Variation of Clasper Scent Gland Composition of Heliconius Butterflies from a Biodiversity Hotspot

Male Heliconius butterflies possess two pheromone emitting structures, wing androconia and abdominal clasper scent glands. The composition of the clasper scent gland of males of 17 Heliconius and Eueides species from an overlapping area in Ecuador, comprising three mimicry groups, was investigated by GC/MS. The chemical signal serves as an anti-aphrodisiac signal that is transferred from males to females during mating, indicating the mating status of the female to prevent them from harassment by other males. In addition, the odour may also serve in predator defence. There is potential for convergence driven by mimicry, although, such convergence might be detrimental for species recognition of the butterflies within the mimicry ring, making mating more difficult. More than 500 compounds were detected, consisting of volatile, semi-volatile or non-volatile compounds, including terpenes, fatty acid esters or aromatic compounds. Several novel esters were identified by GC/MS and GC/IR data, microderivatisation and synthesis, including butyl (Z)-3-dodecenoate and other (Z)-3-alkenoates, 3-oxohexyl citronellate and 5-methylhexa-3,5-dienyl (E)-2,3-dihydrofarnesoate. The secretions were found to be species specific, potentially allowing for species differentiation. Statistical analysis of the compounds showed differentiation by phylogenetic clade and species, but not by mimicry group.

The mystery of the butterfly bush Buddleja davidii: How are the butterflies attracted?

Many plant species are pollinated by butterflies. These insects are primarily attracted by visual flower cues, however, butterflies are also known to respond to flower scents and some butterfly-pollinated plants are strongly scented. One of such plants is the butterfly bush, Buddleja davidii, which is a magnet for butterflies. It is widespread in its native region in Asia and famous for its success in invasive spreading in regions throughout the world. Due to its attractiveness to butterflies and its beautiful and conspicuous inflorescences, it also is an important ornamental, found in many gardens. Here, we elucidated the signaling between the butterfly bush and one of its abundant visitors, the peacock butterfly (Aglais io), using chemical and behavioral approaches. We found that olfactory cues are more attractive than visual cues, and that feeding behavior is only elicited by olfactory cues, most effectively by 4-oxoisophorone and oxoisophorone epoxide. The latter compound was not known to elicit behavioral responses in pollinators before this study. The relative importance of olfactory cues was higher in our study than previously observed in any butterfly pollination system. The identified attractants might contribute to the widespread occurrence of the butterfly bush in its native region in Asia and its success in invasive spreading in regions throughout the world.

Head and Tail Oxidized Terpenoid Esters from Androconia of Heliconius erato Butterflies

Heliconius erato is a neotropical butterfly species that is part of a complex mimicry ring, with colorful wing patterns. For intraspecific communication, males use pheromones that are released from two different scent-emitting structures. Scent glands located near the abdominal claspers of males, containing antiaphrodisiac pheromones, release a highly complex mixture of compounds that is transferred to females during mating, rendering them unattractive to other males. On the other hand, androconia, scent-emitting scale areas on the wings of male butterflies, release a structurally more restricted set of compounds that likely serves an aphrodisiac role. We report here on two structurally related compounds that are the major androconial constituents, produced in high amounts and are not volatile due to their high molecular mass. Their structures were established by extensive analysis of mass, infrared, and NMR spectra, as well as microderivatization reactions of the natural extract. After establishing synthetic access, the compounds were unequivocally identified as two unusual head and tail oxidized terpenoids, (4E,8E,12E)-4,8,12-trimethyl-16-oxoheptadeca-4,8,12-trien-1-yl oleate (1) and stearate (2). Although behavioral assays are necessary to fully comprehend their role in the chemical communication of the species, hypotheses for their use by the butterflies are also discussed.

The scent chemistry of butterflies

Butterflies use structurally highly diverse volatile compounds for communication, in addition to visual signals. These compounds originate from plants or a formed de novo especially by male butterflies that possess specific scent organs.

