Red Queen Hypothesis Research Articles

Fixation probabilities of evolutionary coordination games on two coupled populations.

Evolutionary forces resulted from competitions between different populations are common, which change the evolutionary behavior of a single population. In an isolated population of coordination games of two strategies (e.g., s_{1} and s_{2}), the previous studies focused on determining the fixation probability that the system is occupied by only one strategy (s_{1}) and their expectation times, given an initial mixture of two strategies. In this work, we propose a model of two interdependent populations, disclosing the effects of the interaction strength on fixation probabilities. In the well-mixing limit, a detailed linear stability analysis is performed, which allows us to find and to classify the different equilibria, yielding a clear picture of the bifurcation patterns in phase space. We demonstrate that the interactions between populations crucially alter the dynamic behavior. More specifically, if the coupling strength is larger than some threshold value, the critical initial density of one strategy (s_{1}) that corresponds to fixation is significantly delayed. Instead, the two populations evolve to the opposite state of all (s_{2}) strategy, which are in favor of the red queen hypothesis. We delineate the extinction time of strategy (s_{1}) explicitly, which is an exponential form. These results are validated by systematic numerical simulations.

Comparative genomics reveals convergent rates of evolution in ant-plant mutualisms.

Symbiosis—the close and often long-term interaction of species—is predicted to drive genome evolution in a variety of ways. For example, parasitic interactions have been shown to increase rates of molecular evolution, a trend generally attributed to the Red Queen Hypothesis. However, it is much less clear how mutualisms impact the genome, as both increased and reduced rates of change have been predicted. Here we sequence the genomes of seven species of ants, three that have convergently evolved obligate plant–ant mutualism and four closely related species of non-mutualists. Comparing these sequences, we investigate how genome evolution is shaped by mutualistic behaviour. We find that rates of molecular evolution are higher in the mutualists genome wide, a characteristic apparently not the result of demography. Our results suggest that the intimate relationships of obligate mutualists may lead to selective pressures similar to those seen in parasites, thereby increasing rates of evolution.

Clinical and Epidemiological Evidence of the Red Queen Hypothesis in Pneumococcal Serotype Dynamics.

The Red Queen hypothesis is an evolutionary theory that describes the reciprocal coevolution of competing species. We sought to study whether introduction of the 7- and 13-valent pneumococcal conjugate vaccines (PCV7 and PCV13, respectively) altered pneumococcal serotype dynamics among children with invasive pneumococcal disease (IPD) as predicted by the Red Queen hypothesis. This study examined pneumococcal isolates (n = 641) obtained from children <18 years of age hospitalized with IPD from 1997 to 2014 in Utah. A review of the literature also identified several additional studies conducted in the United States and Europe that were used to test the external generalizability of our Utah findings. Simpson's index was used to quantify pneumococcal serotype diversity. In Utah, the introduction of PCV7 and PCV13 was associated with rapid increases in serotype diversity (P < .001). Serotypes rarely present before vaccine introduction emerged as common causes of IPD. Diversity then decreased (P < .001) as competition selected for the fittest serotypes and new evolutionary equilibriums were established. This pattern was also observed more broadly in the United States, the United Kingdom, Norway, and Spain. This vaccine-driven example of human/bacterial coevolution appears to confirm the Red Queen hypothesis, which reveals a limitation of serotype-specific vaccines and offers insights that may facilitate alternative strategies for the elimination of IPD.

Eco-evolutionary feedback promotes Red Queen dynamics and selects for sex in predator populations

Although numerous hypotheses exist to explain the overwhelming presence of sexual reproduction across the tree of life, we still cannot explain its prevalence when considering all inherent costs involved. The Red Queen hypothesis states that sex is maintained because it can create novel genotypes with a selective advantage. This occurs when the interactions between species induce frequent environmental change. Here, we investigate whether coevolution and eco-evolutionary feedback dynamics in a predator-prey system allows for indirect selection and maintenance of sexual reproduction in the predator. Combining models and chemostat experiments of a rotifer-algae system we show a continuous feedback between population and trait change along with recurrent shifts from selection by predation and competition for a limited resource. We found that a high propensity for sex was indirectly selected and was maintained in rotifer populations within environments containing these eco-evolutionary dynamics; whereas within environments under constant conditions, predators evolved rapidly to lower levels of sex. Thus, our results indicate that the influence of eco-evolutionary feedback dynamics on the overall evolutionary change has been underestimated.

