Inbreeding depression contributes to the maintenance of habitat segregation between closely related monkeyflower species

An evolutionary framework for understanding habitat partitioning in plants

Many plant species with overlapping geographic ranges segregate at smaller spatial scales. This spatial segregation-zonation when it follows an abiotic gradient and habitat partitioning when it does not-has been experimentally investigated for over a century often using distantly related taxa, such as different genera of algae or barnacles. In those foundational studies, trade-offs between stress tolerance and competitive ability were found to be the major driving factors of habitat partitioning for both animals and plants. Yet, the evolutionary relationships among segregating species are usually not taken into account. Since close relatives are hypothesized to compete more intensely and are more likely to interact during mating compared to distant relatives, the mechanisms underlying habitat partitioning may differ depending on the relatedness of the species in question. Here, I propose an integration of ecological and evolutionary factors contributing to habitat partitioning in plants, specifically how the relative contributions of factors predictably change with relatedness of taxa. Interspecific reproductive interactions in particular are understudied, yet important drivers of habitat partitioning. In spatially segregated species, interspecific mating can reduce the fitness of rare immigrants, preventing their establishment and maintaining patterns of spatial segregation. In this synthesis, I review the literature on mechanisms of habitat partitioning in plants within an evolutionary framework, identifying knowledge gaps and detailing future directions for this rapidly growing field of study.

The influence of self-pollen deposition on female reproductive success in a self-incompatible plant, Akebia quinata

Geitonogamy is inevitable in hermaphrodite and monecious. Even for self-incompatible species, the negative effects of self-pollen are unavoidable when geitonogamous or self-mating occurs. However, the influence of self-pollen on consecutive development of flowers (e.g., fruiting and seeding) was seldom evaluated. Here, the self-incompatible monecious species, Akebia quinata, was used to estimate the influence of self-pollen deposition. We evaluated the extent of pollen limitation and geitonogamous mating under natural conditions by count of stigmatic pollen load and pollen tracking experiment. Hand pollination with different amount and combinations of self vs. cross pollen grains was applied to detect the response of fruit and seed set. The results showed that geitonogamy and pollen limitation occurred under natural conditions in A. quinata. Carpel numbers, ratio of self- and cross-pollen, and the interactive effect of ratio of self- and cross-pollen and total mixed pollen numbers, and not total pollen grain number, determined the effect of self-pollen on female reproductive success. The effect of self-pollen depended on its intensity. In general, the transfer of self-pollen significantly affected young fruit set. However, a little self-pollen together with cross-pollen did not reduce young fruit production. Although self-incompatible plants have evolved physiological mechanisms that reduce self-fertilization, our results provide new insights into the effects of self-pollen and the adaptive significance of self-incompatible monecious species.