Estimation of outcrossing rates at hierarchical levels of fruits, individuals, populations and species in Magnolia stellata

Abstract

In plant species with mixed mating systems, differences in diverse factors-including their pollination system, flowering phenology, life form and susceptibility to inbreeding depression-cause variation in outcrossing rates among fruits within individuals, among individuals within populations and among populations within species. To quantify this hierarchical variation, we examined outcrossing rates at the seed stage in five populations of Magnolia stellata, a self-compatible, insect-pollinated and protogynous tree species. For this purpose, we sampled 1498 seeds within 204 fruits obtained from 56 individuals of the five populations, determined genotypes of the sampled seeds and maternal individuals at six polymorphic microsatellite loci, then estimated outcrossing rates and their variance components at four hierarchical levels (fruits, individuals, populations and species) using a nested analysis of variance-type linear model with a Bayesian approach. The species-level outcrossing rate was 0.730 (95% credible interval, 0.595-0.842), indicating that this species has a mixed mating system. Outcrossing rates were not significantly different among populations, but were significantly different among individuals within populations. Variance components at the levels of individual and fruit were statistically supported and were highest for the former. Thus, factors influencing outcrossing rates at the individual level, such as differences in flowering phenology and early-stage inbreeding depression, appear to have important effects within these M. stellata populations, but not among them. The method of hierarchically estimating outcrossing rates using a Bayesian approach, as applied in this study, is compared with conventional methods for estimating outcrossing rates, and the statistical properties of the Bayesian approach are discussed.

Understanding the genetic diversity, spatial genetic structure and mating system at the hierarchical levels of fruits and individuals of a continuous Theobroma cacao population from the Brazilian Amazon

“…Thus, most of the fruits appeared to contain full-sibs. A higher paternity correlation within rather than among fruits has been detected in other plant species (Muona et al, 1991;Sampson, 1998;Quesada et al, 2001;Tamaki et al, 2009). …”

Mating system parameters at hierarchical levels of fruits, individuals and populations in the Brazilian insect-pollinated tropical tree, Tabebuia roseo-alba (Bignoniaceae)

“…An increase in self-fertilization in logged or fragmented populations in comparison to undisturbed populations has also been reported for some tropical tree species (Murawski et al 1994;Aldrich and Hamrick 1998;Cascante et al 2002;Fuchs et al 2003;Lobo et al 2005;Tamaki et al 2009). For example, Paquira quinata, Ceiba pentandra and Samanea saman occurring in continuous forests appear to be self-incompatible; however, in fragmented populations or as isolated trees in pastures, these species show some levels of self-fertilization and a shift to a mixed-mating system (Cascante et al 2002;Fuchs et al 2003;Lobo et al 2005).…”

“…However, this difference is always an underestimate as it depends upon the number of loci used: the more loci used, the closer to the true difference (Ritland 2002). Each parameter was examined at several hierarchical levels (Ritland 1989;Muona et al 1991;Quesada et al 2001;Tamaki et al 2009, Silva et al 2011: between populations; among trees within a population; and among and within fruits of the same seed-tree. Analyses at the population level were carried out using the Newton-Raphson numerical method and at the individual and fruit levels using the Expectation-Maximization numerical method.…”

“…Correlated mating may also occur when the number of potential male parents is low or when mating occurs mainly between near neighbors (Surles et al 1990). However, only a small number of studies have investigated paternity correlation at the different hierarchical levels of fruits and individuals (Schoen and Clegg 1984;Schoen 1985;Ritland 1989;Muona et al 1991;Sampson 1998;Quesada et al 2001;Hardy et al 2004;Tamaki et al 2009, Silva et al 2011.…”

Mating system patterns of natural populations of Pinus koraiensis along its post-glacial colonization route in northeastern China

“…Tan et al (2012) also found a non-significant difference in the t m values (ranging from 1.033 to 1.200) of 8 individuals obtained from a seed orchard of P. massoniana. However, De-Lucas et al (2008) showed that there was a significant difference in the t m values among P. pinaster individuals growing across areas in the Mediterranean region, which may be co-determined by abiotic factors across areas and biotic factors such as florescence synchronism, tree height, and canopy size among individuals in different populations (Tamaki et al, 2009).…”