Significant Fitness Cost Research Articles

Comparing the organophosphorus and carbamate insecticide resistance mutations in cholin- and carboxyl-esterases

Mutant insect carboxyl/cholinesterases underlie over 60 cases of resistance to organophosphorus and/or carbamate insecticides. Biochemical and molecular data on about 20 of these show recurrent use of a very small number of mutational options to generate either target site or metabolic resistance. Moreover, the mutant enzymes are often kinetically inefficient and associated with significant fitness costs, due to impaired performance of the enzymes’ original function. By contrast many bacterial enzymes are now known which can effectively detoxify these pesticides. It appears that the constraints of the genetic code and eukaryote genetic systems have severely limited the evolutionary response of insects to the widespread use of the insecticides over the last 60 years.

The pigtail macaque MHC class I allele Mane‐A*10 presents an immundominant SIV Gag epitope: identification, tetramer development and implications of immune escape and reversion

The pigtail macaque (Macaca nemestrina) is a common model for the study of AIDS. The pigtail major histocompatibility complex class I allele Mane-A*10 restricts an immunodominant simian immunodeficiency virus (SIV) Gag epitope (KP9) which rapidly mutates to escape T cell recognition following acute simian/human immunodeficiency virus infection. Two technologies for the detection of Mane-A*10 in outbred pigtail macaques were developed: reference strand-mediated conformational analysis and sequence-specific primer polymerase chain reaction. A Mane-A*10/KP9 tetramer was then developed to quantify CD8(+) T lymphocytes primed by multigenic DNA vaccination, which have previously been difficult to detect using standard interferon-gamma-based T cell assays. We also demonstrate mutational escape at KP9 following acute SIV infection. Mane-A*10(+) animals have lower set point SIV levels than Mane-A*10(-) animals, suggesting a significant fitness cost of escape. These studies pave the way for a more robust understanding of HIV vaccines in pigtail macaques.

The effects of rearing temperature on developmental stability and learning and memory in the honey bee, Apis mellifera

Honey bee workers maintain the brood nest of their colony within a narrow temperature range of 34.5+/-1.5 degrees C, implying that there are significant fitness costs if brood is reared outside the normal range. However, the effects of abnormal incubation temperatures are subtle and not well documented. Here we show that short-term learning and memory abilities of adult workers are affected by the temperature they experienced during pupal development. In contrast, long-term learning and memory is not significantly affected by rearing temperature. Furthermore, we could detect no effects of incubation temperature on fluctuating asymmetry, as a measure of developmental stability, in workers, queens or drones. We conclude that the most important consequence of abnormal rearing temperatures are subtle neural deficiencies affecting short-term memory rather than physical abnormalities.

Piriformospora indica and Sebacina vermifera increase growth performance at the expense of herbivore resistance in Nicotiana attenuata

A Sebacinales species was recovered from a clone library made from a pooled rhizosphere sample of Nicotiana attenuata plants from 14 native populations. Axenic cultures of the related species, Piriformospora indica and Sebacina vermifera, were used to examine their effects on plant performance. Inoculation of N. attenuata seeds with either fungus species stimulated seed germination and increased growth and stalk elongation. S. vermifera inoculated plants flowered earlier, produced more flowers and matured more seed capsules than did non-inoculated plants. Jasmonate treatment during rosette-stage growth, which slows growth and elicits herbivore resistance traits, erased differences in vegetative, but not reproductive performance resulting from S. vermifera inoculation. Total nitrogen and phosphorous contents did not differ between inoculated and control plants, suggesting that the performance benefits of fungal inoculation did not result from improvements in nutritional status. Since the expression of trypsin proteinase inhibitors (TPI), defensive proteins which confer resistance to attack from Manduca sexta larvae, incur significant growth and fitness costs for the plant, we examined the effect of S. vermifera inoculation on herbivore resistance and TPI activity. After 10 days of feeding on S. vermifera-inoculated plants, larval mass was 46% higher and TPI activity was 48% lower than that on non-inoculated plants. These results suggest that Sebacina spp. may interfere with defense signaling and allow plants to increase growth rates at the expense of herbivore resistance mediated by TPIs.

Biological cost of single and multiple norfloxacin resistance mutations in Escherichia coli implicated in urinary tract infections.

