185
Pulmarí (39°7′ 12″S, 71°5′ 49″W), is a continuous dense forest. A total of 79 and 30
adult trees and 535 and 300 seeds were analysed in Tromen and Pulmarí, respectively, with five microsatellites. Through this analysis of individual mother trees and
their progeny (seeds), applying the TwoGener approach (Smouse et al. 2001), an
average pollen dispersal distance of 1248 m was estimated in the Tromen area, while
a much more reduced dispersal was detected in the denser forest of Pulmarí (71.5 m)
(Moreno et al. 2009; Moreno 2012). Also, to evaluate the proportion of vegetative vs.
generative reproduction, clusters of regeneration surrounding mother trees were genotyped. A higher proportion of sexual reproduction was evident since only 7% of the
seedlings were identical (at least with the analysed markers) to the mother tree.
Moreover, only 40% of the seedlings were assigned as progeny of the central mother
tree, so the seed dispersal effects of rodents (Shepherd and Ditgen 2005, 2013) have
genetic consequences, with an average distance for seedling recruitment of 5–10 m
from the mother tree, related to the seed shadow and the typical spatial distribution of
seeds and recruits in this species (Sanguinetti and Kitzberger 2009).
Altogether, the genetic studies suggest that A. araucana from Argentina has a
weak genetic structure between populations, probably related to the extensive pollen
flow and the transportation of the edible seeds through the original human communities during perhaps 10,000 years. Eastern and more fragile populations still harbour
high levels of genetic diversity, and “frozen genetic diversity” might be maintained
by clonal reproduction. However, local extinction of a species can occur with delay
after habitat degradation due to the so-called relaxation time (Diamond 1972), after
which small and isolated populations will eventually go extinct in a process described
as “extinction debt” (Tilman et al. 1994), meaning that species are fated to extinction, but the actual event has not yet occurred due to the persistence for a time in
small, isolated and degraded habitats. Extinction debt poses a challenge for conservation because the threats to biodiversity are underestimated (Hanski and Ovaskainen
2002). Particularly species with long generation times, like trees, are more likely to
have an extinction debt (Kuussaari et al. 2009; Krauss et al. 2010).
7.1.4 Adaptive Genetic Variation
The analysis of genetic variation at quantitative traits allows studying adaptive processes, because their expression on the phenotype makes them potentially adaptive.
The traditional provenance and progeny tests are a useful tool for this purpose.
These common garden trials allow the estimation of the additive genetic variation
and the heritability, i.e. the portion of the variation that is transmitted from generation to generation. The ability of a population to evolve depends on the existence of
additive genetic variance (Lande and Shannon 1996).
7 Araucaria araucana and Salix humboldtiana…
Pulmarí (39°7′ 12″S, 71°5′ 49″W), is a continuous dense forest. A total of 79 and 30
adult trees and 535 and 300 seeds were analysed in Tromen and Pulmarí, respectively, with five microsatellites. Through this analysis of individual mother trees and
their progeny (seeds), applying the TwoGener approach (Smouse et al. 2001), an
average pollen dispersal distance of 1248 m was estimated in the Tromen area, while
a much more reduced dispersal was detected in the denser forest of Pulmarí (71.5 m)
(Moreno et al. 2009; Moreno 2012). Also, to evaluate the proportion of vegetative vs.
generative reproduction, clusters of regeneration surrounding mother trees were genotyped. A higher proportion of sexual reproduction was evident since only 7% of the
seedlings were identical (at least with the analysed markers) to the mother tree.
Moreover, only 40% of the seedlings were assigned as progeny of the central mother
tree, so the seed dispersal effects of rodents (Shepherd and Ditgen 2005, 2013) have
genetic consequences, with an average distance for seedling recruitment of 5–10 m
from the mother tree, related to the seed shadow and the typical spatial distribution of
seeds and recruits in this species (Sanguinetti and Kitzberger 2009).
Altogether, the genetic studies suggest that A. araucana from Argentina has a
weak genetic structure between populations, probably related to the extensive pollen
flow and the transportation of the edible seeds through the original human communities during perhaps 10,000 years. Eastern and more fragile populations still harbour
high levels of genetic diversity, and “frozen genetic diversity” might be maintained
by clonal reproduction. However, local extinction of a species can occur with delay
after habitat degradation due to the so-called relaxation time (Diamond 1972), after
which small and isolated populations will eventually go extinct in a process described
as “extinction debt” (Tilman et al. 1994), meaning that species are fated to extinction, but the actual event has not yet occurred due to the persistence for a time in
small, isolated and degraded habitats. Extinction debt poses a challenge for conservation because the threats to biodiversity are underestimated (Hanski and Ovaskainen
2002). Particularly species with long generation times, like trees, are more likely to
have an extinction debt (Kuussaari et al. 2009; Krauss et al. 2010).
7.1.4 Adaptive Genetic Variation
The analysis of genetic variation at quantitative traits allows studying adaptive processes, because their expression on the phenotype makes them potentially adaptive.
The traditional provenance and progeny tests are a useful tool for this purpose.
These common garden trials allow the estimation of the additive genetic variation
and the heritability, i.e. the portion of the variation that is transmitted from generation to generation. The ability of a population to evolve depends on the existence of
additive genetic variance (Lande and Shannon 1996).
7 Araucaria araucana and Salix humboldtiana…