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Networks of physiological adjustments and defenses, and their synergy with sodium (Na+) homeostasis explain the hidden variation for salinity tolerance across the cultivated Gossypium hirsutum germplasm

The abilities to mobilize and/or sequester excess ions within and outside the plant cell are important components of salt-tolerance mechanisms. Mobilization and sequestration of Na+ involves three transport systems facilitated by the plasma membrane H+/Na+ antiporter (SOS1), vacuolar H+/Na+ antiporter (NHX1), and Na+/K+ transporter in vascular tissues (HKT1). Many of these mechanisms are conserved across the plant kingdom. While Gossypium hirsutum (upland cotton) is significantly more salt-tolerant relative to other crops, the critical factors contributing to the phenotypic variation hidden across the germplasm have not been fully unraveled. In this study, the spatio-temporal patterns of Na+ accumulation along with other physiological and biochemical interactions were investigated at different severities of salinity across a meaningful genetic diversity panel across cultivated upland Gossypium. The aim was to define the importance of holistic or integrated effects relative to the direct effects of Na+ homeostasis mechanisms mediated by GhHKT1, GhSOS1, and GhNHX1. Multi-dimensional physio-morphometric attributes were investigated in a systems-level context using univariate and multivariate statistics, randomForest, and path analysis. Results showed that mobilized or sequestered Na+ contributes significantly to the baseline tolerance mechanisms. However, the observed variance in overall tolerance potential across a meaningful diversity panel were more significantly attributed to antioxidant capacity, maintenance of stomatal conductance, chlorophyll content, and divalent cation (Mg2+) contents other than Ca2+ through a complex interaction with Na+ homeostasis. The multi-tier macro-physiological, biochemical and molecular data generated in this study, and the networks of interactions uncovered strongly suggest that a complex physiological and biochemical synergy beyond the first-line-of defense (Na+ sequestration and mobilization) accounts for the total phenotypic variance across the primary germplasm of Gossypium hirsutum. These findings are consistent with the recently proposed Omnigenic Theory for quantitative traits and should contribute to a modern look at phenotypic selection for salt tolerance in cotton breeding.

Thermal tolerance and cardiac phenotypes

Adaptation to local environments involves the evolution of ecologically important traits and underlying physiological processes. Here, we used low coverage whole-genome resequencing (lcWGR) on individuals to identify genome regions involved in thermal adaptation in wild redband trout Oncorhynchus mykiss gairdneri, a subspecies of rainbow trout that inhabits ecosystems ranging from cold montane forests to high elevation deserts. This study includes allele frequency-based analyses for selective sweeps among populations, followed by multiple association tests for specific sets of phenotypes measured under thermal stress (acute and chronic survival/mortality; high or low cardiac performance groups). Depending on the groups in each set of analyses, sequencing reads covered between 43-75% of the genome at ≥15X and each analysis included millions of SNPs across the genome. In tests for selective sweeps among populations, a total of six chromosomal regions were significant. However, association tests for specific phenotypes revealed that the region on chromosome 4 was consistently the most significant and contains the cerk gene (ceramide kinase). This study provides insight into a potential genetic mechanism of local thermal adaptation and suggests cerk may be an important candidate gene. However, further validation of this cerk gene is necessary to determine if the association with cardiac performance results in a functional role to influence thermal performance when exposed to high water temperatures and hypoxic conditions.

Data from : Environmental predictability drives adaptive within- and transgenerational plasticity of heat tolerance across life stages and climatic regions

Although environmental variability and predictability have been proposed as the underlying ecological context in which transgenerational plasticity (TGP) arises, the adaptive significance and interaction with within-generation plasticity (WGP) in such scenarios is still poorly understood. In order to investigate these questions, we considered the tolerance to upper thermal limits of larvae and adults of the desert endemic Drosophila mojavensis adapted to different climatic regions (Desert vs Mediterranean climate). Thermal plasticity was investigated by acclimating parents and offspring at 36°C (versus at 25°C). We then used historical temperature variation data from both regions to perform individual-based simulations by modeling expected components of adaptive plasticity in multiple life stages. Thermal response to ramping heat shocks was more pronounced in larvae, where acclimation treatments in parents and offspring increased their heat-shock performance, while heat knockdown in adults was only increased by offspring acclimation of adults. The relative contribution of WGP and TGP was greater for the population from the more thermally variable Sonoran Desert. Similarly, individual-based simulations of evolving maternal effects indicated that variation in tolerance to upper thermal limits across life stages and climates is expected from its adaptive significance in response to environmental predictability. Our approach offers a new perspective and interpretation of adaptive plasticity, demonstrating that environmental predictability can drive thermal responses across generations and life stages in a scenario with regional climate variability.

