Showing papers in "Chemoecology in 2012"

A review of chemical ecology in poison frogs

Abstract: Herein we review what is known about the chemical ecology of poison frogs with a focus on dendrobatid poison frogs. While five anuran families are known to have an alkaloid-derived chemical defense, the dendrobatids have been studied in greatest detail and provides chemical ecologists with a complex model system for understanding how chemical defenses operate in real time and may have evolved through evolutionary time. We describe the diversity of alkaloid defenses known from frogs, alkaloid sequestration, biosynthesis and modification, and we review what is known concerning arthropod sources for alkaloids. There is variation in nearly every attribute of the system and we try to describe some of the challenges associated with unraveling the complexities of this model system.

Sequestered defensive toxins in tetrapod vertebrates: principles, patterns, and prospects for future studies

Abstract: Chemical defenses are widespread among animals, and the compounds involved may be either synthesized from nontoxic precursors or sequestered from an environmental source. Defensive sequestration has been studied extensively among invertebrates, but relatively few examples have been documented among vertebrates. Nonetheless, the number of described cases of defensive sequestration in tetrapod vertebrates has increased recently and includes diverse lineages of amphibians and reptiles (including birds). The best-known examples involve poison frogs, but other examples include natricine snakes that sequester toxins from amphibians and two genera of insectivorous birds. Commonalities among these diverse taxa include the combination of consuming toxic prey and exhibiting some form of passive defense, such as aposematism, mimicry, or presumptive death-feigning. Some species exhibit passive sequestration, in which dietary toxins simply require an extended period of time to clear from the tissues, whereas other taxa exhibit morphological or physiological specializations that enhance the uptake, storage, and/or delivery of exogenous toxins. It remains uncertain whether any sequestered toxins of tetrapods bioaccumulate across multiple trophic levels, but multitrophic accumulation seems especially likely in cases involving consumption of phytophagous or mycophagous invertebrates and perhaps consumption of poison frogs by snakes. We predict that additional examples of defensive toxin sequestration in amphibians and reptiles will be revealed by collaborations between field biologists and natural product chemists. Candidates for future investigation include specialized predators on mites, social insects, slugs, and toxic amphibians. Comprehensive studies of the ecological, evolutionary, behavioral, and regulatory aspects of sequestration will require teams of ecologists, systematists, ethologists, physiologists, molecular biologists, and chemists. The widespread occurrence of sequestered defenses has important implications for the ecology, evolution, and conservation of amphibians and reptiles.

Species-specific responses of herbivores to within-plant and environmentally mediated between-plant variability in plant chemistry

Abstract: Allocation of resources to growth and defense against herbivores crucially affects plant competitiveness and survival, resulting in a specific distribution of assimilates and defense compounds within plant individuals Additionally, plants rarely experience stable environmental conditions, and adaptations to abiotic and biotic stresses may involve shifts in resistance to herbivores We studied the allocation of phytochemicals in Brassica oleracea (Brussels sprouts) due to leaf age, drought stress and herbivore damage and assessed effects on two lepidopteran herbivores differing in diet breadth: the generalist Spodoptera littoralis and the specialist Pieris brassicae Glucosinolates as secondary defense compounds and total nitrogen and carbon were quantified and linked to plant palatability, ie, herbivore feeding preference Herbivore responses were highly species-specific and partially related to changes in phytochemicals Spodoptera littoralis preferred middle-aged leaves with intermediate levels of glucosinolates and nitrogen over young, glucosinolate and nitrogen rich leaves, as well as over old leaves, poor in glucosinolates and nitrogen In contrast, P brassicae preferred young leaves Both species preferred severely drought-stressed plants to the well-watered control, although analyzed glucosinolate concentrations did not differ Both S littoralis and P brassicae feeding induced an increase of indole glucosinolate levels, which may explain a reduced consumption of damaged plants detected for S littoralis but not for P brassicae By revealing distinct, sometimes contrasting responses of two insect herbivores to within-plant and stress-mediated intraspecific variation in phytochemistry of B oleracea, this study emphasizes the need to consider specific herbivore responses to understand and predict the interactions between herbivores and variable plants

Nuchal Glands: A Novel Defensive System in Snakes

Abstract: Of the various chemical defensive adaptations of vertebrates, nuchal glands are among the most unusual. First described in a Japanese natricine snake, Rhabdophis tigrinus, in 1935, these organs are embedded under the skin of the neck region as a series of paired glands that have neither lumina nor ducts. The major chemical components of the glandular fluid are bufadienolides, which are cardiotonic steroids also found in the skin secretion of toads. Here we review early studies of nuchal glands and briefly introduce our recent findings on the sequestration of bufadienolides from consumed toads and the maternal provisioning of those sequestered compounds. We summarize behavioral studies associated with the antipredator function of the nuchal glands, which have been conducted during our more than decade-long collaboration. Results of preliminary analyses on the possible costs of toad-eating and on the ultrastructure of the nuchal glands are also presented. Finally, we discuss the evolutionary origin of the nuchal glands and suggest future directions designed to understand the biological importance of these novel vertebrate organs, which have evolved in a limited number of snake species.

