Ozone alters the chemical signal required for plant - insect pollination: The case of the Mediterranean fig tree and its specific pollinator

Tropospheric ozone (O3) is likely to affect the chemical signal emitted by flowers to attract their pollinators through its effects on the emission of volatile organic compounds (VOCs) and its high reactivity with these compounds in the atmosphere. We investigated these possible effects using a plant-pollinator interaction where the VOCs responsible for pollinator attraction are known and which is commonly exposed to high O3 concentration episodes: the Mediterranean fig tree (Ficus carica) and its unique pollinator, the fig wasp (Blastophaga psenes). In controlled conditions, we exposed fig trees bearing receptive figs to a high-O3 episode (5 h) of 200 ppb and analyzed VOC emission. In addition, we investigated the chemical reactions occurring in the atmosphere between O3 and pollinator-attractive VOCs using real-time monitoring. Finally, we tested the response of fig wasps to the chemical signal when exposed to increasing O3 mixing ratios (0, 40, 80, 120 and 200 ppb). The exposure of the fig tree to high O3 levels induced a significant decrease in leaf stomatal conductance, a limited change in the emission by receptive figs of VOCs not involved in pollinator attraction, but a major change in the relative abundances of the compounds among pollinator-attractive VOCs in O3-enriched atmosphere. Fig VOCs reacted with O3 in the atmosphere even at the lowest level tested (40 ppb) and the resulting changes in VOC composition significantly disrupted the attraction of the specific pollinator. These results strongly suggest that current O3 episodes are probably already affecting the interaction between the fig tree and its specific pollinator.

A new brood-pollination mutualism between Stellera chamaejasme and flower thrips Frankliniella intonsa

BACKGROUND

Brood pollination mutualism is a special type of plant-pollinator interaction in which adult insects pollinate plants, and the plants provide breeding sites for the insects as a reward. To manifest such a mutualism between Stellera chamaejasme and flower thrips of Frankliniella intonsa, the study tested the mutualistic association of the thrips life cycle with the plant flowering phenology and determined the pollination effectiveness of adult thrips and their relative contribution to the host's fitness by experimental pollinator manipulation.

RESULTS

The adult thrips of F. intonsa, along with some long-tongue Lepidoptera, could serve as efficient pollinators of the host S. chamaejasme. The thrips preferentially foraged half-flowering inflorescences of the plants and oviposited in floral tubes. The floral longevity was 11.8 ± 0.55 (mean ± se) days, which might precisely accommodate the thrips life cycle from spawning to prepupation. The exclusion of adult thrips from foraging flowers led to a significant decrease in the fitness (i.e., seed set) of host plants, with a corresponding reduction in thrips fecundity (i.e., larva no.) in the flowers.

CONCLUSIONS

The thrips of F. intonsa and the host S. chamaejasme mutualistically interact to contribute to each other's fitness such that the thrips pollinate host plants and, as a reward, the plants provide the insects with brooding sites and food, indicating the coevolution of the thrips life cycle and the reproductive traits (e.g., floral longevity and morphology) of S. chamaejasme.

Warming and elevated CO2 induces changes in the reproductive dynamics of a tropical plant species

Tropical plant species are vulnerable to climate change and global warming. Since flowering is a critical factor for plant reproduction and seed-set, warming and elevated atmospheric carbon dioxide concentrations (eCO₂) are crucial climate change factors that can affect plant reproductive dynamics and flowering related events in the tropics. Using a combined free-air CO₂ enrichment and a free-air temperature-controlled enhancement system, we investigate how warming (+2 °C above ambient, eT) and elevated [CO₂] (~600 ppm, eCO₂) affect the phenological pattern, plant-insect interactions, and outcrossing rates in the tropical legume forage species Stylosanthes capitata Vogel (Fabaceae). In comparison to the control, a significantly greater number of flowers (NF) per plot (+62%) were observed in eT. Furthermore, in warmed plots flowers began opening approximately 1 h earlier (~09:05), with a canopy temperature of ~23 °C, than the control (~09:59) and eCO₂ (~09:55) treatments. Flower closure occurred about 3 h later in eT (~11:57) and control (~13:13), with a canopy temperature of ~27 °C. These changes in flower phenology increased the availability of floral resources and attractiveness for pollinators such as Apis mellifera L. and visitors such as Paratrigona lineata L., with significant interactions between eT treatments and insect visitation per hour/day, especially between 09:00-10:40. In comparison to the control, the additive effects of combined eCO₂ + eT enhanced the NF by 137%, while the number of A. mellifera floral visits per plot/week increased by 83% during the period of greatest flower production. Although we found no significant effect of treatments on mating system parameters, the overall mean multilocus outcrossing rate (tm = 0.53 ± 0.03) did confirm that S. capitata has a mixed mating system. The effects of elevated [CO₂] and warming on plant-pollinator relationships observed here may have important implications for seed production of tropical forage species in future climate scenarios.

Playing with extremes: Origins and evolution of exaggerated female forelegs in South African Rediviva bees

Despite close ecological interactions between plants and their pollinators, only some highly specialised pollinators adapt to a specific host plant trait by evolving a bizarre morphology. Here we investigated the evolution of extremely elongated forelegs in females of the South African bee genus Rediviva (Hymenoptera: Melittidae), in which long forelegs are hypothesised to be an adaptation for collecting oils from the extended spurs of their Diascia host flowers. We first reconstructed the phylogeny of the genus Rediviva using seven genes and inferred an origin of Rediviva at around 29MYA (95% HPD=19.2-40.5), concurrent with the origin and radiation of the Succulent Karoo flora. The common ancestor of Rediviva was inferred to be a short-legged species that did not visit Diascia. Interestingly, all our analyses strongly supported at least two independent origins of long legs within Rediviva. Leg length was not correlated with any variable we tested (ecological specialisation, Diascia visitation, geographic distribution, pilosity type) but seems to have evolved very rapidly. Overall, our results indicate that foreleg length is an evolutionary highly labile, rapidly evolving trait that might enable Rediviva bees to respond quickly to changing floral resource availability.