Max Planck Institute for Chemical Ecology

Aposematic animals use conspicuous warning signals to advertise their chemical defences to predators. Selection by predators can favour conspicuousness and large pattern elements, which enhance predator avoidance learning. In aposematic species, conspicuousness often varies among individuals. This variation can be explained if conspicuousness reflects the levels of chemical defences, if signal production or defence acquisition is costly, and if physiological trade-offs and opposing selection pressures impose constraints. To understand the link between conspicuousness and chemical defences, we need to quantify the variability in warning signals and identify the chemical compounds involved. Here, we examined the warning signal variability and chemical composition of the red-necked wasp moth (Amata nigriceps). We photographed the wings and abdomens of male and female moths and analysed their chemical composition using ultra-performance liquid chromatography. Females displayed more orange on their wings, a trait known to enhance protection against predators. While we ruled out the presence of pyrrolizidine alkaloids in adult moths, an untargeted metabolomics approach suggests that they sequester other compounds, such as steroidal alkaloids and alkylbenzenes, which may serve as chemical defences. Females had higher concentrations of these compounds than males but ecotoxicology assays with Daphnia showed that male and female moths exhibited similar levels of toxicity.

Plants can generate structural diversity by enzymatic rearrangement of a central intermediate. 19E‐geissoschizine is one such chemically versatile intermediate that plays a central role in the biosynthesis of monoterpene indole alkaloids such as strychnine, ibogaine, and vinblastine. Here we report how 19E‐geissoschizine undergoes oxidative transformations to generate four distinct alkaloid scaffolds through the action of three biosynthetic enzymes. Using in vitro enzymatic assays and gene silencing, we demonstrate how these three cytochrome P450 enzymes in the medicinal plant Catharanthus roseus transform 19E‐geissoschizine into strychnos, sarpagan, akuammiline‐type, and mavacurane‐type alkaloids. We use mutational analysis to show how minimal changes to the active site of these similar enzymes modulate product specificity. This work highlights how substrate reactivity and enzyme mutations work synergistically to generate chemical diversity.

Cellulose degradation by anaerobic bacteria plays an eminent role in the global carbon cycle and is a critical step in biofuel production. The anaerobic thermophile Clostridium thermocellum (now: Acetivibrio thermocellus) is particularly efficient at breaking down biomass and produces a “yellow affinity substance” (YAS), a pigment that has been implicated in signaling and conferring higher affinity of the cellulosome to YAS‐loaded cellulose. However, the nature and biosynthetic origin of YAS have remained elusive. Here, we show by isolation and structure elucidation that YAS is a complex of unusual arylpolyene alkaloids (celluxanthenes). Stable isotope labeling experiments reveal all biosynthetic building blocks for celluxanthene assembly. Through a targeted gene deletion, we identify the celluxanthene (cex) biosynthesis gene cluster and propose a biosynthetic model in which an arylpolyene generated by an iterative type I polyketide synthase (PKS) undergoes a head‐to‐head fusion with a tryptophan‐derived ketoacid to form a tetronate. Genome mining and metabolic profiling revealed that diverse cellulolytic anaerobes harbor cex gene loci and produce celluxanthene congeners. Celluxanthenes show antibiotic activity against Gram‐positive bacteria including clinically relevant strains. This study solves the long‐standing enigma surrounding the nature of YAS and lays the groundwork for elucidating the precise biological roles of these intricate pigments.

