Multiple evolutionary processes drive the patterns of genetic differentiation in a forest tree species complex

Abstract

Forest trees frequently form species complexes, complicating taxonomic classification and gene pool management. This is certainly the case in Eucalyptus, and well exemplified by the Eucalyptus globulus complex. This ecologically and economically significant complex comprises four taxa (sspp. bicostata, globulus, maidenii, pseudoglobulus) that are geographically and morphologically distinct, but linked by extensive “intergrade” populations. To resolve their genetic affinities, nine microsatellites were used to genotype 1200 trees from throughout the natural range of the complex in Australia, representing 33 morphological core and intergrade populations. There was significant spatial genetic structure (FST = 0.10), but variation was continuous. High genetic diversity in southern ssp. maidenii indicates that this region is the center of origin. Genetic diversity decreases and population differentiation increases with distance from this area, suggesting that drift is a major evolutionary process. Many of the intergrade populations, along with other populations morphologically classified as ssp. pseudoglobulus or ssp. globulus, belong to a “cryptic genetic entity” that is genetically and geographically intermediate between core ssp. bicostata, ssp. maidenii, and ssp. globulus. Geography, rather than morphology, therefore, is the best predictor of overall genetic affinities within the complex and should be used to classify germplasm into management units for conservation and breeding purposes.

Genetic control of Eucalyptus globulus seed germination

“…The E. globulus from the Strzelecki Ranges is genetically differentiated from the more coastal populations in the Otway Ranges and islands of the Furneaux group (Jones et al 2013) and is the most drought tolerant of the E. globulus races (Strzelecki>Furneaux>Western Otways; (Dutkowski and Potts 2012)). The ranking of the races in terms of their tolerance to germination at high temperatures (Strzelecki>Western Otways>Furneaux; Fig.…”

Assessing a Bayesian Approach for Detecting Exotic Hybrids between Plantation and Native Eucalypts

“…This required sufficient differentiation in International Journal of Forestry Research allele frequencies so that individuals with genotypes that are admixed between two species could be detected. Yet, the level of differentiation between species estimated from the inbreeding coefficient ST is low in comparison to a range of other eucalypts [63][64][65][66], particularly considering that the comparison is between taxonomically distinct species. However, because the range-wide sampling strategy used here covered geographically discrete populations of these widespread species (Figure 1), it probably captures significant within species differentiation, which could subsequently reduce ST values between species [67][68][69][70].…”

Unravelling the evolutionary history of Eucalyptus cordata (Myrtaceae) using molecular markers

“…Indeed, Vucetich and Waite (2003) have shown that peripheral populations can experience up to 30 times greater genetic drift than central-core populations. Although peripheral populations have traditionally been studied in relation to a continuous central core (Eckert et al 2008;Jones et al 2013), in the case of E. cordata, the cores are not continuous but have become recently fragmented. This hypothesis is supported by the low differentiation between populations within the 'phantom core', which is suggestive of a more continuous distribution in the cores in the recent past.…”

“…The microsatellite and chloroplast markers were chosen so that the results of this study could be compared with previous works (McKinnon et al 2004b;Jones et al 2005Jones et al , 2013Rathbone et al 2007). We used DArT markers, which have wide genome coverage Steane et al 2011), so as to achieve high resolution for the phylogenetic component of the study.…”