Resistance to fluoroquinolones in urinary tract infection (UTIs) caused by Escherichia coli is associated with multiple mutations, typically those that alter DNA gyrase and DNA topoisomerase IV and those that regulate AcrAB-TolC-mediated efflux. We asked whether a fitness cost is associated with the accumulation of these multiple mutations. Mutants of the susceptible E. coli UTI isolate Nu14 were selected through three to five successive steps with norfloxacin. Each selection was performed with the MIC of the selected strain. After each selection the MIC was measured; and the regions of gyrA, gyrB, parC, and parE, previously associated with resistance mutations, and all of marOR and acrR were sequenced. The first selection step yielded mutations in gyrA, gyrB, and marOR. Subsequent selection steps yielded mutations in gyrA, parE, and marOR but not in gyrB, parC, or acrR. Resistance-associated mutations were identified in almost all isolates after selection steps 1 and 2 but in less than 50% of isolates after subsequent selection steps. Selected strains were competed in vitro, in urine, and in a mouse UTI infection model against the starting strain, Nu14. First-step mutations were not associated with significant fitness costs. However, the accumulation of three or more resistance-associated mutations was usually associated with a large reduction in biological fitness, both in vitro and in vivo. Interestingly, in some lineages a partial restoration of fitness was associated with the accumulation of additional mutations in late selection steps. We suggest that the relative biological costs of multiple mutations may influence the evolution of E. coli strains that develop resistance to fluoroquinolones.

Rapid Viral Escape at an Immunodominant Simian-Human Immunodeficiency Virus Cytotoxic T-Lymphocyte Epitope Exacts a Dramatic Fitness Cost

Escape from specific T-cell responses contributes to the progression of human immunodeficiency virus type 1 (HIV-1) infection. T-cell escape viral variants are retained following HIV-1 transmission between major histocompatibility complex (MHC)-matched individuals. However, reversion to wild type can occur following transmission to MHC-mismatched hosts in the absence of cytotoxic T-lymphocyte (CTL) pressure, due to the reduced fitness of the escape mutant virus. We estimated both the strength of immune selection and the fitness cost of escape variants by studying the rates of T-cell escape and reversion in pigtail macaques. Near-complete replacement of wild-type with T-cell escape viral variants at an immunodominant simian immunodeficiency virus Gag epitope KP9 occurred rapidly (over 7 days) following infection of pigtail macaques with SHIVSF162P3. Another challenge virus, SHIVmn229, previously serially passaged through pigtail macaques, contained a KP9 escape mutation in 40/44 clones sequenced from the challenge stock. When six KP9-responding animals were infected with this virus, the escape mutation was maintained. By contrast, in animals not responding to KP9, rapid reversion of the K165R mutation occurred over 2 weeks after infection. The rapidity of reversion to the wild-type sequence suggests a significant fitness cost of the T-cell escape mutant. Quantifying both the selection pressure exerted by CTL and the fitness costs of escape mutation has important implications for the development of CTL-based vaccine strategies.

Single Amino Acid Mutations in the Cadherin Receptor from Heliothis virescens Affect Its Toxin Binding Ability to Cry1A Toxins

Bacillus thuringiensis Cry protein exerts its toxic effect through a receptor-mediated process. Both aminopeptidases and cadherin proteins were identified as putative Cry1A receptors from Heliothis virescens and Manduca sexta. The importance of cadherin was implied by its correlation with a Cry1Ac resistant H. virescens strain (Gahan, L. J., Gould, F., and Heckel, D. G. (2001) Science 293, 857-860). In this study, the Cry1Ac toxin-binding region in H. virescens cadherin was mapped to a 40-amino-acid fragment, from amino acids 1422 to 1440. This site overlaps with a Cry1Ab toxin-binding site, amino acids 1363-1464 recently reported in M. sexta (Hua, G., Jurat-Fuentes, J. L., and Adang, M. J. (2004) J. Biol. Chem. 279, 28051-28056). Further, feeding of the anti-H. virescens cadherin antiserum or the partial cadherins, which contain the toxin-binding region, in combination with Cry1Ab/Cry1Ac reduced insect mortality by 25.5-55.6% to first instar H. virescens and M. sexta larvae, suggesting a critical function for this cadherin domain in insect toxicity. Mutations in this region, to which the Cry1Ac binds through its loop 3, resulted in the loss of toxin binding. For the first time, we show that the cadherin amino acids Leu(1425) and Phe(1429) are critical for Cry1Ac toxin interaction, and if substituted with charged amino acids, result in the loss of toxin binding, with a K(D) of < 10(-5) m. Mutation of Gln(1430) to an alanine, however, increased the Cry1Ac affinity 10-fold primarily due to an increase on rate. The L1425R mutant can result from a single nucleotide mutation, CTG --> CGG, suggesting that these mutants, which have decreased toxin binding, may lead to Cry1A resistance in insects.

