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There is now good evidence that many mutualisms evolved from antagonism; why or how, however, remains unclear. We advance the Co-Opted Antagonist (COA) Hypothesis as a general mechanism explaining evolutionary transitions from antagonism to mutualism. COA involves an eco-coevolutionary process whereby natural selection favors co-option of an antagonist to perform a beneficial function and the interacting species coevolve a suite of phenotypic traits that drive the interaction from antagonism to mutualism. To evaluate the COA hypothesis, we present a generalized eco-coevolutionary framework of evolutionary transitions from antagonism to mutualism and develop a data-based, fully ecologically-parameterized model of a small community in which a lepidopteran insect pollinates some of its larval host plant species. More generally, our theory helps to reconcile several major challenges concerning the mechanisms of mutualism evolution, such as how mutualisms evolve without extremely tight host fidelity (vertical transmission) and how ecological context influences evolutionary outcomes, and vice-versa.

Various physiological and biochemical responses of two good biomonitor plant species i.e. Datura alba and Ricinus communis were studied along two roads in the Punjab, Pakistan. Chlorophyll a, b, total chlorophylls, carotenoids, total free amino acids, total soluble proteins, total antioxidant activity, stomatal conductance, photosynthetic rate, internal CO 2 concentration, transpiration rate, and water use efficiency of D. alba and R. communis were examined at different sites along both roads. Photosynthetic rate of both plant species was found to be affected. Reduced transpiration rate and stomatal conductance were also noted. However, elevated internal CO 2 concentration and water use efficiency were recorded. Total soluble proteins got reduced, but, we found a tremendous increase in total antioxidant activity and total free amino acids in both plant species. D. alba was found to be more affected by the adverse effects of roadside air borne pollutants. Although R. communis was also affected but it showed minimal variation in all parameters compared to the control. Hence, our results suggest that R. communis is more resistant to urban roadside air pollution compared to D. alba and would be a good choice as phytoremediator of traffic borne pollutants, whereas, D. alba could be a better biomonitoring plant., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Brugmansia candida (syn. Datura candida) is a South American native plant that produces tropane alkaloids. Hyoscyamine, 6β-hydroxyhyoscyamine (anisodamine), and scopolamine are the most important ones due to their anticholinergic activity. These bioactive compounds have been historically and widely applied in medicine and their demand is continuous. Their chemical synthesis is costly and complex, and thereby, these alkaloids are industrially produced from natural producer plants. The production of these secondary metabolites by plant in vitro cultures such as hairy roots presents certain advantages over the natural source and chemical synthesis. It is well known that hairy roots produced by Agrobacterium rhizogenes infection are fast-growing cultures, genetically stable and able to grow in hormone-free media. Additionally, recent progress achieved in the scaling up of hairy root cultures makes this technology an attractive tool for industrial processes. This chapter is focused on the methods for the induction and establishment of B. candida hairy roots. In addition, the scaling up of hairy root cultures in bioreactors and tropane alkaloid analysis is discussed.

Insect carnivores frequently use olfactory cues from plants to find prey or hosts. For plants, the benefits of attracting parasitoids have been controversial, partly because parasitoids often do not kill their host insect immediately. Furthermore, most research has focused on the effects of solitary parasitoids on growth and feeding of hosts, even though many parasitoids are gregarious (multiple siblings inhabit the same host). Here, we examine how a gregarious parasitoid, the tachinid fly Drino rhoeo, uses olfactory cues from the host plant Datura wrightii to find the sphingid herbivore Manduca sexta, and how parasitism affects growth and feeding of host larvae. In behavioral trials using a Y-olfactometer, female flies were attracted to olfactory cues emitted by attacked plants and by cues emitted from the frass produced by larval Manduca sexta. M. sexta caterpillars that were parasitized by D. rhoeo grew to lower maximum weights, grew more slowly, and ate less of their host plant. We also present an analytical model to predict how tri-trophic interactions change with varying herbivory levels, parasitization rates and plant sizes. This model predicted that smaller plants gain a relatively greater benefit compared to large plants in attracting D. rhoeo. By assessing the behavior, the effects of host performance, and the variation in ecological parameters of the system, we can better understand the complex interactions between herbivorous insects, the plants they live on and the third trophic level members that attack them.