Comparison of associative learning of host-related plant volatiles in two parasitoids with different degrees of host specificity, Cotesia marginiventris and Microplitis croceipes

Abstract: The ability of parasitoids to learn a wide range of volatiles, including ecologically relevant and novel odors, and respond favorably to the learned stimuli has been documented for various species. Comparison of odor learning in closely related species can elucidate adaptive differences in species responses to infochemicals. The present study used a Y-tube olfactometer to compare odor learning and priming of behavioral responses of two parasitoids, Cotesia marginiventris (Cresson) and Microplitis croceipes (Cresson), to four selected host-related volatile compounds which have been previously shown to elicit behavioral response in both species; trans-2-hexanal, α-pinene, cis-3-hexenyl butyrate, and (E,E)-α-farnesene. The two parasitoid species differ in their degree of specialization at the host level with M. croceipes having a more specialized host range, but otherwise represent infochemical generalist parasitoid species at the plant level. Naive females as well as females that had been trained to associate sugar water with the test compounds were tested. Compared to naive females, trained females of C. marginiventris showed a significant increase in behavioral response to all four tested compounds. In contrast, trained females of M. croceipes showed a significant increase in behavioral response only to α-pinene, and (E,E)-α-farnesene. Overall, the species with a wider host range, C. marginiventris showed a greater learning-induced increase in response than the species with a relatively specialized host range, M. croceipes. The results imply that animals with different ecological constraints may show variations in learning. The adaptive significance of behavioral responses as related to dietary specializations of the parasitoids is discussed.

The occurrence of defensive alkaloids in non-integumentary tissues of the Brazilian red-belly toad Melanophryniscus simplex (Bufonidae)

Abstract: The red-belly toads (Melanophryniscus) of southern South America secrete defensive alkaloids from dermal granular glands. To date, all information on Melanophryniscus alkaloids has been obtained by extraction from either skins or whole organisms; however, in other amphibians, tetrodotoxins, samandarines, and bufadienolides have been detected in both skin and other organs, which raise the possibility that lipophilic alkaloids may occur in non-integumentary tissues in Melanophryniscus as well. To test this hypothesis, we studied the distribution of alkaloids in the skin, skeletal muscle, liver, and mature oocytes of the red-belly toad M. simplex from three localities in southern Brazil. Gas chromatography and mass spectrometry of skin extracts from 11 individuals of M. simplex resulted in the detection of 47 alkaloids (including isomers), 9 unclassified and 38 from 12 known structural classes. Each alkaloid that was present in the skin of an individual was also present in the same relative proportion in that individual’s skeletal muscle, liver, and oocytes. The most abundant and widely distributed alkaloids were the pumiliotoxins 251D, 267C, and 323A, 5,8-disubstituted indolizidines 207A and 223D, 5,6,8-trisubstituted indolizidine 231B, 3,5-disubstituted pyrrolizidines cis-223B and cis- and trans-251K, and izidine 211C. We report the first record of piperidines in Melanophryniscus, bringing the total number of alkaloid classes detected in this genus to 16. Alkaloid composition differed significantly among the three study sites. The functional significance of defensive chemicals in non-integumentary tissues is unknown.

O-Coumaric acid from invasive Eupatorium adenophorum is a potent phytotoxin

Abstract: A phytochemical study of the invasive Eupatorium adenophorum indicated that the plant was rich in a phenolic compound o-coumaric acid (or 2-hydroxycoumaric acid) Biological investigations with the model plant Arabidopsis thaliana and crop plants showed that o-coumaric acid strongly inhibited seed germination, plant growth and root elongation, reduced the photosynthesis in old leaves, and induced the root cell death and the expression of genes related to senescence, oxidative stress, and systemic acquired resistance The phytotoxic effects of o-coumaric acid exhibit selectivity between under- and above-ground parts of test plants and between E adenophorum and other plants These results indicate that o-coumaric acid is a potent toxin that might play an important role in the competition of E adenophorum with its neighboring plants during its invasion and establishment

Chemical investigations of defensive steroid sequestration by the Asian snake Rhabdophis tigrinus

