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

Area of Science:

• Forestry
• Genetics
• Ecology

Background:

• Forest tree species complexes, like Eucalyptus, present challenges in taxonomic classification and gene pool management.
• The Eucalyptus globulus complex, comprising four distinct taxa, is characterized by intergrade populations, complicating its genetic understanding.

Purpose of the Study:

• To resolve the genetic affinities within the Eucalyptus globulus complex.
• To determine the best criteria for classifying germplasm for conservation and breeding.

Main Methods:

• Genotyping of 1200 Eucalyptus trees using nine microsatellites across their natural range in Australia.
• Analysis of genetic structure and diversity in 33 morphological core and intergrade populations.

Main Results:

• Significant spatial genetic structure (F(ST) = 0.10) was observed, with continuous genetic variation.
• High genetic diversity in southern Eucalyptus globulus subspecies maidenii suggests it as the center of origin.
• A cryptic genetic entity was identified, genetically and geographically intermediate between core subspecies, challenging morphological classifications.

Conclusions:

• Geography is a more reliable predictor of genetic affinities within the Eucalyptus globulus complex than morphology.
• Germplasm classification for management units should prioritize geographic data for conservation and breeding purposes.