Evidence of genetic drift in neutral and adaptive genome

GALLO, LEONARDO ARIEL; PASTORINO, MARIO JUAN

San Lorenzo de El Escorial

Conferencia; Evoltree conference Forest Ecosystem Genomics and Adaptation; 2010

Evoltree - INIA

Genetic drift is a stochastic process that affects the entire genome, including genes involved in quantitative characters that are potentially adaptive. However, it is commonly seen as operating exclusively in neutral genes. To our knowledge genetic drift has never been measured in natural forest tree species populations, probably because all requisites for such measurement, i.e. at least two populations of common origin, selection pressure in the same direction and genetic isolation, are rarely fulfilled. We studied two pairs of neighboring populations of the dioecious, wind-pollinated Patagonian Cypress (Austrocedrus chilensis (D.Don) Pic. Ser. et Bizzarri) separated by 1200 m and 2600 m respectively. Within each pair, populations lay on a north-south axis in a xeric environment and consisted of about 100 individuals, with approximately equal number of male and female trees. We reanalysed partial data from previous studies, including that on 26 allozymes from12 loci, 207 alleles from 8 SSRs loci, germination capacity, germination energy and early height growth curves in greenhouse trials, seedling survival and carbon isotope discrimination (ä13) after one year in field trials, and apical damage and maximum photosystem II efficiency (Fv/Fm) after water stress in a greenhouse trial. Genetic drift and genetic isolation were shown by means of fixation and loss of alleles at three isozyme loci and 19 microsatellite private alleles with frequencies above 10 % in one of the paired populations. Surprisingly, genetic and phenotypic values for most of the quantitative traits also differed between neighboring populations, indicating that common origin and/or homogenizing selection have not counteracted the effect of drift. This study offers two important conclusions: 1) wind seems to act as a gene flow barrier in this case, and 2) adaptive genes can be also affected by genetic drift. This have consequences for the management of the genetic resources of any species in the current scenario of climate change.