Effective pollen dispersal is enhanced by the genetic structure of an Aesculus turbinata population

Abstract

Summary1. Studies using highly informative genetic markers (e.g. microsatellites) have revealed effective movement of genes through pollen grains from more distant sources into offspring than those inferred on the basis of physical pollen movement alone. In order to identify the factors that cause such effective pollen movement in tree populations, analyses of the genetic structure of reproductive trees and parentage analyses for seedlings and saplings were conducted in a 110-ha population of Aesculus turbinata , a tall deciduous tree species that is pollinated by insects and has large seeds that are dispersed by gravity and small mammals. 2. By analysing genotypes of seed coats, which are identical to those of the seed parents, and of leaves from seedlings, pollen donors and seed parents were identified for seedlings. Differences in size and dispersal mode between pollen and seeds caused a significant difference in dispersal distances. Reflecting the restricted seed dispersal (25.3 m on average), there was significant positive relatedness between reproductive trees standing within 150 m of each other. 3. The percentage of self-pollinated offspring decreased from 8.3% at the seedling stage to 0.56% at the sapling stage. The disappearance of out-crossed individuals during the stage between seedling and sapling seemed to be associated with the spatial distance separating their parents: the proportion of juvenile trees that died was higher for those that originated from out-crosses between adults standing within 100 m of each other, where positive relatedness was found between adult trees. Consequently, the deaths of individuals arising from self-pollination events and from crosses between reproductive trees that were spatially adjacent caused longer effective pollen movement for the offspring that survived. The distance between the two parents of a tree, which indicates the distance of effective pollen movement, increased from 179.9 m for seedlings to 288.9 m for saplings. 4. The genetic structure of the adult population of A. turbinata affected the survival of offspring through biparental inbreeding depression, and, then, removal of individuals resulting from crosses between related adults in turn promoted effective pollination over longer distances.

Molecular and quantitative signatures of biparental inbreeding depression in the self-incompatible tree species Prunus avium

“…Seeds from one seed-tree (M3) even did not germinate. Loss of genetic diversity could be explained by a reduced fitness in seeds and seedlings leading to mortality, by instance through biparental inbreeding depression (Cheliak et al, 1985;Rajora et al, 2000;Hufford and Hamrick, 2003;Naito et al, 2005;Isagi et al, 2007;Duminil et al, 2009;Hasegawa et al, 2009). However, our data rather showed higher survival of offspring from related parents and fixation index showed excess of heterozygotes.…”

“…Isolation of this P. avium population may have thus resulted in loss of genetic diversity and homozygote excess in seed and seedlings, as a consequence of low pollen immigration (Hanson et al, 2008;Sebbenn et al, 2010), significant spatial genetic structure (see Supplementary File 3; We analysed eight nuclear microsatellite loci and the gametophytic incompatibility locus. Waser and Price, 1994;Isagi et al, 2007;Grindeland, 2008;Hasegawa et al, 2009;Takeuchi et al, 2010), inbreeding (see Supplementary Material 1) or generation overlapping (Litrico et al, 2005). Seed sampling and seed germination resulted in loss of genetic diversity in the stand Bayern only.…”

“…In self-compatible species with a mixed mating system, outcrossing rates tend to increase over life-stages because of late-acting selfincompatibility or inbreeding depression (Hufford and Hamrick, 2003;Naito et al, 2005;Ward et al, 2005;Ishida, 2006;Isagi et al, 2007;Naito et al, 2008;Hasegawa et al, 2009;Tamaki et al, 2009;Philipp and Nielsen, 2010;Kamm et al, 2011), that is, that offspring stemming from self-fertilization will experience reduced fitness. In obligate outcrossing species, biparental inbreeding (that is, mating of two genetically related individuals), might also reduce offspring viability and quality (Nason and Ellstrand, 1995;Teixeira et al, 2009).…”

The Effects of Multilocus Heterozygosity on the Longevity of Seedlings Established on Fallen Logs in <i>Picea jezoensis</i> and <i>Abies sachalinensis</i>

“…At the population level, F IS often decreases from the seedling stage to the mature tree stage (Hufford & Hamrick, 2003;Lian et al, 2008). For example, selfed or inbred progenies tend to be eliminated during the early demographic stages (Karkkainen et al, 1996;Kadomatsu et al, 1997;Isagi et al, 2007;Naito et al, 2005). Selection of inbred individuals eventually affects genetic variation within the population as F IS often decreases from the seedling stage to the mature tree stage (Hufford & Hamrick, 2003;Lian et al, 2008).…”

“…Experimental studies have revealed that selfed and/or inbred progeny suffer from low viability and survivorship (Husband & Schemske, 1996;Kadomatsu et al, 1997;Hirao, 2010). Parentage analyses of naturally established seedlings have revealed that the proportion of selfed individuals decreases from the seedling stage to the sapling stage (Naito et al, 2005;Isagi et al, 2007). However, the relative importance of genetic effects and site conditions on seedling longevity has not been evaluated in a natural forest.…”