Alexander Kubisch

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.

Assortative mating counteracts the evolution of dispersal polymorphisms.

Polymorphic dispersal strategies are found in many plant and animal species. An important question is how the genetic variation underlying such polymorphisms is maintained. Numerous mechanisms have been discussed, including kin competition or frequency‐dependent selection. In the context of sympatric speciation events, genetic and phenotypic variation is often assumed to be preserved by assortative mating. Thus, recently, this has been advocated as a possible mechanism leading to the evolution of dispersal polymorphisms. Here, we examine the role of assortative mating for the evolution of trade‐off‐driven dispersal polymorphisms by modeling univoltine insect species in a metapopulation. We show that assortative mating does not favor the evolution of polymorphisms. On the contrary, assortative mating favors the evolution of an intermediate dispersal type and a uni‐modal distribution of traits within populations. As an alternative, mechanism dominance may explain the occurrence of two discrete morphs.

Optimal Life-History Strategy Differs between Philopatric and Dispersing Individuals in a Metapopulation

Abundant empirical evidence for dispersal syndromes contrasts with the rarity of theoretical predictions about the evolution of life-history divergence between dispersing and philopatric individuals. We use an evolutionary model to predict optimal differences in age-specific reproductive effort between dispersing and philopatric individuals inhabiting the same metapopulation. In our model, only young individuals disperse, and their lifelong reproductive decisions are potentially affected by this initial event. Juvenile survival declines as density of adults and other juveniles increases. We assume a trade-off between reproduction and survival, so that different patterns of age-specific reproductive effort lead to different patterns of aging. We find that young immigrant mothers should allocate more resources to reproduction than young philopatric mothers, but these life-history differences vanish as immigrant and philopatric individuals get older. However, whether the higher early reproductive effort of immigrants results in higher fecundity depends on the postimmigration cost on fecundity. Dispersing individuals have consequently a shorter life span. Ultimately, these life-history differences are due to the fact that young dispersing individuals most often live in recently founded populations, where competition is relaxed and juvenile survival higher, favoring larger investment in offspring production at the expense of survival.

The Adequate Use of Limited Information in Dispersal Decisions.

Several theoretical studies predict that informed (e.g., density-dependent) dispersal should generally result in lower emigration probabilities than uninformed (random) dispersal. In a 2012 publication, Bocedi et al. surprisingly come to the opposite conclusion. For most scenarios investigated, they found that noninformed and, particularly, less precisely informed dispersers evolve lower dispersal propensity than dispersers following “fully informed” strategies. Further, they observed that fully informed individuals evolved a steplike dispersal response—a response to local density that contradicts theoretical predictions for organisms with nonoverlapping generations. Replicating the individual-based simulations of Bocedi et al. we find that these conclusions are not justified and are based on a misinterpretation of simulation results: their controversial findings result from (i) a misleading use of the term “population density,” (ii) a misconception concerning the true informative value of the different decision criteria they compared, and (iii) arbitrary constraints on the evolution of the dispersal response that prevented the evolution of strategies that allow for a fitness-enhancing utilization of available information.

Evolving mutation rate advances the invasion speed of a sexual species

BackgroundMany species are shifting their ranges in response to global climate change. Range expansions are known to have profound effects on the genetic composition of populations. The evolution of dispersal during range expansion increases invasion speed, provided that a species can adapt sufficiently fast to novel local conditions. Genetic diversity at the expanding range border is however depleted due to iterated founder effects. The surprising ability of colonizing species to adapt to novel conditions while being subjected to genetic bottlenecks is termed ‘the genetic paradox of invasive species’. Mutational processes have been argued to provide an explanation for this paradox. Mutation rates can evolve, under conditions that favor an increased rate of adaptation, by hitchhiking on beneficial mutations through induced linkage disequilibrium. Here we argue that spatial sorting, iterated founder events, and population structure benefit the build-up and maintenance of such linkage disequilibrium. We investigate if the evolution of mutation rates could play a role in explaining the ‘genetic paradox of invasive species’ for a sexually reproducing species colonizing a landscape of gradually changing conditions.ResultsWe use an individual-based model to show the evolutionary increase of mutation rates in sexual populations during range expansion, in coevolution with the dispersal probability. The observed evolution of mutation rate is adaptive and clearly advances invasion speed both through its effect on the evolution of dispersal probability, and the evolution of local adaptation. This also occurs under a variable temperature gradient, and under the assumption of 90% lethal mutations.ConclusionsIn this study we show novel consequences of the particular genetic properties of populations under spatial disequilibrium, i.e. the coevolution of dispersal probability and mutation rate, even in a sexual species and under realistic spatial gradients, resulting in faster invasions. The evolution of mutation rates can therefore be added to the list of possible explanations for the ‘genetic paradox of invasive species’. We conclude that range expansions and the evolution of mutation rates are in a positive feedback loop, with possibly far-reaching ecological consequences concerning invasiveness and the adaptability of species to novel environmental conditions.