Abstract: Rhabdophis tigrinus is an Asian natricine snake that possesses unusual defensive glands on the dorsal surface of its neck. These nuchal glands typically contain cardiotonic steroidal toxins known as bufadienolides, which are also abundant in the skin of toads. Feeding experiments demonstrated that toads consumed as prey are the ultimate sources of the bufadienolides in nuchal glands of R. tigrinus. Indeed, snakes on a toad-free Japanese island (Kinkasan, Miyagi Prefecture) lack these compounds in their nuchal glands, confirming that these snakes are unable to synthesize defensive bufadienolides. However, when snakes from Kinkasan are fed toads in the laboratory, they accumulate bufadienolides in their nuchal glands, indicating that they have not lost the ability to sequester defensive compounds from prey. In contrast, R. tigrinus from a toad-rich island (Ishima, Tokushima Prefecture) possess large quantities of bufadienolides, reflecting the abundance of toads from which these compounds can be sequestered. Feeding experiments involving gravid R. tigrinus demonstrated that bufadienolides can be provisioned to offspring so that hatchlings are chemically defended before their first toad meal. Maternal provisioning of bufadienolides can take place through two routes: by deposition in yolk and by diffusion in utero, even late in gestation. We applied bufadienolides to the surface of eggs from Kinkasan and found that the embryos are able to take up these compounds into their nuchal glands, demonstrating the feasibility of uptake across the eggshell. Female R. tigrinus provision bufadienolides to their offspring in direct proportion to their own level of chemical defense. By feeding toad-derived bufotoxins to R. tigrinus hatchlings, we determined that the sequestration of these compounds involves at least three types of modification: hydrolytic cleavage of suberylarginine side chains, hydroxylation, and epimerization.

First-instar monarch larval growth and survival on milkweeds in southern California: effects of latex, leaf hairs and cardenolides

Abstract: Growth rate and survival of first-instar larvae of Danaus plexippus, a milkweed specialist, depended on milkweed species, and was related to the amount of latex produced from wounds, leaf cardenolide concentrations and the presence of leaf hairs. Larval growth was more rapid and survival was higher on leaves of Asclepias californica with experimentally reduced latex, and this species has characteristically high latex, low- to mid-range cardenolide concentrations, and very hirsute leaves. Similarly, growth was higher on reduced latex leaves of both A. eriocarpa (a high latex/high cardenolide, hirsute species) and A. erosa (glabrous fleshy leaves, high latex/high cardenolides). There were no differences in either survival or growth rate between larvae on reduced latex or control leaves of the low latex/low cardenolide A. fascicularis with soft glabrous leaves and both survival and growth rate were higher on this species than the other species tested. Larval growth rates on leaves with reduced latex were similar among ten milkweed species tested to date but differed from growth rates on intact leaves suggesting that latex and possibly included cardenolides are both important in first-instar monarch larval growth, development and survival. We show for a range of ecologically important milkweeds that experiments on cut plant material (no latex outflow) lead to higher growth rates compared to intact plants. Such laboratory assays based on detached leaves will be misleading if the objective is to determine the impact of treatments such as Bt-maize pollen on monarchs on field plants.

Volatile organic compounds and host-plant specialization in European corn borer E and Z pheromone races

Abstract: Plant volatile cues are considered the main source of information for ovipositing moths, which use chemical information to locate and recognize the host plant. In Europe, two sympatric populations of European corn borer (ECB; Ostrinia nubilalis, Hubner), the Z and E-pheromone races, feed mainly on maize and hop or mugwort, respectively. We studied the mechanisms of host-plant recognition and fidelity in ECB pheromone races by testing the attractiveness of host plants to gravid females in a flight tunnel and by analyzing the volatiles released from maize, mugwort, and hop during the scotophase, when the ovipositing flight of the ECB females occurs. In the wind tunnel bioassay, the Z-race and E-race females engaged in upwind flight and expressed a strong host fidelity to their respective main host plants; all three of these host plants possess distinctive volatile profiles specific as to blend and ratio. The host plants shared a certain number of ubiquitous volatiles present in various ratios that likely constitute a species-specific cue to host-seeking ECB moths. Our observations therefore suggest that ECB host fidelity is steered by plant volatiles that are present in species-specific ratios of ubiquitous volatile organic compounds.

Interpopulational variation in chemosensory responses to selected steroids from femoral secretions of male lizards, Podarcis hispanica, mirrors population differences in chemical signals

