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

Contrasting patterns of fig wasp communities along Mt. Wilhelm, Papua New Guinea

The fig (Moraceae) and pollinating fig wasp (Agaonidae) mutualism is best known as a model system for the study of coevolution in plant–pollinator interactions and its central role in shaping vertebrate communities in tropical forests. Figs also host myriad antagonistic parasitic fig wasps which impose costs on both partners threatening mutualism stability. Spatiotemporal variation in parasitic wasp abundance is a key factor in mitigating these effects. Because fig wasps are temperature sensitive and likely vary in their ability to traverse environmental gradients, we expect community assemblages and abundance of both pollinating and non‐pollinating fig wasps to respond to changes along an elevational gradient. In the present study, we compare the fig wasp communities and abundance of three fig species growing along the slopes of the Mount Wilhelm altitudinal gradient in Papua New Guinea. We quantified wasps from over 100 male fig trees and calculated seed set for 55 female trees along each of the species’ distribution on the transect. Our results show that the abundance of both pollinating and non‐pollinating fig wasps follow a mid‐elevation peak, consistent with fig species richness found in the same transect. The patterns, however, are different according to the host's species distribution. Seed set remained relatively constant along the gradient for all species with some decrease along higher elevations, potentially affecting connectivity along the gradient. As suggested for insects in general, temperature and habitat diversity appear to play a fundamental role in the species richness and abundance of fig wasps

Comparison of traditional and DNA metabarcoding samples for monitoring tropical soil arthropods (Formicidae, Collembola and Isoptera)

The soil fauna of the tropics remains one of the least known components of the biosphere. Long-term monitoring of this fauna is hampered by the lack of taxonomic expertise and funding. These obstacles may potentially be lifted with DNA metabarcoding. To validate this approach, we studied the ants, springtails and termites of 100 paired soil samples from Barro Colorado Island, Panama. The fauna was extracted with Berlese-Tullgren funnels and then either sorted with traditional taxonomy and known, individual DNA barcodes (“traditional samples”) or processed with metabarcoding (“metabarcoding samples”). We detected 49 ant, 37 springtail and 34 termite species with 3.46 million reads of the COI gene, at a mean sequence length of 233 bp. Traditional identification yielded 80, 111 and 15 species of ants, springtails and termites, respectively; 98%, 37% and 100% of these species had a Barcode Index Number (BIN) allowing for direct comparison with metabarcoding. Ants were best surveyed through traditional methods, termites were better detected by metabarcoding, and springtails were equally well detected by both techniques. Species richness was underestimated, and faunal composition was different in metabarcoding samples, mostly because 37% of ant species were not detected. The prevalence of species in metabarcoding samples increased with their abundance in traditional samples, and seasonal shifts in species prevalence and faunal composition were similar between traditional and metabarcoding samples. Probable false positive and negative species records were reasonably low (13–18% of common species). We conclude that metabarcoding of samples extracted with Berlese-Tullgren funnels appear suitable for the long-term monitoring of termites and springtails in tropical rainforests. For ants, metabarcoding schemes should be complemented by additional samples of alates from Malaise or light traps

Spatiotemporal variation in the role of floral traits in shaping tropical plant-pollinator interactions.

The pollination syndrome hypothesis predicts that plants pollinated by the same pollinator group bear convergent combinations of specific floral functional traits. Nevertheless, some studies have shown that these combinations predict pollinators with relatively low accuracy. This discrepancy may be caused by changes in the importance of specific floral traits for different pollinator groups and under different environmental conditions. To explore this, we studied pollination systems and floral traits along an elevational gradient on Mount Cameroon during wet and dry seasons. Using Random Forest (Machine Learning) models, allowing the ranking of traits by their relative importance, we demonstrated that some floral traits are more important than others for pollinators. However, the distribution and importance of traits vary under different environmental conditions. Our results imply the need to improve our trait-based understanding of plant-pollinator interactions to better inform the debate surrounding the pollination syndrome hypothesis

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

Wasp y-choice data and morphological measurements

This file includes a brief summary of the y-choice experiments plus the raw data, as well as morphological measurements of wasps used in this study

Volatile data (raw)

Raw volatile data before conversion and filterin

Towards a functional classification of poorly known tropical insects: The case of rhinoceros beetles (Coleoptera, Dynastinae) in Panama

The population dynamics of most tropical insects are unknown and long-term monitoring programmes are urgently needed to evaluate a possible insect decline in the tropics. In this context, functional groups can be used effectively to summarise time-series for species-rich taxa. Neotropical dung beetles have often been catalogued into functional groups, but close relatives also of ecological significance, the Dynastinae, are awaiting such a classification. Here, we examine the functional groups of Dynastinae at the regional (Panama: 147 species) and local (Barro Colorado Island, BCI: 56 species) scales. Our optimum classification of Panamanian species distinguished five groups, one of which is probably artificial and accounts for species ecologically poorly known. Ecological attributes or species traits mainly influencing the delineation of groups were geographical distribution, body length, seasonal aggregation, larval food and whether the adult may be present in decaying wood. Our analyses indicated that (1) missing trait values and the high percentage of ‘cryptic’ species (25%) influenced the delineation of groups; (2) the dendrogram similarity of functional groups versus phylogenetic tree was low, although some traits were phylogenetically conserved; and (3) the overall structure of functional groups was conserved when comparing regional and local data, suggesting no drastic loss of functional groups locally. To proceed with the functional classification of poorly known tropical insects, we recommend a cautious selection of traits a priori, inclusion of ‘cryptic’ species recognised by DNA barcoding, and building phylogenies, which may allow a careful taxonomic imputation to complete species-traits matrices