Latitudinal-diversity gradients can be shaped by biotic processes: new insights from an eco-evolutionary model

The processes involved in shaping latitudinal-diversity gradients (LDGs) have been a longstanding source of debate and research. Climatic, historical and evolutionary factors have all been shown to contribute to the formation of LDGs. However, metaanalyses have shown that different clades have LDG slopes that may vary in more than one order of magnitude. Such large variation cannot be explained solely by climatic or historical factors (e.g. difference in surface area between temperate and tropical zones) given that all clades within a geographic region are subject to the same conditions. Therefore, biotic processes intrinsic to each taxonomic group could be relevant in explaining rate differences in diversity decline across latitudinal gradients among groups. In this study, we developed a model simulating multiple competing species subjected (or not) to a demographic Allee effect. We simulated the range expansion of these species across an environmental gradient to show how these two overlooked factors (competition and Allee effects) are capable of modulating LDGs. Allee effects resulted in a steeper LDG given a higher probability of local extinction and lower colonization capacity compared to species without Allee effects. Likewise, stronger competition also led to a steeper decline in species diversity compared to scenarios with weaker species antagonistic interactions. This pattern occurred mostly due to the strength of priority effects, wherein scenarios with strong competition, species that dispersed earlier in the landscape were able to secure many patches whereas late-arriving species were progressively precluded from expanding their ranges. Overall, our results suggest that the effect of biotic processes in shaping macroecological patterns could be more important than it is currently appreciated.

Evolving mutation rate advances invasion speed of sexual species

The evolution of dispersal during range expansion increases invasion speed, provided that a species can adapt sufficiently fast to novel local conditions. Iterated founder effects during range expansion, however, cause low levels of local genetic diversity at these range margins. Mutation rates can evolve, too, under conditions that favor an increased rate of local adaptation, but this has thus far only been associated with asexual populations. As selection acts on the mutation that occurs at a gene under selection and not on the rate with which such mutations occur, the evolution of mutation rates is the result of indirect selection. The establishment of a particular mutation rate is thus restricted to genetic hitchhiking, which is highly sensitive to recombination. However, under conditions of genetic similarity, typical for expanding range margins, the evolution of mutation rates in sexual populations might be possible. Using an individual-based model we show that natural selection leads to co-evolution of dispersal rates and mutation rates in sexual populations due to spatial sorting. The evolution of mutation rate is adaptive and clearly advances range expansion both through its effect on the evolution of dispersal rate, and the evolution of local adaptation. By this we extend the existing theory on the evolution of mutation rates, which was thought to be limited to asexual populations, with possibly far-reaching consequences concerning invasiveness and the rate at which species can adapt to novel environmental conditions.Many species are shifting their ranges in response to global climate change. The evolution of dispersal during range expansion increases invasion speed, provided that a species can adapt sufficiently fast to novel local conditions. Mutation rates can evolve too, under conditions that favor an increased rate of adaptation. However, evolution at the mutator gene has thus far been deemed of minor importance in sexual populations due to its dependence on genetic hitchhiking with a beneficial mutation at a gene under selection, and thus its sensitivity to recombination. Here we use an individual-based model to show that the mutator gene and the gene under selection can be effectively linked at the population level during invasion. This causes the evolutionary increase of mutation rates in sexual populations, even if they are not linked at the individual level. The observed evolution of mutation rate is adaptive and clearly advances range expansion both through its effect on the evolution of dispersal rate, and the evolution of local adaptation. In addition, we observe the evolution of mutation rates in a spatially stable population under strong directional selection, but not when we add variance to the mean selection pressure. By this we extend the existing theory on the evolution of mutation rates, which is generally thought to be limited to asexual populations, with possibly far-reaching consequences concerning invasiveness and the rate at which species can adapt to novel environmental conditions as experienced under global climate change.