Competition as a demolition derby: Why tolerating competitors is more important than suppressing them

Tolerance and suppression are distinct components of competition among plants, and recognizing how they affect competitive outcomes is important for understanding the mechanisms and consequences of competition. We used simulations informed by experimental trials to ask whether tolerance or suppression of competitors was more important for the survival of native plants experiencing competition with an exotic invasive species. When competition was pairwise, tolerance and suppression contributed equally to competitive rank in simulations. However, when multiple native genotypes competed together against an invader, the ability to tolerate competition was up to 50 times more important than the ability to suppress the invader. In two-competitor communities the chief advantage of suppressing competitors was a global decrease in their abundance, but this advantage did not exist in communities of multiple competitors—which is more representative of natural conditions —because decreased competitor abundance benefited all plants regardless of their competitive ability. We suggest that this concept is analogous to a 'demolition derby,' an automotive contest where participants attempt to have the last functional vehicle on the playing field. Because strong suppressors share the benefits of eliminating competitors with other remaining competitors, we propose that tolerance of competitors is more beneficial than suppression when competition occurs in a multiplayer scenario—in a demolition derby and in nature. This finding has implications for our understanding of how competition influences plant species coexistence, plant community structure, and invasion outcomes.

opencc-zeroNov 2020View details →

Metabolic cost of freeze-thaw and source of CO2 production in the freeze-tolerant cricket Gryllus veletis

Freeze-tolerant insects can survive the conversion of a substantial portion of their body water to ice. While the process of freezing induces active responses from some organisms, these responses appear absent from freeze-tolerant insects. Recovery from freezing likely requires energy expenditure to repair tissues and re-establish homeostasis, which should be evident as elevations in metabolic rate after thaw. We measured carbon dioxide (CO2) production in the spring field cricket (Gryllus veletis) as a proxy for metabolic rate during cooling, freezing and thawing and compared the metabolic costs associated with recovery from freezing and chilling. We hypothesized that freezing does not induce active responses, but that recovery from freeze-thaw is metabolically costly. We observed a burst of CO2release at the onset of freezing in all crickets that froze, including those killed by either cyanide or an insecticide (thiacloprid), implying that the source of this CO2was neither aerobic metabolism or a coordinated nervous system response. These results suggest that freezing does not induce active responses from G. veletis, but may liberate buffered CO2 from hemolymph. There was a transient 'overshoot' in CO2release during the first hour of recovery, and elevated metabolic rates at 24, 48 and 72 hours, in crickets that had been frozen compared to crickets that had been chilled (but not frozen). Thus, recovery from freeze-thaw and the repair of freeze-induced damage appears metabolically costly in G. veletis, and this cost persists for several days after thawing.

zenodo32/100

Echo-CGC: A Communication-Efficient Byzantine-tolerant Distributed Machine Learning Algorithm in Single-Hop Radio Network (video)

Full video presentation of the paper: Echo-CGC: A Communication-Efficient Byzantine-tolerant Distributed Machine Learning Algorithm in Single-Hop Radio Network. Appears in Session 2 of the 24th International Conference on Principles of Distributed Systems OPODIS 2020 <a href="https://opodis2020.unistra.fr">https://opodis2020.unistra.fr</a>

opencc-by-4.0Dec 2020View details →

opencc-zeroDec 2020View details →

Data from: Group-level variation in co-feeding tolerance between two sanctuary-housed communities of chimpanzees (Pan troglodytes)

Social tolerance in group-living animals can be viewed as a counterweight against competitive interests necessary to obtain coexistence equilibrium and maintain group cohesion. As such, it forms an interesting phenomenon to study at the group-level, but how can this be done most informatively? Here, we use three group-level co-feeding assays and social network analysis to study social tolerance in two groups of chimpanzees living under similar circumstances within a sanctuary to i) reassess whether social tolerance may be a group-specific parameter in chimpanzees and derive inferences about its long-term stability, and ii) compare the characteristics and resultant patterns between two established and one new assay. We show that the three assays expose the same (predicted) group-level differences in social tolerance as in the previous study eight years ago, thereby providing preliminary evidence for stability in group-specific levels of social tolerance in chimpanzees, despite changing group compositions. Furthermore, from an experimental point of view, we identify the new assay as more valid than the two established ones based on the consideration that resources may deplete at different rates across groups, which would consequently alter the need for tolerance differentially. We discuss implications for the study of social tolerance and highlight the importance of taking into account intraspecific variation in social animals.