Re-emergence and diversification of a specialized antennal lobe morphology in ithomiine butterflies

How an organism's sensory system functions is central to how it navigates its environment. The insect olfactory system is a prominent model for investigating how ecological factors impact sensory reception and processing. Notably, work in Lepidoptera led to the discovery of vastly expanded structures, termed macroglomerular complexes (MGCs), within the primary olfactory processing centre. MGCs typically process pheromonal cues, are usually larger in males, and provide classic examples of how variation in the size of neural structures reflects the importance of sensory cues. Though prevalent across moths, MGCs were lost during the origin of butterflies, consistent with evidence that courtship initiation in butterflies is primarily reliant on visual cues, rather than long distance chemical signals. However, an MGC was recently described in a species of ithomiine butterfly, suggesting that this once lost neural adaptation has re-emerged in this tribe. Here, we show that MGC-like morphologies are widely distributed across ithomiines, but vary in both their structure and prevalence of sexual dimorphism. Based on this interspecific variation we suggest that the ithomiine MGC is involved in processing both plant and pheromonal cues, which have similarities in their chemical constitution, and co-evolved with an increased importance of plant derived chemical compounds.

3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly Ithomia salapia

Male ithomiine butterflies (Nymphalidae: Danainae) have hairpencils on the forewings (i.e., androconia) that disseminate semiochemicals during courtship. While most ithomiines are known to contain derivatives of pyrrolizidine alkaloids, dihydropyrrolizines, or γ-lactones in these androconia, here we report on a new class of fatty acid esters identified in two subspecies, Ithomia salapia aquinia and I. s. derasa. The major components were identified as isoprenyl (3-methyl-3-butenyl) (Z)-3-acetoxy-11-octadecenoate, isoprenyl (Z)-3-acetoxy-13-octadecenoate (12) and isoprenyl 3-acetoxyoctadecanoate (11) by GC/MS and GC/IR analyses, microderivatizations, and synthesis of representative compounds. The absolute configuration of 12 was determined to be R. The two subspecies differed not only in the composition of the ester bouquet, but also in the composition of more volatile androconial constituents. While some individuals of I. s. aquinia contained ithomiolide A (3), a pyrrolizidine alkaloid derived γ-lactone, I. s. derasa carried the sesquiterpene α-elemol (8) in the androconia. These differences might be important for the reproductive isolation of the two subspecies, in line with previously reported low gene exchange between the two species in regions where they co-occur. Furthermore, the occurrence of positional isomers of unsaturated fatty acid derivatives indicates activity of two different desaturases within these butterflies, Δ9 and Δ11, which has not been reported before in male Lepidoptera.

Stereochemical inversion of pyrrolizidine alkaloids byMechanitis polymnia (Lepidoptera: Nymphalidae: Ithomiinae): Specificity and evolutionary significance

Pyrrolizidine alkaloids (PAs), acquired by adults or larvae of Danainae and Ithomiinae butterflies and Arctiidae moths from plants, protect these lepidopterans against predators and are biosynthetic precursors of male sex pheromones. The investigation of PAs in many species of wild-caught adults of Ithomiinae showed lycopsamine (1) [(7R)-OH, (2'S)-OH, (3'S)-OH] as the main alkaloid. In incorporation experiments, PA-free (freshly emerged) adults of the ithomiineMechanitis polymnia were fed seven PAs: lycopsamine and four of its known natural stereoisomers-indicine (2) [(7R)-OH, (2'R)-OH, (3'S)-OH], intermedine (3) [(7R)-OH, (2'S)-OH, (3'R)-OH], rinderine (4) [(7S)-OH, (2'S)-OH, (3'R)-OH], and echinatine (5) [(7S)-OH, (2'S)-OH, (3'S)-OH], and two PAs without the 7-OH: supinine (6) [(2'S)-OH, (3'R)-OH] and amabiline (7) [(2'S)-OH, (3'S)-OH]. Males epimerized PAs 3, 4, and 5 mainly to lycopsamine (1). Females fed these same three PAs changed a smaller proportion to lycopsamine; their lesser capacity to modify PAs corresponds to their normal acquisition of already transformed PAs from males during mating rather than through visits of adults to plant sources of PAs. The alkaloids1 and2, both 7R and 3'S, were incorporated without or with minimum change by males and females. Feeding experiments with6 and7 (males only) showed an inversion at the 3' center of6 and no change in7. The inversion from 7S to 7R (probably via oxyreduction) may be closely related to the evolution of acquisition of PAs by butterflies and moths. Two hypotheses are discussed: (1) The ancestral butterflies are probably adapted to tolerate, assimilate, and use (7R)-PAs (most common in plants; all widespread 1,2-unsaturated macrocyclic PA diesters show this configuration). The development of (7R)-PA receptors in the butterflies could lead to a specialization on this configuration in two ways: to help find PA plants and to utilize these components in sexual chemical communication. A later appearance of (7S)-PAs in plants could have selected an enzymatic system for the inversion of this chiral center in order to continue producing (7R)-PA-derived pheromones. (2) The inversion would be due to the evolution of a enzyme system specialized in the transport of (7R)-PAs to the integument; the failure of this system to carry (7S)-PAs led to an enzymatic system to invert them to transportable (7R)-PAs. In this case, the 7R configuration is an effect and not a cause of (7R)-PA-derived pheromones. In both hypotheses, the partial inversion of the 3'-asymmetric center, when the butterfly was fed intermedine (3), rinderine (4), and supinine (6), could be fortuitous due to the conformation of the molecule and/or the enzymatic system.