Red Queen dancing in the lek: effects of mating skew on host-parasite interactions.

The RQH (Red Queen hypothesis), which argues that hosts need to be continuously finding new ways to avoid parasites that are able to infect common host genotypes, has been at the center of discussions on the maintenance of sex. This is because diversity is favored under the host–parasite coevolution based on negative frequency‐dependent selection, and sexual reproduction is a mechanism that generates genetic diversity in the host population. Together with parasite infections, sexual organisms are usually under sexual selection, which leads to mating skew or mating success biased toward males with a particular phenotype. Thus, strong mating skew would affect genetic variance in a population and should affect the benefit of the RQH. However, most models have investigated the RQH under a random mating system and not under mating skew. In this study, I show that sexual selection and the resultant mating skew may increase parasite load in the hosts. An IBM (individual‐based model), which included host–parasite interactions and sexual selection among hosts, demonstrates that mating skew influenced parasite infection in the hosts under various conditions. Moreover, the IBM showed that the mating skew evolves easily in cases of male–male competition and female mate choice, even though it imposes an increased risk of parasite infection on the hosts. These findings indicated that whether the RQH favored sexual reproduction depended on the condition of mating skew. That is, consideration of the host mating system would provide further understanding of conditions in which the RQH favors sexual reproduction in real organisms.

The role of biotic forces in driving macroevolution: beyond the Red Queen.

A multitude of hypotheses claim that abiotic factors are the main drivers of macroevolutionary change. By contrast, Van Valen's Red Queen hypothesis is often put forward as the sole representative of the view that biotic forcing is the main evolutionary driver. This imbalance of hypotheses does not reflect our current knowledge: theoretical work demonstrates the plausibility of biotically driven long-term evolution, whereas empirical work suggests a central role for biotic forcing in macroevolution. We call for a more pluralistic view of how biotic forces may drive long-term evolution that is compatible with both phenotypic stasis in the fossil record and with non-constant extinction rates. Promising avenues of research include contrasting predictions from relevant theories within ecology and macroevolution, as well as embracing both abiotic and biotic proxies while modelling long-term evolutionary data. By fitting models describing hypotheses of biotically driven macroevolution to data, we could dissect their predictions and transcend beyond pattern description, possibly narrowing the divide between our current understanding of micro- and macroevolution.

Parasite Selection and the Fitness of Sexual Reproduction

Sexual reproduction is a very costly process: the growth rate of asexual lineages exceeds that of sexual lineages. Nonetheless, sex is prevalent in nature. The Red Queen Hypothesis argues that, because sex and recombination generate genetically variable offspring that may escape infection by coevolving parasites, parasites select for sex in hosts (Lively &amp; Dybdahl, 2000). Our research directly tests if the Red Queen can explain the maintenance of sex in a natural population. This experiment focuses on a natural population of the snail Potamopyrgus antipodarum, which is native to New Zealand. Individuals of this species are either diploid and sexually reproducing or triploid and asexually reproducing (Lively &amp; Osnas, 2006). This snail is naturally infected by the trematode parasite, Microphallus, which is sterilizing and thus exerts strong selection on its host. The Red Queen Hypothesis predicts that parasites should periodically increase the fitness of sexual relative to asexual individuals. We accordingly established mesocosms containing both sexual and asexual snails from the same natural population. Half of these mesocosms were exposed to parasites and the other half were not. These snails were then allowed to reproduce over the course of a year. We used flow cytometry to determine the frequency of diploids in the parents and the offspring, and thereby the fitness of sexual individuals in the presence and absence of parasites. Interestingly, we find that sexual individuals are currently more susceptible to parasites than are asexual individuals. In tanks in which sexual parents are relatively more infected, the frequency of sexual individuals declined significantly more in the offspring generation, indicating a fitness consequence of parasitism for sexual reproduction. Our findings suggest that parasite selection can indeed operate on reproductive mode. Moreover, our results are consistent with theory (King, Delph, Jokela, &amp; Lively, 2009) and a prior field study in our system indicating that the direction of parasite selection is variable, such that parasites periodically select against sexual reproduction (Vergara, Lively, King, &amp; Jokela, 2013). This current experiment will continue for multiple years in order to track the variation in parasite selection on sex through time.

Unmasking host and microbial strategies in the Agrobacterium-plant defense tango.

