An experimental analysis of the relationships between fitness components and malic enzyme genotypes inTribolium confusum

The hypothesis that natural selection is capable of maintaining allozyme variation in natural populations was tested using a species of flour beetles,Tribolium confusum. We selected a polymorphic locus (a locus encoding variation for malic enzyme) in an experimental population ofT. confusum and scored the genotypes at this locus for a series of fitness components on different flour types. Measurements included survival rate, development time, fecundity, and rate of egg cannibalism. Flour type had significant effects on most traits. Significant differences among genotypes for fecundity and rates of egg cannibalism and the presence of genotype × flour type interactions for development time were demonstrated. Thus, changes in allele frequencies at the malic enzyme locus could in part be under the influence of natural selection. The existence of genotype × flour type interactions suggests that environmental heterogeneity could maintain allozyme variation at the malic enzyme locus.     

Greenhouse-Selected Resistance to Cry3Bb1-Producing Corn in Three Western Corn Rootworm Populations

Transgenic corn producing the Bacillus thuringiensis (Bt) toxin Cry3Bb1 has been useful for controlling western corn rootworm, Diabrotica virgifera virgifera LeConte, one of the most economically important crop pests in the United States. However, rapid evolution of resistance by this beetle to Bt corn producing Cry3Bb1 has been reported previously from the laboratory, greenhouse, and field. Here we selected in the greenhouse for resistance to Cry3Bb1 corn in three colonies of WCR derived from Kansas, Minnesota, and Wisconsin, respectively. Three generations of rearing on Cry3Bb1 corn significantly increased larval survival on Cry3Bb1 corn, resulting in similar survival in the greenhouse for selected colonies on Cry3Bb1 corn and isoline corn that does not produce Bt toxin. After four to seven generations of rearing on Cry3Bb1 corn, survival in the field on Cry3Bb1 corn relative to isoline corn more than doubled for selected colonies (72%) compared with control colonies (33%). For both selected and control colonies, survival in the field was significantly lower on Cry3Bb1 corn than on isoline corn. On isoline corn, most fitness components were similar for selected colonies and control colonies. However, fecundity was significantly lower for selected colonies than control colonies, indicating a fitness cost associated with resistance. The rapid evolution of resistance by western corn rootworm to Bt corn reported here and previously underlines the importance of effective resistance management for this pest.     

Naturally segregating loci exhibit epistasis for fitness

The extent to which gene interaction or epistasis contributes to fitness variation within populations remains poorly understood, despite its importance to a myriad of evolutionary questions. Here, we report a multi-year field study estimating fitness of Mimulus guttatus genetic lines in which pairs of naturally segregating loci exist in an otherwise uniform background. An allele at QTL x5b—a locus originally mapped for its effect on flower size—positively affects survival if combined with one genotype at quantitative trait locus x10a (aa) but has negative effects when combined with the other genotypes (Aa and AA). The viability differences between genotypes parallel phenotypic differences for the time and node at which a plant flowers. Viability is negatively correlated with fecundity across genotypes, indicating antagonistic pleiotropy for fitness components. This trade-off reduces the genetic variance for total fitness relative to the individual fitness components and thus may serve to maintain variation. Additionally, we find that the effects of each locus and their interaction often vary with the environment.     

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.     

Biology,host preferences and fitness of <Emphasis Type="Italic">Oulema melanopus</Emphasis> (Coleoptera: Chrysomelidae), a recent invasive pest in Western Canada

The developmental parameters and fitness of a recent invasive insect pest of cereals in western Canada, the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae), were compared on live plants and excised leaves of commercial cultivars of potential cereal hosts including wheat (winter and spring), oats, barley, corn, rye and triticale. Host preference and utilization within the fundamental host range of O. melanopus differed. The biological parameters differed significantly when the larvae were reared on excised tissues versus on live host plants. In both studies, wheat (winter and spring), oat (cv. Morgan) and barley were the most preferred hosts in terms of development, survivorship, adult weights and fecundity. Prolonged development with low fitness gains was noted on corn. Although the development on hosts such as rye and triticale was prolonged and adult fitness was low, the survivorship was high on these hosts. Hence, these crops can act as secondary hosts for the beetle in its new eco-region. Larvae fed foliage of Waldern, a local oat cultivar, had increased developmental time and lower survivorship compared with other cereal hosts. Despite differences in fitness gains among hosts, similar numbers of eggs were laid on all hosts. Hence, the oviposition choice of O. melanopus may not be driven by fitness gains alone and it may indicate adaptive strategy to hosts in newer environments.     