Abstract: Chemical signals are important for mate and species recognition If variation in chemical signals occurs between populations of the same species, these differences could later preclude mating between populations and lead to speciation In the Iberian wall lizard, Podarcis hispanica, the lipophilic fraction of femoral secretions of males is mainly a mix of steroids and fatty acids Among steroids, the most abundant compounds are cholesterol and cholesta-5,7-dien-3-ol, which are implicated in intraspecific communication and sexual selection Interpopulational differences in chemical signals of males, and in response to these chemicals, could contribute to reproductive isolation between populations, which would explain the known genetic differences between these populations Chemical analyses indicated that five distinct populations of this lizard from Madrid (Central Spain) differed in the proportions of two steroids (cholesterol and cholesta-5,7-dien-3-ol) in femoral secretions Moreover, lizards discriminated and had high chemosensory responses (ie, high tongue-flick rates) to these steroids, but showed interpopulational differences Lizards from populations with cold temperatures and high relative humidity (ie, northern Madrid) elicited higher responses to these steroids, whereas the converse occurred for lizards from populations occupying dry and hot habitats (ie, southern Madrid) Interestingly, the magnitude of the chemosensory responses to cholesta-5,7-dien-3-ol in each population mirrored the abundance of this compound in secretions of males of that population These results suggest that the importance of cholesta-5,7-dien-3-ol in males’ secretions might be lower for lizards from the southern populations These differences in the relative importance of chemical signals could explain reproductive isolation and cryptic speciation between populations of this lizard

Transient abiotic stresses lead to latent defense and reproductive responses over the Brassica rapa life cycle

Abstract: Plants can alter physiological and developmental trajectories in response to environmental cues by means of phenotypic plasticity. While cases of immediate plastic responses to different environments are well studied, phenotypic changes can also be delayed and occur in later life cycle stages. In this study, we investigated latent phenotypic plasticity in the development and chemical profile of Brassica rapa plants exposed to transient stress as seedlings. Four different stresses were applied to germinating seedlings: salinity, drought, nutrient deficiency, or acidity. Growth, reproduction, and glucosinolate chemical defenses (in leaves and seeds) were measured over the plants’ life cycles after normal conditions were restored. Despite initial stunting, B. rapa individuals recovered in total stem length and seed count compared with unstressed controls. There were, however, latent responses in flowering time, which was delayed in salinity-, drought-, or acid-stressed plants. Reductions in total flower count and total seed pod count were also observed in nutrient-deficiency stressed plants. Strikingly, previously stressed plants also showed latent differences in glucosinolate chemical defenses. Acid-stressed plants had higher concentrations of the plants’ major glucosinolate, gluconapin (3-butenylglucosinolate), in leaves and seeds, while nutrient deficiency-stressed plants had lower seed levels of gluconapin. Our experiments show that, despite outward recovery of growth, previously stressed B. rapa plants alter later defense and reproduction, leading to a plastic response delayed across life cycle stages. Thus, even transient, recoverable stress can have latent consequences for ecologically important chemical traits.

Screening and field evaluation of synthetic volatile blends attractive to adults of the tea weevil, Myllocerinus aurolineatus

Abstract: Plant volatiles are known to play a role in host location in many herbivorous insects. Although a few studies have determined the role of specific chemicals from herbivore-induced plant volatiles (HIPVs) in mediating interactions between conspecifics in insects belonging to Curculionidae, little is known about how this process works when different components are used. By measuring the behavioral responses of the tea weevil, Myllocerinus aurolineatus (Voss) (Coleoptera: Curculionidae), to a series of chemicals in a Y-tube olfactometer, we found that a blend containing (E/Z)-β-ocimene and (Z)-3-hexenyl acetate was attractive to male M. aurolineatus adults, and a blend containing 2-phenylethanol and (Z)-3-hexenyl acetate was attractive to female M. aurolineatus adults; both blends were as attractive to the insects as the volatiles emitted by the tea plants infested with adult weevils. A net cage experiment in the laboratory showed that traps baited with (E/Z)-β-ocimene plus (Z)-3-hexenyl acetate attracted the male herbivores, whereas the traps baited with 2-phenylethanol and (Z)-3-hexenyl acetate did not. Field experiments verified that tea plants exposed to a blend of (E/Z)-β-ocimene plus (Z)-3-hexenyl acetate attracted significantly more weevils than did the control plants or sticky traps baited with the above lure. These results suggest that the blend of (E/Z)-β-ocimene and (Z)-3-hexenyl acetate is an important signal which the tea weevil uses to locate its host, and is a strong candidate for an attractant that could be used to control the weevil.

Predators usurp prey defenses? Toxicokinetics of tetrodotoxin in common garter snakes after consumption of rough-skinned newts

Abstract: Snakes are common predators of organisms, such as amphibians, with toxic defenses that can be lethal to other predators. Because snakes do not have the option of dissecting prey into edible versus inedible components, they face a full dose of any chemical defenses encountered during attempted predation. This limitation has likely resulted in intense selection favoring the evolution of alternative mechanisms for dealing with prey toxins. These mechanisms can be physiological (e.g., resistance to prey toxins) or behavioral (e.g., toxin sampling and rejection). When physiological resistance arises, the possibility of bioaccumulation of a toxin results. We examined the coevolutionary interaction between the common garter snake (Thamnophis sirtalis) and the rough-skinned newt (Taricha granulosa), which contains a powerful neurotoxin called tetrodotoxin (TTX). In some populations syntopic with newts, individuals of T. sirtalis have evolved resistance to TTX. We examined the persistence of TTX in T. sirtalis after administration of an oral dose of TTX to investigate the possibility that snakes are sequestering TTX. The half-life of TTX in snake liver was estimated at 8.1 days. Accordingly, clearance of 99% of a single dose of TTX averages 61 days. Negative fitness consequences of intoxication during and after newt consumption may be balanced by co-opting the newts’ chemical defense for protection from the snakes’ own predators. Accounting of the coevolutionary dynamic between snakes and newts must incorporate post-consumption affects of lingering TTX.

