Different cone colours pay off: lessons learnt from European larch (Larix decidua) and Norway spruce (Picea abies)
The colour morphs of immature female cones in European larch (Larix decidua Mill.) and Norway spruce (Picea abies (L.) Karst.) are green, red, and intermediate in colour. For the first time, these three colour morphs were studied to verify the thermoregulatory hypothesis and to investigate its underlying genetic spatial pattern. The study was based on an extensive systematic sampling, and data were analysed using principal component analysis (PCA), binary logistic regression (BLR), and spatial autocorrelation. Correlations between the nontransformed environmental variables and PC scores revealed two main ecological gradients, (i) altitude–temperate and (ii) annual precipitation. Loadings of the first two principal components exceeded 85% in both species. BLR was used to test the effect of the altitude–temperature gradient on the probability of occurrence of a specific cone colour. In both species, the occurrence of red cones was significantly positively related to high altitude with low temperatures, while green cones were significantly negatively correlated with decreasing temperature and increasing altitude. In both species the spatial pattern based on a putative Mendelian gene was nonrandom as indicated by significantly high Moran’s I values based on altitudinal distance. Spatial genetic structure was probably maintained by limited gene flow and balanced selection that maintained short-distance genetic differentiation.