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Land plants are typically photosynthetic, but some species have lost the ability to photosynthesize, instead relying on mycorrhizal fungi to obtain carbon. Increasing levels of partial mycoheterotrophy, in which seemingly autotrophic plants receive fungal carbon from their fungal partners, and reduced sprouting in concert with greater reproduction when sprouting, may be intermediate steps in the evolution of this trait.We studied the microevolutionary demography of Pyrola japonica and the closely related species P. subaphylla, which are currently considered sister species. While these species are both partially mycoheterotrophic, P. subaphylla is more strongly so, indicating that it may be closer to evolving full mycoheterotrophy. We tracked individuals in two nearby populations in Fukushima, Japan from 2015 to 2020. We analysed vital rates, population trends and long‐run population structure with historical function‐based matrix projection models. We assessed how shifts in P. subaphylla demography relate to fitness using a stochastic life table response experiment (SLTRE).P. subaphylla exhibited strong costs of growth to survival and of reproduction to sprouting, size and fecundity. It sprouted more than P. japonica but to smaller stages. P. subaphylla's flowering frequency was approximately four times that of P. japonica, but after flowering it was smaller and more likely to die.These life history costs appeared to drive differences in fitness, measured as stochastic population growth rate. Relative to P. japonica, shifts in fitness in P. subaphylla were due more to shifts in means than standard deviations of matrix elements. Shifts in growth transitions had the strongest negative impacts on fitness but also had the strongest positive impacts. Increased shifts to small non‐flowering stages were associated with increased fitness, while transitions involving dormancy were associated more strongly with drops in fitness.Synthesis. As far as we are aware, we found the first evidence that costs of growth and reproduction drive the evolution of increased sprouting and smaller size as a species becomes more intensely mycoheterotrophic. Surprisingly, vegetative dormancy did not evolve with mycoheterotrophy. We suggest further studies assessing whether these seemingly maladaptive trends result from genetic drift, genetic linkage or another mechanism. [ABSTRACT FROM AUTHOR]

Premise: Difficulties in comparing extremely divergent features in fully mycoheterotrophic plants with those in closely related chlorophyllous plants have complicated attempts to reveal the evolutionary patterns and processes of fully mycoheterotrophic plants. Albino mutants of partially mycoheterotrophic plants, generally observed in Orchidaceae, have provided an ideal model for investigating the evolution of mycoheterotrophy within similar genetic backgrounds. In 2018, we found a putative albino population of Pyrola (Ericaceae). Here we aimed to reveal the identity of the albino pyroloid and confirm its fully mycoheterotrophic status. Methods: To reveal the putative albino pyroloid's identity, we examined its morphology and sequenced its chloroplast DNA. In addition, we assessed the trophic status of the putative albino pyroloid by analyzing chlorophyll fluorescence, chlorophyll concentration, and natural 13C and 15N abundances. Results: We identified albino individuals as P. japonica—otherwise a partially mycoheterotrophic species. We confirmed their albino status by their considerably lower chlorophyll fluorescence and concentrations than those of sympatrically occurring chlorophyllous plants. 13C abundance in the albino individuals was significantly higher than in the green individuals of P. japonica. Conclusions: This first report of albino mutants from partially mycoheterotrophic species in angiosperms other than orchids will play a valuable role in further studies focused on mycoheterotrophy. For instance, their δ13C and δ15N values represent a reference for fully mycoheterotrophic plants in Pyrola. Our findings also indicate the strong dependence of some leafy Pyrola species on fungal C during their entire life cycle. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Although the evolution of full mycoheterotrophy has attracted many plant researchers, molecular phylogenetic studies that focus on the transition from partial tofull mycoheterotrophy are limited to a few taxa. Pyrola japonica sensu lato is an ideal model for examining the evolution of mycoheterotrophy, owing to its variable leaf size, which suggests that the species comprises several transitional stages. METHODS: To elucidate the molecular and morphological changes that occur during the evolutionary transition between partial and full mycoheterotrophy in P. japonica s.l. from 18 populations in Japan, we estimated a parsimony network of plastid haplotypes based on three noncoding regions, measured the leaf size and scape color of the shoots, and compared morphology among haplotypes. key RESULTS: The seven haplotypes exhibited star-like relationships, and at least three divergent haplotypes were associated with differences in morphology. The first was mainly observed in large-leaved and green-scaped populations, whereas the second was observed in extremely small-leaved and reddish-scaped populations, which indicated a high degree of mycoheterotrophy, and the last was detected among mixed populations with both greenand reddish-scaped shoots with intermediate leaf sizes. In addition, the inconsistent association between the haplotypes and morphology suggests a complex relationship. CONCLUSIONS: Pyrola japonica s.l. has at least three separate genetic lineages that have different leaf morphologies. The genetic lineages and their coexistence could have led to the variable leaf size and suggest the possibility that gene flow from partial tofull mycoheterotrophs could reverse the evolutionary transition tofull mycoheterotrophy. [ABSTRACT FROM AUTHOR]