GENETIC VARIANCE FOR RATE OF POPULATION INCREASE IN NATURAL POPULATIONS OF FLOUR BEETLES,TRIBOLIUM SPP.

The genetic and ecological effects of population subdividsion were investigated for two wild strains of Tribolium castaneum and two wild strains of T. confusum and compared with the effects of population subdivision on the synthetic laboratory strain of T. castaneum (c-SM), used extensively in earlier experiments. For the c-SM strain, it has been shown repeatedly, for a variety of different population structures (different combinations of effective numbers, N_e, and migration rates, m), that large heritable differences in population growth rate arise among demes during 10 to 15 generations of population subdivision. Because this laboratory strain was synthesized by mass mating several “inbred” strains in 1973 (80 to 100 generations ago), it is possible that it has genetic variation for fitness (measured as the heritable variance among demes in the rate of population increase) unusually large compared to natural populations of flour beetles. In this paper, I report that natural populations of flour beetle exhibit as much or more phenotypic and genetic variation in the effects of population structure on fitness than the laboratory strain, c-SM. The observation of substantial heritable variation for fitness in natural populations is unexpected under additive theory and may be indicative of nonadditive genetic variance.     

An Experimental Test of the Relationship between Genetic Variation and Environmental Variation in Tribolium Flour Beetles

The hypothesis that a component of genetic variation for polygenic fitness traits is maintained by environmental heterogeneity was tested using an experimental system involving two species of flour beetles, Tribolium castaneum and T. confusum. Replicated populations of each species from a number of environmental treatments were analyzed for various fitness components following almost 60 generations of natural selection. Environmental differences consisted of flours of cereals commonly invaded by natural populations of these insects.—Tests for adaptation to environments were based on experiments in which populations were reared factorially on each flour, such that population treatment x flour interactions could be detected. Measurements were made of survival, growth rate, larval weight, pupal weight, developmental time, fecundity of individuals at low density and fecundity and cannibalism at high density in both fresh and conditioned media.—Flour differences were found to have significant effects on most traits. Evidence for significant genetic variation and significant genotype x environment interaction was also found. However, no evidence could be found to support the hypothesis that genetic variation was maintained by environmental heterogeneity in food resources. The absence of adaptation to the experimental treatments despite the presence of genetic variation in fitness components suggests that pleiotropy may assume an important role in determining net fitness values of polygenes.     

Potential of the neonicotinoid imidacloprid and the oxadiazine indoxacarb for controlling five coleopteran pests of stored grain

Abstract The potential for using imidacloprid (a neonicotinoid) and indoxacarb (an oxadiazine) as grain protectants was investigated in bioassays against resistant strains of five stored grain beetles. The species investigated were Rhyzopertha dominica (F.) (the lesser grain borer), Sitophilus oryzae (L.) (the rice weevil), Tribolium castaneum (Herbst) (the rust‐red flour beetle), Oryzaephilus surinamensis (L.) (the saw tooth flour beetle), and Cryptolestes ferrugineus (Stephens) (the flat grain beetle). Each of these species has developed resistance to one or more protectants, including organophosphorus insecticides, synthetic pyrethroids and the juvenile hormone analogue methoprene. Mortality and reproduction after a 2‐week exposure of adults to treated wheat depended on species, dose and insecticide. Imidacloprid had no effect on S. oryzae at any dose, but none of the other species produced any live progeny at 10 mg/kg. Indoxacarb had no effect on T. castaneum at any dose, but none of the other species produced any live progeny at 5 mg/kg. The results show that although both imidacloprid and indoxacarb can control at least four of the five key pests tested at doses comparable to those used for organophosphorus protectants, more potent neonicotinoid or oxadiazine insecticides would be needed than either of these to provide broad spectrum protection of stored grain.     

