Floral distribution, clonal structure, and their effects on pollination success in a self-incompatible Convallaria keiskei population in northern Japan

Abstract

In plant species, when clonal growth produces a patchy structure and flowering ramets are clustered, the amount of pollen contributing to reproductive success is often regulated by pollinator efficiency and geitonogamy. The spatial population structure may influence reproductive success. We examined the clonal structure, the spatial ramet distribution, and their combined effects on fruit set in a natural population of the insect-pollinated, self-incompatible clonal herb, Convallaria keiskei, in northern Japan. The number of shoots, flowers, and fruits in 1-m 2 quadrats were counted at every 5 m grid point in an established 100 × 90-m study plot. From all the quadrats where shoots existed, leaf samples were collected for allozyme analysis. Using the two spatial parameters of flowering ramet densities and genotypes, we then constructed individual-based fruit-set models. A total of 236 quadrats contained shoots, and 135 contained flowering ramets, which indicated expanded distribution of this plant throughout the study plot, while shoots, flowers and fruits all showed clustering 3 distributions. Allozyme analysis of 282 samples revealed 94 multilocus genotypes. The largest clone extended to more than 40 m, whereas 56 genotypes were detected in only one sample. Several large clones and many small clones were distributed close to each other.Fine-scale spatial modelling revealed that the neighbouring flower numbers of different genotypes, compared with local genet or flower diversity, more influenced fruit set, in which the range of the neighbour was 14.5 m. These findings indicate that the compatible pollen dispersed by insect pollinators has a significant effect on sexual reproduction, in this C. keiskei population. Consequently, the spatial structure, which includes both genet distribution and clonal expansion by ramets, had a significant effect on pollination success.

Spatial distribution pattern of a clonal species: effects of differential production of clonal and sexual offspring

“…In particular, in species with linked growth such as Pteridium aquilinum (Parks and Werth 1993), Rubus chamaemorus (Korpelainen et al 1999), Cypripedium calceolus (Brzosko et al 2002, Maianthemum bifolium (Honnay et al 2006), and Convallaria keiskei (Araki et al 2007), the level of intermingling among genets is related to the strategy of clonality, and in some cases animals and human activities contribute to the dispersion of ramets up to one hundred meters (Parks and Werth 1993;Brzosko et al 2002). In contrast, in species with non-linked growth that produce bulbils such as Saxifraga cernua (Gabrielsen and Brochmann 1998;Kjølner et al 2006) and Polygonum viviparum (Diggle et al 1998), the spatial arrangement of genets is more intermingled.…”

Reproductive demography of ramets and genets in a rhizomatous clonal plant Convallaria keiskei

“…In our exploratory observation, a fresh shoot elongated again at the same position as an established shoot, suggesting that it was possible to keep track of the fate of ramets in this perennial herb. In addition, our previous analysis of the clonal structure implied notable clonal growth contributing to population maintenance in C. keiskei (Araki et al 2007). Nevertheless, it is still uncertain how clonal growth performs under ground and how it is concerned with the dynamics of ramets and genets; in particular, rhizome connectedness between ramets, growth patterns of rhizomes, relationships between seed production, and clonal growth per a ramet, or ramet recruitment in a genet.…”

“…The flowers attract insect pollinators of the orders Diptera, Coleoptera, and Hymenoptera, which maintain sexual reproduction of this self-incompatible plant (Araki et al 2005). C. keiskei also propagates clonally by growing linear rhizomes, forming a single clonal patch up to a maximum of 40 m wide (Araki et al 2007). …”

“…Due to plastic clonal growth foraging for locally suitable conditions (Bell 1984;Pitelka and Ashmun 1985;de Kroon et al 2005), variable responses to the heterogeneous habitats by ramets, not only of the same genets but also of the different genets (de Kroon et al 1992;Jónsdóttir and Watson 1997;Tamm et al 2002), would result in spatially heterogeneous clonal expansion or intermingled distribution between genets (McLellan et al 1997;Charpentier 2002;Reusch 2006;Araki et al 2007). However, because physical and/or physiological connections occurring below the ground are difficult to observe and are not necessarily permanent, there is a certain limit to understanding the relationship between each above-ground ramet and the extent of clonal spreading.…”

Comparison of light harvesting and resource allocation strategies between two rhizomatous herbaceous species inhabiting deciduous forests

“…In contrast, clonal propagation may be important to maintain the population of S. japonica, which has a perennial rhizome system. Although seed production is potentially low in this species, seed dispersal, which occasionally occurs, may contribute to the maintenance of genetic diversity within populations (Watkinson and Powell 1993;Araki et al 2007). Although assimilation of S. japonica is independent of spatiotemporal light fluctuations, this species usually produces more flowers than fruits develop.…”