What Goes in Must Come Out? The Metabolic Profile of Plants and Caterpillars, Frass, And Adults of Asota (Erebidae: Aganainae) Feeding on Ficus (Moraceae) in New Guinea.

Insect herbivores have evolved a broad spectrum of adaptations in response to the diversity of chemical defences employed by plants. Here we focus on two species of New Guinean Asota and determine how these specialist moths deal with the leaf alkaloids of their fig (Ficus) hosts. As each focal Asota species is restricted to one of three chemically distinct species of Ficus, we also test whether these specialized interactions lead to similar alkaloid profiles in both Asota species. We reared Asota caterpillars on their respective Ficus hosts in natural conditions and analyzed the alkaloid profiles of leaf, frass, caterpillar, and adult moth samples using UHPLC-MS/MS analyses. We identified 43 alkaloids in our samples. Leaf alkaloids showed various fates. Some were excreted in frass or found in caterpillars and adult moths. We also found two apparently novel indole alkaloids-likely synthesized de novo by the moths or their microbiota-in both caterpillar and adult tissue but not in leaves or frass. Overall, alkaloids unique or largely restricted to insect tissue were shared across moth species despite feeding on different hosts. This indicates that a limited number of plant compounds have a direct ecological function that is conserved among the studied species. Our results provide evidence for the importance of phytochemistry and metabolic strategies in the formation of plant-insect interactions and food webs in general. Furthermore, we provide a new potential example of insects acquiring chemicals for their benefit in an ecologically relevant insect genus.

Predicting distributions of Wolbachia strains through host ecological contact-Who's manipulating whom?

Reproductive isolation in response to divergent selection is often mediated via third-party interactions. Under these conditions, speciation is inextricably linked to ecological context. We present a novel framework for understanding arthropod speciation as mediated by Wolbachia, a microbial endosymbiont capable of causing host cytoplasmic incompatibility (CI). We predict that sympatric host sister-species harbor paraphyletic Wolbachia strains that provide CI, while well-defined congeners in ecological contact and recently diverged noninteracting congeners are uninfected due to Wolbachia redundancy. We argue that Wolbachia provides an adaptive advantage when coupled with reduced hybrid fitness, facilitating assortative mating between co-occurring divergent phenotypes-the contact contingency hypothesis. To test this, we applied a predictive algorithm to empirical pollinating fig wasp data, achieving up to 91.60% accuracy. We further postulate that observed temporal decay of Wolbachia incidence results from adaptive host purging-adaptive decay hypothesis-but implementation failed to predict systematic patterns. We then account for post-zygotic offspring mortality during CI mating, modeling fitness clines across developmental resources-the fecundity trade-off hypothesis. This model regularly favored CI despite fecundity losses. We demonstrate that a rules-based algorithm accurately predicts Wolbachia infection status. This has implications among other systems where closely related sympatric species encounter adaptive disadvantage through hybridization.

Compound Specific Trends of Chemical Defences in Ficus Along an Elevational Gradient Reflect a Complex Selective Landscape.

Elevational gradients affect the production of plant secondary metabolites through changes in both biotic and abiotic conditions. Previous studies have suggested both elevational increases and decreases in host-plant chemical defences. We analysed the correlation of alkaloids and polyphenols with elevation in a community of nine Ficus species along a continuously forested elevational gradient in Papua New Guinea. We sampled 204 insect species feeding on the leaves of these hosts and correlated their community structure to the focal compounds. Additionally, we explored species richness of folivorous mammals along the gradient. When we accounted for Ficus species identity, we found a general elevational increase in flavonoids and alkaloids. Elevational trends in non-flavonol polyphenols were less pronounced or showed non-linear correlations with elevation. Polyphenols responded more strongly to changes in temperature and humidity than alkaloids. The abundance of insect herbivores decreased with elevation, while the species richness of folivorous mammals showed an elevational increase. Insect community structure was affected mainly by alkaloid concentration and diversity. Although our results show an elevational increase in several groups of metabolites, the drivers behind these trends likely differ. Flavonoids may provide figs with protection against abiotic stressors. In contrast, alkaloids affect insect herbivores and may provide protection against mammalian herbivores and pathogens. Concurrent analysis of multiple compound groups alongside ecological data is an important approach for understanding the selective landscape that shapes plant defences.

Faster speciation of fig-wasps than their host figs leads to decoupled speciation dynamics: Snapshots across the speciation continuum.