Agriotes proximus and A. lineatus (Coleoptera: Elateridae): a comparative study on the pheromone composition and cytochrome c oxidase subunit I gene sequence

Abstract: The presence of geranyl octanoate, previously found in pheromone gland extracts of Agriotes lineatus females, was also demonstrated in gland extracts of A. proximus females. Similar to A. lineatus, geranyl butanoate was present only in trace amounts in A. proximus female gland extracts. In air entrainment samples of female A. lineatus and A. proximus beetles, the relative ratio of geranyl butanoate and geranyl octanoate was higher than that in gland extracts. In addition, comparison of a segment of the mitochondrial cytochrome c oxidase subunit I gene of feral specimens of A. lineatus and A. proximus showed >99% similarity. Both pheromone profile and nucleotide sequence analysis delineate close relationship between the investigated taxa and postulate taxonomic revision. Further studies on sympatric populations of A. lineatus and A. proximus are underway to investigate and better understand possible processes of species diversification.

Chemical profile of Festuca arundinacea extract showing allelochemical activity

Abstract: The allelopathic potential of fescue (Festuca arundinacea Shreb.) was investigated under field and laboratory conditions. In the field, incorporation of fescue aboveground biomass into the soil provided an effective weed control as it significantly reduced both the number and the dry weight of all weed species. The effect on weeds was species specific. The reduction of the most abundant species, Picris echioides, with respect to the number of individuals and their dry weight was 67 and 45%. Fescue aboveground biomass, harvested immediately before soil incorporation, was utilized in a bioassay-oriented fractionation, aimed at identifying the compounds in the toxic extracts of the plant. While phytotoxic activity was detected for the n-butanol fraction, no activity was found for the aqueous one. Germination of an indicator species, lettuce (Lactuca sativa L.), was reduced by 33% at the higher extract concentration of 20 mg/mL, owing to the increase of the number of abnormal seedlings. The LC/MS profile of the extract revealed the presence of two alkaloids, seven flavonol glycosides, and two flavonol aglyca. Quercetin 3-O-rutinoside, isorhamnetin 3-O-rutinoside, and kaempferol 3-O-rutinoside were reported in fescue for the first time.

Turning the game around: toxicity in a nudibranch-sponge predator–prey association

Abstract: Escalation theory proposes enemy-related selection as the most relevant factor of natural selection among individual organisms. When hazardous to predators, prey might be considered enemies that influence predator evolution. Opisthobranch molluscs that prey on chemically defended prey are an interesting study case on this subject. Predation on chemically defended species paved the way for opisthobranchs to enter in an arms race, developing means to detoxify and/or excrete harmful compounds, which led to the sequestration of those compounds and their self-defensive use, an escalation of defenses. Here we aim to understand whether the opisthobranch predator is better protected than its chemically defended prey, using as predator–prey model, a nudibranch (Hypselodoris cantabrica) and the sponge it preys upon (Dysidea fragilis), and from which it obtains deterrent chemical compounds. Specimens of both species were collected on the Portuguese coast, and their crude extracts were analyzed and used in palatability tests. Nudibranchs revealed a higher natural concentration of crude extract, probably due to a progressive accumulation of the compounds. Both predator and prey extracts revealed similar mixtures of deterrent metabolites (furanosesquiterpenes). Palatability tests revealed a more effective deterrence in the nudibranch extracts because significant rejection rates were observed at lower concentrations than those necessary for the sponge extracts to have the same effect. We concluded that the predator is chemically better protected than its prey, which suggests that its acquisition of chemical defenses reveals a defensive escalation.