Ideal flea constraints on group living: unwanted public goods and the emergence of cooperation

Long ago, Hamilton (1971) proposed that the ‘‘selfish herd’’ effect, while primarily thought to reduce predation risk, might also apply to avoiding parasites. Solitary individuals suffer higher ectoparasite burdens if they lack conspecifics either to absorb collateral damage from the local ectoparasite population or to remove ectoparasites by allogrooming. By grouping, therefore, animals may reduce their individual risk of exposure to parasites (Mooring and Hart, 1992). This is important because there are significant fitness costs associated with ectoparasite loads. More ectoparasites take more blood, cause more irritation, increase the probability of infection, and decrease the time available for other activities, because grooming becomes a higher priority. These costs vary with group size because a greater number of hosts and shared den sites means ectoparasites are more likely to survive stochastic variation. The dynamics of parasite control might therefore present crucial constraints on group size and a novel origin for sociality itself. We present a model suggesting that these constraints may lead to an egalitarian system among social host species, who need to cooperate to get rid of their ectoparasites. Mobile ectoparasites are moderated by two mechanisms: (1) the dilution of ectoparasites toward an ideal free distribution (IFD) among hosts, and (2) the removal of ectoparasites by cooperative host allogrooming. Host interactions represent a ‘‘biological market,’’ in which the benefit of cooperation varies with the relative amount of the tradable commodity (the ectoparasites) each individual has. This is not, however, a normal market as the goods are unwanted. Nevertheless, the dilution effect means that all individuals in a group have a common stake in reducing the mean parasite burden, which may preclude or reduce any advantage of cheating. Predictions of the model were tested with empirical data from a longterm study of badgers, Meles meles, and their flea burdens in Wytham Woods, Oxford. A basic tenet in models of population dynamics (Hanski, 1999; Sutherland, 1996) is IFD, a general explanation for fluctuating distributions of animals as they move to find sites where the rewards are highest and individuals optimize their fitness (Fretwell, 1972; Fretwell and Lucas, 1970). Assuming individuals really are free (i.e., no resource defense and perfect information), this represents a process whereby consumers become diluted among all available sites. In short, the ratio between the numbers of individuals in sites A and B should be proportional to the relative availability of resources Behavioral Ecology Vol. 15 No. 1: 181–186 DOI: 10.1093/beheco/arg093

Why do melanin ornaments signal individual quality? Insights from metal element analysis of barn owl feathers.

Melanin-based variation in colour patterns is under strong genetic control and not, or weakly, sensitive to the environment and body condition. Current signalling theory predicts that such traits may not signal honestly phenotypic quality because their production does not entail a significant fitness cost. However, recent studies revealed that in several bird species melanin-based traits covary with phenotypic attributes. In a first move to understand whether such covariations have a physiological basis, we quantified concentrations of five chemical elements in two pigmented plumage traits in the barn owl (Tyto alba). This bird shows continuous variation from immaculate to heavily marked with black spots (plumage spottiness) and from dark reddish-brown to white (plumage coloration), two traits that signal various aspects of individual quality. These two traits are sexually dimorphic with females being spottier and darker coloured than males. We found an enhancement in calcium and zinc concentration within black spots compared with the unspotted feather parts. The degree to which birds were spotted was positively correlated with calcium concentration within spots, whereas the unspotted feather parts of darker reddish-brown birds were more concentrated in zinc. This suggests that two different pigments are responsible for plumage spottiness and plumage coloration. We discuss the implications of our results in light of recent experimental field studies showing that female spottiness signals offspring humoral response towards an artificially administrated antigen, parasite resistance and fluctuating asymmetry of wing feathers.