Elevated O3 reduces the fitness of Bemisia tabaci via enhancement of the SA-dependent defense of the tomato plant

The effect of elevated O₃ on tomato plants of three different genotypes (wild-type, a jasmonic acid (JA) defense-enhanced genotype (35S) and a JA-deficient genotype (spr2)) grown in association with the whitefly Bemisia tabaci Gennadius biotype B was examined in the field in open-top chambers. We experimentally tested the hypothesis that elevated O₃ tends to reduce the nutrition of tomato plants, and to increase the SA-dependent pathway defenses and the secondary metabolites, and therefore decrease the population fitness of the whitefly. The results show that for all three tomato genotypes, elevated O₃ reduced the soluble sugars and free amino acids, increased the phenylalanine ammonia-lyase enzyme activity and the accumulated salicylic acid (SA), and up-regulated the pathogenesis-related protein (PR1), which is commonly considered to be the whitefly-resistance gene product involved in SA-dependent defense. Elevated O₃ did not affect the JA level in any of the three plant genotypes, but it increased the levels of some secondary metabolites, including total phenolics and condensed tannins. Elevated O₃ prolonged the developmental time of whiteflies fed on the three plant genotypes, and it also reduced the fecundity and the intrinsic rate of increase of whiteflies fed on either the 35S or the wild-type plants. These results suggest that elevated O₃ reduces the nutrition of tomato plants and enhances their SA content, relative PR mRNA expression and secondary metabolism, resulting in decreased fitness of whiteflies on these tomato plants.     

Fitness of Allozyme Variants in DROSOPHILA PSEUDOOBSCURA. I. Selection at the PGM-1 and ME-2 Loci

We have studied in Drosophila pseudoobscura the effect of allozyme variation on seven fitness components: female fecundity, egg hatchability, egg-to-adult survival under near-optimal and under competitive conditions, rate of development under near-optimal and under competitive conditions, and mating capacity of males. Three genotypes at each of two loci, Pgm-1 and Me-2, have been studied in various combinations. These two loci are highly polymorphic in natural populations of D. pseudoobscura. Statistically significant differences involving one or more genotypes exist for all components of fitness. No single genotype is best for all fitness components; rather the relative fitnesses of genotypes are reversed when different parameters are considered, or when they are studied in different environmental conditions. Also, the average egg-to-adult survival and rate of development are better when different genotypes are reared together than when they occur in pure culture. Four different modes of selection have been uncovered by our experiments. These forms of selection may account for the persistence of the two allozyme polymorphisms in nature, and for previously observed seasonal fluctuations of the allelic frequencies in natural populations.     

嗜卷书虱的实验生态研究

在8种温度(17.5～35℃)及5种相对湿度(50%、60%、70%、80%和90%)条件下,以全麦粉、酵母粉、脱脂奶粉(10∶1∶1)为食料,系统研究了嗜卷书虱Liposcelis bostrychophila Badonnel实验种群生态学特性。获得了该虫在不同温、湿度条件下生长发育、生存和繁殖的一系列特性和参数,包括各虫态发育历期、存活率、发育起点温度、有效积温和平均繁殖力等,并建立了发育速率、存活率及繁殖力的理论模型。     

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.     

Variation in the mating system of Sitka spruce (Picea sitchensis): evidence for partial assortative mating

Five allozyme polymorphisms were used to analyze the mating system in a Sitka spruce seed orchard in Saanichton, British Columbia. Allelic frequencies differed between the pollen and maternal pools at three of the five loci, with alleles rare in the maternal pool being even rarer in the effective pollen pool. Minor differences in pollen allelic frequencies were observed in the upper vs. lower crown. The multilocus outcrossing rate of the upper crown (t_m = 0.909) exceeded that of the lower crown (t_m = 0.764). Single-locus estimates of the outcrossing rate were significantly heterogeneous, with the lowest estimate of outcrossing, t = 0.773, observed for PGM-2 locus. Analyses of the mating system for the three maternal PGM-2 genotypes revealed heterogeneous pollen allelic frequencies and heterogeneous outcrossing rates, possibly due to assortative mating at this locus.     