GENOTYPE-ENVIRONMENT INTERACTION FOR CLIMATE AND COMPETITION IN A NATURAL POPULATION OF FLOUR BEETLES,TRIBOLIUM CASTANEUM

The norm of reaction, the set of average phenotypes produced by a genotype in different environments, can be affected by spatial variation in natural selection especially when there exists genotype-environment interaction. In subdivided populations, the greater the genotype-environment interaction variance and the lower the migration rate, the more independent are the possible evolutionary trajectories for local adaptation. I examined genotype-environment interaction in the rate of population increase for lineages randomly derived from a wild population of Tribolium castaneum across a series of ecologically important environments. The lineages were derived from an outbred, wild-caught population by 14 generations of random genetic drift, during which the effective size of each lineage was approximately 22 breeding adults. The environments studied were the classic temperate-wet and cold-dry climates of Park (1954) in factorial combination with two genetic strains of a congeneric competitor, T. confusum. Much among-lineage genetic variation for rate of population increase was found for each of these ecologically important environments of climate and competition. Genotype-environment interaction accounted for 40.5% of the total among-lineage variance in rate of population increase signifying that the performance of a lineage in one environment is not necessarily a good predictor of its performance in another. Changing the genetic identity of the competitor changed the rate of increase of some lineages as much or more than changing the climatic conditions of temperature and humidity. This is the first empirical study to characterize the genotype-environment interaction variance associated with genetic variation in a competing congeneric species. This competitor-specific genetic variation in competitive ability may play an important role in coevolution in subdivided populations.     

Living in a jar: genetic variation and differentiation among laboratory strains of the red flour beetle

The red flour beetle, Tribolium castaneum, is a common pest, which has become an important model study organism, especially in genetic, ecological and evolutionary research. Although almost all studies on this species have been conducted using established laboratory strains, very little is known about the loss of genetic diversity within the strains and genetic divergence between different laboratory stocks. In this study, five long‐term laboratory strains and one wild strain were examined for genetic variation at 12 microsatellite loci, which were designed using publicly available sequences. One of the laboratory strains is resistant to phosphine and one to organophosphorous insecticides. All strains had significant amounts of molecular variation, but genetic diversity in the laboratory strains was lower than in the wild‐derived strain used as control. We observed significant molecular divergence among the strains, however, the relationship between them reflected resistance status rather than geographic origins. We found no evidence for recent bottlenecks, but the wild‐derived population showed signs of demographic expansion. A novel multivariate method, multiple co‐inertia analysis, revealed that the two loci contributing most to the divergence between the resistant strains were located on the eighth chromosome, near genes associated with insecticide resistance.     

Response of Tribolium castaneum and Rhyzopertha dominica to various resources,near and far from grain storage

Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.) are common cosmopolitan pests of stored grain and grain products. We evaluated the relative attraction of T. castaneum and R. dominica to wheat, sorghum and cotton seeds in the field, near grain storage facilities and well away from storages in southern and central Queensland using multiple trapping techniques. The results show that T. castaneum is more strongly attracted to linted cotton seed relative to wheat, whereas R. dominica did not respond to cotton seed at all and was attracted only to wheat. Significantly more adults of T. castaneum (10–15 times) were attracted to traps placed on the ground, near grain storage, than to equivalent traps that were suspended (1.5 m above the ground) nearby. These results suggest that Tribolium beetles detect and respond to resources towards the end of their dispersal flight, after which they localize resources while walking. By contrast R. dominica was captured only in suspended traps, which suggests they fly directly onto resources as they localize them. The ability of both species to colonize and reproduce in isolated resource patches within the relatively short time of 1 month is illustrated by the returns from the traps deployed in the field (at least 1 km from the nearest stored grain) even though they caught only a few beetles. The results presented here provide novel insights about the resource location behaviours of both T. castaneum and R. dominica. In particular, the relationship of T. castaneum with non‐cereal resources that are not conventionally associated with this species suggests an emphasis on these other resources in investigating the resource location behaviour of these beetles. This new perspective on the ecology of T. castaneum highlights the potential role of non‐cereal resources (such as the lint on cotton seed) in the spread of grain pest infestations.     

Susceptibility of laboratory and field strains of four stored-product insect species to spinosad