Age-dependent fitness costs of alarm signaling in aphids

For an alarm signal to evolve, the benefits to the signaler must outweigh the costs of sending the signal. Research has largely focused on the benefits of alarm signaling, and the costs to an organism of sending an alarm signal are not well known. When attacked by a predator, aphids secrete cornicle droplets, containing an alarm pheromone, for individual protection and to warn clonemates. As aphid alarm pheromone is synthesized de novo in a feedback loop with juvenile hormone, we hypothesized that the secretion of cornicle droplets may result in a direct fitness cost to the emitter. We show that the secretion of a single cornicle droplet by pre-reproductive (third- and fourth-instar) pea aphids, Acyrthosiphon pisum, directly altered the timing and number of offspring produced. Third-instar pea aphids delayed offspring production but produced more offspring overall than non-secreting aphids, demonstrating a life-history shift but no significant fitness cost of droplet secretion. Fourth-instar pea aphids also delayed offspring production but produced the same number of offspring as non-secretors, resulting in a direct fitness cost of droplet secretion. Offspring production by adult, reproductive pea aphids that secreted a cornicle droplet did not differ from that of non-secretors. Thus, the fitness costs of secreting cornicle droplets containing an alarm signal are age-dependent.

The evolution of infertility: does hatching rate in birds coevolve with female polyandry?

Abstract Natural levels of infertility in many taxa are often remarkably high, amounting to a considerable fitness cost which one expects to be minimized by natural selection. Several mechanisms have been proposed as potential causes of infertility, including inbreeding depression, genetic incompatibilities and selfish genetic elements. Infertility may also be an inherent result of conflict over fertilization between the sexes in polyandrous species, either because too many sperm enter the egg or because of over-efficient barriers to such polyspermic fertilizations. We generated phylogenetic independent contrasts to examine the variation in hatching success for a maximum of 58 species of birds in relation to two measures of female polyandry. Hatching success varied enormously across species (range: 61–100%), with a mean of 12% of eggs failing to hatch, but was not related to either the rate of extrapair paternity or to relative testes size. Thus, the causes of this significant fitness cost remains unclear and merits further examination by evolutionary biologists.

Why should parasite resistance be costly?

Parasite resistance is sometimes associated with fitness costs. Costs of resistance are fundamentally important in epidemiology, and in the ecology and evolution of host-parasite interactions. The cost of resistance is often envisioned as the cost of re-allocating limiting resources to resistance machinery from other traits. This popular paradigm has resulted in a spate of research that assumes a fitness cost to resistance. We comment on this trend and propose a working framework of various resistance means and mechanisms. Within these means and mechanisms, we suggest that many are not likely to incur significant fitness costs.

Meta-Analysis of Sources of Variation in Fitness Costs of Plant Antiherbivore Defenses

Plant defense theories predict that allocation to antiherbivore defenses should impose a cost on plants, manifested as a reduction in growth and reproduction. However, the empirical evidence for the existence of such trade-offs is conflicting, suggesting that significant fitness costs of defense arise in some circumstances but not in others. A meta-analysis of 70 studies assessing the relationship between measures of plant defense and growth or reproduction has been conducted to examine the relative importance of several potential sources of variation in the fitness costs of defense. The magnitude of fitness costs varied depending on whether they were measured at the level of phenotype or genotype. The mean magnitude of among-genotype correlations (AGCs) between defense and fitness measures (r = −0.30) was higher than that of among-phenotype correlations (APCs; r = −0.15). Moreover, AGCs tended to be more negative when defense was assessed as the inverse of herbivore densities or damage rather than in terms of single specific chemical or structural traits. The magnitude of APCs was greatly influenced by environmental variation; phenotypic costs were lowest under controlled experimental conditions and highest in studies that minimized genetic variation among plants. In addition, the magnitude and sign of APCs varied depending on nutrient availability and the type of defensive compound. APCs were negative at high levels of nutrient availability and for defenses associated with alkaloids and phenolics but tended to be positive at low levels of nutrient availability and for defenses associated with terpenoids. In contrast, the magnitude of fitness costs was not significantly affected by the presence of herbivores, type of plant, type of defense (constitutive, mechanical, or induced), concentrations of defensive compounds, or measure of plant fitness. The above patterns of variation in the magnitude of correlations between defense and fitness measures are inconsistent with the notion that fitness costs are incurred through diversion of common limited resources from growth and reproduction to defense (allocation costs). Instead, the prevalence of significant negative correlations under uncontrolled environmental conditions and their persistence in the presence of herbivores both imply that fitness costs of defense may often arise through interactions between plants and their abiotic and biotic environment (competitors, pollinators, different types of herbivores, their natural enemies, and various types of abiotic stresses). Because the above aspects have usually been excluded in studies aiming at detecting internal allocation trade-offs, the failure to detect costs in some cases may be a consequence of the experimental design. Future studies should examine the relative importance of opportunity and ecological types of costs by manipulating various aspects of plant environment.

