Effect of population spatial structure on pollination and seed set of a clonal distylous plant,Persicaria japonica (Polygonaceae)

Abstract

In order to assess the mechanisms through which the spatial structure of the population influences female reproductive success, spatial distribution of clones, degrees of limitation of legitimate (inter-morph) pollination, type and abundance of pollen loaded on the stigmas, and seed set were measured for many clones of two natural populations of the distylous clonal plant, Persicaria japonica. Within the populations, according to the spatial relation to the nearest opposite morph clone, individual clones were assorted into two spatial types, Le., clones that congregated with clones of the opposite morph (congregating clones), and clones that occurred singly at a considerable distance from the nearest opposite-morph clone (single clones). The pollination success, i.e., the proportion of legitimately pollinated flowers, and seed set were severely limited in the single clones compared to the congregating clones. Since artificial legitimate pollination improved the seed set in single clones, at least to some degree pollination failure was responsible for the reduced seed set in the single clones.

What influences pollen dispersal in the clonal distylous Menyanthes trifoliata (Menyanthaceae)?

“…However, other stud-ies reported that illegitimate pollination due to the spatial clumping of the morphs of M. trifoliata might also result in compatible pollen wastage and clogging of the stigmas with illegitimate pollen (Nic Lughadha & Parnell 1989, Thompson et al 1998. Whether it may reduce seed set as found in other insect-pollinated heterostylous species (Nishihiro & Washitani 1998, Wang et al 2005, Ishihama et al 2006, Scobie & Wilcock 2009, and affect the long-term viability of the populations, still needs to be evaluated.…”

“…Austerlitz et al 2004, Hardy et al 2004, Van Rossum 2009. In case of a clumped distribution of the morphs, pollen deposition at short distances is expected to lead to illegitimate pollination, as neighbouring plants likely belong to the same morph, except at the borders of patches of different morphs (Nishihiro & Washitani 1998, Charpentier 2001, Wang et al 2005. Consequently legitimate pollen dispersal, compared to overall (i.e.…”

“…This may in turn interfere with legitimate (between-morph) pollen dispersal due to pollinator foraging behaviour (Nishihiro & Washitani 1998, Charpentier 2001, Wang et al 2005. Indeed, pollinators often fly short distances between flowers, and the distribution of pollen dispersal is often leptokurtic, meaning that most pollen is deposited at short distances (e.g.…”

Population size affects genetic diversity and fine-scale spatial genetic structure in the clonal distylous herb Menyanthes trifoliata

“…reproductive success of small and more spatially structured populations of M. trifoliata may be reduced as a result of clogging of stigmas with incompatible pollen (e.g., Nishihiro and Washitani, 1998;Wang et al, 2005).…”

“…In self-compatible species, geitonogamy increases the selfing rate and thus the risk of inbreeding depression (Charpentier, 2002;Chung et al, 2006). In selfincompatible species, geitonogamous pollination reduces seed production due to clogging of stigmas with incompatible pollen (Nishihiro and Washitani, 1998;Charpentier, 2002;Wang 20 et al, 2005).…”