Pattern of natural introgression in a Nothofagus hybrid zone from South American temperate forests

EL MUJTAR VERONICA; SOLA GEORGINA; APARICIO ALEJANDRO; GALLO LEONARDO

TREE GENETICS & GENOMES

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2017 vol. 13 p. 1 - 13

1614-2942

Interspecific gene flow is a common phenomenonin Nothofagaceae species; however, the dynamics of introgressionin hybrid zones remains largely unknown. We focusedon two ecologically and morphologically differentNothofagus species from Patagonia, Nothofagus nervosa andNothofagus obliqua. In a natural hybrid zone, we establishedtwo plots 280mapart in altitude (ca. 1.9 °C difference in meantemperature), and two subplots which captured microsite variation(abundance and spatial distribution of species and predominanceof wind direction). We used intensive sampling ofindividuals (2055, including adults and regeneration) and moleculargenotyping of 6 highly species-specific nuclearmicrosatellites for the identification and classification of hybrids,based on estimates of ancestry and interclass heterozygosity.We evaluated the relative contribution of our samplingeffects to variation in hybrid incidence and direction of introgressionusing generalized linear mixed effects models. Wedetermined that introgressive hybridization occurs at a globalrate of 7.8% and that variation was mostly explained by plots(frequency at low altitude was approximately twice that foundat high altitude), while it was less influenced by subplots. Thehigh altitude plot was dominated by late-generation backcrossesto N. obliqua (asymmetric bimodality), whereas thelow altitude plot consisted of intermediate hybrids(unimodality) and showed asymmetry for introgression betweensubplots. Differences were not detected between adultsand regeneration, suggesting early-acting reproductive isolatingbarriers. F1 hybrids occur at a global frequency of 3.8%,and are fertile, as the detection of first- and late-generationhybrids indicates.