Postinfection Development of Rotylenchulus reniformis on Resistant Gossypium barbadense Accessions

The reniform nematode (Rotylenchulus reniformis) causes significant cotton (Gossypium hirsutum) losses in the southeastern United States. The research objective was to describe the effects of two resistant G. barbadense lines (cultivar TX 110 and accession GB 713) on development and fecundity of reniform nematode. Nematode development and fecundity were evaluated on the resistant lines and susceptible G. hirsutum cultivar Deltapine 16 in three repeated growth chamber experiments. Nematode development on roots early and late in the infection cycle was measured at set intervals from 1 to 25 d after inoculation (DAI) and genotypes were compared based on the number of nematodes in four developmental stages (vermiform, swelling, reniform, and gravid). At 15, 20, and 25 DAI, egg production by individual females parasitizing each genotype was measured. Unique reniform nematode developmental patterns were noted on each of the cotton genotypes. During the early stages of infection, infection and development occurred 1 d faster on susceptible cotton than on the resistant genotypes. Later, progression to the reniform and gravid stages of development occurred first on the susceptible genotype, followed by G. barbadense cultivar TX 110, and finally G. barbadense accession GB 713. Egg production by individual nematodes infecting the three genotypes was similar. This study corroborates delayed development previously reported on G. barbadense cultivar TX 110 and is the first report of delayed infection and development associated with G. barbadense accession GB 713. The different developmental patterns in the resistant genotypes suggest that unique or additional loci may confer resistance in these two lines.     

Divergent allele advantage at MHC-DRB through direct and maternal genotypic effects and its consequences for allele pool composition and mating

It is still debated whether main individual fitness differences in natural populations can be attributed to genome-wide effects or to particular loci of outstanding functional importance such as the major histocompatibility complex (MHC). In a long-term monitoring project on Galápagos sea lions (Zalophus wollebaeki), we collected comprehensive fitness and mating data for a total of 506 individuals. Controlling for genome-wide inbreeding, we find strong associations between the MHC locus and nearly all fitness traits. The effect was mainly attributable to MHC sequence divergence and could be decomposed into contributions of own and maternal genotypes. In consequence, the population seems to have evolved a pool of highly divergent alleles conveying near-optimal MHC divergence even by random mating. Our results demonstrate that a single locus can significantly contribute to fitness in the wild and provide conclusive evidence for the ‘divergent allele advantage’ hypothesis, a special form of balancing selection with interesting evolutionary implications.     

Oviposition preferences of the Hessian fly and their consequences for the survival and reproductive potential of offspring

1. The relationship between oviposition preference and offspring performance was investigated experimentally for the Hessian fly Mayetiola destructor (Say) using 10 grass genotypes that represented five different genera and six different species. Oviposition preferences were quantified in a choice test using arrays of 200–400 plants. Offspring performance was estimated by recording survival during three phases of the insect–plant association and by measuring wing length, a correlate of adult reproductive potential. Density effects were examined for all offspring variables, and were taken into account when offspring performance was compared across the 10 grasses. 2. Egg counts from the oviposition choice test revealed a consistent ranking of plants: 18ITSN triticale > Otane bread wheat = Caldwell bread wheat = Stacy bread wheat > 3424 bread wheat = PND durum wheat = Fleet barley = Valetta barley = Matua brome grass > Awapuni oat. 3. Survival and adult wing length varied significantly on the 10 plant types. Survival was ranked: Otane bread wheat > 3424 bread wheat = Fleet barley = Matua brome grass > Caldwell bread wheat = Valetta barley > 18ITSN triticale = PND durum wheat = Stacy bread wheat > Awapuni oat. Adult male and female wing lengths were greatest on Otane, the bread wheat that also provided the best survival. 4. For Hessian flies on each of the 10 plant types, data on survival, wing length, and wing length–fecundity relationships were combined into a single fitness measure. When these fitness measures were compared with egg counts, no overall pattern emerged. On seven of the 10 plant types, there was a positive linear relationship between egg counts and offspring fitness. On the other three plant types, egg counts were high while fitness was low. Possible reasons why Hessian fly females lay eggs on plants that are poor hosts for their offspring are discussed.     

