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

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

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

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

The times are changing: understanding past, current and future resource use in rural Papua New Guinea using participatory photography

There is a need to include local people’s voices in research and planning processes to better understand what they see as opportunities and challenges for their future. This is necessary because of the intrinsic importance of public participation, and because it can help produce more useful and implementable adaptation plans. We apply participatory photography in a Papua New Guinean smallholder farming community to explore local perspectives on resource management, drivers of change and adaptive strategies. Twenty-four farmers of different clans, genders and ages took photos of items important to their livelihoods, focusing separately on the past, present and future. We discussed the photos and their meanings in individual and group interviews, encouraging farmers to lead the conversations. Results show that farmers are shifting from relying mainly on natural capitals to using financial, social and physical capitals, and that this causes changes in people’s well-being. Villagers see cash crop diseases, land shortages and lack of training as their main challenges. So far, people have adapted to changes by shifting to crop species that still yield well, and setting up small businesses and projects to have additional sources of income. Farmers see education as key to their future as it would allow for better land management and diversification of livelihoods. The participatory photography process provided triangulation of scientific studies, gave insights into farmers’ perceptions, and highlighted adaptive strategies and the complexities of realising them. Overall, the results can be used in future research and planning processes in Papua New Guinea

Quantifying unintended effects of an agroecological research project on farmers’ practices and social network in Papua New Guinea

1. Agroecological researchers and advocates often make assumptions about the social impact and dissemination of their work: researchers may assume that their work has impact through post-research dissemination, while advocates may assume that new agroecological practices can be effectively spread through existing social networks. 2. Here we test these assumptions by quantifying the effects of an agroecological research project on farming practices and the social network in a village community in Papua New Guinea. The project aimed to test the effect of applying banana peel compost, chicken manure and NPK fertiliser on sweet potato yields. Local farmers were involved in the research as project garden owners or research assistants. Using stochastic actor-oriented modelling, we tracked changes in farming practices and the social network. 3. Over the course of the research project, more people started to use food waste on their farms, while animal manure and NPK fertiliser were not frequently adopted. Farmers also took up practices that were not directly researched, such as mulching and planting the specific variety of sweet potato that was used in the project. This suggests that local farmers created meaning from the project, despite the researchers not intending to give advice until the end of the project. 4. The research project also affected the community’s social network. Research assistants became more often sought-after for advice, while knowledge about the project did not flow far from those directly involved. These results indicate that who gets involved in a project may have social consequences, and show the importance of understanding existing social networks before they are relied upon for spreading farming practices. 5. Overall, this work challenges often-held assumptions about the social impact and dissemination of agroecological research, provides insights into the types of agricultural innovations more likely to be accepted among farmers, and explores how new practices may most effectively be promoted within a community.</p

Using locally available fertilisers to enhance the yields of swidden farmers in Papua New Guinea

Context Swidden agriculture (a type of small-scale agriculture) is crucial to the livelihood and food security of millions of people in tropical regions. Social-ecological changes, including population growth and anti-swidden policies, are putting pressure on the existing swidden system to increase agricultural productivity in a sustainable way. Enhancing soil fertility is a promising option for increasing crop yields and extending lifetimes of agricultural fields, thereby reducing the demand to clear new land. However, there is limited information on how swidden farmers can best maintain soil fertility. Objective Our aim was to investigate whether using locally available fertilisers can increase soil quality, crop yields and lifetimes of swidden fields. Methods We established experimental gardens on the land of swidden farmers in the Lowlands of Papua New Guinea, where the majority of the population depends on swidden agriculture. Gardens were set up on two types of sites; five were established on new sites that had just been prepared for gardening by cutting and burning vegetation after a fallow period, whereas another five were prepared on garden sites that were just being fallowed. We applied three treatments; i) compost consisting of decaying banana peels, ii) chicken manure, and iii) NPK fertiliser to different plots within each garden; and tracked soil quality and yields of sweet potato over 12 months (three post-intervention cropping periods). We also conducted in-depth interviews with local farmers to understand their perspective on soil management. Results and conclusions Few farmers typically used compost, chicken manure or NPK fertiliser. Many were keen to try these fertilisers, provided they had more information. The performance of treatments depended on the type of garden with chicken manure increasing tuber yields in fallowed gardens but not new gardens, and banana peel compost also increasing tuber yields in fallowed gardens although not significantly. NPK fertiliser was the best option because it was the only fertiliser that increased yields in both new and fallowed gardens, produced tubers of similar quality and taste to control plots and was financially profitable. Treatments affected yield through increasing available nitrogen and reducing soil moisture. We also found that farmers fallow their gardens despite adequate sweet potato yields, so whether using fertilisers can enhance the lifetime of fields will depend on additional factors such as labour input needed. Significance Our work shows how swidden agriculture can potentially be adapted so that it continues to be a sustainable way of farming and living

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

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