Akira S. Hirao

Adaptive significance of self-fertilization in a hermaphroditic perennial, Trillium camschatcense (Melanthiaceae)

The evolution of self-fertilization from primarily outcrossing ancestors is one of the most common evolutionary transitions in plants; however, the ecological mechanisms that maintain self-fertilization have remained controversial. Theoretical studies suggest that selfing is advantageous over outcrossing in terms of genetic transmission and assurance of seed production under pollen-limited circumstances. Trillium camschatcense is a herbaceous perennial distributed in Hokkaido and northern Honshu, Japan. Geographical variation in the breeding system (self-compatible, SC; or self-incompatible, SI) has been reported in populations in Hokkaido. Here, we used several SC and SI populations of T. camschatcense to investigate the adaptive significance and the evolutionary basis of self-fertilization. Pollination experiments and genetic analyses demonstrated that the potential availability of outcross pollen in SC populations was sufficient and that the number of pollen donors was equal to that of SI populations. However, despite the high availability of outcross pollen, the SC populations produced seeds predominantly by selfing and so underwent severe inbreeding depression. Although none of the suggested advantages for self-fertilization were supported by our analyses, we propose two possible scenarios for the evolution of self-fertilization in T. camschatcense.

Changes in pollinator fauna affect altitudinal variation of floral size in a bumblebee-pollinated herb.

Geographic trait variations are often caused by locally different selection regimes. As a steep environmental cline along altitude strongly influences adaptive traits, mountain ecosystems are ideal for exploring adaptive differentiation over short distances. We investigated altitudinal floral size variation of Campanula punctata var. hondoensis in 12 populations in three mountain regions of central Japan to test whether the altitudinal floral size variation was correlated with the size of the local bumblebee pollinator and to assess whether floral size was selected for by pollinator size. We found apparent geographic variations in pollinator assemblages along altitude, which consequently produced a geographic change in pollinator size. Similarly, we found altitudinal changes in floral size, which proved to be correlated with the local pollinator size, but not with altitude itself. Furthermore, pollen removal from flower styles onto bees (plants male fitness) was strongly influenced by the size match between flower style length and pollinator mouthpart length. These results strongly suggest that C. punctata floral size is under pollinator-mediated selection and that a geographic mosaic of locally adapted C. punctata exists at fine spatial scale.

Genetic structure of a hybrid zone between two violets, Viola rossii Hemsl. and V. bissetii Maxim.: dominance of F1 individuals in a narrow contact range

The genetic composition of a hybrid zone can provide insight into the evolution of diversification in plants. We carried out morphological and amplified fragment length polymorphism analyses to investigate the genetic composition of a hybrid zone between two violets, Viola bissetii Hemsl. and Viola rossii Maxim. Our aim was to clarify the formation and maintenance of hybrids between these Viola species. We found that most hybrid individuals (V. bissetii × V. rossii) were of the F1 generation, with a few of the F2 generation. We found no backcrosses. The scarcity of post-F1 hybrids indicates that a species barrier is established between the parental species. The F1-dominated hybrid zone occupied only a narrow, intermediate ecotone between the parental habitats, suggesting that selection by environmental factors against hybrids may help to maintain the current conditions in this hybrid zone.

Development and Evaluation of Microsatellite Markers for Acer miyabei (Sapindaceae), a Threatened Maple Species in East Asia

Premise of the study: Twelve microsatellite markers were developed and characterized in a threatened maple species, Acer miyabei (Sapindaceae), for use in population genetic analyses. Methods and Results: Using Ion Personal Genome Machine (PGM) sequencing, we developed microsatellite markers with perfect di- and trinucleotide repeats. These markers were tested on a total of 44 individuals from two natural populations of A. miyabei subsp. miyabei f. miyabei in Hokkaido Island, Japan. The number of alleles per locus ranged from two to eight. The observed and expected heterozygosities per locus ranged from 0.05 to 0.75 and from 0.05 to 0.79, respectively. Some of the markers were successfully transferred to the closely related species A. campestre, A. platanoides, and A. pictum. Conclusions: The developed markers will be useful in characterizing the genetic structure and diversity of A. miyabei and will help to understand its spatial genetic variation, levels of inbreeding, and patterns of gene flow, thereby providing a basis for conservation.

Development and Evaluation of Microsatellite Markers for the Gynodioecious Shrub Daphne jezoensis (Thymelaeaceae)

Premise of the study: Ten microsatellite markers were developed and characterized in a gynodioecious summer-deciduous shrub, Daphne jezoensis, to facilitate studies of the evolution of gynodioecy in the species. Methods and Results: We used a next-generation sequencing approach with the Ion Personal Genome Machine (PGM) system to identify and develop microsatellite markers with perfect di- and trinucleotide repeats. These markers were tested with 47 samples from two natural populations. The mean observed and expected heterozygosities per population ranged from 0.40 to 0.46 and 0.60 to 0.66, respectively. Conclusions: The developed markers will be useful to study the mating system, gene flow, and population genetic structure of D. jezoensis.

Plant Genetic Diversity and Plant–Pollinator Interactions Along Altitudinal Gradients

Alpine plants are thought to be particularly vulnerable to extinction as a result of global warming because their habitat ranges are expected to shift upward until, eventually, no higher habitats remain into which they can escape. Moreover, even mountain plants distributing across wide altitudinal ranges are likely to experience range shifts, raising the possibility of local extinctions, especially of genetically and ecologically differentiated types with narrow distribution ranges. In this chapter, we examine to what extent plants genetically and ecologically differentiate along altitude and how altitudinal changes in pollinator assemblages affect floral evolution. First, by literature survey, we demonstrate that although altitudinal patterns of species and genetic diversity have been extensively investigated, few clear-cut examples of altitudinal genetic differentiation of neutral markers have been identified. On the other hand, many studies have shown that adaptive traits of plants differentiate along altitude, although their adaptive genetic background is yet to be uncovered. We then briefly introduce three case studies of mountain herbaceous plant species displaying cryptic neutral genetic or adaptive trait differentiation. The first two case studies show that the floral size of both Campanula punctata and Prunella vulgaris differs among populations along altitude and is adapted to altitudinally variable pollinator size. The third case study demonstrates that Cimicifuga simplex is composed of three genetically differentiated ecotypes that are distributed parapatrically or allopatrically along an altitudinal gradient. To meet the challenges posed by future climate warming, it is essential to clarify the genetic and ecological differentiation of mountain plants along altitude.