Ecotypic adaptation in Austrocedrus chilensis in cuticular hydrocarbon composition

Abstract

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.

Evolutionary divergence in the pan‐Atlantic mangrove Avicennia germinans

“…Multivariate analyses of the inter-trait correlations suggest a geographic structuring of populations, with French Guyana forming a nexus between African populations on the one hand and north American populations on the other hand. In earlier work on a south American conifer, Dodd et al (1998) interpreted geographic structure among populations in cuticular hydrocarbon profiles as being largely owing to genetic adaptation, populations from more arid environments adapting to having cuticles with increased proportions of longer-chain hydrocarbons. It was suggested that this might be under selection pressure because of increased resistance to water loss offered by longer-chain hydrocarbons, following a structural model proposed by Reynhardt & Reiderer (1994).…”

“…Variation in cuticular hydrocarbon profiles is under strong genetic control, as shown by genetic studies of crop plants (von Wettstein-Knowles, 1982 ;Bianchi, 1987 ;Jenks et al, 1992) and by taxonomic studies of both insect and plant cuticles. Their relative composition is generally species-specific, providing a useful tool in biosystematic studies of insects (Lockey & Metcalfe, 1988 ;Phillips et al, 1990 ;Estrada-Pen4 a et al, 1993 ;Chapman et al, 1995 ;Neems & Butlin, 1995) and of plants (Eglinton et al, 1962 ;Gu$ lz, 1994 ;Maffei, 1995 ;Dodd et al, 1998). The biosynthesis of the alkane series typically found in plants is known to begin with a common precursor, the C "' fatty acid (Bianchi, 1987 ;Dennis & Kolattukudy, 1991).…”

“…However, such tests are unable simultaneously to evaluate several potentially causal factors. Partial Mantel tests (Dodd et al, 1998 ;Manly, 1991 ;Sokal et al, 1991 ;Thorpe, 1996) permit the study of several interacting factors simultaneously, and thus can be used to test relative contributions of historic events, such as phylogeny and isolation, at the same time as effects of local genetic adaptation.…”

“…Gas-chromatographic analyses of the cuticular waxes were conducted according to Dodd et al (1998). Briefly, an approximately equal surface area of foliage (on average three leaves) for each individual was extracted in n-hexane for 1.5 min.…”

Seasonal Variation and Resin Composition in the Andean Tree Austrocedrus chilensis

“…The distribution range of A. chilensis covers two wide parallel areas in the Cordillera de los Andes, in both sides of the mountain range in Chile and Argentina. It includes the west Andean populations in the Mediterranean region of Chile, east Andean populations ranging from humid rain forest to the steppe ecotone and coastal mountain populations from Mediterranean Chile [1][2][3]. This species is more common in the eastern Andes (Argentina), where the wide precipitation gradient ranges from 2500 to 4000 mm per year [3].…”