opencc-zeroDec 2015View details →

Data from: Thermal plasticity in farmed, wild and hybrid Atlantic salmon during early development: has domestication caused divergence in low temperature tolerance?

Background: In the past three decades, millions of domesticated Atlantic salmon Salmo salar L. have escaped from farms into the wild. Their offspring display reduced survival in the natural environment, which demonstrates that gene-flow is likely to have a negative effect on wild populations. However, inter-population differences in introgression of farmed salmon have been observed, and the underlying ecological mechanisms remain enigmatic. We hypothesised that domestication-driven divergence in tolerance to low temperatures during early development may contribute to lower survival of farmed salmon offspring in the wild, which in turn, may influence patterns of introgression among populations exposed to different temperature regimes. We reared the offspring of 35 families of wild, farmed and hybrid origin at three temperatures (3.9, 5.6 and 12 °C) from the onset of exogenous feeding and throughout their first summer. Thermal reaction norms for growth and survival were investigated along the gradient. Results: The main results of this study, which is based upon the analysis of juvenile salmon from five wild strains, two farmed strains and two hybrid strains, can be summarised as; (i) salmon of all origins were able to successfully initiate feeding at all temperatures and similar survival reaction norms were detected in all strains across the temperature gradient; (ii) deviating growth reaction norms were detected between strains, although this result was most likely due to an overall lack of growth in the lower temperature treatments. Conclusions: This study revealed no evidence of domesticated-driven divergence in low temperature tolerance in Atlantic salmon during early development. Although the potential interaction between low temperature and other river-specific factors cannot be excluded, our results indicate that the reduced survival of farmed offspring in the wild is not explained by farmed salmon displaying impaired abilities to initiate feeding at low temperatures. We therefore suggest that the observed inter-population patterns of introgression are not low-temperature driven and that other ecological or biological factors may explain why detection of farmed salmon in wild rivers is not synonymous with introgression. In general, our results support the literature indicating that phenotypic plasticity instead of thermal adaption has been selected for in Atlantic salmon.

opencc-zeroDec 2010View details →

Data from: What makes a leaf tough? Patterns of correlated evolution between leaf toughness traits and demographic rates among 197 shade-tolerant woody species in a neotropical forest

Slow-growing juveniles of shade-tolerant plant species are predicted to have tough leaves because of the high cost of leaf replacement in shade relative to potential carbon gain. We assessed the degree of correlated evolution among eight traits associated with leaf toughness and their relationships with growth and mortality rates of 197 tree and shrub species from the understory of the 50-hectare forest dynamics plot on Barro Colorado Island, Panama. Path analysis with phylogenetically independent contrasts revealed that leaves attained material toughness (resistance to fracture per unit fracture area) through increases in tissue density, percent cellulose per unit dry mass, and vein fracture toughness. Lamina density and cellulose content evolved independently, and thus represent different paths to material toughness. Structural toughness (resistance to fracture per unit fracture length) depended on material toughness and lamina thickness. Mortality rates of individuals 1-10 cm in stem diameter were negatively correlated with material toughness and lamina density, but were independent of structural toughness and cell wall fiber contents. Leaf toughness traits were uncorrelated with relative growth rates. These results imply that material toughness enhances resistance to natural enemies, which increases survival and offsets the biomass allocation cost of producing tough leaves in the shaded understory.

Data from: GlobTherm, a global database on thermal tolerances for aquatic and terrestrial organisms

How climate affects species distributions is a longstanding question receiving renewed interest owing to the need to predict the impacts of global warming on biodiversity. Is climate change forcing species to live near their critical thermal limits? Are these limits likely to change through natural selection? These and other important questions can be addressed with models relating geographical distributions of species with climate data, but inferences made with these models are highly contingent on non-climatic factors such as biotic interactions. Improved understanding of climate change effects on species will require extensive analysis of thermal physiological traits, but such data are scarce and scattered. To overcome current limitations, we created the GlobTherm database. The database contains experimentally derived species' thermal tolerance data currently comprising over 2,000 species of terrestrial, freshwater, intertidal and marine multicellular algae, pl ants, fungi, and animals. The GlobTherm database will be maintained and curated by iDiv with the aim of expanding it, and enable further investigations on the effects of climate on the distribution of life on Earth.