Effects of primary seed dormancy on lifetime fitness of Arabidopsis thaliana in the field

Background and AimsSeed dormancy determines the environmental niche of plants in seasonal environments, and has consequences for plant performance that potentially go far beyond the seed and seedling stages. In this study, we examined the cascading effects of seed dormancy on the expression of subsequent life-history traits and fitness in the annual herb Arabidopsis thaliana.MethodsWe planted seeds of >200 recombinant inbred lines (RILs) derived from a cross between two locally adapted populations (Italy and Sweden), and both parental genotypes at the native site of the Swedish population in three consecutive years. We quantified the relationship between primary seed dormancy and the expression of subsequent life-history traits and fitness in the RIL population with path analysis. To examine the effects of differences in dormancy on the relative fitness of the two parental genotypes, we planted dormant seeds during the seed dispersal period and non-dormant seeds during the germination period of the local population.Key ResultsIn the RIL population, strong primary dormancy was associated with high seedling survival, but with low adult survival and fecundity, and path analysis indicated that this could be explained by effects on germination timing, rosette size and flowering start. The relationship between primary seed dormancy and germination proportion varied among years, and this was associated with differences in seasonal changes in soil moisture. The planting of dormant and non-dormant seeds indicated that the lower primary dormancy of the local Swedish genotype contributed to its higher germination proportion in two years and to its higher fecundity in one year.ConclusionsOur results show that seed dormancy affects trait expression and fitness components across the life cycle, and suggest that among-year variation in the incidence of drought during the germination period should be considered when predicting the consequences of climatic change for population growth and evolution.     

Fitness comparison of Plutella xylostella on original and marginal hosts using age‐stage,two‐sex life tables

The diamondback moth, Plutella xylostella, is an important agricultural pest that severely damages cruciferous vegetables. Although previously considered a threat only to Brassica species, P. xylostella has been observed to feed on noncruciferous vegetables. Here, we established a population of P. xylostella on the pea Pisum sativum (PxP population). We compared this PxP population''s performance on the pea host plant to a population (PxR) reared on the original host plant radish (Raphanus sativus) for several generations using an age‐stage, two‐sex life table and analyzed the correlations between different fitness parameters. In the 1st generation of the PxP population, survival rate of immature stage was 17%, while the survival rate of PxR was 68%; the duration of the 4th larval instar (5.30 d) and mortality (25%) of this generation were significantly longer (2.8 d) and higher (1%) than that of PxR, respectively (both p < .001). Upon long‐term acclimation, the PxP fitness improved significantly, especially that the survival rate of immature stages increased to approximately 60% in the 15th, 30th, and 45th generations. However, PxP feeding on pea exhibited poorer fitness with longer larval developmental time, shorter total life span, lighter pupa, and lower fecundity in different generations compared with PxP feeding on radish. PxP feeding on pea also showed a significantly lower intrinsic rate of increase (r), net reproduction rate (R ₀), finite increase rate (λ), and longer mean generation time (T) than PxP feeding on radish in all generations tested. Significant positive correlations were observed between pupal weight and female fecundity in pea‐fed populations, and between female longevity and female fecundity in pea‐fed and radish‐fed populations. Our findings suggest that P. xylostella adaptation to pea does not improve overall fitness compared with the original host radish, making pea a marginal host for P. xylostella.     

Development of European corn borer larvae on Event 176 Bt corn: influence on survival and fitness

European corn borer larvae, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) that have completed development on Event 176 Bt corn hybrids have survived exposure to sublethal doses of the Cry1Ab Bt toxin or are exploiting plant tissues that do not express the toxin. To evaluate the impact of such exposure, diapausing larvae were collected from Event 176 and conventional hybrids and compared for rates of pupation, parasitism, fitness (pupal weight, longevity, and fecundity) and susceptibility to the Cry1Ab toxin. Larvae completing development on Event 176 corn exhibited approximately 10% higher survival rates and correspondingly lower parasitism rates than larvae completing development on conventional hybrids. No significant differences were detected in pupal weight, fecundity, longevity or susceptibility to the Cry1Ab Bt toxin. These results indicate that survival on Event 176 corn are not adversely affect fitness and does not cause increased tolerance to the Cry1Ab toxin in subsequent generations.     

Chromosomal location of wheat genes of the carotenoid biosynthetic pathway and evidence for a catalase gene on chromosome 7A functionally associated with flour b* colour variation