The beetle family Ptinidae contains a number of economically important pests, such as the cigarette beetle Lasioderma serricorne , the drugstore beetle Stegobium paniceum , and the diverse spider beetles. Many of these species are stored product pests, which target a diverse range of food sources, from dried tobacco to books made with organic materials. Despite the threat that the 2,200 species of Ptinidae beetles pose, fewer than 50 have been surveyed for microbial symbionts, and only a handful have been screened using contemporary genomic methods. In this study, we screen 116 individual specimens that cover most subfamilies of Ptinidae, with outgroup beetles from closely related families Dermestidae, Endecatomidae, and Bostrichidae. We used 16S ribosomal RNA gene amplicon data to characterize the bacterial microbiomes of these specimens. The majority of these species had never been screened for microbes. We found that, unlike in their sister family, Bostrichidae, that has two mutualistic bacteria seen in most species, there are no consistent bacterial members of ptinid microbiomes. For specimens which had Wolbachia infections, we did additional screening using multilocus sequence typing and showed that our populations have different strains of Wolbachia than noted in previous publications. IMPORTANCE Ptinid beetles are both household pests of pantry goods and economic pests of dried goods warehouses and cultural archives, such as libraries and museums. Currently, the most common pest control measures for ptinid beetles are phosphine and/or heat treatments. Many ptinid beetles have been observed to have increasing resistance to phosphine, and heat treatments are not appropriate for many of the goods commonly infested by ptinids. Pest control techniques focused on symbiotic bacteria have been shown to significantly decrease populations and often have the beneficial side effect of being more specific than other pest control techniques. This survey provides foundational information about the bacteria associated with diverse ptinid species, which may be used for future control efforts.

Plants can generate structural diversity by enzymatic rearrangement of a central intermediate. 19E‐geissoschizine is one such chemically versatile intermediate that plays a central role in the biosynthesis of monoterpene indole alkaloids such as strychnine, ibogaine and vinblastine. Here we report how 19E‐geissoschizine undergoes oxidative transformations to generate four distinct alkaloid scaffolds through the action of three biosynthetic enzymes. Using in vitro enzymatic assays and gene silencing, we demonstrate how these three cytochrome P450 enzymes in the medicinal plant Catharanthus roseus transform 19E‐geissoschizine into strychnos, sarpagan, akuammiline‐type, and mavacurane‐type alkaloids. We use mutational analysis to show how minimal changes to the active site of these similar enzymes modulate product specificity. This work highlights how substrate reactivity and enzyme mutations work synergistically to generate chemical diversity.

Urbanization, characterized by increased impervious surface coverage (ISC), higher temperatures, and reduced vegetation, presents both challenges and opportunities for studying plant responses to environmental stress. This study examines how urbanization influences the phenotypic expression of functional traits in an alien herb (Ruellia nudiflora) across five tropical cities in the Yucatán Peninsula, México. Given environmental contrasts between rural and urban areas, we predicted consistent patterns of trait divergence across cities. Our results confirm that urban environments exhibit higher ISC, lower vegetation cover, and increased dry heat compared to rural settings. Urban plants showed lower trichome density, thinner leaves, higher total phenolics and leaf C%, and a lower C:N ratio, while leaf N% remained similar across environments. However, only thinner leaves, lower C%, and lower C:N in urban plants were consistent across all cities. A trade-off between structural and chemical traits was evident, where increased leaf thickness and trichome density correlated with reduced total phenolic content. The expression of this trade-off, along with leaf C%, was driven by dry heat, though its effects are mitigated in urban environments. Notably, these patterns remained consistent across cities, highlighting urban ecosystems as valuable models for studying plant stress-response syndromes and predicting trait shifts under environmental change. Thus, urban ecology is a powerful framework for understanding plant strategies to cope with stress and for improving trait-based predictions in a rapidly changing world.

Cellulose degradation by anaerobic bacteria plays an eminent role in the global carbon cycle and is a critical step in biofuel production. The anaerobe thermophile Clostridium thermocellum (now: Acetivibrio thermocellus) is particularly efficient at breaking down biomass and produces a 'yellow affinity substance' (YAS), a pigment that has been implicated in signaling and conferring a higher affinity of the cellulosome to YAS‐loaded cellulose. However, despite its importance, the nature and biosynthetic origin of YAS have remained elusive. Here we show by isolation and structure elucidation that YAS is a complex of unusual arylpolyene alkaloids (celluxanthenes). Stable isotope labeling experiments reveal all biosynthetic building blocks for celluxanthene assembly. Through a targeted gene deletion, we identify the celluxanthene (cex) biosynthesis gene cluster and propose a biosynthetic model in which an arylpolyene generated by an iterative type I polyketide synthase (PKS) undergoes a head‐to‐head fusion with a tryptophan‐derived ketoacid to form a tetronate. Genome mining and metabolic profiling revealed that diverse cellulolytic anaerobes harbor cex gene loci and produce celluxanthene congeners. Celluxanthenes show antibiotic activity against Gram‐positive bacteria. This study work solves the long‐standing enigma surrounding the nature of YAS, establishes bioengineering approaches, and helps elucidating the biological roles of these intricate pigments.