Coevolutionary forces drive adaptation of both plant-associated microbes and their hosts. Eloquently captured in the Red Queen Hypothesis, the complexity of each plant–pathogen relationship reflects escalating adversarial strategies, but also external biotic and abiotic pressures on both partners. Innate immune responses are triggered by highly conserved pathogen-associated molecular patterns, or PAMPs, that are harbingers of microbial presence. Upon cell surface receptor-mediated recognition of these pathogen-derived molecules, host plants mount a variety of physiological responses to limit pathogen survival and/or invasion. Successful pathogens often rely on secretion systems to translocate host-modulating effectors that subvert plant defenses, thereby increasing virulence. Host plants, in turn, have evolved to recognize these effectors, activating what has typically been characterized as a pathogen-specific form of immunity. Recent data support the notion that PAMP-triggered and effector-triggered defenses are complementary facets of a convergent, albeit differentially regulated, set of immune responses. This review highlights the key players in the plant’s recognition and signal transduction pathways, with a focus on the aspects that may limit Agrobacterium tumefaciens infection and the ways it might overcome those defenses. Recent advances in the field include a growing appreciation for the contributions of cytoskeletal dynamics and membrane trafficking to the regulation of these exquisitely tuned defenses. Pathogen counter-defenses frequently manipulate the interwoven hormonal pathways that mediate host responses. Emerging systems-level analyses include host physiological factors such as circadian cycling. The existing literature indicates that varying or even conflicting results from different labs may well be attributable to environmental factors including time of day of infection, temperature, and/or developmental stage of the host plant.

Host-parasite coevolutionary dynamics with generalized success/failure infection genetics.

Host-parasite infection genetics can be more complex than envisioned by classic models such as the gene-for-gene or matching-allele models. By means of a mathematical model, I investigate the coevolutionary dynamics arising from a large set of generalized models of infection genetics in which hosts are either fully resistant or fully susceptible to a parasite, depending on the genotype of both individuals. With a single diploid interaction locus in the hosts, many of the infection genetic models produce stable or neutrally stable genotype polymorphisms. However, only a few models, which are all different versions of the matching-allele model, lead to sustained cycles of genotype frequency fluctuations in both interacting species ("Red Queen" dynamics). By contrast, with two diploid interaction loci in the hosts, many infection genetics models that cannot be classified as one of the standard infection genetics models produce Red Queen dynamics. Sexual versus asexual reproduction and, in the former case, the rate of recombination between the interaction loci have a large impact on whether Red Queen dynamics arise from a given infection genetics model. This may have interesting but as yet unexplored implications with respect to the Red Queen hypothesis for the evolution of sex.

Diversity and the maintenance of sex by parasites.

The Red Queen hypothesis (RQH) predicts that parasite-mediated selection will maintain sexual individuals in the face of competition from asexual lineages. The prediction is that sexual individuals will be difficult targets for coevolving parasites if they give rise to more genetically diverse offspring than asexual lineages. However, increasing host genetic diversity is known to suppress parasite spread, which could provide a short-term advantage to clonal lineages and lead to the extinction of sex. We test these ideas using a stochastic individual-based model. We find that if parasites are readily transmissible, then sex is most likely to be maintained when host diversity is high, in agreement with the RQH. If transmission rates are lower, however, we find that sexual populations are most likely to persist for intermediate levels of diversity. Our findings thus highlight the importance of genetic diversity and its impact on epidemiological dynamics for the maintenance of sex by parasites.

Do gynogenetic species escape evolving enemies?

Gynogenetic organisms are asexual females of one species that require sperm from males of another species to initiate reproduction (but except in rare instances of ‘paternal leakage’, those sperm do not contribute to the genetic make-up of the gynogens’ offspring). Gynogenetic organisms seem to combine disadvantages of both sexual and asexual reproductive strategies (e.g., mating costs, reduced genetic diversity). We borrowed logic from the Red Queen Hypothesis (RQH) to help explain the persistence of gynogenetic species in nature, which is a paradox. The RQH is the most oft-cited explanation for the maintenance of sex. It states that evolving enemies generate a constantly changing environment, which provides the conditions that make sex advantageous. Under this scenario, asexual organisms cannot evolve fast enough to ‘keep up’ with co-evolving parasites and disease causing organisms, and ultimately show reduced fitness compared to sexual individuals. The RQH tends to view asexuality generally, ignoring important nuance in nature like gynogenetic species in mixed assemblages with closely related sexual species. We outline tests of the argument that sperm dependency prevents asexual gynogens from outcompeting sexuals in mixed species assemblages and that this further allows gynogens to escape evolving enemies.