Pollinators use their sense of smell to locate flowers from long distances, but little is known about how they are able to discriminate their target odor from a mélange of other natural and anthropogenic odors. Here, we measured the plume from Datura wrightii flowers, a nectar resource for Manduca sexta moths, and show that the scent was dynamic and rapidly embedded among background odors. The moth's ability to track the odor was dependent on the background and odor frequency. By influencing the balance of excitation and inhibition in the antennal lobe, background odors altered the neuronal representation of the target odor and the ability of the moth to track the plume. These results show that the mix of odors present in the environment influences the pollinator's olfactory ability., (Copyright © 2014, American Association for the Advancement of Science.)

Host plant choice is of vital importance for egg laying herbivorous insects that do not exhibit brood care. Several aspects, including palatability, nutritional quality and predation risk, have been found to modulate host preference. Olfactory cues are thought to enable host location. However, experimental data on odor features that allow choosing among alternative hosts while still in flight are not available. It has previously been shown that M. sexta females prefer Datura wrightii compared to Nicotiana attenuata. The bouquet of the latter is more intense and contains compounds typically emitted by plants after feeding-damage to attract the herbivore's enemies. In this wind tunnel study, we offered female gravid hawkmoths (Manduca sexta) odors from these two ecologically relevant, attractive, non-flowering host species. M. sexta females preferred surrogate leaves scented with vegetative odors form both host species to unscented control leaves. Given a choice between species, females preferred the odor bouquet emitted by D. wrightii to that of N. attenuata. Harmonizing, i.e. adjusting, volatile intensity to similar levels did not abolish but significantly weakened this preference. Superimposing, i.e. mixing, the highly attractive headspaces of both species, however, abolished discrimination between scented and non-scented surrogate leaves. Beyond ascertaining the role of blend composition in host plant choice, our results raise the following hypotheses. (i) The odor of a host species is perceived as a discrete odor 'Gestalt', and its core properties are lost upon mixing two attractive scents (ii). Stimulus intensity is a secondary feature affecting olfactory-based host choice (iii). Constitutively smelling like a plant that is attracting herbivore enemies may be part of a plant's strategy to avoid herbivory where alternative hosts are available to the herbivore.

We evaluated the costs and benefits of continuous high-level expression of defenses relative to naturally-induced defenses in field-grown Datura wrightii in the presence and absence of herbivores. We induced D. wrightii plants with monthly applications of the plant hormone methyl jasmonate (MeJA) and assessed levels of inducible proteinase inhibitors (Pins). MeJA application increased Pin production by 124 %, whereas the increase in Pins due to herbivory was more modest (36 %). Pin induction was costly and significantly reduced plant fitness compared to unmanipulated plants both in the presence and absence of herbivores. Although MeJA-treated plants exposed to herbivory suffered significantly less herbivore damage than unmanipulated plants exposed to herbivory, this was not accompanied by a corresponding fitness benefit. In contrast to glasshouse studies in which protected plants never expressed Pins, Pin induction occurred in field-grown plants not treated with MeJA and completely protected from herbivory. Subsequent experiments confirmed that putative herbivore defenses can be induced abiotically in D. wrightii as: 1) Pin levels did not differ significantly between field-grown plants protected from herbivory and plants exposed to chronic herbivory over the full season; and 2) plants exposed to ambient UV-B light in the absence of herbivory expressed low levels of Pins after two wk of exposure, whereas plants protected from UV-B remained uninduced. The costs of induced responses may be relatively easily determined under field conditions, but there may be many inducing agents in the field, and the benefits of induction may be difficult to associate with any single inducing agent.

Plants experiencing herbivory suffer indirect costs beyond direct loss of leaf area, but differentially so based on the herbivore involved. We used a combination of chlorophyll fluorescence imaging and gas exchange techniques to quantify photosynthetic performance, the efficiency of photochemistry, and heat dissipation to examine immediate and longer-term physiological responses in the desert perennial Datura wrightii to herbivory by tobacco hornworm, Manduca sexta. Herbivory by colony-reared larvae yielded no significant reduction in carbon assimilation, whereas herbivory by wild larvae induced a fast and spreading down-regulation of photosynthetic efficiency, resulting in significant losses in carbon assimilation in eaten and uneaten leaves. We found both an 89 % reduction in net photosynthetic rates in herbivore-damaged leaves and a whole-plant response (79 % decrease in undamaged leaves from adjacent branches). Consequently, herbivory costs are higher than previously estimated in this well-studied plant-insect interaction. We used chlorophyll fluorescence imaging to elucidate the mechanisms of this down-regulation. Quantum yield decreased up to 70 % in a small concentric band surrounding the feeding area within minutes of the onset of herbivory. Non-photochemical energy dissipation by the plant to avoid permanent damage was elevated near the wound, and increased systematically in distant areas of the leaf away from the wound over subsequent hours. Together, the results underscore not only potential differences between colony-reared and wild-caught herbivores in experimental studies of herbivory but also the benefits of quantifying physiological responses of plants in unattacked leaves.