Attraction of Drosophila melanogaster toward by-products of alcoholic fermentation, especially ethanol, has been extensively studied. Previous research has provided several interpretations of this attraction, including potential drug abuse, or a self-medicating coping strategy after mate rejection. We posit that the ecologically adaptive value of alcohol attraction has not been fully explored. Here, we assert a simple yet vital biological rationale for this alcohol preference. Flies display attraction to fruits rich in alcohol, specifically ethanol and methanol, where contact results in a rapid amplification of fatty acid–derived pheromones that enhance courtship success. We also identify olfactory sensory neurons that detect these alcohols, where we reveal roles in both attraction and aversion, and show that valence is balanced around alcohol concentration. Moreover, we demonstrate that methanol can be deadly, and adult flies must therefore accurately weigh the trade-off between benefits and costs for exposure within their naturally fermented and alcohol-rich environments.

Through niche construction, organisms actively shape their environment, thereby influencing their evolutionary trajectories via ecological inheritance. Red flour beetles ( Tribolium castaneum ) achieve niche construction through secretion of antimicrobial compounds from the stink glands. It has recently been demonstrated that the experimental removal of niche construction using RNAi of a key gene needed to produce stink gland secretions altered the pace and mechanisms of resistance adaptation to the bacterial entomopathogen Bacillus thuringiensis within nine host generations. However, it is unknown whether the microbiome and secretions produced by beetles undergo changes during experimental evolution. We continued the evolution experiment with an additional nine generations of selection. We found that host resistance continued to increase in selection regimes with pathogen exposure, whereas host development and fecundity remained stable, thereby confirming our previous findings. We then profiled larvae-associated microbiota in generations 12 and 15 via 16S rRNA sequencing and measured the stink gland secretion profiles of adults via gas chromatography-flame ionization detection in generation 18. While adaptation to the pathogen did not affect the microbiota, lines evolving with the possibility to construct their niches showed increased microbial diversification, and chemical secretion profiles did not change in either of the selection regimes. Together, our results highlight the role of niche construction in shaping host–microbe interactions. These effects seemed to be independent of any microevolutionary changes in the secretions as a niche-constructing trait.

Larvae of the black soldier fly, Hermetia illucens , are currently intensively studied, owing to their potential importance in various fields such as waste bioconversion, forensic entomology, and food supply for humans and life stock. Despite the increased attention, a detailed anatomical documentation of the larvae using modern methods is lacking, and even statements on the number of larval stages are contradictory. Misinterpretations of the ontogeny of this species have led to frequent erroneous identifications of the last larval instar as pupa. Consequently, many studies with a focus on larval morphology have neglected the last larval stage. In this contribution, we describe and document morphological changes of the larval head throughout the postembryonic development, with emphasis on the transition between the last two instars. This is characterized by a crucial behavioral shift from a feeding stage to a stage of increased vagility. We show that different cephalic structures undergo major changes, especially the mandibulo‐maxillary complex and the digestive tract, and associated muscles. Our measurements of the body length and the length of the head capsule tentatively confirm that the larval development of H. illucens passes through seven instars.

The green-brown polymorphism in Orthoptera is a prominent example of the coexistence of multiple color variants, especially since this polymorphism is shared by many species. The processes that maintain phenotypic polymorphisms depend on the underlying genetic and developmental regulation of body coloration, but these are not well understood for Orthoptera. Here we report on the inheritance of the green-brown polymorphism in the meadow grasshopper Pseudochorthippus parallelus, a species with four discrete color morphs that differ in the distribution of green coloration across the body. We provide the most detailed analysis of the green-brown polymorphism to date using half-sib full-sib breeding and phenotyping of 4,300 offspring. The data strongly support a simple Mendelian control of the presence/absence of green color in different regions of the body, involving four autosomal loci, two of which are genetically linked. However, estimation of population allele and haplotype frequencies using probabilistic simulations shows weak linkage disequilibrium in the population. The contrast between pedigree and population linkage suggests the presence of long-standing allelic variation and thus corroborates that long-term balancing selection is acting. Our study confirms and extends our understanding of inheritance patterns within the Chorthippus clade, providing unprecedented insights into the number and linkage of loci involved. The results have implications for the maintenance of polymorphisms and suggest that fluctuations in the phenotypic composition of populations can be generated by the segregation of genetic variants even in the absence of fluctuating selection.