Predator-Prey Dynamics and the Red Queen Hypothesis: Putting Limits on the Evolutionary Arms Race

Computer simulations of complex food-webs are an important tool for deepening our understanding of these systems. Yet most computer models assume, rather than generate, key system-level patterns, or use mathematical modeling approaches that make it difficult to account fully for non-linear dynamics. In this article we present a computer simulation model that addresses these concerns by focusing on assumptions of agent attributes rather than agent outcomes. Our model utilizes the techniques of Complex Adaptive Systems and Agent-Based Modeling so that system-level patterns of a general ecosystem emerge from the interactions of thousands of individual simulated agents. This methodology has been validated in previous work by using this general simulation model to replicate fundamental properties of an ecosystem, including: (1) the predator-prey oscillations found in Lotka-Volterra; (2) the “stepped pattern” of biomass accrual from resource enrichment; (3) the Paradox of Enrichment; and (4) Gause’s Law. In this work we explore further the fundamental properties of this generative model in the context of the Red Queen Hypothesis, also referred to as the “arms race” between antagonistic species, e.g. predators and prey. We find that improvements in the competitive landscape for a single entity in a predator species does not generally confer a benefit on the predator species as a whole, and may even be detrimental to the predator population. This non-intuitive result is shown through two methods of adjusting the predators effectiveness in consuming prey. We further explore this idea by explicitly accounting for individual entity's energy requirements, and also allowing evolutionary adaptation for an effectiveness / energy trade-off. 1.0 Overview The literature on marine and terrestrial ecosystems is long and varied, encompassing both theoretical models (e.g.: Grimm, 1999; DeAngelis & Mooij, 2005) and empirical surveys (e.g.: Christensen et al., 2003; Frank et al., 2005). Some significant differences between model results and real-world surveys have persisted for years, and it has been difficult identifying fundamental principles relative to the many complicating factors that can be found in existent ecosystems. For example, in the early 1980s Oksanen et al. examined multiple trophic levels in a predator-prey system using mathematical models, in order to determine whether species population (bio-mass) is fundamentally controlled by resources – as was the conventional wisdom at the time – or dominated by predation (Oksanen et al., 1981). In describing this work, Power states that these models produce “a stepped pattern of biomass accrual” (Power, 1992); Brett and Goldman further characterize the Oksanen et al. results, saying that “In food webs with an odd number of trophic levels, increases in primary production should lead to increased biomass for odd-numbered trophic levels and no change in biomass for even-numbered trophic levels. Conversely, in food webs with an even number of trophic levels, increases in primary production should lead to increased biomass for even-numbered trophic levels and no change in biomass for odd-numbered trophic levels” (Brett & Goldman,

A phylogenetic test of the Red Queen Hypothesis: outcrossing and parasitism in the Nematode phylum.

Sexual outcrossing is costly relative to selfing and asexuality, yet it is ubiquitous in nature, a paradox that has long puzzled evolutionary biologists. The Red Queen Hypothesis argues that outcrossing is maintained by antagonistic interactions between host and parasites. Most tests of this hypothesis focus on the maintenance of outcrossing in hosts. The Red Queen makes an additional prediction that parasitic taxa are more likely to be outcrossing than their free-living relatives. We test this prediction in the diverse Nematode phylum using phylogenetic comparative methods to evaluate trait correlations. In support of the Red Queen, we demonstrate a significant correlation between parasitism and outcrossing in this clade. We find that this correlation is driven by animal parasites, for which outcrossing is significantly enriched relative to both free-living and plant parasitic taxa. Finally, we test hypotheses for the evolutionary history underlying the correlation of outcrossing and animal parasitism. Our results demonstrate that selfing and asexuality are significantly less likely to arise on parasitic lineages than on free-living ones. The findings of this study are consistent with the Red Queen Hypothesis. Moreover, they suggest that the maintenance of genetic variation is an important factor in the persistence of parasitic lineages.

Running with the Red Queen: the role of biotic conflicts in evolution.

