Evolutionary ecology of microsporidia associated with the invasive ladybird Harmonia axyridis

Invasive species are characterized by the rapid growth and spread of their populations after establishing a foothold in new habitats, and there are now many examples of such species negatively affecting biodiversity and the economy. It is unclear why some species can become successful invaders, whereas most （even if closely related） remain noninvasive. We previously proposed a hypothesis that parasites associated with invading species can promote their invasive success if they are harmless toward the invaders but harmful to their competitors and/or predators in the newly colonized habitat. Here we discuss whether microsporidia that have recently been discovered in the invasive ladybird Harmonia axyridis contribute to its invasive success. We show that all H. axyridis beetles sourced from diverse collection sites all over the world carry abundant microsporidia. This suggests that both native and invasive H. axyridis populations are associated with these tolerated parasites, which were likely to have existed in native populations before expansion rather than being acquired in newly colonized areas. We describe the pathogenesis of the microsporidia during different developmental stages of H. axyridis and we address the possibility that the predation of its infected eggs and larvae by competing native ladybird species may lead to their infection and ultimately to their decline. Finally, we discuss our initial hypothesis： microsporidia that are tolerated by an invasive vector insect can be active against susceptible native competitors and/or predator species.

Path-dependent speciation in dynamic fitness landscapes

Species is a fundamental concept in evolutionary biology and biodiversity.However,existing species definitions are often influenced by artificial factors or are challenging in practical application,leading to confusion in species classification.Due to uncertain environmental changes and random genetic drift,the fitness expectations of a population may shift,causing species to evolve to a new evolutionary state based on their current instantaneous fitness within a dynamic fitness landscape.This contrasts with the classic static fitness landscape,where fitness expectations are constant.In a dynamic fitness landscape,speciation may exhibit path dependence,where the evolution of traits follows a probabilistic path,creating feedback that shapes evolutionary trajectories.The path-dependent evolutionary mechanism suggests that species survival within an ecosystem is not directly determined by their fitness but by the probability of their evolutionary pathways.This model also indicates that species can coexist with varying probabilities under limited environmental pressures.Consequently,new species,cryptic species,or sympatric species may emerge via path-dependent evolutionary processes.Within this framework,we developed a mathematical species concept,which may guide future species classification methodologies.

The ecology of sexual dimorphism in size and shape of the freshwater blenny Salaria fluviatilis

Sexual selection is considered the major cause of sexual dimorphism, but recent observations suggest that natural selection may play a more important role in the evolution of sex differentiation than previously recognized. Therefore, studying the trade-offs between natural selection and sexual selection is crucial to a better understanding of the ecology underlying the evolution of sexual dimorphism. The freshwater blenny Salaria fluviatilis, a fish inhabiting lakes and rivers around the Mediterranean Sea, displays strong sexual dimorphism in size, shape, and behavior （i.e., larger body and head size for males and higher swimming requirements for females during the reproductive period）. We tested for differences in sexual dimorphism in size and shape between the populations from lake and river habitats with the goal of identifying the trade-offs between natural and sexual se- lection that underlie variations in sexual dimorphism in this species. Our results show i） differences in sexual size dimorphism （SSizeD） in accordance to Rensch＇s rule （i.e., larger individuals in rivers associated with higher SSizeD）, and ii） a decrease in shape differentiation between males and fe- males in lake populations. Together, this suggests that the different environmental conditions between lake and river habitats （e.g., resource limitations, predation pressure, water velocity） affect the relative importance of sexual selection in the display of sexual dimorphism within the species. This study highlights the importance of considering the environmental conditions to which populations are exposed to better understand the ecology underlying the evolution of sexual dimorphism.

Applied evolutionary biology could aid management of invaded ecosystems

Invasive plant species subvert essential ecosystem services through a reduction in the abundance and genetic diversity of native plant species.A major challenge now facing land managers and policy makers is how to ensure persistence of native plants while limiting harmful impacts of invasions.Results from recent empirical studies suggest that native plants may evolve adaptations to invasive plants and that adaptive evolution in invasive plants could lessen the negative impacts of invasions.Here,we suggest ways in which knowledge of adaptive evolution in invasive and native plants could be utilized to more effectively manage invaded ecosystems.

Populations with individual variation in dispersal in heterogeneous environments: Dynamics and competition with simply diffusing populations

We consider a model for a population in a heterogeneous environment, with logistic-type local population dynamics, under the assumption that individuals can switch between two different nonzero rates of diffusion. Such switching behavior has been observed in some natural systems. We study how environmental heterogeneity and the rates of switching and diffusion affect the persistence of the population. The reactiondiffusion systems in the models can be cooperative at some population densities and competitive at others. The results extend our previous work on similar models in homogeneous environments. We also consider competition between two populations that are ecologically identical, but where one population diffuses at a fixed rate and the other switches between two different diffusion rates. The motivation for that is to gain insight into when switching might be advantageous versus diffusing at a fixed rate. This is a variation on the classical results for ecologically identical competitors with differing fixed diffusion rates, where it is well known that "the slower diffuser wins".

Simulating the evolution of a clonal trait in plants with sexual and vegetative reproduction

Aims Phenotypic optimality models neglect genetics.However,especially when heterozygous genotypes are fittest,evolving allele,genotype and phenotype frequencies may not correspond to predicted optima.This was not previously addressed for organisms with complex life histories.Methods Therefore,we modelled the evolution of a fitness-relevant trait of clonal plants,stolon internode length.We explored the likely case of an asymmetric unimodal fitness profile with three model types.In constant selection models(CSMs),which are gametic,but not spatially explicit,evolving allele frequencies in the one-locus and fiveloci cases did not correspond to optimum stolon internode length predicted by the spatially explicit,but not gametic,phenotypic model.This deviation was due to the asymmetry of the fitness profile.Gametic,spatially explicit individual-based(SEIB)modeling allowed us relaxing the CSM assumptions of constant selection with exclusively sexual reproduction.Important findings For entirely vegetative or sexual reproduction,predictions of the gametic SEIB model were close to the ones of spatially explicit nongametic phenotypic models,but for mixed modes of reproduction they approximated those of gametic,not spatially explicit CSMs.Thus,in contrast to gametic SEIB models,phenotypic models and,especially for few loci,also CSMs can be very misleading.We conclude that the evolution of traits governed by few quantitative trait loci appears hardly predictable by simple models,that genetic algorithms aiming at technical optimization may actually miss the optimum and that selection may lead to loci with smaller effects in derived compared with ancestral lines.