The ecological factors driving specialisation in species interaction networks along environmental gradients at large spatial scales are poorly understood. Although such drivers can have synergistic impacts, previous work has mainly assessed effects of network type and the abiotic environment separately. We conducted a meta-analysis of existing network data to assess the interactive effects and relative importance of these drivers of specialisation in ant-plant networks at global scales. We collated 74 ant plant networks from 1979–2023, categorised into four network types: plants that provide ants nesting sites (myrmecophytes); plants that provide only food sources (myrmecophiles); plants for which ants disperse seeds (myrmecochories); plants on which ants forage only (foraging). We explored how network specialisation varies between interaction types with elevation, latitude, and anthropogenic disturbance. We used a standard measure of network specialisation (H2’), tested whether standardising this against network null models influenced results (H2’ z-score), and measured phylogenetic network specialisation (dsi*). We found that H2’ was strongly affected by habitat disturbance, elevation and interaction type in a manner congruent with previous work, However, these effects disappeared once H2’ was standardised (H2’ z-score). The disappearance of these effects indicates that previous results may relate to variation in network structure rather than specialisation. This is supported by the existence of correlations between network species richness/weighted connectance and H2’. Phylogenetic network specialisation (dsi*) was greater for myrmecophytes than for other three network types. This probably relates to closer co-evolution between partners in myrmecophytic network. Phylogenetic network specialisation did not vary significantly with elevation, latitude or anthropogenic disturbance. Our results demonstrate that ant-plant network types, in this case relating to strength of mutualistic interaction, is the main driver of network specialisation, and that previously reported impacts of latitude, elevation and anthropogenic habitat disturbance are likely to have been mediated mediated via correlations with network size.

Barriers to gene-flow within populations, typically in response to divergent selection, are often mediated via third-party interactions. Under these conditions speciation is inextricably linked to ecological context. We present a novel framework for studying arthropod speciation as mediated by Wolbachia, a microbial endosymbiont capable of causing host cytoplasmic incompatibility (CI) via alternative strain associations. Building on empirical findings, our model predicts that sympatric host sister-species harbour paraphyletic 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 may provide an adaptive advantage when coupled with reduced hybrid fitness (via trait mismatching), by facilitating assortative mating between co-occurring divergent phenotypes – the contact contingency hypothesis. To test this, we applied a custom-built predictive algorithm to empirical data from host-specific pollinating fig wasps, achieving ≤88.46% accuracy. We then considered post-zygotic offspring mortality during CI matings by developing a model featuring fitness clines across oviposition resources. This oviposition trade-off model, tested through simulation, favoured CI at realistic conspecific mating frequencies 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 hybridisation.

Current climate change is disrupting biotic interactions and eroding biodiversity worldwide. However, species sensitive to drought, high temperatures and climate variability might persist in microclimatic refuges, such as leaf shelters built by arthropods. We conducted a distributed experiment across an 11,790 km latitudinal gradient to explore how the importance of leaf shelters for terrestrial arthropods changes with latitude, elevation and underlying climate. Our analyses revealed leaf shelters to be key facilitative elements for the diversity of arthropods. Predator diversity and overall biomass within shelters increased with local drought and temperature variability, regardless of latitude and elevation. In contrast, shelter usage by herbivores increased with abundance of predators on those same plants and in wetter climates. Projected increase in climatic variability and drought in certain geographic regions is therefore likely to enhance the importance of biotic refuges, especially for predators, in mitigating the impact of climate change on species persistence.