The influence of seed dispersal mechanisms on the genetic structure of plant populations

Abstract

Abstract. The plant electrophoretic literature was reviewed to determine whether seed dispersal mechanisms effectively predict the distribution of genetic variation within and among plant populations. To consider the relationship between seed dispersal and genetic differentiation on a local scale, nine species of tropical trees from the same lowland forest community in Panama were examined electrophoretically. In both cases, the association between seed dispersal and the distribution of genetic variation was not as significant as expected. To better understand the processes underlying the development of genetic structure within plant populations, the genetic consequences of two generalized patterns of seed dispersal were explored. In the Platypodium model, seeds were wind disseminated and leptokurtically distributed, while the Piper model had the highly clumped dispersal pattern characteristic of many species with animalingested seeds. Variable breeding structures and the selective mortality of seeds and seedlings were also incorporated, since these factors can have important effects on population structure. The problem of obtaining quantitative estimates of these evolutionary parameters from natural populations is discussed. An analytical procedure (paternity exclusion analysis) is suggested which could be instrumental in elucidating those mechanisms which interact to produce genetic structure in natural plant populations.

Temporal aspects of the fine-scale genetic structure in a population of Cinnamomum insularimontanum (Lauraceae)

“…However, in other species, where birds move seeds in groups (say of half-sibs) owing to seed-caching behavior (eg, Pinus albicaulis; Furnier et al, 1987) or the dispersal of intact fruits (eg, Cecropia obtusifolia; Epperson and AlvarezBuylla, 1997), seedlings may exhibit striking spatial structuring within local populations, even if the seeds or fruits move long distances. These studies provide important implications that the amount of spatial genetic structure among seedlings may depend on the type of fruit and the behavior of individual birds or other animals (Hamrick and Loveless, 1986). Particularly important is whether or not birds cause correlated seed dispersal into a given local area or gap.…”

“…Many bird species in northeastern Asia consume the fleshy fruits of the members of Lauraceae (Neolitsea spp, Litsea spp, and Persea spp) along coastal areas (Kitamura and Murata, 1987), and have been observed feeding on C. insularimontanum in southern Korea (MY Chung and MG Chung, personal observation). Since the fruits of these species are often consumed and dispersed singly or a few at a time, this type of seed dispersal may serve to weaken spatial genetic structuring within and among populations (Hamrick and Loveless, 1986).…”

Genetic Structure of Age Classes in Camellia Japonica (Theaceae)

“…Genetic and demographic factors, such as pollen and seed dispersal from neighboring parents, past major reproductive events, selection, and other processes determining the life history of a species, influence population genetic processes (Jain and Bradshaw 1966;Schaal and Levin 1976;Linhart et al 1981;Hamrick and Loveless 1986;Ritland 1989;Schoen and Latta 1989;Epperson 1993;Smouse and Peakall 1999;Kalisz et al 2001). More recently, studies of spatial population genetic structure with respect to distinct age or stage cohorts in plant populations have been stressed because this permits the detection of genetic dynamics over the life cycle and thus provides clues regarding the various potential ecological and evolutionary causes of spatial population genetic structure (Kalisz et al 2001).…”

A note on the relationship between outcrossing rate and gene flow in plants

“…The coefficient of determination, r2, between Nm and t was, however, low (0135), suggesting that nearly 87 per cent of the total gene flow was determined by factors other than pollen flow in the species examined. The low r2 may be due to several factors; firstly, data on t and Nm were derived from different sources; secondly, both and Nm show temporal and spatial variations (Brown, 1979;Sanders and Hamrick, 1980;Clegg, 1980;Handel, 1983;Govindaraju, 1988b); thirdly, in the absence of selection, gene flow via pollen grains is only half as effective as that via seeds (Hamrick and Loveless, 1986).…”

“…Therefore, all other factors being equal, the contribution of pollen flow toward total amount of gene flow may be less in self-pollinated plants than in obligate outcrossers. Information on the relative contributions of pollen flow and seed flow in relation to mating systems and life histories of plants can only result from quantitative estimates (from methods similar to the estimation of outcrossing rates) of seed flow for a large number of species (Hamrick and Loveless, 1986 Outcrossing rate (t) Figure 1 Relationship between gene flow (Nm) and outcrossing r,ate (t). …”