Two field strains of the Indianmeal moth, Plodia interpunctella (Hübner); red flour beetle, Tribolium castaneum (Herbst); and lesser grain borer, Rhyzopertha dominica (F.), and one field strain of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), were collected from hard red winter wheat stored on farms in northeastern Kansas. Fifty eggs of P. interpunctella and 25 beetle adults of each species were exposed to 100 g of untreated wheat or wheat treated with various rates of spinosad, to determine susceptibility of the field and corresponding insecticide-susceptible laboratory strains. Mortality of beetle adults and P. interpunctella larvae was assessed after 7 and 21 d postinfestation, respectively. Field strains of P. interpunctella, C. ferrugineus, and T. castaneum were less susceptible to spinosad than the corresponding laboratory strains. The LD50 and LD95 values for P. interpunctella and C. ferrugineus field strains were 1.7-2.5 times greater than values for corresponding laboratory strains. Adults of both laboratory and field strains of T. castaneum were tolerant to spinosad, resulting in <88% mortality at 8 mg/kg. The LD50 and LD95 values for the field strains of T. castaneum were 2.0-7.5 times greater compared with similar values for the laboratory strain. The field and laboratory strains of R. dominica were highly susceptible to spinosad, and one of the field strains was relatively less susceptible to spinosad than the laboratory strain. Our results confirm a range of biological variability in field populations, which is consistent with findings for other compounds, and underscores the need to adopt resistance management programs with stored grain insect pests. The baseline data generated on the susceptibility of the four insect species to spinosad will be useful for monitoring resistance development and for setting field rates.     

Identification of microsatellite markers in the red flour beetle,Tribolium castaneum

We isolated and characterized microsatellite markers for the red flour beetle Tribolium castaneum, an important model species for studies in various areas of evolutionary biology and ecology. A microsatellite‐enriched genomic library was constructed and screened with single stranded oligonucleotide probes [(CCT)₁₇, (AAT)₁₇ and (CAG)₁₇]. Forty‐five primer pairs were designed of which 19 pairs produced successful amplification. Polymorphism screening involved beetles from five beetle strains and revealed 15 polymorphic and four monomorphic markers. The development of polymorphic microsatellite markers will facilitate future ecological and genetic studies involving T. castaneum beetles.     

The process of adaptation of flour beetles to new environments

Five populations derived from a composite, genetically heterogeneous strain of the flour beetle, Tribolium castaneum, were selected on new diets (dog food, powdered rice, brewers' yeast, wheat flour and oats) for 13–16 generations. A control population was reared on the standard medium (flour + 5% brewers' yeast). Adaptedness was measured in terms of (1) fitness parameters (survival and developmental time), (2) amylase activity levels (amylase is an essential digestive enzyme in flour beetles) and (3) food preference behavior.There were significant temporal trends in fitness components in the selected populations. Survival was initially low but increased with time. Developmental time decreased in later generations of selection. The control population showed the smallest increase in survival and no decrease in developmental time. When tested at the end of the experiment, survival to adulthood of eggs from each selected population on its selective diet was higher than that of control eggs. On the standard medium, no differences in survival among populations were detected. These results suggest that the improvement in fitness may indicate adaptation to the new environments created by the different food media.Amylase activity also increased temporally in 4 selected populations but not in the control (nor on unenriched wheat flour). Tests at the end of the experiment, however, suggest that this increase was, in large part, environmentally induced. We found no evidence that an adaptive genetic change in amylase regulation took place.There were no temporal trends in food-preference behavior during the selection process.     

The dietary relationships of Tribolium castaneum (Herbst) with microfungi

The ecology of Tribolium castaneum (Herbst) outside of grain storage facilities is poorly known. However, high densities of T. castaneum adults are known to infest stored cotton seeds (Gossypium hirsutum (L.)) in Queensland, Australia, despite the absence of stored food products in the immediate vicinity. Previous studies suggest that the beetles are attracted to the fungal colonies growing on the residual fibres that remain on the cotton seeds after ginning, but the specifics of this remain unclear, even as to the species of fungi involved. In the current study, 14 fungal species were isolated from stored cotton seeds collected from four sites in Queensland. The feeding preferences of the adult beetles and the developmental success of the larvae were recorded for each fungal species. Gut analyses of T. castaneum adults, after exposure in no-choice feeding tests, showed that the beetles will feed on any one of the 14 fungal species when exposed (over 14 days) to cotton seeds that had been inoculated with one particular fungal species. The developmental success of the larvae varied depending on the fungal species, with most fungal species supporting only low levels of successful development (<30%). Tests with each fungal species and the volatiles they release revealed that neither adult nor larval survival was significantly affected by the presence of any particular fungal isolate. These results indicate that T. castaneum will feed on a variety of fungal species but that none of the tested fungal species on its own provides a good larval diet for T. castaneum.     

