Mycorrhizal Specificity Contributed to Speciation in Two Fully Mycoheterotrophic Plants
Wan-Rou Lin1*, Ren-Cheng Liu2, Pi-Han Wang2
1 Bioresource Collection and Research Center (BCRC), Food Industry Research and Development Institute (FIRDI), Hsinchu, Taiwan.
2 Department of Life Science, Tunghai University, Taichung, Taiwan.
Fully mycoheterotrophic plants (MHP) lack chlorophyll and depend on their mycorrhizal fungi for carbon and nutrient supply throughout their lifecycle. The shift in mycorrhizal fungal communities may play a crucial role in the speciation of these unique plants. Monotropastrum humiles, a fully MHP, is often classified into two varieties, var. humile and var. glaberrimum. In Taiwan, both varieties of M. humiles coexist in the same geographic area, offering an excellent opportunity to investigate the mycorrhizal fungal communities associated with these closely related fully MHP in sympatry. This study aims to explore the mycorrhizal diversity of M. humiles var. humile (Mhh) and M. humiles var. glaberrimum (Mhg) and determine their respective fungal associations. Our results demonstrate that Mhh and Mhg are predominantly associated with different lineages of Russulaceae fungi. Mhh consistently associates with members of Russula, while Mhg is associated with members of Lactarius, indicating a discrete set of fungal partners for these sympatric plant species. The findings suggest that the mycobiont shift-triggered ecological speciation is possible between these sympatric variants. Furthermore, although Mhh and Mhg share a significant portion of their geographic distribution in Taiwan, they exhibit distinct flowering phenology in sympatric sites. The observed pre-mating barrier, potentially caused by differences in blooming time, may lead to reproductive isolation. Phenological isolation, combined with the complete dependence on mycorrhizal partners, reinforces the decrease in hybridization and contributes to speciation between Mhh and Mhg.