Knowledge of molecular and genetic mechanisms controlling wheat grain quality characteristics is significant for improving flour for end-product functionality. Flour b* colour is an important quality trait for breeding wheat varieties to produce grain for specific market requirements. The degree of flour yellowness is due to the accumulation of carotenoids in grain, particularly lutein. Flour b* is under polygenic control and quantitative trait loci (QTL) have frequently been reported on chromosome 7AL. Analysis of carotenoid genes showed that phytoene synthase (PSY) co-located to the QTL on 7AL but other genes at this locus are also thought to contribute flour b* colour variation. This study used the wheat genome survey sequence and identified the chromosomal location of all wheat carotenoid genes, but none other than PSY were located on 7AL and, therefore, other genes may control flour b* colour variation including oxidative genes that degrade carotenoids. An investigation of EST bin mapped to 7AL identified a gene encoding a catalase enzyme (Cat3-A1) that was phylogenetically related to other plant class III enzymes, co-located to the QTL for flour b* colour variation on 7AL in three mapping populations and expressed during seed development. Therefore, Cat3-A1 was functionally associated with flour b* colour variation. Catalase acts upon hydrogen peroxide as a substrate and it was postulated that Cat3-A1 alleles control varying degrees of bleaching action on lutein in developing wheat grain. Markers for Cat3-A1 developed in this study can be used in conjunction with other candidate gene markers including phytoene synthase and lycopene-ε-cylase to develop a molecular signature for selecting lines with specific flour b* colour values in wheat breeding.     

Alleles at storage protein loci in Triticum spelta L. accessions and their occurrence in related wheats

The diversity at eight storage protein loci was analyzed in the collection of Triticum spelta accesssions from the National Center for Plant Genetic Resources of Ukraine (most of accessions were European spelts). Seven alleles at the Gli-B1 locus; five alleles at the Gli-A1 and Glu-B1 loci; three alleles at the Glu-B1 locus; and two alleles at the Gli-D1, Gli-B5, Glu-A1, and Glu-D1 loci were identified. Most alleles are found among common wheat cultivars; only five spelt-specific alleles were detected. The high frequency of the GliB1hs* and h alleles encoding the 45-type γ-gliadin among European spelt and durum wheat, as well as the occurrence of these alleles in T. dicoccum (particularly, in emmer accessions from Switzerland and Germany), are evidence in favor of von Büren’s hypothesis that the European spelt arose from the hybridization between tetraploid wheat with the 45-type γ-gliadin and hexaploid wheat. The analysis of genetic distances based on the genotypes at eight storage protein loci allowed differentiating the Asian spelt accession from European spelts.     

Sublethal effects of abamectin on the development,fecundity, and wing morphs of the brown planthopper Nilaparvata lugens

The brown planthopper Nilaparvata lugens negatively affects rice yield by sucking nutrients from the rice stem and spreading viruses. In this study, the effects of sublethal concentrations of abamectin on development, fecundity, and wing morphs of N. lugens were investigated. Treatment with sublethal concentrations of abamectin showed no significant effects on the developmental period of F₀ nymphs. Although LC₁₀ and LC₂₅ treatments resulted in 10% and 25% mortality, the LC₂₅ treatment significantly prolonged the lifespan of macropterous and brachypterous females. Abamectin-treated brachypterous females showed significantly lower fecundity than control females. Furthermore, abamectin treatment showed no significant effects on the developmental period of F₁ nymphs. However, LC₂₅ treatment significantly inhibited the fecundity of brachypterous F₁ females and significantly reduced the proportion of macropterous F₁ females and brachypterous F₁ males. LC₂₅ treatment showed no significant effects on the fecundity of macropterous F₁ females. Considering the proportion of macropterous and brachypterous F₁ females, the relative fitness of the macropterous F₁ nymphs in the control, LC₁₀, and LC₂₅ treatment groups was 1, 1.02, and 0.84, respectively, and that of brachypterous F₁ nymphs was 1, 0.79, and 0.93, respectively. Sublethal concentrations of abamectin inhibited N. lugens emergence. The present findings indicate the potential of abamectin for N. lugens field control.     

The effect of plant phenology on the induction of alatae and the development of populations of Metopolophium dirhodum (Walker), the rose-grain aphid, on winter wheat

In field experiments apterous Metopolophium dirhodum produced significantly more alatae when reared on mature plants (milky ripe stage) than on young plants. Nymphal and adult survival and relative growth rate were little affected by the developmental stage of the host plant. Relative growth rate and fecundity were strongly related to temperature. Laboratory experiments confirmed that the developmental stage of wheat had no significant effect on survival or relative growth rate of the aphids. However, laboratory grown plants did not produce the levels of alate production seen in field crops and in the field experiments. It is suggested that in investigations into the effects of the host plant on cereal aphids field grown plants should be used whenever possible. Alate production is proposed as the major plant induced factor affecting the development of M. dirhodum populations on wheat in the field. Alatae developed on mature plants even when the number of aphids was very low.