Beneficial bacterial symbionts are widespread in insects and affect the fitness of their hosts by contributing to nutrition, digestion, detoxification, communication or protection from abiotic stressors or natural enemies. Decades of research have formed our understanding of the identity, localization and functional benefits of insect symbionts, and the increasing availability of genome sequences spanning a diversity of pathogens and beneficial bacteria now enables comparative approaches of their metabolic features and their phylogenetic affiliations, shedding new light on the origin and function of beneficial symbioses in insects. In this Review, we explore the symbionts' metabolic traits that can provide benefits to insect hosts and discuss the evolutionary paths to the formation of host-beneficial symbiotic associations. Phylogenetic analyses and molecular studies reveal that extracellular symbioses colonizing cuticular organs or the digestive tract evolved from a broad diversity of bacterial partners, whereas intracellular beneficial symbionts appear to be restricted to a limited number of lineages within the Gram-negative bacteria and probably originated from parasitic ancestors. To unravel the general principles underlying host-symbiont interactions and recapitulate the early evolutionary steps leading towards beneficial symbioses, future efforts should aim to establish more symbiotic systems that are amenable to genetic manipulation and experimental evolution.

Using a combination of RP-C18 chromatography, MS and NMR techniques a new class of homologous modular ascarosides carrying a 4’- ortho -aminobenzoyl moiety was identified from Caenorhabditis nigoni and Caenorhabditis tropicalis . These...

Division of labour (DOL) plays a key role across all scales of biological organization, but how its expression varies across contexts is still poorly understood. Here, we measure DOL in a crucial task, colony defence, in a social insect that affords precise experimental control over individual and colony traits, the clonal raider ant (Ooceraea biroi). We find that DOL in defence behaviour emerges within colonies of near-identical workers, likely reflecting variation in individual response thresholds, and that it increases with colony size. Additionally, colonies with pupae show higher defence levels than those without brood. However, we do not find evidence for a behavioural syndrome linking defence with exploration and activity, as previously reported in other systems. By showing how colony composition and size affect group response to potential threats, our findings highlight the role of the social context in shaping DOL. This article is part of the theme issue ‘Division of labour as key driver of social evolution’.

Plants are challenged regularly with multiple types of biotic stress factors, such as pathogens or insect herbivores, in their environment. To detect and defend against pathogens, plants have evolved an innate immune system in which intracellular receptors in the so-called effector-triggered immunity play a vital role. In Arabidopsis thaliana the Toll/interleukin-1 receptors (TIRs) domain is related to intracellular immunity receptors, for example in TIR-NBS-LRR (TNL) proteins. Among the TIR domain carrying proteins, very little is known about the function of the TIR-X proteins. Here, we focus on the recently described TIR-X (TIRP; At5g44900) to analyze its role in phytohormone-mediated plant defense through gene expression and phytohormone quantification. Therefore, we employed two fungal pathogens, the necrotrophic Alternaria brassicicola and the hemibiotrophic Verticillium dahliae, to infect A. thaliana WT (Col-0), TIRP knock-out, and TIRP overexpressing lines for comparative analyses. Furthermore, we included the insect herbivore Spodoptera littoralis and a treatment with S. littoralis egg extract on the plants to analyze any role of TIRP during these attacks. We found that both A. brassicicola and V. dahliae infections increased TIRP gene expression systemically. The salicylic acid content was higher in the TIRP overexpressing line, corresponding to a better S. littoralis larval growth performance in feeding assays. However, since we never observed clear infection-related differences in jasmonate or salicylic acid levels between the wild type and the two transgenic Arabidopsis lines, our results rule out the possibility that TIRP acts via the regulation of phytohormone synthesis and accumulation.

