166
h
2
= 0) than the heritability values obtained for post-summer survival. Another main
result was an apparent north (mean h
2
= 0.84) to south (mean h
2
= 0.28) structure of
the populations, according to their heritabilities of survival under summer drought.
This structure seems consistent with previous results on the patterns of genetic variation of the initial growth rhythm (Fig. 6.7) and also coincident with the general
patterns of selectively neutral variation of the species (Pastorino et al. 2004;
Pastorino and Gallo 2009; Arana et al. 2010). This suggests a greater relative importance of the northern region of the cypress distribution in Argentina for the conservation of its genetic resources, focusing on both neutral and adaptive variation.
6.4 First Definition of Provenance Regions for a Forest Tree
Species in Argentina
We mentioned above that based on a detailed mapping of the distributional range
and information on selectively neutral genetic variation, Pastorino and Gallo (2009)
have recognized five distinctive genetic clusters or zones (GZ) in Argentina. Based
on them, at least five seed transfer zones were subsequently indicated as necessary
to preserve the genetic identity of the Argentine natural populations of the Patagonian
cypress (Pastorino 2012). With this pattern in mind, the information extracted from
the studies on the species’ quantitative variation was superimposed for delineating
provenance regions (PR, Pastorino et al. 2015) by means of the agglomerative
method, that is, the grouping of known forest patches of the species of interest,
genetically and environmentally characterized (CTGREF 1976). PRs are groups of
natural populations with geographic continuity, which belong to the same GZ, and
for which similar adaptive responses are expected as verified in genetic trials and/or
inferred given homogeneous environmental conditions.
One main conclusion of the works on the cypress’ quantitative and neutral variation was that the overall differentiation between populations was relatively low.
This hints that there would not be necessary too many PR for the conservation and
breeding of the species. In turn, several results gave clues that the marginal xeric
populations should be taken into account for the definition of operational genetic
management units (OGMUs), not so much by criteria of differentiation with the rest
of the species’ forests but by its levels of intra-population variance and typical fragmentary and/or isolation conditions. As shown previously, most of the marginal
populations seemed to retain at least the same levels of variation than the mesic and
humid, but they showed also the ability to respond to less rigorous environments
than those of their home habitats. Both experimental and empirical evidence also
indicate that the xeric margin of the cypress should not be considered as depressed
in genetic diversity and therefore adaptively unviable or functionless. For example,
in the cited study on seedling emergence (Pastorino et al. 2012), the marginal xeric
populations did not show loss of seed viability, a predictable problem for “relict”
populations, reported in other Mediterranean Cupressaceae (e.g., Montesinos et al.
A. G. Aparicio and M. J. Pastorino
h
2
= 0) than the heritability values obtained for post-summer survival. Another main
result was an apparent north (mean h
2
= 0.84) to south (mean h
2
= 0.28) structure of
the populations, according to their heritabilities of survival under summer drought.
This structure seems consistent with previous results on the patterns of genetic variation of the initial growth rhythm (Fig. 6.7) and also coincident with the general
patterns of selectively neutral variation of the species (Pastorino et al. 2004;
Pastorino and Gallo 2009; Arana et al. 2010). This suggests a greater relative importance of the northern region of the cypress distribution in Argentina for the conservation of its genetic resources, focusing on both neutral and adaptive variation.
6.4 First Definition of Provenance Regions for a Forest Tree
Species in Argentina
We mentioned above that based on a detailed mapping of the distributional range
and information on selectively neutral genetic variation, Pastorino and Gallo (2009)
have recognized five distinctive genetic clusters or zones (GZ) in Argentina. Based
on them, at least five seed transfer zones were subsequently indicated as necessary
to preserve the genetic identity of the Argentine natural populations of the Patagonian
cypress (Pastorino 2012). With this pattern in mind, the information extracted from
the studies on the species’ quantitative variation was superimposed for delineating
provenance regions (PR, Pastorino et al. 2015) by means of the agglomerative
method, that is, the grouping of known forest patches of the species of interest,
genetically and environmentally characterized (CTGREF 1976). PRs are groups of
natural populations with geographic continuity, which belong to the same GZ, and
for which similar adaptive responses are expected as verified in genetic trials and/or
inferred given homogeneous environmental conditions.
One main conclusion of the works on the cypress’ quantitative and neutral variation was that the overall differentiation between populations was relatively low.
This hints that there would not be necessary too many PR for the conservation and
breeding of the species. In turn, several results gave clues that the marginal xeric
populations should be taken into account for the definition of operational genetic
management units (OGMUs), not so much by criteria of differentiation with the rest
of the species’ forests but by its levels of intra-population variance and typical fragmentary and/or isolation conditions. As shown previously, most of the marginal
populations seemed to retain at least the same levels of variation than the mesic and
humid, but they showed also the ability to respond to less rigorous environments
than those of their home habitats. Both experimental and empirical evidence also
indicate that the xeric margin of the cypress should not be considered as depressed
in genetic diversity and therefore adaptively unviable or functionless. For example,
in the cited study on seedling emergence (Pastorino et al. 2012), the marginal xeric
populations did not show loss of seed viability, a predictable problem for “relict”
populations, reported in other Mediterranean Cupressaceae (e.g., Montesinos et al.
A. G. Aparicio and M. J. Pastorino