Even though speciation involving multiple interacting partners, such as plants and their pollinators, has attracted much research, most studies focus on isolated phases of the process. This currently precludes an integrated understanding of the mechanisms leading to cospeciation. Here, we examine population genetic structure across six species-pairs of figs and their pollinating wasps along an elevational gradient in New Guinea. Specifically, we test three hypotheses on the genetic structure within the examined species-pairs and find that the hypothesized genetic structures represent different phases of a single continuum, from incipient cospeciation to the full formation of new species. Our results also illuminate the mechanisms governing cospeciation, namely that fig wasps tend to accumulate population genetic differences faster than their figs, which initially decouples the speciation dynamics between the two interacting partners and breaks down their one-to-one matching. This intermediate phase is followed by genetic divergence of both partners, which may eventually restore the one-to-one matching among the fully formed species. Together, these findings integrate current knowledge on the mechanisms operating during different phases of the cospeciation process. They also reveal that the increasingly reported breakdowns in one-to-one matching may be an inherent part of the cospeciation process. Mechanistic understanding of this process is needed to explain how the extraordinary diversity of species, especially in the tropics, has emerged. Knowing which breakdowns in species interactions are a natural phase of cospeciation and which may endanger further generation of diversity seems critical in a constantly changing world.

Chemical cues and genetic divergence in insects on plants: conceptual cross pollination between mutualistic and antagonistic systems.

Cascading or reciprocal genetic diversification of herbivores, parasitoids, and pollinators can track chemotypic variation in host resources, and can lead to non-overlapping communities. Because plants simultaneously interact with both pollinators and herbivores, models investigating the genetic divergence of antagonistic herbivores and mutualistic pollinators should be merged in order to study how both processes interact using a common conceptual and methodological approach. We expect insects to mediate divergence in many systems, with outcomes depending on the level of pollinator or herbivore specialisation, and the relative selective pressures they impose. Applying approaches widely used to study insect pollinators, for example genomic tools and integration of behavioural, genetic and chemical data, to both pollinators and herbivores in the same system will facilitate our understanding of patterns of genetic divergence across multiple interacting species.

Community structure of insect herbivores is driven by conservatism, escalation and divergence of defensive traits in Ficus.

Escalation (macroevolutionary increase) or divergence (disparity between relatives) in trait values are two frequent outcomes of the plant-herbivore arms race. We studied the defences and caterpillars associated with 21 sympatric New Guinean figs. Herbivore generalists were concentrated on hosts with low protease and oxidative activity. The distribution of specialists correlated with phylogeny, protease and trichomes. Additionally, highly specialised Asota moths used alkaloid rich plants. The evolution of proteases was conserved, alkaloid diversity has escalated across the studied species, oxidative activity has escalated within one clade, and trichomes have diverged across the phylogeny. Herbivore specificity correlated with their response to host defences: escalating traits largely affected generalists and divergent traits specialists; but the effect of escalating traits on extreme specialists was positive. In turn, the evolution of defences in Ficus can be driven towards both escalation and divergence in individual traits, in combination providing protection against a broad spectrum of herbivores.

Variably hungry caterpillars: predictive models and foliar chemistry suggest how to eat a rainforest.

A long-term goal in evolutionary ecology is to explain the incredible diversity of insect herbivores and patterns of host plant use in speciose groups like tropical Lepidoptera. Here, we used standardized food-web data, multigene phylogenies of both trophic levels and plant chemistry data to model interactions between Lepidoptera larvae (caterpillars) from two lineages (Geometridae and Pyraloidea) and plants in a species-rich lowland rainforest in New Guinea. Model parameters were used to make and test blind predictions for two hectares of an exhaustively sampled forest. For pyraloids, we relied on phylogeny alone and predicted 54% of species-level interactions, translating to 79% of all trophic links for individual insects, by sampling insects from only 15% of local woody plant diversity. The phylogenetic distribution of host-plant associations in polyphagous geometrids was less conserved, reducing accuracy. In a truly quantitative food web, only 40% of pair-wise interactions were described correctly in geometrids. Polyphenol oxidative activity (but not protein precipitation capacity) was important for understanding the occurrence of geometrids (but not pyraloids) across their hosts. When both foliar chemistry and plant phylogeny were included, we predicted geometrid-plant occurrence with 89% concordance. Such models help to test macroevolutionary hypotheses at the community level.