153
et al. 1996; Marchelli et al. 1998; Allnutt et al. 1999; Premoli et al. 2000; Pastorino
and Gallo 2002; Azpilicueta et al. 2009; Cosacov et al. 2010), on which other effects
of local scale can be superimposed.
The patterns of genetic variation of the cypress in Argentina have been characterized by means of isoenzymes (Pastorino 2001; Pastorino and Gallo 2002, 2009;
Pastorino et al. 2004; Souto et al. 2012) and nuclear microsatellites (Arana et al.
2010). The general result of the studies with isozymes is that the intra-population
genetic variation of cypress is relatively low in terms of allelic variants (number of
alleles per locus A L = 1.520; number of effective alleles Ae = 1.163) and moderate
in terms of heterozygosity (Ho = 0.135) (Pastorino and Gallo 2009). With microsatellites, the number of allelic variants per locus was rather high (A L = 12.08) (Arana
et al. 2010). On the other hand, its degree of genetic differentiation between populations is low for both types of markers (Pastorino and Gallo 2009: F ST = 0.06; Arana
et al. 2010: R ST = 0.08), that is, their populations differ little, even those that are
subject to contrasting rainfall regimes or separated by hundreds of kilometers.
With respect to the structuring of the genetic variation of the species, all the studies agree in a latitudinal pattern, with the northern range of the distribution being on
average more variable. This pattern has been interpreted as an effect of the last
glaciation, with larger and/or more abundant refuges located in the north according
to a lesser northwards development of the Andean glacial cover. In turn, another
consistent finding in the studies of the different authors is a greater genetic variation
in the steppe populations of the center and north of the species’ range in Argentina.
This is surprising, since these are mostly marginal forest patches of a few dozen
trees and completely isolated by distance from the forest continuum. Low diversity
values and the occurrence of inbreeding and genetic drift processes would be
expected for these populations according to a center-periphery hypothesis (Pironon
et al. 2016).
“Leading” and “rear” edges can be distinguished in the natural distribution of
species (Hampe and Petit 2005). The first consists of relatively new marginal populations that act as a colonization front in the distributional adjustment that occurs
following environmental changes, such as post-glacial climate change. The rear
edge is the opposite margin of the distribution, which may end up being extinguished, and this will imply a displacement of the distribution area or otherwise
persist (stable edge), implying this an expansion of the total distribution area. These
stable populations, capable of surviving in situ the climatic oscillations of the
Quaternary, would be relicts two or three orders of magnitude older than the rest of
the populations and could be essential for the long-term conservation of genetic
diversity and the evolutionary potential of species. In cypress, the results with neutral markers support the hypothesis that the steppe marginal forests represent the
stable rear edge of the Argentine distribution of the species. They are located outside of the glaciated area, so they could have persisted during the last glacial maximum, and moreover, they could have been the glacial refuges from where the
species initiated the post-glacial recolonization.
As for the presumption of inbreeding, we know that self-pollination is not possible in the Patagonian cypress, since it is a dioecious species, but it could still be
6 Patagonian Cypress (Austrocedrus chilensis): The Cedarwood…
et al. 1996; Marchelli et al. 1998; Allnutt et al. 1999; Premoli et al. 2000; Pastorino
and Gallo 2002; Azpilicueta et al. 2009; Cosacov et al. 2010), on which other effects
of local scale can be superimposed.
The patterns of genetic variation of the cypress in Argentina have been characterized by means of isoenzymes (Pastorino 2001; Pastorino and Gallo 2002, 2009;
Pastorino et al. 2004; Souto et al. 2012) and nuclear microsatellites (Arana et al.
2010). The general result of the studies with isozymes is that the intra-population
genetic variation of cypress is relatively low in terms of allelic variants (number of
alleles per locus A L = 1.520; number of effective alleles Ae = 1.163) and moderate
in terms of heterozygosity (Ho = 0.135) (Pastorino and Gallo 2009). With microsatellites, the number of allelic variants per locus was rather high (A L = 12.08) (Arana
et al. 2010). On the other hand, its degree of genetic differentiation between populations is low for both types of markers (Pastorino and Gallo 2009: F ST = 0.06; Arana
et al. 2010: R ST = 0.08), that is, their populations differ little, even those that are
subject to contrasting rainfall regimes or separated by hundreds of kilometers.
With respect to the structuring of the genetic variation of the species, all the studies agree in a latitudinal pattern, with the northern range of the distribution being on
average more variable. This pattern has been interpreted as an effect of the last
glaciation, with larger and/or more abundant refuges located in the north according
to a lesser northwards development of the Andean glacial cover. In turn, another
consistent finding in the studies of the different authors is a greater genetic variation
in the steppe populations of the center and north of the species’ range in Argentina.
This is surprising, since these are mostly marginal forest patches of a few dozen
trees and completely isolated by distance from the forest continuum. Low diversity
values and the occurrence of inbreeding and genetic drift processes would be
expected for these populations according to a center-periphery hypothesis (Pironon
et al. 2016).
“Leading” and “rear” edges can be distinguished in the natural distribution of
species (Hampe and Petit 2005). The first consists of relatively new marginal populations that act as a colonization front in the distributional adjustment that occurs
following environmental changes, such as post-glacial climate change. The rear
edge is the opposite margin of the distribution, which may end up being extinguished, and this will imply a displacement of the distribution area or otherwise
persist (stable edge), implying this an expansion of the total distribution area. These
stable populations, capable of surviving in situ the climatic oscillations of the
Quaternary, would be relicts two or three orders of magnitude older than the rest of
the populations and could be essential for the long-term conservation of genetic
diversity and the evolutionary potential of species. In cypress, the results with neutral markers support the hypothesis that the steppe marginal forests represent the
stable rear edge of the Argentine distribution of the species. They are located outside of the glaciated area, so they could have persisted during the last glacial maximum, and moreover, they could have been the glacial refuges from where the
species initiated the post-glacial recolonization.
As for the presumption of inbreeding, we know that self-pollination is not possible in the Patagonian cypress, since it is a dioecious species, but it could still be
6 Patagonian Cypress (Austrocedrus chilensis): The Cedarwood…