Heterogeneous distribution of resources in most plant populations results in a mosaic of plant physiological responses tending to maximize plant fitness. This includes plant responses to trophic interactions such as herbivory and mycorrhizal symbiosis which are concurrent in most plants. We explored fitness costs of 50% manual defoliation and mycorrhizal inoculation in Datura stramonium at different light availability and soil fertility environments in a greenhouse experiment. Overall, we showed that non-inoculated and mycorrhiza-inoculated plants did not suffer from 50% manual defoliation in all the tested combinations of light availability and soil fertility treatments, while soil nutrients and light availability predominately affected plant responses to the mycorrhizal inoculation. Fifty percent defoliation had a direct negative effect on reproductive traits whereas mycorrhiza-inoculated plants produced larger flowers than non-inoculated plants when light was not a limiting factor. Although D. stramonium is a facultative selfing species, other investigations had shown clear advantages of cross-pollination in this species; therefore, the effects of mycorrhizal inoculation on flower size observed in this study open new lines of inquiry for our understanding of plant responses to trophic interactions. Also in this study, we detected shifts in the limiting resources affecting plant responses to trophic interactions.

• Although a major expectation of coevolutionary theory between plants and herbivores is the occurrence of reciprocal local adaptation, this has remained almost untested. Thus, we evaluated the presence and variation in the patterns of reciprocal local adaptation between an herbivorous insect and its host plant. • Two four-by-four cross-infestation experiments were performed under similar abiotic conditions. The first one was done under laboratory conditions to estimate herbivore individual performance while the second one was performed in a common garden to simultaneously estimate herbivore population growth rate as well as seed production and plant defenses (resistance and tolerance to herbivory). • The patterns of population differentiation for the herbivore and the plant were not independent of each other, showing all the possible outcomes from locally adapted to maladapted populations. These results indicate differences in the magnitude of local adaptation. While an association between resistance and herbivore performance was observed, there was no clear pattern between tolerance and herbivore local adaptation. • Our results demonstrated the occurrence of reciprocal local adaptation following the pattern expected by theory: when the herbivores or the plants were adapted, the other species was non-adapted or even maladapted., (© 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.)

Herbivores may induce plants to produce an array of volatile organic compounds (herbivore-induced plant volatiles, or HIPVs) after damage, and some natural enemies of herbivores are attracted by those HIPVs. The production of HIPVs by the undomesticated species Datura wrightii was quantified in response to damage by its natural community of herbivores or the plant hormone methyl jasmonate (MeJA) over plant's 6-month growing season. Patterns of HIPV production were compared to the seasonal abundance of D. wrightii's two most abundant herbivores, the chrysomelid beetle Lema daturaphila and the mirid bug Tupiocoris notatus, and their shared generalist predator, the lygaeid bug Geocoris pallens. HIPV production was especially high in the spring, when plants were growing vegetatively, but HIPV production declined after plants began to flower and produce fruit, and these volatiles no longer were inducible by September. The composition of the HIPV blends also changed seasonally. HIPV production and composition were partially restored by "rejuvenating" plants back to the vegetative growth stage independently of season by cutting them back and allowing them to resprout and regrow vegetatively. HIPV production of D. wrightii in the field is limited to the earlier ontogenetic stages of growth, despite the fact that both herbivores and their shared natural enemy inhabited plants throughout the full season. The adaptive value of HIPV production in D. wrightii may be constrained by plant ontogeny to the vegetative stages of plant growth.