Data from: The interaction of exposure and warming tolerance determines fish species vulnerability to warming stream temperatures

Species vulnerability to climate change involves an interaction between the magnitude of change (exposure) and a species' tolerance to change. We evaluated fish species vulnerability to predicted stream temperature increases by examining warming tolerances across the Wyoming fish assemblage. Warming tolerance combines stream temperature with a thermal tolerance metric to estimate how much warming beyond current conditions a species can withstand. Brown trout, rainbow trout, and burbot had the lowest warming tolerances and highest proportion of currently occupied sites that will become unsuitable under predicted temperature increases. These most vulnerable species were coldwater species, but had neither the lowest thermal tolerances, nor would they experience the greatest temperature increases. Our results highlight the importance of considering the interaction of exposure and warming tolerance when predicting climate change vulnerability and demonstrate an approach that can be applied broadly.

opencc-zeroNov 2019View details →

Data from: Rain shadow effects predict population differences in thermal tolerance of leaf-cutting ant workers (Atta cephalotes)

Tests of hypotheses for the evolution of thermal physiology often rely on mean temperatures, but mounting evidence suggests geographic variation in temperature extremes is also an important predictor of species' thermal tolerances. Although the tropics are less thermally variable than higher latitude regions, rain shadows on the leeward sides of mountains can experience greater diel and seasonal variation in temperature than windward sites. Rain shadows provide opportunities to test predictions about the relationships of extreme temperatures with thermal physiology while controlling for latitude. We tested the hypothesis that populations of leaf-cutting ants (Atta cephalotes) in leeward, montane, and windward sites in Costa Rica would differ in upper thermal tolerances (CTmax) of workers. As predicted from rain shadow effects via extreme high temperatures, the leeward rain-shadow site yielded the highest mean CTmax (rain shadow site 42.1±0.3 °C, Montane site 38.2±0.5 °C, windward site 38.2±0.3 °C). This suggests that high-temperature extremes in tropical rain shadow forests can select for higher thermal tolerances. CTmax increased with worker body size within sites, but CTmax increased with body size more gradually at the two lowland sites, as predicted if local high temperatures selected more strongly on the most thermally vulnerable society members (small workers). This suggests that warmer lowland climates selected for colonies with less variation in heat tolerance than cooler high elevation climates.

opencc-zeroDec 2013View details →

Data from: Genetic variation in resistance and fecundity tolerance in a natural host-pathogen interaction

Individuals vary in their ability to defend against pathogens. Determining how natural selection maintains this variation is often difficult, in part because there are multiple ways that organisms defend themselves against pathogens. One important distinction is between mechanisms of resistance that fight off infection, and mechanisms of tolerance that limit the impact of infection on host fitness without influencing pathogen growth. Theory predicts variation among genotypes in resistance, but not necessarily in tolerance. Here, we study variation among pea aphid (Acyrthosiphon pisum) genotypes in defense against the fungal pathogen Pandora neoaphidis. It has been well established that pea aphids can harbor symbiotic bacteria that protect them from fungal pathogens. However, it is unclear whether aphid genotypes vary in defense against Pandora in the absence of protective symbionts. We therefore measured resistance and tolerance to fungal infection in aphid lines collected without symbionts, and found variation among lines in survival and in the percent of individuals that formed a sporulating cadaver. We also found evidence of variation in tolerance to the effects of pathogen infection on host fecundity, but no variation in tolerance of pathogen-induced mortality. We discuss these findings in light of theoretical predictions about host-pathogen coevolution.