Phylogeography of Buddleja crispa (Buddlejaceae) and its correlation with drainage system evolution in southwestern China

PREMISE OF THE STUDY

Southwestern China is an area of active tectonism and erosion, yielding a dynamic, deeply eroded landscape that is hypothesized to have influenced the genetic structure of the resident populations of plants and animals. However, few studies have been conducted to examine the influence of changing river channels, particularly in the Yarlung Tsangpo area, on genetic distributions in plants. We here examine the population structure of Buddleja crispa, a dominant element of the dry, warm/hot river-valley communities, seeking to delimit the current population genetic structure and its relation to past changes in the courses of the major rivers in this area. •

METHODS

Two chloroplast DNA fragments were used to estimate the genetic variation and phylogeographic structure of the populations, and to infer nested clades, of the species. •

KEY RESULTS

We detected low intrapopulational haplotype diversity and higher overall population haplotype diversity (h(S) = 0.085, h(T) = 0.781). Molecular variance was mainly observed between groups (81.42%). Robust population genetic structure were detected by AMOVA (F(ST) = 0.967), coinciding with three nested clades (identified by NCPA) and five phylo-groups linked with paleo-drainage systems (identified by SAMOVA). No support for extensive spatial or demographical expansion was obtained. •

CONCLUSIONS

A general pattern of genetic isolation by vicariance was inferred, and detected disjunct patterns strongly indicate that currently discontinuous drainage systems were historically linked. Most importantly, population subdivisions and genetic variation perfectly reflect the putative Paleo-Red-River drainage pattern, and Yarlung Tsangpo populations are closely related to Central Yunnan Plateau populations, indicating that they were previously connected by ancient river courses. Divergence times between these river systems estimated by molecular dating (in the Pleistocene) agree with previous findings.

Major components in the hairpencil secretion of a butterfly, Euploea mulciber (Lepidoptera, Danaidae): their origins and male behavioral responses to pyrrolizidine alkaloids

Two compounds, 9,10-epoxytetrahydroedulan (ET) and viridiflorine beta-lactone (VL), were identified as major components from the hairpencils of field-caught males of a danaid butterfly, Euploea mulciber. By contrast, laboratory-reared males entirely lacked VL, but possessed a significant quantity of ET. Various feeding experiments with larvae and indoor adult males strongly suggested that ET is biosynthesized de novo only after eclosion from nutrients ingested during the larval development. Since VL was suspected to be derived from pyrrolizidine alkaloids (PAs) acquired as an adult, tests for feeding response to and oral administration of four PAs (a 4:1 mixture of intermedine/lycopsamine, heliotrine, monocrotaline, and retronecine) were conducted. When the tarsi or proboscis were stimulated with PA solutions, males showed positive feeding responses (proboscis extension and sucking movements) to intermedine/lycopsamine, heliotrine, and retronecine in decreasing order of responsiveness, thereby providing evidence that male adults are endowed with taste receptor(s) specific to PAs on the legs as well as on the proboscis. Differently from gustatory responsiveness, only males fed with intermedine/lycopsamine produced a significant quantity of VL (ca. 35 microg/male), whereas those that ingested heliotrine or monocrotaline hydrochloride produced traces of VL (<0.18 microg/male). Uptake of retronecine did not lead to VL formation at all. In behavioral bioassays to test the attractivity of PAs to males, all individuals tested were attracted exclusively to intermedine/lycopsamine. This shows that certain PA(s) per se serve as attractant(s) for males in locating PA sources, and further suggests that in the field, males will seek particular PA(s) that are indispensable as precursors for the efficient biosynthesis of VL.