Dietary niche and population dynamic feedbacks in a novel habitat

Population dynamics and resource use are often intricately connected via density‐dependent intraspecific competition. However, experimental studies of concurrent change in population and resource use dynamics are scarce. In particular, the impact of factors such as genetic diversity, which can affect both population dynamics and competition, remains unexplored. Using stable isotope analysis and periodic population censuses, we quantified both diet and population dynamics in wheat‐adapted Tribolium castaneum (flour beetle) populations provided with an additional novel resource (corn). Populations were initiated with different levels of genetic variation for traits relevant to population growth and resource use (e.g. fecundity and survival).We found that high population size decreased subsequent corn use, and high corn use in turn lowered population size. Surprisingly, we did not detect a significant effect of founding genetic variation on resource niche expansion, although genetic variation increased overall population size and stability. In contrast, dietary niche expansion decreased both population size and stability. Finally, larval and adult niche dynamics were uncorrelated, suggesting that various life stages perceive or respond differentially to intraspecific competition and resource availability. Our experiments indicate that population performance in a novel habitat depends on stage‐specific interactions between resource use, standing genetic variation, and population size.     

Dietary Effects on Fitness Components at the PGM-1 Locus of TRIBOLIUM CASTANEUM

The pattern of genetic differentiation among experimental populations of the flour beetle Tribolium castaneum suggested the hypothesis that relative fitness of three genotypes at the PGM-1 locus (or other linked loci) depends directly on diet. This hypothesis was tested by measuring several fitness components (developmental time, survival, fecundity, rate of egg cannibalism) on groups of individuals differing at the PGM-1 locus that were reared on three types of flour (wheat, corn and a mixture of wheat, corn, barley and rye). Flour type had large effects on all traits except larval survival to 3 weeks of age. Relative fitnesses of the three genotypes differed significantly for fecundity. Diet was found to significantly influence the relative developmental times of the three genotypes.     

TEMPERATURE EFFECTS AND GENOTYPE-BY-ENVIRONMENT INTERACTIONS IN HYBRIDS: HALDANE'S RULE IN FLOUR BEETLES

When males of the flour beetle, Tribolium castaneum, are crossed to females of its close relative T. freemani, the sex ratio of the hybrids is female biased, owing in part to hybrid male mortality. Morphological abnormalities are also frequent in the surviving hybrid males, but not in the hybrid females. The finding that the heterogametic sex (male) is more adversely affected in interspecific crosses than the homogametic sex is consistent with Haldane's rule, which predicts that hybrid dysfunction should emerge as an indirect byproduct of divergent adaptation to differing environments. If so, environmental effects and genotype-by-environment interactions (GEI) should characterize the expression of Haldane's rule and interspecific hybrid traits in general. We used two wild-collected populations of T. castaneum (from Infantes, Spain, and Madagascar) to investigate the effects of environmental variation on the expression of Haldane's rule. Males from each population were mated to several T. freemani females and the half-sibling hybrid progenies were reared across a series of temperature regimes. For both populations, we found that hybrids raised at higher temperatures exhibited a more extreme expression of Haldane's rule: The hybrid sex ratios were more biased toward females and hybrid males had a much higher incidence of morphological abnormalities. The average response to temperature, the norm of reaction for Haldane's rule, varied between the two populations, and we found considerable and significant GEI for both hybrid traits within both populations. The evolutionary implications of these findings are discussed in the context of speciation arising as an indirect effect of local adaptation.     

Concentration of ergosterol in small-grained naturally contaminated and inoculated cereals

Ergosterol (ERG) is a major sterol constituent of most fungi. Its concentration is negligible in higher plants, but can be used as a chemical marker of the presence of fungal contaminations. In this study, ERG concentration was assessed in randomly collected samples of naturally contaminated grain (wheat, barley and oat) and in samples of grain (wheat, barley, triticale and oat) harvested after inoculation of heads with conidia of different Fusarium species. Wheat samples were analysed at three stages of grain development. The lowest ERG concentration was found in non-inoculated samples at the first stage of grain development. This concentration was increasing with grain ripening. In naturally contaminated samples collected after harvest, ERG concentration was lower in wheat than in barley and oat. ERG concentrations in inoculated samples varied significantly, but were always significantly higher than in naturally contaminated samples. In the above cereal samples it was much lower than the levels assayed in laboratory cultures inoculated with fungi from genus Fusarium. The content of ERG was also analyzed in milling products of small-grained cereals and other foodstuffs, where a considerable variation was observed. The lowest ERG amounts were assayed in flours with a high degree of purification, while the highest ones in case of flours and products with a low purification rate. The results indicate the potential application of HPLC combined with microwave-assisted extraction both when assaying samples with low ERG concentrations (naturally contaminated) and those characterized with high contents of fungal biomass (strongly infected, artificially inoculated). It also facilitates analyses of fungal biomass in technological processes, where results may be expected to vary considerably.     