Data from: Broad thermal tolerance is negatively correlated with virulence in an opportunistic bacterial pathogen

Predicting the effects of global increase in temperatures on disease virulence is challenging, especially for environmental opportunistic bacteria, because pathogen fitness may be differentially affected by temperature within and outside host environment. So far, there is very little empirical evidence on the connections between optimal temperature range and virulence in environmentally growing pathogens. Here we explored if the virulence of an environmentally growing opportunistic fish pathogen, Flavobacterium columnare, is malleable to evolutionary changes via correlated selection on thermal tolerance. To this end, we experimentally quantified the thermal performance curves (TPCs) for maximum biomass of 49 F. columnare isolates from eight different geographic locations in Finland over ten years (2003-2012). We also characterized virulence profiles of these strains in a zebra-fish (Danio rerio) infection model. We show that virulence among the strains increased over the years, but tolerance to higher temperatures was negatively associated with virulence. Our data suggest that temperature has a strong effect on the pathogen genetic diversity, and therefore presumably also on disease dynamics. However, the observed increase in frequency and severity of F. columnare epidemics over the last decade cannot be directly linked to bacterial evolution due to increased mean temperature, but is most likely associated with factors related to increased length of growing season, or other time dependent change in environment. Our study demonstrates that complex interactions between the host, the pathogen and the environment influence disease virulence of environmentally growing opportunistic pathogen.

opencc-zeroDec 2014View details →

Data from: Heat tolerance in Drosophila subobscura along a latitudinal gradient: contrasting patterns between plastic and genetic responses

Susceptibility to global warming relies on how thermal tolerances respond to increasing temperatures through plasticity or evolution. Climatic adaptation can be assessed examining the geographic variation in thermal-related traits. We studied latitudinal patterns in heat tolerance in Drosophila subobscura reared at two temperatures. We used four static stressful temperatures to estimate the thermal death time curves (TDT), and two ramping assays with fast and slow heating rates. TDT curves allow estimating the critical thermal maximum CTmax, by extrapolating to the temperature that would knockdown the flies almost 'instantaneously', and the thermal sensitivity to increasing stressful temperatures. We found a positive latitudinal cline for CTmax, but no clinal pattern for knockdown temperatures estimated from the ramping assays. Although high-latitude populations were more tolerant to an acute heat stress, they were also more sensitive to prolonged exposure to less stressful temperatures, supporting a trade-off between acute and chronic heat tolerances. Conversely, developmental plasticity did not affect CTmax but increased the tolerance to chronic heat exposition. The patterns observed from the TDT curves help to understand why the relationship between heat tolerance and latitude depends on the methodology used and, therefore, these curves provide a more complete and reliable measurement of heat tolerance.

opencc-zeroDec 2013View details →

Data from: Adaptive phenotypic plasticity and local adaptation for temperature tolerance in freshwater zooplankton

Many organisms have geographical distributions extending from the tropics to near polar regions or can experience up to 30°C temperature variation within the lifespan of an individual. Two forms of evolutionary adaptation to such wide ranges in ambient temperatures are frequently discussed: local adaptation and phenotypic plasticity. The freshwater planktonic crustacean Daphnia magna, whose range extends from South Africa to near arctic sites, shows strong phenotypic and genotypic variation in response to temperature. In this study, we use D. magna clones from 22 populations (one clone per population) ranging from latitude 0° (Kenya) to 66° North (White Sea) to explore the contributions of phenotypic plasticity and local adaptation to high temperature tolerance. Temperature tolerance was studied as knockout time (time until immobilization, Timm) at 37°C in clones acclimatized to either 20°C or 28°C. Acclimatization to 28°C strongly increased Timm, testifying to adaptive phenotypic plasticity. At the same time, Timm significantly correlated with average high temperature at the clones' sites of origin, suggesting local adaptation. As earlier studies have found that haemoglobin expression contributes to temperature tolerance, we also quantified haemoglobin concentration in experimental animals and found that both acclimatization temperature (AccT) and temperature at the site of origin are positively correlated with haemoglobin concentration. Furthermore, Daphnia from warmer climates upregulate haemoglobin much more strongly in response to AccT, suggesting local adaptation for plasticity in haemoglobin expression. Our results show that both local adaptation and phenotypic plasticity contribute to temperature tolerance, and elucidate a possible role of haemoglobin in mediating these effects that differs along a cold–warm gradient.