Soil nitrogen availability and herbivore attack influence the chemical defenses of an invasive plant (Linaria dalmatica; Plantaginaceae)

Abstract: Chemical defenses are thought to contribute to the invasion success and impacts of many introduced plants; however, for most of these species, little is known about these compounds and how they vary in natural environments. Plant allelochemical concentrations may be affected by a variety of abiotic and biotic factors, including soil nutrients and herbivores. Moreover, such quantitative variation is likely to play an important role in species interactions involving these invasive plants. The purpose of this study was to examine patterns of variation in iridoid glycoside concentrations of the invasive plant Linaria dalmatica (Plantaginaceae). We conducted a greenhouse experiment to investigate the effect of soil nitrogen availability on iridoid glycoside concentrations. Results from this experiment showed that plant iridoid glycoside concentrations decreased with increased nitrogen availability. Additionally, plants were collected from multiple field sites in order to characterize the influence of population, soil nitrogen availability, and herbivore attack on iridoid glycoside variation. Results from field studies indicated that plants demonstrated considerable seasonal variation, as well as variation within and among populations, with iridoid glycoside concentrations ranging from approximately 1 to 15% dry weight. The relationship between soil nitrogen and plant iridoid glycosides varied among populations, with a strong negative correlation in one population, a marginally significant negative relationship in a second population, and no relationship in the remaining two populations. Additionally, we found a negative relationship between iridoid glycoside concentrations and plant injury by an introduced biocontrol agent, the stem-mining weevil Mecinus janthinus (Cucurlionidae). These results show that plant allelochemical concentrations can vary widely in natural environments and suggest that levels of plant defense may be reduced by increased soil nitrogen availability and herbivore attack in this invasive plant species.

Chemical camouflage of the slave-making ant Polyergus samurai queen in the process of the host colony usurpation (Hymenoptera: Formicidae)

Abstract: Founding queens of the obligatory social parasite ant Polyergus samurai usurp the host ant Formica japonica colony. The aggressive behaviors of F. japonica workers on the parasite queen disappear after the parasite queen kills the resident queen. To determine whether the parasite queen chemically mimics the host ants, we examined the aggressive behavior of F. japonica workers toward glass dummies applied with various extracts of the parasite queen and host workers. The crude extracts and hydrocarbon fraction reproduced the host workers’ behavior to the live ants. The extracts of the post-adoption parasite queen, as well as the nestmate extracts of F. japonica, did not elicit the aggressive behavior, but the extract of the pre-adoption parasite queen triggered attacks by the host workers. The nestmate recognition of host workers did not change, regardless of contact with the parasite. The gas chromatography and gas chromatography–mass spectrometry analyses indicated that the cuticular hydrocarbon (CHC) profile of the parasite queen drastically changed during the process of usurpation. Discriminant analysis showed the successfully usurped P. samurai queen had colony-specific CHC profiles. CHC profiles of the P. samurai queen who killed the host queen were more similar to those of the host queen than the workers, while the P. samurai queen who usurped the queenless colony had a profile similar to those of host workers. These results suggest that the P. samurai queen usually acquires the CHCs from the host queen during the fight, but from host wokers in queenless host colonies.

‘Push’ and ‘pull’ responses by fig wasps to volatiles released by their host figs

Abstract: In the specific mutualism between fig trees (Ficus) and their obligate pollinating fig wasps (Agaonidae), it is crucial that fig wasps can recognize the developmental stages of their host figs. However, the responses of fig wasps to volatiles released from figs during their developmental phases are less clearly understood and are the focus of this study. We extracted and identified the volatiles released from the figs of Ficus curtipes throughout their development. Using Y-tube choice experiments, we also compared the behavioural responses of the tree’s pollinator (Eupristina sp.) to figs at different developmental stages, and compared these results to those obtained by trapping fig wasps as they arrived at a tree with a developing fig crop. The chemical composition of the fig volatiles changed during fig development with the blends exhibiting clear segregation among figs at different developmental phases. Male phase figs had the most distinct blend. Fig wasp females were preferentially attracted to receptive figs, but figs at most other developmental phases were also attractive. Conversely, male phase figs had a repellent effect. These results were supported by the behaviour of the wasps under natural conditions, with small numbers of fig wasps arriving at the tree before and after receptive figs were present. These results indicate a more complex relationship between fig volatiles and fig wasp behaviour than previously realized, with volatiles mediating both the initial meeting of the mutualists to achieve pollination and egg laying and the subsequent departure of the next generation of fig wasps. This offers an explanation for the specialization and long-term coexistence of figs and fig wasps.

d-Pinitol as a key oviposition stimulant for sulfur butterfly, Colias erate: chemical basis for female acceptance of host- and non-host plants

