The role of glaciation, fragmentation and hybridization in shaping the distribution of the genetic variation in a Patagonian southern beech.

MARCHELLI, P; GALLO, L A

JOURNAL OF BIOGEOGRAPHY

Blackwell Publishing Ltd.

Año: 2004 vol. 31 p. 451 - 460

0305-0270

Aim The distribution of the genetic variation in long-lived species is acombination of both, historical and current processes. In Nothofagus nervosa(Phil.) Dim. et Mil., the possible existence of multiple glacial refugia, theunidirectional gene flow along fragmented areas and the natural hybridizationwith the related species Nothofagus obliqua (Mirb.) Oerst. highlights as the mostimportant factors responsible for modelling its genetic structure. The presentstudy aims to find out the relative importance of these evolutionary processes indetermining the distribution pattern of the genetic variation in N. nervosa.Location The study was carried out in north-western Patagonia, Argentina.Twenty populations covering the entire distribution range of N. nervosa inArgentina were analysed. For comparison purposes, three populations from Chilewere also included.Methods Genetic variation was detected using isozyme gene markers; diversityand differentiation parameters were calculated. A cluster analysis was performedand the correlation between genetic and geographical distances was tested.Results Levels of genetic variation were relatively high given the smalldistribution range of the species in Argentina. Genetic and geographicaldistances were not correlated and a longitudinal trend in the genetic variationwas evident. Hotspots of diversity with rare and private alleles were observedamong western populations, while hybrid seeds were found almost exclusivelyamong eastern populations.Main conclusions The higher level of diversity observed in western populationscould be related with the location of glacial refugia. Furthermore, it should alsoreflect low levels of gene flow given the eastward unidirectional winds. On thecontrary, ancient and current interspecific hybridization processes would mainlycause the particular genetic constitution of the eastern populations. Evidence ispresented supporting that glaciations and hybridization were the main factorsshaping the distribution of the genetic variation in N. nervosa.