META-ANALYSIS OF SOURCES OF VARIATION IN FITNESS COSTS OF PLANT ANTIHERBIVORE DEFENSES

Plant defense theories predict that allocation to antiherbivore defenses should impose a cost on plants, manifested as a reduction in growth and reproduction. However, the empirical evidence for the existence of such trade-offs is conflicting, suggesting that significant fitness costs of defense arise in some circumstances but not in others. A meta-analysis of 70 studies assessing the relationship between measures of plant defense and growth or reproduction has been conducted to examine the relative importance of several potential sources of variation in the fitness costs of defense. The magnitude of fitness costs varied depending on whether they were measured at the level of phenotype or genotype. The mean magnitude of among-genotype correlations (AGCs) between defense and fitness measures (r = −0.30) was higher than that of among-phenotype correlations (APCs; r = −0.15). Moreover, AGCs tended to be more negative when defense was assessed as the inverse of herbivore densities or damage rather than in ter...

An Ecological Genetic Approach to the Study of Coevolution

Almost forty years ago, Ehrlich and Raven (1964) hypothesized that the great diversity of plants and the herbivores that feed on them arose from a process of coevolution. Plants do possess an amazing diversity of traits that are easily imagined as having arisen from an antagonistic interaction between plants and herbivores. Two basic assumptions lie at the root of most theories of coevolution between plants and their herbivores. First, herbivores are agents of natural selection on plant resistance traits. Second, plants incur a significant fitness cost for possessing these resistance traits. An ecological genetic approach can provide rigorous evidence for these coevolutionary assumptions. In this paper, I present new experimental work on the subject of costs of resistance and review and discuss my own previous work bearing directly on these questions. Using both field experiments on natural populations of the mouse-ear cress (Arabidopsis thaliana) and laboratory experiments using genetically modified plants, I demonstrate that herbivores are exerting selection on both a chemical and physical resistance trait and that there are significant fitness costs to possessing these two traits. These results provide direct confirmation that our current models of the evolution of plant defenses are appropriate.

An Ecological Genetic Approach to the Study of Coevolution1

SYNOPSIS. Almost forty years ago, Ehrlich and Raven (1964) hypothesized that the great diversity of plants and the herbivores that feed on them arose from a process of coevolution. Plants do possess an amazing diversity of traits that are easily imagined as having arisen from an antagonistic interaction between plants and herbivores. Two basic assumptions lie at the root of most theories of coevolution between plants and their herbivores. First, herbivores are agents of natural selection on plant resistance traits. Second, plants incur a significant fitness cost for possessing these resistance traits. An ecological genetic approach can provide rigorous evidence for these coevolutionary assumptions. In this paper, I present new experimental work on the subject of costs of resistance and review and discuss my own previous work bearing directly on these questions. Using both field experiments on natural populations of the mouse-ear cress (Arabidopsis thaliana) and laboratory experiments using genetically modified plants, I demonstrate that herbivores are exerting selection on both a chemical and physical resistance trait and that there are significant fitness costs to possessing these two traits. These results provide direct confirmation that our current models of the evolution of plant defenses are appropriate. THE PROBLEM

Testing the assumptions of conditional handicap theory: costs and condition dependence of a sexually selected trait

Conditional handicap models of sexual selection predict that sexual traits are reliable signals of male quality because they are (a) condition dependent and (b) costly to produce or maintain. In this study, my objective was to experimentally investigate whether the drumming of male Hygrolycosa rubrofasciata wolf spiders is a condition-dependent costly trait. Males court females by drumming dry leaves with their abdomen and females preferentially mate with males drumming at higher rates. I manipulated male phenotypic condition and drumming rate simultaneously by keeping males on three different food rations and either introducing or not introducing them to a female. Food ration treatment affected male condition, as males on a low food ration lost mass while males on a high food ration maintained their mass at a constant level. The manipulation of food ration affected male drumming rate: males on a low food ration had the lowest drumming rate while males on a high food ration drummed at the highest rate. Manipulation of drumming rate incurred significant fitness costs: males induced to drum at higher rates suffered higher mortality than other males. Furthermore, there was a significant female introduction by food ration by male size interaction on male survival. When induced to increase their drumming rate, large males manipulated to be in good condition survived better than large males manipulated to be in poor condition. There was no such difference in small males. When drumming rate was not increased, the slopes between males survival and size were homogeneous and weakly positive across each condition treatment. Despite the higher mortality when introduced to females, there was still a significant positive correlation between drumming rate and survival. My results demonstrate that sexual signalling in H. rubrofasciata is condition dependent and costly, thus supporting conditional handicap models of sexual selection.