Abstract: The sulfur butterfly, Colias erate, utilizes various legumes as host plants. We examined the chemical constituents of its primary host plant, Trifolium repens (white clover), to identify phytochemicals inducing oviposition by C. erate females. Since one of the four aqueous subfractions prepared from a methanolic extract of the plant has previously been shown to be the most responsible for the oviposition-stimulatory activity exerted by the plant, chemical analyses were conducted of the fraction concerned. Activity-directed fractionation of the subfraction by ion-exchange chromatography revealed that the key substance(s) resided in the neutral fraction. Preparative TLC of the neutral fraction and subsequent spectral analyses identified d-(+)-pinitol, glycerin, methyl β-d-glucoside, and myo-inositol as characteristic components together with ubiquitous sugars (e.g., sucrose and glucose). Of these, only pinitol singly evoked significant oviposition responses at concentrations over 0.05%. In dual-choice bioassays, however, females laid significantly more eggs on pinitol solutions admixed with glycerin or methyl β-d-glucoside than on pinitol alone. Two cyanoglucosides, linamarin, and lotaustralin, occurring in the other aqueous subfractions, also synergistically increased the oviposition response in combination with pinitol. The results clearly indicated that pinitol is a crucial oviposition stimulant involved in host recognition, while glycerin, methyl β-d-glucoside, linamarin, and lotaustralin function as synergists. We further examined the oviposition responses of C. erate females to aqueous fractions, along with their chemical compositions, that had been prepared from five other host plants and a non-host plant, Aristolochia debilis (Aristolochiaceae), on which oviposition occasionally took place in an outdoor cage during the experiments. The plant species accepted by ovipositing females were all found to contain pinitol in amounts enough to induce egg laying by the butterfly, thus leading to the conclusion that pinitol serves as the essential mediator in recognizing and accepting potential host plants.

Behavioral and antennal electrophysiological responses of a predator ant to the pygidial gland secretions of two species of Neotropical dung roller beetles

Abstract: The pygidial gland secretions of Neotropical dung roller beetles appear to function as defensive agents against predator ants. Behavioral and electrophysiological tests were used to evaluate the responses of the ant Camponotus sericeiventris to pygidial compounds secreted by the dung roller beetles Canthon cyanellus cyanellus and Canthon femoralis femoralis (Coleoptera: Scarabaeidae). Our behavioral investigation revealed a lower aggressive response of C. sericeiventris to the dung roller beetles compared to their response to the fly Anastrepha ludens. Additionally, C. sericeiventris workers attacked C. f. femoralis more often than C. c. cyanellus. The behavioral aggression of C. sericeiventris was greater toward male than female C. c. cyanellus. Electroantennography showed that the antennae of C. sericeiventris react to pygidial extracts from C. c. cyanellus and C. f. femoralis. Three compounds from male and female C. f. femoralis and C. c. cyanellus elicited coupled gas chromatography-electroantennogram (GC-EAD) activity in the antennae of C. sericeiventris. Geraniol and an unknown compound (A) were specific for C. f. femoralis, whereas guaiacol and another unknown compound (B) were specific to C. c. cyanellus; phenol was shared by both beetle species. This is the first report confirming that the pygidial gland secretions of dung roller beetles play a role in their defense against predators.

Biotransformation of 4-nerolidylcatechol by Heraclides brasiliensis (Lepidoptera: Papilionidae) reduces the toxicity of Piper umbellata (Piperaceae)

Abstract: Heraclides brasiliensis (Lepidoptera: Papilionidae) larvae feed preferably on Piperaceae, foraging successfully on leaf tissues even though species of this contain high levels of secondary metabolites such as amides and lignans, associated with diverse biological activities including insecticidal properties. Studies examining the metabolism of chemical constituents in Piperaceae by insects are rare. In this study, we characterized the metabolites of 4-nerolidylcatechol (4-NC), the major constituent of Piper umbellata (Piperaceae), and E-2,3-dihydro-3-(3,4-dihydroxyphenyl)farnesoic acid, compounds from fecal material of H. brasiliensis larvae fed a diet containing only P. umbellata leaves. The biotransformed product was also detected in larval and pupal tissues. Moreover, we observed deactivation of the toxicity of P. umbellata leaves against brine shrimp after their metabolism in H. brasiliensis larvae from a LC50 of 523.3 to 3,460.7 μg/mL. This deactivation is closely associated with the biotransformation of 4-NC to E-2,3-dihydro-3-(3,4-dihydroxyphenyl)farnesoic acid, which showed LC50 of 8.0 and >1,000 μg/mL, respectively.

Differing patterns of sequestration of iridoid glycosides in the Mecininae (Coleoptera, Curculionidae)

Abstract: We analyzed several species of the weevil family Mecininae (Coleoptera, Curculionidae) that all feed on iridoid glycoside (IG) containing plants of the Plantaginaceae to investigate whether the beetles sequester these deterrent substances from their host plants. Within the Mecininae two genera of the tribe Cionini were found to sequester aucubin and catalpol: Cionus Clairvilleand Schellenberg and Cleopus Dejean. Both analyzed genera of the Mecinini, Mecinus Germar and Rhinusa Stephens, do not sequester IGs although the compounds are present in their food plants. They thus represent the first case of specialists on IG plants that have not evolved adaptations to use the compounds. However, in contrast to the Cionini these genera have a hidden lifestyle, so that their need for defence might be lower. Both Cionus and Cleopus, sequester catalpol with a higher efficiency than aucubin. However, in contrast to Cionus species, Cleopus species only sequester catalpol. In species feeding on Scrophularia, the aucubin concentration is higher while in beetles on Verbascum catalpol is usually dominating. This pattern can also be detected in the only species living on both plants, Cionus hortulanus. The ability to sequester IGs must have a single origin at the base of the sister genera Cionus and Cleopus.