Phylogenetic fragrance patterns in Nicotiana sections Alatae and Suaveolentes

We analyzed floral volatiles from eight tobacco species (Nicotiana; Solanaceae) including newly discovered Brazilian taxa (Nicotiana mutabilis and "Rastroensis") in section Alatae. Eighty-four compounds were found, including mono- and sesquiterpenoids, nitrogenous compounds, benzenoid and aliphatic alcohols, aldehydes and esters. Floral scent from recent accessions of Nicotiana alata, Nicotiana bonariensis and Nicotiana langsdorffii differed from previously published data, suggesting intraspecific variation in scent composition at the level of biosynthetic class. Newly discovered taxa in Alatae, like their relatives, emit large amounts of 1,8-cineole and smaller amounts of monoterpenes on a nocturnal rhythm, constituting a chemical synapomorphy for this lineage. Fragrance data from three species of Nicotiana sect. Suaveolentes, the sister group of Alatae, (two Australian species: N. cavicola, N. ingulba; one African species: N. africana), were compared to previously reported data from their close relative, N. suaveolens. Like N. suaveolens, N. cavicola and N. ingulba emit fragrances dominated by benzenoids and phenylpropanoids, whereas the flowers of N. africana lacked a distinct floral scent and instead emitted only small amounts of an aliphatic methyl ester from foliage. Interestingly, this ester also is emitted from foliage of N. longiflora and N. plumbaginifolia (both in section Alatae s.l.), which share a common ancestor with N. africana. This result, combined with the synapomorphic pattern of 1,8 cineole emission in Alatae s.s., suggests that phylogenetic signal explains a major component of fragrance composition among tobacco species in sections Alatae and Suaveolentes. At the intraspecific level, interpopulational scent variation is widespread in sect. Alatae, and may reflect edaphic specialization, introgression, local pollinator shifts, genetic drift or artificial selection in cultivation. Further studies with genetically and geographically well-defined populations are needed to distinguish between these possibilities.

Specific mixtures of secretions from male scent organs of African milkweed butterflies (Danainae)

The abdominal androconial organs (hairpencils: male scent glands) of samples of ten African milkweed butterfly species (Lepidoptera: Danainae) belonging to Danaus, Tirumala and Amauris , including all nine species commonly encountered in Kenya, have been analysed by gas chromatography and mass spectrometry. A total of 214 compounds have been identified, belonging to 14 chemical classes: hydrocarbons, alcohols, aldehydes, ketones, esters, lactones, carboxylic acids, oxidized carboxylic acids, aromatics, derivatives of pyrrolizidine alkaloids (PAs), monoterpenes, sesquiterpenes, other terpenoids and tetrahydrofurans. Various compounds only rarely or never found in insects before, including some previously unknown in nature, are present in the hairpencils. Excluding the numerous tetrahydrofurans, which were not investigated systematically, the number of compounds ranges from 12-59 per species. All ten species have distinct mixtures of volatiles, including, in all cases, species-specific compounds (autapomorphies). In addition, the co-occurrence of compounds between species (synapomorphies) exhibits a strongly hierarchical chemo-taxonomic pattern which has been demonstrated to be largely consistent with a previous cladistic analysis based on adult morphology. The potential significance of these findings in relation to chemical communication and speciation in these mimetic butterflies is discussed.

The pheromone system of the male danaine butterfly, Idea leuconoe

Male Idea leuconoe butterflies release a complex mixture of volatiles from their pheromone glands (hairpencils) during courtship. The pheromone components geranyl methyl thioether (2), viridifloric beta-lactone (3) and 6-hydroxy-4-dodecanolide (10) have been synthesized for the first time. Therefore, the structural assignment of these new natural products could be proved. Related 7-hydroxy-5-alkanoides are also present in the extract. The volatiles are embedded in a lipidic, matrix with more than 150 components. This matrix consists of alkanes, alkenes, 2,5-dialkyltetrahydrofurans, secondary alkanols and alkenols as well as alkanones and alkenones. Several regioisomers of the oxidized hydrocarbons occur. The elucidation of double bond positions has been performed by MS using DMDS adducts.