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climatic conditions at these latitudes by the early Holocene (10,000–8500 years BP)
(Markgraf et al. 2003), i.e., lack of seasonality and a drier and warmer environment
(Manzini et al. 2008). Reinforcing this, three different zones based on a palynological reconstruction representing paleo-climates (Markgraf et al. 1996) were identified (north of 43° S, between 43° and 51° S, and south of 51° S).
The distribution of chloroplast genetic variation helps to thoroughly comprehend
how forests were modeled after glaciation. Considering its slow evolution rate as
well as the uniparental (maternal) inheritance, chloroplast DNA is a useful tool tracing the effective dispersal of seeds. Polymorphisms from cpDNA non-coding
regions were screened in 40 Argentinean populations of N. pumilio and N. antarctica (Soliani et al. 2012; Table 5.1) and used to define haplotypes, coming from the
following restricted regions: trnD-trnT/HinfI, trnC-trnD/taqI, and atpH-atpI/
HinfI. Point mutations in the restriction site and indels (insertion/deletions) allowed
identifying 9 and 13 haplotypes in N. pumilio and N. antarctica, respectively (based
on different combinations of length variants). Eight haplotypes were shared among
the species, with N. antarctica being the most variable with five unique haplotypes.
A genetic diversity trend along latitude, decreasing in both species from north to
south, as well as a significant phylogeographic structure between the two main
groups of populations and haplotypes (north and south of 42° S), evidenced regional
footprints of glaciations (Fig. 5.2). The hypothesis of multiple glacial refugia is supported by these results (Premoli et al. 2000; Marchelli and Gallo 2006; Sérsic et al.
2011). In addition, a meeting area where migration routes could have encounter was
proposed (ca. 42–43° S), which agrees with stratigraphic and palynological evidence. A geographical segregation of genetic lineages was identified (Mathiasen
and Premoli 2010; Soliani et al. 2012), like in other widely distributed species of the
region, such as Austrocedrus chilensis (Pastorino and Gallo 2002) and Pilgerodendron
uviferum (Premoli et al. 2002). Alternatively, the great divergence between haplogroups was interpreted as isolated forest patches due to the settlement of preQuaternary depression areas (paleobasins) (Premoli et al. 2012).
Both species presented similar levels of average within-population gene diversity
(h s ), total genetic diversity (h t ), and gene differentiation based on frequency (G ST )
and ordered alleles (N ST ) (Table 5.2). Cryptic refugia might be inferred from population allelic richness (A R ), a parameter independent from population size (Widmer
and Lexer 2001) and with a significant value in conservation decisions (Petit et al.
1998). Northern populations (40° S) (4, IV) harbor the highest diversity in both species; at mid-latitudes (42–43° S), three populations of lenga (a, 12, 14) and two of
ñire (XIII, XIV) showed a higher allelic richness. In southern Patagonia (54° S), one
lenga population (XIX) was the most diverse. Trends of genetic diversity clearly
follow the geographical latitude.
Haplotype sharing (cpDNA or mtDNA) among closely related species that
hybridize naturally and occur in sympatry is very common (Rieseberg and Soltis
1991), signaling population variation. Introgression in this Nothofagus species complex (IG = 0.90; Soliani et al. 2012) could be occurring due to interspecific gene
flow and backcrossing offspring. A similar geographical pattern for haplotype
distribution in both species supports the idea of recent or at least postglacial
5 Nothofagus pumilio and N. antarctica: The Most Widely Distributed…
climatic conditions at these latitudes by the early Holocene (10,000–8500 years BP)
(Markgraf et al. 2003), i.e., lack of seasonality and a drier and warmer environment
(Manzini et al. 2008). Reinforcing this, three different zones based on a palynological reconstruction representing paleo-climates (Markgraf et al. 1996) were identified (north of 43° S, between 43° and 51° S, and south of 51° S).
The distribution of chloroplast genetic variation helps to thoroughly comprehend
how forests were modeled after glaciation. Considering its slow evolution rate as
well as the uniparental (maternal) inheritance, chloroplast DNA is a useful tool tracing the effective dispersal of seeds. Polymorphisms from cpDNA non-coding
regions were screened in 40 Argentinean populations of N. pumilio and N. antarctica (Soliani et al. 2012; Table 5.1) and used to define haplotypes, coming from the
following restricted regions: trnD-trnT/HinfI, trnC-trnD/taqI, and atpH-atpI/
HinfI. Point mutations in the restriction site and indels (insertion/deletions) allowed
identifying 9 and 13 haplotypes in N. pumilio and N. antarctica, respectively (based
on different combinations of length variants). Eight haplotypes were shared among
the species, with N. antarctica being the most variable with five unique haplotypes.
A genetic diversity trend along latitude, decreasing in both species from north to
south, as well as a significant phylogeographic structure between the two main
groups of populations and haplotypes (north and south of 42° S), evidenced regional
footprints of glaciations (Fig. 5.2). The hypothesis of multiple glacial refugia is supported by these results (Premoli et al. 2000; Marchelli and Gallo 2006; Sérsic et al.
2011). In addition, a meeting area where migration routes could have encounter was
proposed (ca. 42–43° S), which agrees with stratigraphic and palynological evidence. A geographical segregation of genetic lineages was identified (Mathiasen
and Premoli 2010; Soliani et al. 2012), like in other widely distributed species of the
region, such as Austrocedrus chilensis (Pastorino and Gallo 2002) and Pilgerodendron
uviferum (Premoli et al. 2002). Alternatively, the great divergence between haplogroups was interpreted as isolated forest patches due to the settlement of preQuaternary depression areas (paleobasins) (Premoli et al. 2012).
Both species presented similar levels of average within-population gene diversity
(h s ), total genetic diversity (h t ), and gene differentiation based on frequency (G ST )
and ordered alleles (N ST ) (Table 5.2). Cryptic refugia might be inferred from population allelic richness (A R ), a parameter independent from population size (Widmer
and Lexer 2001) and with a significant value in conservation decisions (Petit et al.
1998). Northern populations (40° S) (4, IV) harbor the highest diversity in both species; at mid-latitudes (42–43° S), three populations of lenga (a, 12, 14) and two of
ñire (XIII, XIV) showed a higher allelic richness. In southern Patagonia (54° S), one
lenga population (XIX) was the most diverse. Trends of genetic diversity clearly
follow the geographical latitude.
Haplotype sharing (cpDNA or mtDNA) among closely related species that
hybridize naturally and occur in sympatry is very common (Rieseberg and Soltis
1991), signaling population variation. Introgression in this Nothofagus species complex (IG = 0.90; Soliani et al. 2012) could be occurring due to interspecific gene
flow and backcrossing offspring. A similar geographical pattern for haplotype
distribution in both species supports the idea of recent or at least postglacial
5 Nothofagus pumilio and N. antarctica: The Most Widely Distributed…