Influence of processing and substrate variety on survival and development of Tribolium confusum (Coleoptera: Tenebrionidae)

Tribolium confusum is a major pest of grains and grain products. Some legumes hitherto not used as major food are gaining interest due to increase in human population and the need of food and feeds. Susceptibility of fresh and processed Glycine max and Cajanus cajan flours, and white wheat flour (control) to T. confusum was studied towards effective storage techniques and cheap insect diet. Ten copulating pairs of the beetle were introduced into twenty grams of each flour. Number of eggs laid, emerged larvae, pupae, eclosed adults, and duration of development of each stage was used as indices of survival of T. confusum. Proximate composition, saponin; and α-amylase and protease inhibitors determined suitability of flours as insect diet. This work discusses the significance of proximate composition and anti-nutrient properties in fresh and roasted processed flours on the development and survival of T. confusum.     

An unusual barrier to gene flow: perpetually immature larvae from inter-population crosses in the flour beetle, Tribolium castaneum

We genetically characterize an unusual hybrid incompatibility phenotype manifest in F₁ offspring of crosses between two populations of Tribolium castaneum. Hybrid larvae cease development at the third larval instar, persisting as ‘perpetually immature larvae’ thereafter. Although unable to produce viable adult hybrid offspring with one another, each population produces abundant, fertile hybrids with other populations, indicating a recent origin of the incompatibility and facilitating genetic studies. We mapped the paternal component of the hybrid phenotype to a single region, which exhibits two characteristics common to hybrid incompatibility: marker transmission ratio distortion within crosses and elevated genetic divergence between populations. The incompatible variation and an elevation in between‐population genetic divergence is associated with a region containing the T. castaneum ecdysone receptor homologue, a major regulatory switch, controlling larval moults, pupation and metamorphosis. This contributes to understanding the genetics of speciation in the Coleoptera, one of the most speciose of all arthropod taxa.     

Productivity modifications to flour beetles (Coleoptera: Tenebrionidae) by gamma radiation (60Co) of one or both sexes and by the addition of radiated males or females to population

The effects on productivity by the addition of various numbers of radiated adult males or females to populations of two densities were determined for two species of flour beetles. Modifications in productivity after exposure to gamma radiation from⁶⁰Co included:

1. females of T. confusum were sterilized by an exposure between 2620 to 5230 R.
2. females of T. castaneum were not sterilized by 10, 200 R.
3. males were not sterilized by 10, 200 R.
4. sterile females may serve as depositories for normal sperm thereby reducing the productivity. Addition of such females to populations of flour beetles did not reduce the numbers of progeny.
5. since sterile females did not suppress population development, and since they destroy grain and cereal products, they should be eliminated from control programs featuring the sterile insect release technique.
6. population density decreased the numbers of progeny.

The use of the sterile insect release technique to control insects of stored grain products does not seem likely with present day sanitary standards since large numbers of insects need be added to effect control.     

Larval RNA Interference in the Red Flour Beetle,Tribolium castaneum

The red flour beetle, Tribolium castaneum, offers a repertoire of experimental tools for genetic and developmental studies, including a fully annotated genome sequence, transposon-based transgenesis, and effective RNA interference (RNAi). Among these advantages, RNAi-based gene knockdown techniques are at the core of Tribolium research. T. castaneum show a robust systemic RNAi response, making it possible to perform RNAi at any life stage by simply injecting double-stranded RNA (dsRNA) into the beetle’s body cavity.In this report, we provide an overview of our larval RNAi technique in T. castaneum. The protocol includes (i) isolation of the proper stage of T. castaneum larvae for injection, (ii) preparation for the injection setting, and (iii) dsRNA injection. Larval RNAi is a simple, but powerful technique that provides us with quick access to loss-of-function phenotypes, including multiple gene knockdown phenotypes as well as a series of hypomorphic phenotypes. Since virtually all T. castaneum tissues are susceptible to extracellular dsRNA, the larval RNAi technique allows researchers to study a wide variety of tissues in diverse contexts, including the genetic basis of organismal responses to the outside environment. In addition, the simplicity of this technique stimulates more student involvement in research, making T. castaneum an ideal genetic system for use in a classroom setting.     

