Ecotypic adaptation in Austrocedrus chilensis in cuticular hydrocarbon composition

Abstract

An homologous series of hydrocarbons ranging from C₂₁ to C₃₇ (was detected in foliar cuticular waxes of Austrocedrus chilensis (D. Don) Pic.-Ser. & Bizz., by gas chromatography. Qualitatively, the chromatograms were similar for all individuals sampled from 29 natural populations in Chile and Argentina, showing C₃₃ and C₃₅ alkanes to be dominant. Quantitatively, the chromatograms varied significantly among populations. Multivariate analyses showed that arid zone populations from mediterranean Chile and the Patagonian steppe were different from one another and were distinct from mesic populations close to the Valdivian rainforest vegetation zone. Mediterranean Chilean populations were characterized by higher concentrations of the longer carbon-chain alkanes, but retained equal amounts of shorter-chain homologues as the mesic populations. A greater variation in chain lengths and higher concentrations of longer carbon chains in the mediterranean populations is consistent with a model for the adaptation to reduced cuticular permeability. Partial Mantel matrix tests revealed significant climatic and inter-population distance effects with taxonomic distances based on multivariate and univariate hydrocarbon data. Annual rainfall was overall the most significant factor, particularly in regressions with the shorter-chain hydrocarbons. Annual mean temperature was most significant for the longer-chain hydrocarbons. This suggests, on the one hand, ecogenic adaptation to both temperature and precipitation of cuticular hydrocarbon composition, and, on the other hand, a weaker, but important effect of gene flow in determining hydrocarbon composition in this species. The northernmost populations at San Felipe and San Gabriel were the most distinctive. This could result from the effects of random changes in allele frequencies and/or to founder effects in isolated and small populations. These populations show some East-Andean affinities presumably due to historic migration patterns.