| Myco-heterotrophic plants of the Monotropoideae (Ericaceae) have long been used as model organisms for studies of non-photosynthetic plant biology. These taxa have evolved unique morphological and life history adaptations, not found in most photosynthetic taxa, and experience a unique set of ecological and evolutionary limitations resulting from highly specialized associations with mycorrhizal fungi. Although much is known about the symbiotic mode of carbon acquisition and many convergent life history traits shared across myco-heterotrophic taxa, the reproductive ecology and population genetic structure of these plants is poorly understood. To assess the complexity and specialization in myco-heterotroph reproductive ecology, a comparative analysis was conducted between two closely related genera, Monotropa L. and Monotropsis Schwein. ex Elliot, using three plant species. Three consecutive years of field observations and manipulations on various components of plant reproduction revealed that the species Monotropa uniflora L. and color forms within the congener Monotropa hypopitys L. each exhibited unique reproductive traits (e.g., differences in seasonal timing and duration of reproductive development and phenology, specialization on Bombus spp. pollinators, and breeding systems), many of which differed considerably from Monotropsis odorata Schwein. ex Elliot. Additionally, 11 microsatellite markers were developed for Monotropa hypopitys to assess for the first time, the population genetic structure of myco-heterotrophic plants, while also addressing the appropriate taxonomic placement of the red and yellow color forms of M. hypopitys. Results from this study demonstrated relatively low to moderate levels of genetic variation and high levels of genetic differentiation across most populations. In addition, genetic structuring between red and yellow color forms was suggestive of speciation and the need for a taxonomic revision. Finally, analyses were conducted to determine if cryptic mimicry functions as an effective defense strategy for herbivore avoidance in Monotropsis odorata. Although a substantial body of functional data supports cryptic mimicry as a defense adaptation in animal systems, it has only been hypothesized to exist in plants. Here we show for the first time, through empirical manipulations and reflectance data that M. odorata possesses adaptive morphology and coloration that mimics leaf-litter, and this functions as a defense strategy for avoiding attacks from visually guided herbivores. |