In southwestern USA, the jimsonweed Datura wrightii and the nocturnal moth Manduca sexta form a pollinator-plant and herbivore-plant association. Because the floral scent is probably important in mediating this interaction, we investigated the floral volatiles that might attract M. sexta for feeding and oviposition. We found that flower volatiles increase oviposition and include small amounts of both enantiomers of linalool, a common component of the scent of hawkmoth-pollinated flowers. Because (+)-linalool is processed in a female-specific glomerulus in the primary olfactory centre of M. sexta, we hypothesized that the enantiomers of linalool differentially modulate feeding and oviposition. Using a synthetic mixture that mimics the D. wrightii floral scent, we found that the presence of linalool was not necessary to evoke feeding and that mixtures containing (+)- and/or (-)-linalool were equally effective in mediating this behaviour. By contrast, females oviposited more on plants emitting (+)-linalool (alone or in mixtures) over control plants, while plants emitting (-)-linalool (alone or in mixtures) were less preferred than control plants. Together with our previous investigations, these results show that linalool has differential effects in feeding and oviposition through two neural pathways: one that is sexually isomorphic and non-enantioselective, and another that is female-specific and enantioselective.

Background and Aims: A deeper understanding of mutualism can be reached by studying systems with measurable costs and benefits. Most studies of this type focus on an unusual class of obligate, species-specific pollination mutualisms. The interaction between Datura wrightii (Solanaceae) and the hawkmoth Manduca sexta offers similar advantages but greater generality. Adult moths both nectar at and deposit eggs on the same plant; larvae are herbivorous. The antagonistic component of this interaction has been well studied. Here the role of M. sexta as a pollinator of D. wrightii, particularly in the context of this moth's frequent nectaring visits to the bat-pollinated plant Agave palmeri, is documented., Methods: Hand-pollinations were used to determine breeding system and the reproductive consequences of mixed loads of A. palmeri and D. wrightii pollen. Plants and moths were caged overnight to assess whether nectaring visits led to fruit and seed set. Finally, pollen deposited on field-collected stigmas was identified, with a particular focus on documenting the presence of D. wrightii and A. palmeri grains., Key Results: Datura wrightii is highly self-compatible, and a visit that deposits either outcross or self pollen almost doubles fruit and seed set compared with unvisited flowers. Manduca sexta transferred enough pollen to produce fruit and seed sets comparable to hand-pollination treatments. Agave palmeri did not interfere with D. wrightii success: in the field, stigmas received almost pure D. wrightii pollen, and hand-addition of large quantities of A. palmeri pollen had no measurable effect on fruit and seed set., Conclusions: The floral visitation component of the D. wrightii-M. sexta interaction is indeed mutualistic. This finding is essential background to future development of this interaction as a model system for studying mutualism's costs and benefits. It is already proving valuable for dissecting third-species effects on the outcome of mutualism. Results indicate that M. sexta's heavy visitation to A. palmeri has no negative effect on the benefits conferred to D. wrightii. However, it can be predicted to augment M. sexta populations to the point where the costs of the interaction begin to exceed its benefits.

In soil, chromium can be found in two main valence states: hexavalent Cr(VI) and trivalent Cr(III). In this study, we investigated the impact of Cr on photosynthetic gas exchange, photosystem II (PSII) activity, Cr translocation and accumulation, proline content and alkaloids production, i.e. scopolamine and hyoscyamine, in Datura innoxia. Cr uptake was influenced by its oxidation state and its concentration in growth medium. The plant roots were determined as being the main organ of Cr accumulation. Cr(VI) was more toxic than Cr(III) as indicated by reduction in plant biomass and net photosynthesis. The stomatal conductance showed a similar trend to that of photosynthetic capacity. Cr(III) and Cr(VI) had a different impact on substomatal CO(2) concentration then Cr toxicity was related to its oxidation states. In plants stressed with a Cr(VI) excess, a down regulation of PSII activity was observed with an impairment of photochemical activity. Indeed, the maximum quantum yield of PSII (F(v)/F(m)), the quantum yield of PSII (PhiPSII) and the efficiency of excitation capture by open centers (F'(v)/F'(m)) decreased. Cr(III) had little effects on PSII primary photochemistry, whatever its form induces an increase of scopolamine content without changes in hyoscyamine content in leaves of D. innoxia. These results provide that chromium contamination can change the secondary metabolites composition of leaves, thereby, impacting the quality, safety and efficacy of natural plant products synthesized by D. innoxia plants.