Effect of synthetic B-vitamin and natural enrichment of flour on larval development and fecundity of Tribolium confusum and T. castaneum

Larval developmental time and adult fecundity of the flour beetles Tribolium confusum and T. castaneum were measured on twelve different diets: top patent fluor; top patent flour enriched with riboflavin, thiamine and niacin, singly or in combinations; top patent flour mixed with bran, germ or both; and whole wheat flour.Larval mortality did not exceed 5% on any of the diets. Larvae of both species developed slightly faster and laid significantly more eggs in flour enriched with the three vitamins than in unenriched patent flour. The improvement was due to the addition of riboflavin. The addition of thiamine or niacin or both did not accelerate development or increase fecundity. It was concluded that top patent flour contains enough thiamine and niacin but not enough riboflavin for proper growth and development of flour beetles.Whole wheat flour was the best diet for T. castaneum, and the flour-germ-bran mixture for T. confusum. Larvae of T. confusum developed as rapidly in the mixture, as in whole wheat flour, but the adults laid significantly more eggs. T. castaneum was equally fecund on these diets, but developed faster in the coarser whole wheat flour. In both species, especially T. castaneum, dietary components had a greater effect on fecundity than on rate of larval development.

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Résumé Le taux de développement larvaire et la fécondité des sujets adultes du Tribolium brun de la farine, Tribolium confusum Jacquelin duVal, et du Tribolium rouge de la farine, Tribolium castaneum Herbst, ont été examinés en rapport avec 12 formules alimentaires différentes: fleur de farine; fleur de farine enrichie de riboflavine, de thiamine et de niacine, seules ou combinées; fleur de farine mélangée de son, de germe de blé ou de ces deux éléments à la fois; enfin, farine de blé entier.Dans chacun de ces régimes, la mortalité larvaire n'a jamais été supérieure à 5%. Les larves de ces deux espèces se sont developpées légèrement plus vite et ont pondu beaucoup plus d'oeufs avec le régime de fleur de farine enrichie de trois vitamines qu'avec le régime de fleur de farine non enrichie. Ces améliorations du développement sont dûes à la riboflavine, car l'addition de thiamine ou de niacine, seules ou associées, n'a ni accéléré le développement ni augmenté la fécondité. On en a conclu que la fleur de farine contenait assez de thiamine et de niacine, mais qu'il y avait une insuffisance en riboflavine pour assurer le développement et la croissance des Tribolium spp.La farine de blé entier a été la plus efficace pour les T. castaneum, et le mélange de farine, de germe et de son a eu les mêmes effets sur les T. confusum. Les larves des T. confusum se sont développées au même rythme dans ce mélange que dans la farine de blé entier, toutefois les sujets adultes ont pondu une quantité d'oeufs beaucoup plus grande dans ce même mélange. Les T. castaneum étaient également féconds dans ce mélange, mais se sont développés plus rapidement dans la farine plus grossière de blé entier.Pour les deux espèces, mais spécialement pour les T. castaneum, les composants du régime ont eu un plus grand effet sur la fécondité que sur le développement larvaire.

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Contribution No. 708 of the Canada Agriculture Research Station, Winnipeg.     

Genetic variance in fitness and its cross-sex covariance predict adaptation during experimental evolution

The additive genetic variation (V_A) of fitness in a population is of particular importance to quantify its adaptive potential and predict its response to rapid environmental change. Recent statistical advances in quantitative genetics and the use of new molecular tools have fostered great interest in estimating fitness V_A in wild populations. However, the value of V_A for fitness in predicting evolutionary changes over several generations remains mostly unknown. In our study, we addressed this question by combining classical quantitative genetics with experimental evolution in the model organism Tribolium castaneum (red flour beetle) in three new environmental conditions (Dry, Hot, Hot-Dry). We tested for potential constraints that might limit adaptation, including environmental and sex genetic antagonisms captured by negative genetic covariance between environments and female and male fitness, respectively. Observed fitness changes after 20 generations mainly matched our predictions. Given that body size is commonly used as a proxy for fitness, we also tested how this trait and its genetic variance (including nonadditive genetic variance) were impacted by environmental stress. In both traits, genetic variances were sex and condition dependent, but they differed in their variance composition, cross-sex and cross-environment genetic covariances, as well as in the environmental impact on V_A.