Detection and visualization of spatial genetic structure in continuous Eucalyptus globulus forest

Abstract

Visualizing the pattern of variation using microsatellites within a Eucalyptus globulus forest on the island of Tasmania provided surprising insights into the complex nature of the fine-scale spatial genetic structure that resides in these forests. We used spatial autocorrelation and principal coordinate analysis to compare fine-scale genetic structure between juvenile and mature cohorts in a study area, 140 m in diameter, located within a typical, continuous E. globulus forest. In total, 115 juvenile and 168 mature individuals were genotyped with eight highly polymorphic microsatellite loci. There was no significant difference in the level of genetic diversity between cohorts. However, there were differences in the spatial distribution of the genetic variation. Autocorrelation analysis provided clear evidence for significant spatial genetic structure in the mature cohort and significant, but weaker, structure in the juvenile cohort. The spatial interpolation of principal coordinate axes, derived from ordination of the genetic distance matrix between individuals, revealed a spatially coherent family group which was evident in both cohorts. Direct comparison of the genetic structure within each cohort allowed visualization of a shift in the spatial distribution of genetic variation within the population of approximately 10 m. As the shift coincided with the direction of prevailing winds, it is hypothesized that this phenomenon is due to downwind dispersal of seeds and is indicative of the important role of prevailing winds in forcing eastward gene flow in these high-latitude forests.

Optimal sample sizes and allelic diversity in studies of the genetic variability of mycobiont and photobiont populations

“…In these cases, it would be desirable to considerably increase the number of individuals sampled within a population, and sample fewer populations. For instance, studies of fine-scale genetic structure typically sample more than 100 individuals from one or very few populations for plants (Chung et al 2005;Dutech et al 2005;Jones et al 2006;Yamagishi et al 2007) or fungi (Linde et al 2002). The required sampling effort critically depends on the spatial scale of interest.…”

A latitudinal cline in disease resistance of a host tree

“…The species has a mixed mating system and while molecular studies suggest the pollen dispersal curve is flat-tailed, most gene flow occurs over o100 m (Jones et al, 2007;Mimura et al, 2009). Drift, selection and hybridisation have all been shown to impact the evolutionary dynamics of the species (Steane et al, 2006;Jones et al, 2007;McKinnon et al, 2010;Yeoh et al, 2012).…”

“…The quantitative genetic variation in E. globulus and its intergrade populations has been summarised by partitioning the geographic distribution into 13 races and 420 subraces (Dutkowski and Potts, 1999), which molecular studies classify into three to five major lineages (Steane et al, 2006;Yeoh et al, 2012). The species has a mixed mating system and while molecular studies suggest the pollen dispersal curve is flat-tailed, most gene flow occurs over o100 m (Jones et al, 2007;Mimura et al, 2009). Drift, selection and hybridisation have all been shown to impact the evolutionary dynamics of the species (Steane et al, 2006;Jones et al, 2007;McKinnon et al, 2010;Yeoh et al, 2012).…”

Progress in Myrtaceae genetics and genomics: Eucalyptus as the pivotal genus

“…A study of different-aged cohorts of individuals (mature trees vs. small suppressed seedlings) within E. globulus forest using microsatellite markers allowed detection of a shift in the spatial distribution of the family structure of approximately 10 m between the two cohorts. As this shift coincided with the prevailing winds direction, it was argued to be due to limited effective seed dispersal (Jones et al 2007). …”