Low population genetic structure in five Chilean Nothofagus species and high fluctuating asymmetry in Nothofagus pumilio x N. antarctica putative hybrids.

Background: Following historic natural disturbances, interspecific hybridization has been documented between several Nothofagus species in Chilean forests. While hybridization can contribute to survival by enhancing genetic diversity, it may lead to developmental instability, reflected in higher leaf fluctuating asymmetry. Our goal was to investigate if hybrid individuals between N. pumilio and N. antarctica had developmental instabilities observable through high leaf fluctuating asymmetry and to examine evidence of potential hybridization and population genetic structure across five Nothofagus species.

Results: We collected N. pumilio, N. antarctica, and putative hybrid leaves for morphological analysis and chloroplast DNA sequencing. We also performed population genetic analysis on additional Nothofagus species (N. pumilio, N. antarctica, N. betuloides, N. dombeyi, and N. nitida) using microsatellite markers (eight loci). The putative hybrids with intermediate phenotypes displayed significantly higher fluctuating asymmetry than morphologically unambiguous N. pumilio and N. antarctica. Yet despite clear phenotypic differences, N. pumilio and N. antarctica shared cpDNA and had almost identical microsatellite composition. Our microsatellite analysis of five Nothofagus species found high allelic variation within species and subpopulations but low genetic structure between species and populations.

Conclusions: Our findings reveal possible developmental instability in putative N. pumilio and N. antarctica hybrids characterized by leaf morphology. Though nuclear ITS sequences have phylogenetically differentiated pure Nothofagus taxa, we found little to no genetic differentiation between sympatric or allopatric Nothofagus species from microsatellite data, particularly N. pumilio and N. antarctica. This is a surprising result given the clear morphological and biogeographical differences between the Chilean Nothofagus. While N. pumilio and N. antarctica are named species, matching the ecological species concept, whole genome analyses is needed to test if they are distinct enough to be classified as separate species under the phylogenetic species concept.