Datura (Solanaceae)is a small genus of plants that,for long, was thought to occur naturally in both the New and Old Worlds. However, recent studies indicate that all species in the genus originated in the Americas. This finding has prompted the conclusion that no species of Datura could have been present in the Old World prior to its introduction there by Europeans in the early 16th century CE. Further, the textual evidence traditionally cited in support of a pre-Columbian Old World presence of Datura species is suggested to be due to the misreading of classical Greek and Arabic sources. As a result, botanists generally accept the opinion that Datura species were transferred into the Old World in the post-Columbian period. While the taxonomic and geographic evidence for a New World origin for all the Datura species appears to be well supported, the assertion that Datura species were not known in the Old World prior to the 16th century is based on a limited examination of the pre-Columbian non-Anglo sources. We draw on old Arabic and Indic texts and southern Indian iconographic representations to show that there is conclusive evidence for the pre-Columbian presence of at least one species of Datura in the Old World. Given the systematic evidence for a New World origin of the genus, the most plausible explanation for this presence is a relatively recent but pre-Columbian (probably first millennium CE) transfer of at least one Datura species, D. metel, into the Old World. Because D. metel is a domesticated species with a disjunct distribution,this might represent an instance of human-mediated transport from the New World to the Old World, as in the case of the sweet potato (Ipomoea batatas).

Plants in the family Solanaceae possess numerous traits that are induced from damage from herbivores. Many of these also can be induced by exposing plants to the plant hormone jasmonic acid or its volatile ester methyl jasmonate. Datura wrightii (Solanaceae) is dimorphic for leaf trichome morphology in most southern California populations. Trichome phenotype is governed by a single gene, and the glandular trichome condition is dominant and under developmental control. This study addressed two major objectives. The first was to determine if mature plants with glandular or nonglandular trichomes responded differentially to methyl jasmonate. The second objective was to determine if exposure of seedlings to methyl jasmonate during the period of trichome differentiation altered either the phenotype or the density of trichomes that mature plants expressed. Methyl jasmonate induced from 200 to 800 microg/ml of proteinase inhibitor activity and increased the activity of polyphenol oxidase by more than threefold depending on the experiment. These increases did not differ significantly between plants expressing glandular or nonglandular trichomes. Methyl jasmonate exposure did not increase the activity of peroxidase or the concentration of scopolamine or hyoscyamine, the two major alkaloids of Datura. Exposure to methyl jasmonate during trichome differentiation did not affect either the final trichome phenotype or the density of either type of trichome, but did increase the production of acylsugars in glandular trichomes by 44%. Because trichome phenotype was not inducible, and because both trichome phenotypes showed similar increases in proteinase inhibitors and polyphenol oxidase activity, the methyl-jasmonate-inducible responses of D. wrightii are independent of trichome phenotype in D. wrightii.

The costs and benefits of defensive traits in plants can have an ecological component that arises from the effect of defenses on the natural enemies of herbivores. We tested if glandular trichomes in Datura wrightii, a trait that confers resistance to several species of herbivorous insects, impose an ecological cost by decreasing rates of predation by the natural enemies of herbivores. For two common herbivores of D. wrightii, Lema daturaphila and Tupiocoris notatus, several generalized species of natural enemies exhibited lower rates of predation on glandular compared to non-glandular plants. Lower rates of predation were associated with reductions in the residence time and foraging efficiency of natural enemies on plants with glandular trichomes, but not with direct toxic effects of glandular exudate. Our results suggest that the benefit of resistance to herbivores conferred by glandular trichomes might be offset by the detrimental effect of this trait on the natural enemies of herbivores, and that the fitness consequences of this trichome defense might depend on the composition and abundance of the natural-enemy community.

Hairy roots obtained by transformation via Agrobacterium rhizogenes provide an artificial plant material devoid of aerial parts with high growth on hormone-free media. Fundamental knowledge of hairy root physiology is essential to develop and control its culture. In contrast to shake-flask cultures, a bioreactor set-up combined with on-line data logging provides an efficient tool to study rapid physiological variations in hairy root cultures. Datura innoxia hairy roots were grown in a bioreactor equipped with on-line data analyses of pH, dissolved oxygen (pO2), conductivity, oxygen, and carbon dioxide. The experiments were done at a constant temperature and in the absence of light cues. The results obtained showed that the carbon dioxide evolution rate (CER) presented regular oscillations during the culture. Similar oscillations were also observed for the oxygen uptake rate (OUR). These signals were treated mathematically to look for the existence of a rhythm. An autocorrelation function was used to detect any periodic components. The results demonstrate that hairy root respiration exhibited peaks of 1 day. These oscillations, having a period of about 24 h, were also observed in pH and conductivity signals, although not for the pO2 signal. The data acquired in the absence of hairy roots showed that the observed periodic behavior was not an artifact. No effect on rhythms was observed by the imposition of an external "day/night" cycle. The fact that oscillations persisted in the absence of external stimuli, with a free-running period of 24 h, suggests that a circadian rhythm exists in hairy roots of D. innoxia.