Ferns, known for their adaptability and widespread presence, form a diverse group of plants. However, the mechanisms underlying terpenoid production, which are often linked to plant adaptation, are not well understood in ferns. Here, we report that Dryopteris fragrans ( D. fragans ) produces diverse terpenoids in glandular trichomes (GTs) through the activities of microbial‐type terpene synthases. Using microscopy methods, capitate GTs were found to occur on various organs throughout the development of D. fragrans . In D. fragrans leaves, 13 terpenoids, most being sesquiterpenoids, were identified. By comparing the terpenoid chemistry of intact leaves, GT‐removed leaves, and isolated GTs, GTs were concluded to be the main site of terpenoid storage. Next, transcriptomes of D. fragrans leaves and GTs were created and mined for genes of the terpenoid biosynthetic pathway. Among them were nine putative full‐length microbial terpene synthase‐like ( MTPSL ) genes designated DfMTPSL1–9 . Using in vitro enzyme assays, six of the nine DfMTPSLs were demonstrated to have sesquiterpene synthase activities. Of them, DfMTPSL1 catalyzes the formation of (−)‐9‐ epi ‐presilphiperfolan‐1‐ol, the most abundant sesquiterpenoid in leaves. DfMTPS2 produces α‐muurolene, another major sesquiterpenoid from D. fragrans . The catalytic activities of DfMTPSLs together with the GT‐enriched expression of their respective genes support that GTs are also the main site of terpenoid biosynthesis in D. fragrans . Methyl jasmonate treatment induced the expression of DfMTPSL genes and the emission of terpenoid volatiles, suggesting that GT‐produced terpenoids play a role in defense against biotic stresses in D. fragrans , similar to their counterparts in seed plants.

Thyme species, including Thymus vulgaris, T. kotschyanus (drought-tolerant) and T. serpyllum (drought-sensitive), are valuable medicinal herbs. They are often grown in arid regions and are increasingly suffering from water stress due to climate change. Here, we analyzed the metabolome and expression of selected genes in leaves of these species under drought stress with and without treatment with the phytohormone abscisic acid (ABA). Among the terpenes, dominant metabolites in thyme, thymol was the most important terpenoid component, followed by thymoquinone, carvacrol and p-cymene in all three species. Drought stress reduced terpene concentrations, while moderate ABA levels increased them. T. kotschyanus showed the highest concentrations of thymol and carvacrol after combined treatment with drought and ABA. Metabolite accumulation was partially correlated with genes related to terpenoid biosynthesis. The combined treatment of drought stress and ABA resulted in a significant reduction of the stress hormone jasmonic acid and an increase of its biosynthetic precursor, OPDA (cis-12-oxophytodienoic acid), in all species. The present research results indicate that ABA treatment at moderate concentrations could be used as a measure to increase the production of some pharmaceutically active phenolic monoterpenes in T. vulgaris, T. serpyllum and T. kotschyanus and increase the stress resistance of the plants.

Silphopsyllus desmanae , a species of the small subfamily Platypsyllinae of Leiodidae, lives in the fur of the semiaquatic Russian desman, and is apparently adapted to this highly specialized life style. Even though the morphology of adults of the species was described almost 70 years ago, we re‐examined it with modern methods and documented its external and internal features in detail, and discuss them with respect to phylogeny and function. Our analyses of morphological data place Leptinillus as the sister group of the remaining genera of Platypsyllinae, and Leptinus as the sister group of Silphopsyllus + Platypsyllus . Platypsyllinae are supported by many putative autapomorphies: supraantennal ridges directed mesad but not extending beyond the antennal insertions and not forming a transverse ridge; tentorium without connected laminatentoria anterior to the tentorial bridge; submentum subrectangular; labrum about as wide as the maxillary‐labial complex; elongate and posteriorly projecting lateral lobes of the mentum; antennomeres lacking periarticular gutters (and Hamann's organs); cervical sclerites absent; precoxal prosternal region distinctly longer than the coxal rests; mesocoxal cavities situated closer to the body midline than to the lateral mesothoracic margins; metanepisterna fused with the metaventrite; metascutum laterally overlapping the meso‐ and metapleural regions; procoxae subglobose or only slightly elongate; mesocoxae subglobose. Platypsyllinae are most likely the sister group of Coloninae + Cholevinae. Eight unique apomorphies differentiating Platypsyllus from all the remaining Platypsyllinae are mainly adaptations for living in the fur of beavers. Silphopsyllus is much less adapted to life on a semiaquatic host than Platypsyllus .