Quaternary evolutionary history of Austrocedrus chilensis, a cypress native to the Andean-Patagonian Forest

PASTORINO, MARIO JUAN; GALLO, LEONARDO ARIEL

JOURNAL OF BIOGEOGRAPHY

Blackwell Science Ltd.

Año: 2002 vol. 29 p. 1167 - 1178

0305-0270

Aim The Quaternary life history of a species determines its current range and the degree and distribution of its present genetic variation. Past climates, ecological relationships and disturbances in connection to evolutionary factors have determined the genetic and geographical distribution patterns of the current vegetation, and consequently, evolutionary processes can be inferred from those patterns. The aim of the present study is to find a plausible evolutionary explanation for the current natural range and genetic variation patterns of Austrocedrus chilensis (D.Don) Florin et Boutelje in Argentina. Location The studied species ranges naturally over a narrow strip not wider than 50 km that runs parallel to the Cordillera de los Andes from 32º 39’ S in Chile to 43º 44’ S in Argentina. The studied populations are located in the Argentine range, especially in its central part. Methods Information on palynological data, current geographical distribution and on amount and distribution of genetic variation of the species in Argentina was the basis for an integrating analysis and discussion. Results Palynological evidence of the past presence of A. chilensis before and immediately after last glaciation on the east side of the Andes was reported. The most conspicuous present populations of A. chilensis are located in areas that were covered by ice during the Last Glacial Maximum. The allelic multiplicity and diversity as well as the population differentiation of the species in Argentina were shown to be small, while the levels of heterozygosity were moderate. A latitudinal gradient trend was recognized as a pattern of distribution of variation in Argentina, the northerly populations being more variable. Extreme marginal populations located in the steppe, out of the glaciated area, show the greatest levels of variation. Main Conclusions Evidence was shown supporting that the major factor responsible of the variation pattern found in Austrocedrus chilensis were the glacial processes. In the Argentine side of the Cordillera de los Andes the species could survive only in a narrow strip between the coldness of the ice sheet and the dryness of the steppe. That implies a generalized genetic drift process. Multiple small refuges in the eastern side of the Cordillera are hypothesized where this cypress would have survived to glaciation. Those refuges are postulated to have been chiefly localized slightly eastward to the present distribution area and most probably in a northern location, at least from 42º S of latitude to the north.