Data from: Cardiac plasticity influences aerobic performance and thermal tolerance in a tropical, freshwater fish at elevated temperatures

Fishes faced with novel thermal conditions often modify physiological functioning to compensate for elevated temperatures. This physiological plasticity (thermal acclimation) has been shown to improve metabolic performance and extend thermal limits in many species. Adjustments in cardiorespiratory function are often invoked as mechanisms underlying thermal plasticity because limitations in oxygen supply have been predicted to define thermal optima in fishes, however few studies have explicitly linked cardiorespiratory plasticity to metabolic compensation. Here we quantify thermal acclimation capacity in the commercially harvested Nile perch (Lates niloticus) of East Africa, and investigate mechanisms underlying observed changes. We reared juvenile Nile perch for 3 months under two temperature regimes, and then measured a series of metabolic traits (e.g., aerobic scope, AS) and critical thermal maximum (CTmax) upon acute exposure to a range of experimental temperatures. We also measured morphological traits of heart ventricles, gills, and brains to identify potential mechanisms for compensation. We found that long-term (3-months) exposure to elevated temperature induced compensation in upper thermal tolerance (CTmax) and metabolic performance (SMR, MMR and AS), and induced cardiac remodeling in Nile perch. Furthermore, variation in heart morphology influenced variations in metabolic function and thermal tolerance. These results indicate that plastic changes enacted over longer exposures lead to differences in metabolic flexibility when acutely exposed to temperature variation. Furthermore, we established functional links between cardiac plasticity, metabolic performance, and thermal tolerance, providing evidence that plasticity in cardiac capacity may be one mechanism for coping with climate change.

opencc-zeroDec 2013View details →

Data from: Ecologically differentiated, stress tolerant endosymbionts in the dinoflagellate genus Symbiodinium (Dinophyceae) Clade D are different species.

We used an integrative genetics approach using sequences of (1) nuclear ribosomal rDNA (internal transcribed spacers and partial large subunit rDNA), (2) single-copy microsatellite nuclear DNA, (3) chloroplast-encoded 23S rDNA, (4) mitochondrial cytochrome b, and (5) repeat variation at eight microsatellite markers, to test the hypothesis that the stress-tolerant, 'morphologically cryptic' Clade D Symbiodinium (Dinophyceae) was composed of more than one species. Concordant phylogenetic and population genetic evidence clearly differentiate separately evolving, reproductively isolated lineages. We describe Symbiodinium boreum sp. nov. and S. eurythalpos sp. nov., two symbionts known to occur in colonies of the zebra coral, Oulastrea crispata (Scleractinia), which lives in turbid, marginal habitats extending from equatorial Southeast Asia to the main islands of Japan in the temperate northwest Pacific Ocean. Symbiodinium boreum was associated with O. crispata in temperate latitudes and S. eurythalpos was common to colonies in the tropics. The geographical ranges of both symbiont species overlapped in the subtropics where they sometimes co-occurred in the same host colony. Symbiodinium trenchii sp. nov. is also described. As a host-generalist symbiont, it often occurs in symbiosis with various species of Scleractinia possessing open (horizontal) modes of symbiont acquisition and is common to reef coral communities thriving in warm turbid reef habitats in the western Pacific Ocean, Indian Ocean, Arabian/Persian Gulf, Red Sea and western Atlantic (Caribbean). As is typical for dinoflagellates, S. boreum and S. eurythalpos were haploid, but microsatellite loci from field-collected and cultured S. trenchii often possessed two alleles, implying that a genome-wide duplication occurred during the evolution of this species. The recognition that Clade D Symbiodinium contains species exhibiting marked differences in host specificity and geographical distribution will yield greater scientific clarity about how stress-tolerant symbionts function in the ecological response of coral–dinoflagellate symbioses to global climate change.

opencc-zeroDec 2016View details →

Data from: Intra- and intersexual differences in parasite resistance and female fitness tolerance in a polymorphic insect

To understand host–parasite interactions, it is necessary to quantify variation and covariation in defence traits. We quantified parasite resistance and fitness tolerance of a polymorphic damselfly (Ischnura elegans), an insect with three discrete female colour morphs but with monomorphic males. We quantified sex and morph differences in parasite resistance (prevalence and intensity of water mite infections) and morph-specific fitness tolerance in the females in natural populations for over a decade. There was no evidence for higher parasite susceptibility in males as a cost of sexual selection, whereas differences in defence mechanisms between female morphs are consistent with correlational selection operating on combinations of parasite resistance and tolerance. We suggest that tolerance differences between female morphs interact with frequency-dependent sexual conflict, which maintains the polymorphism locally. Host–parasite interactions can therefore shape intra- and intersexual phenotypic divergence and interfere with sexual selection and sexual conflict.