As part of a study of the roles of the sensory subsystem devoted to CO(2) in the nectar-feeding moth Manduca sexta, we investigated CO(2) release and nectar secretion by flowers of Datura wrightii, a preferred hostplant of Manduca. Datura flowers open at dusk and wilt by the following noon. During the first hours after dusk, when Manduca feeds, the flowers produce considerable amounts of nectar and emit levels of CO(2) that should be detectable by moths nearby. By midnight, however, both nectar secretion and CO(2) release decrease significantly. Because nectar production requires high metabolic activity, high floral CO(2) emission may indicate food abundance to the moths. We suggest that hovering moths could use the florally emitted CO(2) to help them assess the nectar content before attempting to feed in order to improve their foraging efficiency.

Models accounting for genetic variation for resistance to herbivores within plant populations often postulate a balance between the costs of that resistance and its benefits. The production of glandular trichomes by Datura wrightii was shown to be costly in a previous one-year study because plants producing glandular trichomes (sticky plants), a factor conferring resistance to some insect herbivores, also produced 45% fewer seeds than plants producing nonglandular trichomes (velvety plants) when grown in a common garden. Because sticky plants tended to be larger than velvety plants but produced fewer seed capsules, we postulated an allocation trade-off in which velvety plants are more reproduction-dominated whereas sticky plants are more growth-dominated. If a greater commitment to vegetative growth eventually allows sticky plants to compensate for reduced seed production, we would expect a reduction or elimination of the cost of resistance over time in this perennial plant. We monitored growth, survival, and seed production of plants from defined crosses of local populations for three years in a common garden when exposed to and protected from herbivores, and with and without supplemental water. The majority of plants exposed to herbivores had died by the end of the study. We used standard life-table methods to determine the net reproductive rate (R0) and the finite rate of increase (lambda) of plants of each trichome type. After three years, when plants were protected from herbivores, sticky plants were 187-245% larger than velvety plants, depending upon irrigation treatment, but sticky plants continued to be less efficient in producing seeds per unit of canopy volume. Even though the total seed production of sticky plants eventually equaled that of velvety plants, the advantage of earlier reproduction by velvety plants increased lambda by 55-230% over that of sticky plants, depending upon herbivore and irrigation treatment. Exposure to herbivores reduced lambda by 69-83%, depending upon plant type and irrigation treatment, whereas supplemental irrigation increased lambda by 29-175%, depending upon plant type and exposure to herbivores. Although there was a large allocation trade-off between growth and reproduction, the benefits of such a trade-off did not emerge before most plants were killed by herbivores. The cost of producing glandular trichomes strictly for herbivore resistance continued to exceed its benefits, and in the absence of other, unmeasured benefits from the suite of life-history characters associated with glandular trichome production, natural selection is expected to eliminate this costly resistance trait from D. wrightii populations.

Regeneration of adventitious shoots from young leaves of Datura metel is described. Shoot buds developed on MS medium with 2 mg/l and elongated on hormone-free solid basal medium. The microshoots failed to produce alkaloids, but a number of steroidal compounds were detected. The C(28) sterol 3beta,24xi-dihydroxy-ergosta-5,25-dienolide, regarded as the precursor of withanolides and related steroidal lactones, was identified. The withanolide 12-deoxywithastramonolide was also detected.

This study evaluated how natural selection act upon two proposed alternatives of defence (growth and resistance) against natural enemies in a common garden experiment using genetic material (full-sibs) from three populations of the annual plant Datura stramonium. Genetic and phenotypic correlations were used to search for a negative association between both alternatives of defence. Finally, the presence/absence of natural enemies was manipulated to evaluate the selective value of growth as a response against herbivory. Results indicated the presence of genetic variation for growth and resistance (1--relative damage), whereas only population differentiation for resistance was detected. No correlation between growth and resistance was detected either at the phenotypic or the genetic level. Selection analysis revealed the presence of equal fitness benefits of growth and resistance among populations. The presence/absence of natural herbivores revealed that herbivory did not alter the pattern of selection on growth. The results indicate that both strategies of defence can evolve simultaneously within populations of D. stramonium.