What are the causes of natural selection? Over 40 years ago, Van Valen proposed the Red Queen hypothesis, which emphasized the primacy of biotic conflict over abiotic forces in driving selection. Species must continually evolve to survive in the face of their evolving enemies, yet on average their fitness remains unchanged. We define three modes of Red Queen coevolution to unify both fluctuating and directional selection within the Red Queen framework. Empirical evidence from natural interspecific antagonisms provides support for each of these modes of coevolution and suggests that they often operate simultaneously. We argue that understanding the evolutionary forces associated with interspecific interactions requires incorporation of a community framework, in which new interactions occur frequently. During their early phases, these newly established interactions are likely to drive fast evolution of both parties. We further argue that a more complete synthesis of Red Queen forces requires incorporation of the evolutionary conflicts within species that arise from sexual reproduction. Reciprocally, taking the Red Queen's perspective advances our understanding of the evolution of these intraspecific conflicts.

The red queen model of recombination hotspots evolution in the light of archaic and modern human genomes.

Recombination is an essential process in eukaryotes, which increases diversity by disrupting genetic linkage between loci and ensures the proper segregation of chromosomes during meiosis. In the human genome, recombination events are clustered in hotspots, whose location is determined by the PRDM9 protein. There is evidence that the location of hotspots evolves rapidly, as a consequence of changes in PRDM9 DNA-binding domain. However, the reasons for these changes and the rate at which they occur are not known. In this study, we investigated the evolution of human hotspot loci and of PRDM9 target motifs, both in modern and archaic human lineages (Denisovan) to quantify the dynamic of hotspot turnover during the recent period of human evolution. We show that present-day human hotspots are young: they have been active only during the last 10% of the time since the divergence from chimpanzee, starting to be operating shortly before the split between Denisovans and modern humans. Surprisingly, however, our analyses indicate that Denisovan recombination hotspots did not overlap with modern human ones, despite sharing similar PRDM9 target motifs. We further show that high-affinity PRDM9 target motifs are subject to a strong self-destructive drive, known as biased gene conversion (BGC), which should lead to the loss of the majority of them in the next 3 MYR. This depletion of PRDM9 genomic targets is expected to decrease fitness, and thereby to favor new PRDM9 alleles binding different motifs. Our refined estimates of the age and life expectancy of human hotspots provide empirical evidence in support of the Red Queen hypothesis of recombination hotspots evolution.

The Toxoplasma Pseudokinase ROP5 Is an Allosteric Inhibitor of the Immunity-related GTPases

The Red Queen hypothesis proposes that there is an evolutionary arms race between host and pathogen. One possible example of such a phenomenon could be the recently discovered interaction between host defense proteins known as immunity-related GTPases (IRGs) and a family of rhoptry pseudokinases (ROP5) expressed by the protozoan parasite, Toxoplasma gondii. Mouse IRGs are encoded by an extensive and rapidly evolving family of over 20 genes. Similarly, the ROP5 family is highly polymorphic and consists of 4-10 genes, depending on the strain of Toxoplasma. IRGs are known to be avidly bound and functionally inactivated by ROP5 proteins, but the molecular basis of this interaction/inactivation has not previously been known. Here we show that ROP5 uses a highly polymorphic surface to bind adjacent to the nucleotide-binding domain of an IRG and that this produces a profound allosteric change in the IRG structure. This has two dramatic effects: 1) it prevents oligomerization of the IRG, and 2) it alters the orientation of two threonine residues that are targeted by the Toxoplasma Ser/Thr kinases, ROP17 and ROP18. ROP5s are highly specific in the IRGs that they will bind, and the fact that it is the most highly polymorphic surface of ROP5 that binds the IRG strongly supports the notion that these two protein families are co-evolving in a way predicted by the Red Queen hypothesis.

Multidimensional epistasis and the transitory advantage of sex.

Identifying and quantifying the benefits of sex and recombination is a long-standing problem in evolutionary theory. In particular, contradictory claims have been made about the existence of a benefit of recombination on high dimensional fitness landscapes in the presence of sign epistasis. Here we present a comparative numerical study of sexual and asexual evolutionary dynamics of haploids on tunably rugged model landscapes under strong selection, paying special attention to the temporal development of the evolutionary advantage of recombination and the link between population diversity and the rate of adaptation. We show that the adaptive advantage of recombination on static rugged landscapes is strictly transitory. At early times, an advantage of recombination arises through the possibility to combine individually occurring beneficial mutations, but this effect is reversed at longer times by the much more efficient trapping of recombining populations at local fitness peaks. These findings are explained by means of well-established results for a setup with only two loci. In accordance with the Red Queen hypothesis the transitory advantage can be prolonged indefinitely in fluctuating environments, and it is maximal when the environment fluctuates on the same time scale on which trapping at local optima typically occurs.

