Joint evolution of mutualistic interactions, pollination, seed dispersal mutualism, and mycorrhizal symbiosis in trees.

Mycorrhizal symbiosis, seed dispersal, and pollination are recognized as the most prominent mutualistic interactions in terrestrial ecosystems. However, it remains unclear how these symbiotic relationships have interacted to contribute to current plant diversity. We analyzed evolutionary relationships among mycorrhizal type, seed dispersal mode, and pollination mode in two global databases of 699 (database I) and 10 475 (database II) tree species. Although database II had been estimated from phylogenetic patterns and therefore had lower certainty of the mycorrhizal type than database I, whose mycorrhizal type was determined by direct observation, database II allowed analysis of many more taxa from more regions than database I. We found evidence of joint evolution of all three features in both databases. This result is robust to the effects of both sampling bias and missing taxa. Most arbuscular mycorrhizal-associated trees had endozoochorous (biotic) seed dispersal and biotic pollination, with long dispersal distances, whereas most ectomycorrhizal-associated trees had anemochorous (abiotic) seed dispersal and wind (abiotic) pollination mode, with shorter dispersal distances. These results provide a novel scenario in mutualistic interactions, seed dispersal, pollination, and mycorrhizal symbiosis types, which have jointly evolved and shaped current tree diversity and forest ecosystem world-wide.

Evolutionary ecology of masting: mechanisms, models, and climate change.

Many perennial plants show mast seeding, characterized by synchronous and highly variable reproduction across years. We propose a general model of masting, integrating proximate factors (environmental variation, weather cues, and resource budgets) with ultimate drivers (predator satiation and pollination efficiency). This general model shows how the relationships between masting and weather shape the diverse responses of species to climate warming, ranging from no change to lower interannual variation or reproductive failure. The role of environmental prediction as a masting driver is being reassessed; future studies need to estimate prediction accuracy and the benefits acquired. Since reproduction is central to plant adaptation to climate change, understanding how masting adapts to shifting environmental conditions is now a central question.

Night interruption provides evidence for photoperiodic regulation of bud burst in Japanese beech, Fagus crenata.

Some of trees in cool and temperate regions regulate bud burst by perceiving photoperiod. However, it is not clear whether the difference in bud burst timing between the two photoperiod conditions is due to differences in perception of day length or the daily light integral (DLI) because majority of studies concerning the photoperiodic regulation of bud burst make use of an experimental design that compares the differential timing of bud burst between long and shortday length. We conducted night and day interrupt experiments using twig cuttings of Japanese beech, Fagus crenata, to investigate the effect of photoperiod on bud burst. Twigs with leaf buds were collected in winter (February 2020) and maintained in four conditions: 1) long day length (16L8D; LD), 2) short day length (8L16D; SD), 3) day interruption for 2-h in the middle of the 16-h light period and a 6-h dark period (DI; total time of light period is the same as LD), and 4) night interruption with 2-h of light in the middle of the dark period and a 6-h light period (NI; total time of light period is the same as SD) for a duration of 40 d. We then measured the number of days until burst for each bud. Timing of bud burst was delayed in the SD treatment compared to the LD, DI, and NI treatments. These results demonstrate that the difference in bud burst phenology observed between SD and LD conditions is mainly due to day length perception rather than DLI, and an uninterrupted night period plays a major role in the perception of photoperiod. Our results provide the experimental evidence of perception of photoperiod regulating bud burst in spring.

Assessing temporal dynamics of predation and effectiveness of caterpillar visual defense using sawfly larval color and resting posture as a model.

Caterpillars (Lepidoptera and Symphyta larvae) employ diverse visual defensive tactics, and effectiveness of such tactics may be highly dynamic across time due to seasonal changes in the predator assemblages and their preferences. However, this has rarely been studied especially in tropical regions. Here we assessed temporal changes in the defensive value of caterpillar color and shape, using six types of plasticine dummy caterpillars: three colors (green, black, and white) × two shapes (curled and straight). These dummy caterpillars were deployed five times over different seasons in tropical forests of Xishuangbanna (China) and, as a comparison, twice in a temperate forest of Hirosaki (Japan). The colors and shapes of dummy caterpillars simulate visual traits of black sawfly larvae which take the curled resting posture in tropical rainforests of Xishuangbanna, apparently masquerading excrements commonly found on plants, while in Hirosaki there is no black-curled sawfly larvae and few excrements on plants. We found no significant effects of caterpillar colors or shapes on predation in Hirosaki. In contrast, black and curled caterpillars received significantly lower predation by birds in Xishuangbanna constantly across time. However, we were unable to provide evidence that the black-curled sawfly larvae are masquerading as excrements. Shapes of the dummy caterpillars also affected the predation by ants and parasitoid wasps at certain times. This is the first report on ecological function of the curled posture of sawfly larvae, and we demonstrated the importance to assess the temporal dynamics of predation and effectiveness of defensive tactics in tropical forests.