167
2007, in Juniperus thurifera) and frequently attributed to depression due to inbreeding (e.g., Ferriol et al. 2011). Moreover, relatively low levels of inbreeding have
been found in xeric cypress populations quite small in size (Colabella et al. 2014).
Indeed, such levels of inbreeding could be the result of grouped mating, related to
the typical low tree density in the arid marginal forests (Pastorino and Gallo 2002)
rather than to the effect of extreme reductions in genetic variance. Arana et al.
(2010), in their study including 7 of the 11 marginal xeric populations reported in
Table 6.4, did not find evidence of recent bottlenecks, using nuclear microsatellite
markers under 2 different models. Other observations, such as the high production
of normal pollen and seeds in trees of different cohorts, or the total survival of the
seedlings produced in a large nursery trial reported by Aparicio (2013, and derived
papers), are indicators of the viability of the xeric margins of the cypress.
Nevertheless, based on population genetics theory and on several contrasting results
between neighbor populations, both in neutral and selective variation, it must be
considered that adaptation might not prevail against the predictable effects of
genetic drift. This was considered for defining six OGMUs of local scope, named
Restricted Area Provenance Regions (RAPR). This was done by joining individuals
and small forests patches, sometimes separated by a few kilometers, assuming certain genetic unity between them and based on their differential genetic character.
The six RAPR defined are Leleque, Pilcaniyeu, Cerro Los Pinos, Catán Lil, Riscos
Bayos-Trolope, and Huingan-có (Fig. 6.7), and their detailed descriptions can be
found in Pastorino et al. (2015).
Another conclusion of the quantitative studies was that the range of the arid margin north of 40.5° S presented higher levels of additive variation for several traits of
the annual growth rhythm, linked to the cessation of the vegetative activity, which
could be regulated by the annual evolution of aridity. This was also observed as a
heritable variation of survival after strong summer drought. Added to the background on neutral variation, this information indicates that the northern range of the
cypress should be a priority for the conservation of the species’ genetic resources.
For the definition of PR, we proposed that one main north-south grouping of populations should be considered, with a dividing zone at approximately 40.5 °S in
latitude.
We have also found evidence of ecotypic variation associated to geographic altitude, in traits linked to initial light uptake (degree of sylleptic branching) and initiation of primary growth (a phenological trait) and its maximum annual rate. This
could be attributed to adaptation to altitude (i.e., thermal regimes), which may in
turn determine different probabilities of episodic winter heat events and different
interspecific competition pressures (Aparicio 2013). Our results suggested that for
long-term ex situ conservation or breeding, population samples from different
altitudinal levels should not be mixed. We proposed therefore to separate the large
North GZ into two PR, i.e., North High and North Low, taking into account the
average altitude, which in the region correlates quite well with latitude. The limit
between the North Low and the Central PR is defined by an abrupt change in mean
altitude and a large discontinuity in the presence of cypress, which gives place to
pure forests of Nothofagus antarctica. The Central PR coincides with the Central
6 Patagonian Cypress (Austrocedrus chilensis): The Cedarwood…
2007, in Juniperus thurifera) and frequently attributed to depression due to inbreeding (e.g., Ferriol et al. 2011). Moreover, relatively low levels of inbreeding have
been found in xeric cypress populations quite small in size (Colabella et al. 2014).
Indeed, such levels of inbreeding could be the result of grouped mating, related to
the typical low tree density in the arid marginal forests (Pastorino and Gallo 2002)
rather than to the effect of extreme reductions in genetic variance. Arana et al.
(2010), in their study including 7 of the 11 marginal xeric populations reported in
Table 6.4, did not find evidence of recent bottlenecks, using nuclear microsatellite
markers under 2 different models. Other observations, such as the high production
of normal pollen and seeds in trees of different cohorts, or the total survival of the
seedlings produced in a large nursery trial reported by Aparicio (2013, and derived
papers), are indicators of the viability of the xeric margins of the cypress.
Nevertheless, based on population genetics theory and on several contrasting results
between neighbor populations, both in neutral and selective variation, it must be
considered that adaptation might not prevail against the predictable effects of
genetic drift. This was considered for defining six OGMUs of local scope, named
Restricted Area Provenance Regions (RAPR). This was done by joining individuals
and small forests patches, sometimes separated by a few kilometers, assuming certain genetic unity between them and based on their differential genetic character.
The six RAPR defined are Leleque, Pilcaniyeu, Cerro Los Pinos, Catán Lil, Riscos
Bayos-Trolope, and Huingan-có (Fig. 6.7), and their detailed descriptions can be
found in Pastorino et al. (2015).
Another conclusion of the quantitative studies was that the range of the arid margin north of 40.5° S presented higher levels of additive variation for several traits of
the annual growth rhythm, linked to the cessation of the vegetative activity, which
could be regulated by the annual evolution of aridity. This was also observed as a
heritable variation of survival after strong summer drought. Added to the background on neutral variation, this information indicates that the northern range of the
cypress should be a priority for the conservation of the species’ genetic resources.
For the definition of PR, we proposed that one main north-south grouping of populations should be considered, with a dividing zone at approximately 40.5 °S in
latitude.
We have also found evidence of ecotypic variation associated to geographic altitude, in traits linked to initial light uptake (degree of sylleptic branching) and initiation of primary growth (a phenological trait) and its maximum annual rate. This
could be attributed to adaptation to altitude (i.e., thermal regimes), which may in
turn determine different probabilities of episodic winter heat events and different
interspecific competition pressures (Aparicio 2013). Our results suggested that for
long-term ex situ conservation or breeding, population samples from different
altitudinal levels should not be mixed. We proposed therefore to separate the large
North GZ into two PR, i.e., North High and North Low, taking into account the
average altitude, which in the region correlates quite well with latitude. The limit
between the North Low and the Central PR is defined by an abrupt change in mean
altitude and a large discontinuity in the presence of cypress, which gives place to
pure forests of Nothofagus antarctica. The Central PR coincides with the Central
6 Patagonian Cypress (Austrocedrus chilensis): The Cedarwood…