Natural selection on coding and noncoding DNA sequences is associated with virulence genes in a plant pathogenic fungus.

Natural selection leaves imprints on DNA, offering the opportunity to identify functionally important regions of the genome. Identifying the genomic regions affected by natural selection within pathogens can aid in the pursuit of effective strategies to control diseases. In this study, we analyzed genome-wide patterns of selection acting on different classes of sequences in a worldwide sample of eight strains of the model plant-pathogenic fungus Colletotrichum graminicola. We found evidence of selective sweeps, balancing selection, and positive selection affecting both protein-coding and noncoding DNA of pathogenicity-related sequences. Genes encoding putative effector proteins and secondary metabolite biosynthetic enzymes show evidence of positive selection acting on the coding sequence, consistent with an Arms Race model of evolution. The 5′ untranslated regions (UTRs) of genes coding for effector proteins and genes upregulated during infection show an excess of high-frequency polymorphisms likely the consequence of balancing selection and consistent with the Red Queen hypothesis of evolution acting on these putative regulatory sequences. Based on the findings of this work, we propose that even though adaptive substitutions on coding sequences are important for proteins that interact directly with the host, polymorphisms in the regulatory sequences may confer flexibility of gene expression in the virulence processes of this important plant pathogen.

Structural basis for the recognition-evasion arms race between Tomato mosaic virus and the resistance gene Tm-1.

The tomato mosaic virus (ToMV) resistance gene Tm-1 encodes a protein that shows no sequence homology to functionally characterized proteins. Tm-1 binds ToMV replication proteins and thereby inhibits replication complex formation. ToMV mutants that overcome this resistance have amino acid substitutions in the helicase domain of the replication proteins (ToMV-Hel). A small region of Tm-1 in the genome of the wild tomato Solanum habrochaites has been under positive selection during its antagonistic coevolution with ToMV. Here we report crystal structures for the N-terminal inhibitory domains of Tm-1 and a natural Tm-1 variant with an I91-to-T substitution that has a greater ability to inhibit ToMV RNA replication and their complexes with ToMV-Hel. Each complex contains a Tm-1 dimer and two ToMV-Hel monomers with the interfaces between Tm-1 and ToMV-Hel bridged by ATP. Residues in ToMV-Hel and Tm-1 involved in antagonistic coevolution are found at the interface. The structural differences between ToMV-Hel in its free form and in complex with Tm-1 suggest that Tm-1 affects nucleoside triphosphatase activity of ToMV-Hel, and this effect was confirmed experimentally. Molecular dynamics simulations of complexes formed by Tm-1 with ToMV-Hel variants showed how the amino acid changes in ToMV-Hel impair the interaction with Tm-1 to overcome the resistance. With these findings, together with the biochemical properties of the interactions between ToMV-Hel and Tm-1 variants and effects of the mutations in the polymorphic residues of Tm-1, an atomic view of a step-by-step coevolutionary arms race between a plant resistance protein and a viral protein emerges.

Role of parasite load and differential habitat preferences in maintaining the coexistence of sexual and asexual competitors in fish of theCobitis taeniahybrid complex

In the context of the paradoxical ubiquity of sex, we tested whether stable coexistence of sexual and asexual fish of the genus Cobitis is mediated by parasites, as asexual fish suffer more from parasitic infections because of their lower genetic variability [the Red Queen hypothesis (RQH)], or by partial niche shift of the two strains differing in mode of reproduction. We did not find a clear correlation between infection risk with a helminth parasite and the proportion of sexuals, and we found similar infection rates among sexual females and co-occurring asexuals in general, including the most frequent clone in particular. These results suggest that the mechanisms of the RQH are not directly engaged in stabilizing this asexual complex. On the other hand, the temporally stable gradient in sexual/asexual proportions along the river correlated with gradients in environmental parameters (physicochemical water parameters, velocity, and shading of the habitat) and turnover in the fish assemblage structure. Sexual and asexual forms thus appear to prefer different habitats. The Cobitis teania asexual complex thus contributes to the view that persistence of sex may, as in many taxa, be driven by case-specific processes.