of natural populations. Individuals differ greatly in the likelihood and distance of dispersal, but it is generally unclear to what extent intrinsic, possibly genetic, differences contribute. Here we present the first explicit empirical evidence for genetic coupling of local dispersal and exploratory behaviour, a key 'animal personality' trait. Using relatedness data from a multi-generation pedigree of free-living great tits (Parus major), we find quantitative genetic variation for both the distance of local dispersal within our study area and the rate at which individuals explore a novel environment. Moreover, we find a strongly positive genetic correlation between local dispersal distance and exploration rate, despite a weak and non-significant phenotypic correlation. These findings demonstrate a potentially important behavioural mechanism underlying heritable differences in local dispersal and highlight the potential for concerted evolution of dispersal and animal personality in response to selection.

Bacterial motility confers fitness advantage in the presence of phages

Dispersal provides the opportunity to escape harm and colonize new patches, enabling populations to expand and persist. However, the benefits of dispersal associated with escaping harm will be dependent on the structure of the environment and the likelihood of escape. Here, we empirically investigate how the spatial distribution of a parasite influences the evolution of host dispersal. Bacteriophages are a strong and common threat for bacteria in natural environments and offer a good system with which to explore parasite-mediated selection on host dispersal. We used two transposon mutants of the opportunistic bacteria, Pseudomonas aeruginosa, which varied in their motility (a disperser and a nondisperser), and the lytic bacteriophage ФKZ. The phage was distributed either in the central point of colony inoculation only, thus offering an escape route for the dispersing bacteria; or, present throughout the agar, where benefits of dispersal might be lost. Surprisingly, we found dispersal to be equally advantageous under both phage conditions relative to when phages were absent. A general explanation is that dispersal decreased the spatial structuring of host population, reducing opportunities for parasite transmission, but other more idiosyncratic mechanisms may also have contributed. This study highlights the crucial role the parasites can play on the evolution of dispersal and, more specifically, that bacteriophages, which are ubiquitous, are likely to select for bacterial motility.

Dispersal and species’ responses to climate change

Dispersal is fundamental in determining biodiversity responses to rapid climate change, but recently acquired ecological and evolutionary knowledge is seldom accounted for in either predictive methods or conservation planning. We emphasise the accumulating evidence for direct and indirect impacts of climate change on dispersal. Additionally, evolutionary theory predicts increases in dispersal at expanding range margins, and this has been observed in a number of species. This multitude of ecological and evolutionary processes is likely to lead to complex responses of dispersal to climate change. As a result, improvement of models of species’ range changes will require greater realism in the representation of dispersal. Placing dispersal at the heart of our thinking will facilitate development of conservation strategies that are resilient to climate change, including landscape management and assisted colonisation.SynthesisThis article seeks synthesis across the fields of dispersal ecology and evolution, species distribution modelling and conservation biology. Increasing effort focuses on understanding how dispersal influences species' responses to climate change. Importantly, though perhaps not broadly widely‐recognised, species' dispersal characteristics are themselves likely to alter during rapid climate change. We compile evidence for direct and indirect influences that climate change may have on dispersal, some ecological and others evolutionary. We emphasise the need for predictive modelling to account for this dispersal realism and highlight the need for conservation to make better use of our existing knowledge related to dispersal.

Evolution of dispersal and life history interact to drive accelerating spread of an invasive species

Populations on the edge of an expanding range are subject to unique evolutionary pressures acting on their life-history and dispersal traits. Empirical evidence and theory suggest that traits there can evolve rapidly enough to interact with ecological dynamics, potentially giving rise to accelerating spread. Nevertheless, which of several evolutionary mechanisms drive this interaction between evolution and spread remains an open question. We propose an integrated theoretical framework for partitioning the contributions of different evolutionary mechanisms to accelerating spread, and we apply this model to invasive cane toads in northern Australia. In doing so, we identify a previously unrecognised evolutionary process that involves an interaction between life-history and dispersal evolution during range shift. In roughly equal parts, life-history evolution, dispersal evolution and their interaction led to a doubling of distance spread by cane toads in our model, highlighting the potential importance of multiple evolutionary processes in the dynamics of range expansion.