The biological basis of grooming in moose: programmed versus stimulus-driven grooming

In domestic and wild mammals, tick infestation can be a significant fitness cost. Grooming behaviour has been shown to be effective in removing ticks. We studied grooming by moose,Alces alces, infested with winter ticks,Dermacentor albipictus, to determine which of two nonexclusive models for the regulation of tick-removal grooming, programmed or stimulus driven, best fit this host–parasite relationship. The programmed grooming model states that most grooming is driven by an internal timing mechanism which periodically evokes a bout a grooming independent of peripheral stimulation from tick bites. Because programmed grooming is preventive, the model predicts that those animals that groom the most will carry the fewest ticks, and a baseline level of programmed grooming is predicted even in a tick-sparse or tick-free environment. The stimulus-driven grooming model, on the other hand, states that grooming is a direct response to cutaneous irritation caused by tick bites and other sources of irritation. This stimulus-driven model predicts that (1) animals showing the highest rate of grooming will carry the most ticks and (2) animals will groom little when tick challenge is low. Both predictions of the stimulus-driven model were supported for moose: (1) calves oral-groomed three times more than cows, and tick densities on calves were three times higher than on cows; and (2) although all moose carried high densities of immature winter ticks (larvae, nymphs) from October through to February, grooming rate was very low until adult ticks started feeding in March–April. Peak grooming rates occurred during adult tick engorgement in March–April. Because an engorging adult female tick produces far more irritation than an engorging nymphal or larval tick, moose appeared to groom in direct proportion to the degree of cutaneous irritation and did not show a baseline level of grooming. The predominance of stimulus-driven grooming and apparent absence of programmed grooming may be the result of relaxed selection pressure for grooming in the evolutionary history of moose. Because the winter tick appears to have been introduced to moose from deer relatively recently, moose may not have had the time to adapt to winter ticks. The coevolutionary relationship between moose and winter ticks may be of insufficient duration for the evolution and/or maintenance of programmed grooming.

Cost of Resistance to Natural Enemies in Field Populations of the Annual Plant Arabidopsis thaliana

The annual plant Arabidopsis thaliana is widely used as a model system in molecular genetics, but little is known about populations in the field. In this experimental field study of natural populations of Arabidopsis, I tested the assumption that plant resistance has fitness costs. Models of the evolution of resistance assume a cost, which is envisioned as a reduction in fitness in the absence of natural enemies, such as insect herbivores and pathogens. The presumed basis of this cost is the diversion of limiting resources away from present and future growth and reproduction. Recent failures to detect allocation costs of resistance to herbivores have raised questions about whether costs exist and, thus, about the appropriateness of theories that postulate such costs. I found genetic variation for two traits commonly thought to function as resistance characters: trichome density and total glucosinolate concentration. Under field conditions, these characters both reduced damage by the natural assemblage of herbivores and exhibited significant fitness costs.

Costs of Resistance to Natural Enemies in Field Populations of the Annual PlantArabidopsis thaliana

The annual plant Arabidopsis thaliana is widely used as a model system in molecular genetics, but little is known about populations in the field. In this experimental field study of natural populations of Arabidopsis, I tested the assumption that plant resistance has fitness costs. Models of the evolution of resistance assume a cost, which is envisioned as a reduction in fitness in the absence of natural enemies, such as insect herbivores and pathogens. The presumed basis of this cost is the diversion of limiting resources away from present and future growth and reproduction. Recent failures to detect allocation costs of resistance to herbivores have raised questions about whether costs exist and, thus, about the appropriateness of theories that postulate such costs. I found genetic variation for two traits commonly thought to function as resistance characters: trichome density and total glucosinolate concentration. Under field conditions, these characters both reduced damage by the natural assemblage of herbivores and exhibited significant fitness costs.