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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.

Macrolides are a relatively common structural motif prevalent in Nature. However, the structures of these large ring lactones have been relatively difficult to elucidate via NMR spectroscopy due to the minute amounts of compounds that are sometimes obtainable from natural sources. Thus, GC-MS analysis of individual macrolactones has become the method of choice for the structural identification of these compounds. Here we discuss the mass spectrometric behavior of aliphatic macrolides, evaluating spectra from numerous compounds of various ring size, including derivatives containing methyl branches as well as double bonds. The specific fragmentation of these macrolactones under electron impact conditions allows for the development of a general rule set aimed at the identification of similar compounds by mass spectrometry. In addition, the mass spectra of dimethyl disulfide adducts of unsaturated macrolides are discussed. The mass spectra of almost 50 macrolides are presented.

International audience; Ithomiine butterflies use pyrrolizidine alkaloids (PAs) as precursors for malepheromones, such as dihydropyrrolizines or lactones. In contrast to most other ithomiine genera,none of these compounds have ever been detected in Oleria species. The absence of thesecompounds is thought to be the result of limited access to PA-containing plants. Here weinvestigate the contents of the androconia of Oleria onega caught in the wild when PA containingplants were abundant. Although the PA lycopsamine was detected in the hairpencils, none of theother known PA-derived compounds were present. Instead, the unsubstituted core of the PA necinebase, 1-methylene-1H-pyrrolizine (13), a very unstable compound, was found. The identity of thiscompound was proven by synthesis. Although its formation in nature appears very likely, 13 isalso formed during GC analysis of PAs, making its natural formation ambiguous. Nevertheless, itsreactivity makes it a good candidate for a signaling compound, because its rapid degradation canbe used for transporting spatial and time information. In addition, several other compounds, likelyused in intraspecific communication, were identified. All these compounds are reported for thefirst time as natural products or from insects. These include 9-hydroxynonanoic acid (21) and (Z)-9-hydroxy-6-enoic acid (18), as well as their condensation products with 11-hexadecenoic- andoctadecenoic acids. Furthermore, self-condensation products, such as (Z)-9-[(9-hydroxynon-6-enoyl)oxy]- and 9-[(9-hydroxynonanoyl)oxy]nonanoic acid and non-6-enoic acids (35, 36, 38, 40)were identified, together with the known compounds 2-heptadecanol (39) and 6,10,14-trimethylpentadecan-2-ol (37). In summary, O. onega appears to lack enzymes to producedihydropyrrolizines. In stark contrast to other ithomiine genera, a unique blend of oxidized fattyacids seems to be used instead.

Identifying the traits causing reproductive isolation and the order in which they evolve is fundamental to understanding speciation. Here, we quantify prezygotic and intrinsic postzygotic isolation among allopatric, parapatric, and sympatric populations of the butterflies Heliconius elevatus and Heliconius pardalinus. Sympatric populations from the Amazon (H. elevatus and H. p. butleri) exhibit strong prezygotic isolation and rarely mate in captivity; however, hybrids are fertile. Allopatric populations from the Amazon (H. p. butleri) and Andes (H. p. sergestus) mate freely when brought together in captivity, but the female F1 hybrids are sterile. Parapatric populations (H. elevatus and H. p. sergestus) exhibit both assortative mating and sterility of female F1s. Assortative mating in sympatric populations is consistent with reinforcement in the face of gene flow, where the driving force, selection against hybrids, is due to disruption of mimicry and other ecological traits rather than hybrid sterility. In contrast, the lack of assortative mating and hybrid sterility observed in allopatric populations suggests that geographic isolation enables the evolution of intrinsic postzygotic reproductive isolation. Our results show how the types of reproductive barriers that evolve between species may depend on geography.

Neotropical Heliconius butterflies are members of various mimicry rings characterized by diverse colour patterns. In the present study we investigated whether a similar diversity is observed in the chemistry of volatile compounds present in male wing androconia. Recent research has shown that these androconia are used during courting of females. Three to five wild-caught male Heliconius individuals of 17 species and subspecies were analyzed by GC/MS. Most of the identified compounds originate from common fatty acids precursors, including aldehydes, alcohols, acetates or esters preferentially with a C18 and C20 chain, together with some alkanes. The compounds occurred in species-specific mixtures or signatures. For example, octadecanal is characteristic for H. melpomene, but variation in composition between the individuals was observed. Cluster analysis of compound occurrence in individual bouquets and analyses based on biosynthetic motifs such as functional group, chain length, or basic carbon-backbone modification were used to reveal structural patterns. Mimetic pairs contain different scent bouquets, but also some compounds in common, whereas sympatric species, both mimetic and non-mimetic, have more distinct compound compositions. The compounds identified here may play a role in mate choice thus helping maintain species integrity in a butterfly genus characterized by pervasive interspecific gene flow. © 2017, Springer Science+Business Media, LLC.