Selective sequestration of cardenolide isomers by two species of Danaus butterflies (Lepidoptera: Nymphalidae: Danainae)

Abstract: Several species of milkweed butterflies (Danaini) are known to sequester cardenolides from their milkweed host plants. In adults of Danaus plexippus and D. gilippus, jointly raised on Asclepias curassavica (Asclepiadaceae), two host-plant cardenolides (calotropin and calactin) were found in significantly different ratios: in D. plexippus and the plant, they occurred in roughly equal ratios, but in D. gilippus, calotropin had a 10–12 times lower concentration, suggesting a selective sequestration of calactin. The two Danaus species belong to different subgenera and the results may be relevant to a better understanding of the evolution of cardenolide sequestration in Danaini.

Garter snakes do not respond to TTX via chemoreception

Abstract: Snakes detect and recognize prey through chemoreception using their tongue, but can they also detect toxins secreted by prey? Taste-rejection has been described in predators as a means of sampling prey for toxicity prior to ingestion but at the cost of minor intoxication and energy expenditure. Toxin detection prior to attack of prey might reduce these costs. Thamnophissirtalis (common garter snake) is among the predators that have been shown to employ taste-rejection of toxic prey but, as with all snakes, they primarily use vomeronasal chemoreception to evaluate potential prey. We investigated whether T. sirtalis use chemoreception as means of perceiving tetrodotoxin (TTX) found in their newt prey. We used the common tongue-flick behavioral assay to evaluate response to TTX and found that naive T. sirtalis did not respond differently to the toxin than a control. We conclude that T. sirtalis cannot detect TTX by chemoreception, or do not alter their behavior if they do.

Sequestration of defensive toxins by tetrapod vertebrates: contributions in memory of John W. Daly

Abstract: By the early 1990s John W. Daly, of the National Institutes of Health, had been collecting and cataloguing toxins from the skins of frogs for about 30 years, on the assumption that the enormous variety of alkaloid toxins (by then numbering in the hundreds) were synthesized by the frogs themselves (Daly 1998). However, he had begun to detect patterns that suggested the toxins might have a dietary origin, including temporal variation in toxin profiles within a population, similarity of toxins among frogs of four distantly related families (and even in a bird), the absence of alkaloids in captive-bred frogs, and the discovery of some identical compounds in a variety of small arthropods (Saporito et al. 2009). In a series of experiments in the mid1990s, Daly and his collaborators demonstrated that captive-reared and nontoxic frogs of the genus Dendrobates could acquire toxins from prey that had been dusted with alkaloids in the lab (Daly et al. 1994b). Furthermore, captive-reared frogs would, if housed with access to wild arthropods as prey, acquire alkaloid toxins (Daly et al. John W. Daly in the field in Colombia, 1970 (left from Myers 2009, courtesy of Charles W. Myers and Robert W. Hansen) and Panama, 2003 (right courtesy of Maureen A. Donnelly)

The effects of simulated acid rain and heavy metal pollution on the mountain birch–autumnal moth interaction

Abstract: The exposure of plants to abiotic stresses like air pollutants may increase their susceptibility to herbivores. However, abiotic stresses often induce the accumulation of phenolic compounds that may have adverse effects on plant-eating animals. In this study, we examined the effects of long-term (14 years) deposition of simulated acid rain (H2SO4) and heavy metals (CuNi) on the plant–herbivore interaction. The used species were well-known model species of plant–herbivore interaction, namely the mountain birch (Betula pubescens ssp. czerepanovii) and autumnal moth (Epirrita autumnata). The study set-up was factorial with four combinations of two treatments: −acid−CuNi, +acid−CuNi, −acid+CuNi, and +acid+CuNi. The deposition of pollutants had no marked effects on the growth, survival, or immune function of the autumnal moth although the chemistry of birch leaves was markedly affected. The concentrations of gallic acid, chlorogenic acid, three of hydrolyzable tannins (HTs), and quercetin glycosides were induced by the acid rain treatment when compared to leaves not treated with acid rain. We concluded that an increase in compounds with high redox capacity was a defense against oxidative stress caused by pollution treatments. We suggested that pollution might have increased the deposition of non-phenolic antioxidants like ascorbate that diminish the adverse effects of phenolics on herbivores. We also stated that abiotic stresses might play an equally strong role in the evolution of phenolics than herbivory if not larger.