The Geography of Phytochemical Races

170 3 After the Ice
In order to test these predictions, Premoli et al. (2000) collected plant material
from 24 populations of Fitzroya, 12 on each side of the Andes, and subjected the
foliage to appropriate isolation procedures and electrophoresis. Reliable information
was obtained for 21 loci. Populations on the eastern side of the Andes were
more variable than populations on the western side, as the following pairs of fi gures
show: number of alleles per locus, 1.58 versus 1.37; total number of alleles,
33 versus 29; number of rare alleles, 5 versus 3.08; percent polymorphic loci, 39.3
versus 26.6; observed heterozygosity, 0.090 versus 0.057; and expected heterozygosity,
0.091 versus 0.063. Also, genetic identities of populations on the western
slopes of the Andes were higher than those of populations from the eastern slopes.
The higher levels of variation in eastern populations were in accord with preliminary
studies using DNA markers (Allnutt et al., 1999).
The isozyme frequency data were then subjected to discriminant function analysis.
Poor discrimination between groups was observed when the single refugium model
was tested. However, when the data were analyzed using the groups suggested by
the multiple refugia hypothesis, both scenarios, Cordillera effect and extent-of-theice
effect, were supported. Although the data clearly suggest that multiple refugia
existed, it is not possible on the basis of the available data to say how many were
there. The data do suggest, however, that the southernmost populations in Argentina
have been separated from western ones for a considerable period of time, and that
a southeastern refugium may have existed. Much of the variation can be accounted
for by northward fl ow from the southeastern refugium and eastward fl ow from the
Chilean coastal refugium. The authors pointed out that the existence of a southeastern
refugium, farther south than was expected, is another example of how patterns
of glaciation differed in South America, where ice cover was often patchy, as compared
to North America where ice cover was essentially total. Revegetation in South
America, thus, started from several (many?) refugial centers, whereas revegetation
in North America involved continent-wide movement northward.
3.4.2 Austrocedrus chilensis (Cupressaceae)
Although the impact of Pleistocene glaciation was not addressed in the following
study, it did involve attempts to measure genetic variation in another South American
tree species, Austrocedrus chilensis (D. Don) Pic.-Ser. and Bizz. This monotypic
genus occurs in the cordillera of Chile and Argentina and disjunctly in the coastal
mountains of Chile. Dodd and Rafi i (1995) examined the seed megagametophyte
fatty acids from 104 trees from 13 natural populations representing the range of the
species, San Felipe in the north (32°39′S) to Corcovado in the south (43°32′S). Identifi
ed acids ranged from palmitic (16:0) to 5,11,14,17-eicosatetraenoic acid (20:4).
The main compounds were shown to be oleic (18:1), linoleic (18:2), linolenic (18:3),
and 5,11,14,17-eicosatetraenoic acids. Multivariate statistical analysis revealed a
separation of the specimens into two groups, one comprising populations in the