Meiotic behaviour, karyotype analyses and pollen viability in species ofTamarix(Tamaricaceae)

Samadi N., Ghaffari S. M. & Akhani H.: Meiotic behaviour, karyotype analyses and pollen viability in species of Tamarix (Tamaricaceae). — Willdenowia 43: 195–203. June 2013. — Online ISSN 1868-6397; © 2013 BGBM Berlin-Dahlem. Stable URL: http//dx.doi.org/10.3372/wi.43.43121This study elucidates cytological aspects of the complex genus Tamarix (Tamaricaceae). Chromosome counts were performed and meiotic behaviour recorded on 30 accessions belonging to 15 taxa and three putative hybrids from different parts of Iran. Karyotype data were analysed in five species. Both gametic and somatic chromosome counts showed most species are diploid (n = 12 and 2n = 24), but polyploidy (n = 24 and 2n = 36) was found in six taxa. All the studied species showed predominance of submetacentric chromosomes and a lower proportion of metacentric pairs. The chromosomes in studied species were found to be small with a mean chromosome length of 1.05 to 2.8 µm. Karyotype analyses showed different formulas from 12sm to 7m 5sm. Pollen viability in most species was more than 79 %, with low viability (28.5 %) observed only in T. cf. kermanensis, as a triploid taxon. This study reveals that polyploidy and hybridization could be important reasons for taxonomic complexity in Tamarix. Hybridization and the high chance of establishing hybrids by vegetative reproduction are major adaptive mechanisms in the successful growing, dispersal and probable rapid evolution of this genus in its native range. Furthermore these mechanisms could facilitate the spreading of Tamarix species outside their native range as aggressive invasive plants.

Dispersing away from bad genotypes: the evolution of Fitness-Associated Dispersal (FAD) in homogeneous environments

BackgroundDispersal is a major factor in ecological and evolutionary dynamics. Although empirical evidence shows that the tendency to disperse varies among individuals in many organisms, the evolution of dispersal patterns is not fully understood. Previous theoretical studies have shown that condition-dependent dispersal may evolve as a means to move to a different environment when environments are heterogeneous in space or in time. However, dispersal is also a means to genetically diversify offspring, a genetic advantage that might be particularly important when the individual fitness is low. We suggest that plasticity in dispersal, in which fit individuals are less likely to disperse (Fitness-Associated Dispersal, or FAD), can evolve due to its evolutionary advantages even when the environment is homogeneous and stable, kin competition is weak, and the cost of dispersal is high.ResultsUsing stochastic simulations we show that throughout the parameter range, selection favors FAD over uniform dispersal (in which all individuals disperse with equal probability). FAD also has significant long-term effects on the mean fitness and genotypic variance of the population.ConclusionsWe show that FAD evolves under a very wide parameter range, regardless of its effects on the population mean fitness. We predict that individuals of low quality will have an increased tendency for dispersal, even when the environment is homogeneous, there is no direct competition with neighbors, and dispersal carries significant costs.

THE EVOLUTION OF PALEARCTIC MIGRATION—THE CASE FOR SOUTHERN ANCESTRY

ABSTRACT The thesis developed in this paper is that the phenomenon of bird migration is founded on (1) pre-adaptations for flight that reduce the cost of long-distance directional movement, and (2) intensive reproductive effort that makes the use of the northern short season of high food abundance very beneficial for breeding. It is proposed that the first step in the evolution of migration is long-distance pre-breeding dispersal of a fraction of the juveniles of southern species to northern latitudes, where they breed sind then disperse south. Further adaptations for timing and navigation mechanisms turn the dispersal into directional seasonal migration. Finally, reproductive isolation, drift, and selection result in speciation of the northern-breeding migratory fraction from the nonmigratory southern-breeding ancestor species. The evidence supporting this hypothesis is scanty and circumstantial, and includes the high incidence of migration among northern species, several examples of species that represe...

