Understanding selective pressures on trichome distribution in Nothofagus pumilio (lenga) along multiple gradients

ARBETMAN M., P. MATHIASEN & A.C. PREMOLI

Bariloche

Congreso; VI Southern Connection Congress; 2010

Variable conditions along physical gradients influence patterns of genetic differentiation in trees. Patagonia is characterized by sharp gradients in temperature and humidity that are inhabited by Nothofagus pumilio. We evaluate the presence of trichomes to understand adaptive-plastic responses. Such trichomes are diagnostic features of N. pumilio leaves and their presence and function has not been established yet. Locally, we analyzed the effect of contrasting altitudes, recording the presence of trichomes at seedlings of a reciprocal transplant experiment. Regionally, we quantified the frequency of trichomes along the whole range of the species in about 10 individuals at each of 88 populations. Chi-square test shows statistical differences in the frequency of individuals presenting hairs at populations growing in high vs low elevations. After the reciprocal transplant those differences persist. Multiple regression analysis at the regional scale showed a significant increase of the presence of trichomes with latitude. Populations south of 43ºS were homogeneous and most of them consisted of individuals with trichomes while in the north populations were heterogeneous and eastern populations either lack or yielded less proportion of individuals with hairs. Experimental results show that the presence of trichomes in N. pumilio is fixed genetically and that the distribution along the range is not random and could be related to wettability and/or herbivory pressure.