Population sex ratio and dispersal in experimental, two‐patch metapopulations of butterflies

1. Sex-biased dispersal, that is, the difference in dispersal between males and females, is thought to be the consequence of any divergent evolutionary responses between sexes. In anisogamous species, asymmetry in parental investment may lead to sexual conflict, which entails male-male competition (for sexual partner access), female-female competition (for feeding or egg-laying habitat patches) and/or male-female competition (antagonistic co-evolution). 2. As competition is one of the main causes of dispersal evolution, intra- and intersexual competition should have strong consequences on sex-biased dispersal. However, very few experimental studies, if any, have simultaneously addressed the effect of biased sex ratio on (i) each dispersal stage (emigration, transience, immigration), (ii) the dispersal phenotype and (iii) the colonization success of new habitat in order to fully separate the effects of varying male and female density. 3. Here, we used the Metatron, a unique experimental system composed of 48 interconnected enclosed patches dedicated to the study of dispersal in meta-ecosystems, to investigate the effect of sex ratio on dispersal in a butterfly. We created six populations with three different sex ratios in pairs of patches and recorded individual movements in these simple metapopulations. 4. Emigration was higher when the proportion of males was higher, and individuals reached the empty patch at a higher rate when the sex ratio in the departure patch was balanced. Males had a better dispersal success than females, which had a lower survival rate during dispersal and after colonization. We also showed that sex and wing size are major components of the dispersal response. 5. We did not observe sex-biased dispersal; our results thus suggest that female harassment by males and male-male competition might be more important mechanisms for the dispersal of females and males, than the search for a mating partner. Furthermore, the demonstration of a differential mortality between males and females during dispersal provides causal hypotheses of the evolution of sex-biased dispersal.

Kin Competition as a Major Driving Force for Invasions

Current theory explains accelerating invasions with increased levels of dispersal as being caused by "spatial selection." Here we argue that another selective force, strong kin competition resulting from high relatedness due to subsequent founder effects at the expanding margin, is of at least comparable importance for dispersal evolution during invasions. We test this hypothesis with individual-based simulations of a spatially structured population invading empty space. To quantify the relative contribution of kin competition to dispersal evolution, we contrast two scenarios, one including kin effects and one excluding them without influencing spatial selection. We find that kin competition is a major determinant for dispersal evolution at invasion fronts, especially under environmental conditions that favor a pronounced kin structure (i.e., small patches, low environmental stochasticity, and high patch isolation). We demonstrate the importance of kin competition and thus biotic influences on dispersal evolution during invasions.

Social mating system and sex-biased dispersal in mammals and birds: a phylogenetic analysis.

The hypothesis that patterns of sex-biased dispersal are related to social mating system in mammals and birds has gained widespread acceptance over the past 30 years. However, two major complications have obscured the relationship between these two behaviors: 1) dispersal frequency and dispersal distance, which measure different aspects of the dispersal process, have often been confounded, and 2) the relationship between mating system and sex-biased dispersal in these vertebrate groups has not been examined using modern phylogenetic comparative methods. Here, we present a phylogenetic analysis of the relationship between mating system and sex-biased dispersal in mammals and birds. Results indicate that the evolution of female-biased dispersal in mammals may be more likely on monogamous branches of the phylogeny, and that females may disperse farther than males in socially monogamous mammalian species. However, we found no support for a relationship between social mating system and sex-biased dispersal in birds when the effects of phylogeny are taken into consideration. We caution that although there are larger-scale behavioral differences in mating system and sex-biased dispersal between mammals and birds, mating system and sex-biased dispersal are far from perfectly associated within these taxa.