62
of pollination comes from within a 50 m radius (99.8%) indicating that pollination
is mostly local.
In a more recent study (Sola et al. 2020b), gene dispersal distance of N. alpina
and N. obliqua was indirectly estimated based on fine-scale spatial genetic structure
(Vekemans and Hardy 2004). Additionally, the same study made direct estimates of
seed and pollen dispersal based on spatially explicit mating models (Chybicki and
Burczyk 2010) for both species in a plot that had been silviculturally managed
20 years ago (2.85 ha). Significant genetic correlation at the first distance class
(<40 m) was detected for both species. Accordingly, restricted gene flow (≤45 m)
was estimated, along with contemporary restricted seed (≤28 m) and pollen dispersal (≤46 m). Significant seed and pollen immigration (up to 57%) was detected;
these migration events would correspond, however, to short dispersal distance as the
study plot/area belongs to a region of continuous Nothofagus forests. This interpretation agrees with the fitting of seed and pollen dispersal kernels to exponential
functions (b = 1), and the significant fine-scale spatial genetic structure was consistent with the restricted seed and pollen dispersal. Despite the existence of groups of
related individuals, no significant inbreeding coefficients (selfing (s) = 0 for both
species) were detected, a result that agrees with the high degree of self- incompatibility
previously reported for Nothofagus (Riveros et al. 1995). On the other hand, size of
trees (DBH and height) was significantly associated with female and/or male fertility, highlighting the importance of vigorous trees to increase fecundity and dispersion maintaining forest genetic diversity. Therefore, the local movement of genes
has several implications both for understanding the evolution of the species and for
defining conservation and management actions.
3.3 Adaptive Genetic Variation: Patterns of Variation
Among Populations at Quantitative Traits
Neutral markers cannot unravel genetic variation resulting from adaptive processes.
Instead, classic provenance and progeny trials are appropriate to analyse variation
in quantitative traits, which due to their expression on the phenotype are potentially
adaptive. The seedling and sapling phases of plant development are the most important and acute selective stages in the life span of a tree species (Moles and Westoby
2004). Therefore, knowing selection drivers at these phases is crucial to understand
the natural processes of extinction or persistence and to take management decisions
in afforestation programmes.
In order to study genetic variation at juvenile stages, a nursery trial (Trial 1,
Table 3.1) was conducted with potted seedlings of 74 open-pollinated families corresponding to 7 Argentine natural populations (Duboscq-Carra et al. 2018). Several
shoot and root traits were measured at the end of the first growing season (Table 3.1),
and mixed linear models were applied to perform variance analysis on these traits.
Intra-population variation resulted to be quite variable among populations and traits
P. Marchelli et al.
of pollination comes from within a 50 m radius (99.8%) indicating that pollination
is mostly local.
In a more recent study (Sola et al. 2020b), gene dispersal distance of N. alpina
and N. obliqua was indirectly estimated based on fine-scale spatial genetic structure
(Vekemans and Hardy 2004). Additionally, the same study made direct estimates of
seed and pollen dispersal based on spatially explicit mating models (Chybicki and
Burczyk 2010) for both species in a plot that had been silviculturally managed
20 years ago (2.85 ha). Significant genetic correlation at the first distance class
(<40 m) was detected for both species. Accordingly, restricted gene flow (≤45 m)
was estimated, along with contemporary restricted seed (≤28 m) and pollen dispersal (≤46 m). Significant seed and pollen immigration (up to 57%) was detected;
these migration events would correspond, however, to short dispersal distance as the
study plot/area belongs to a region of continuous Nothofagus forests. This interpretation agrees with the fitting of seed and pollen dispersal kernels to exponential
functions (b = 1), and the significant fine-scale spatial genetic structure was consistent with the restricted seed and pollen dispersal. Despite the existence of groups of
related individuals, no significant inbreeding coefficients (selfing (s) = 0 for both
species) were detected, a result that agrees with the high degree of self- incompatibility
previously reported for Nothofagus (Riveros et al. 1995). On the other hand, size of
trees (DBH and height) was significantly associated with female and/or male fertility, highlighting the importance of vigorous trees to increase fecundity and dispersion maintaining forest genetic diversity. Therefore, the local movement of genes
has several implications both for understanding the evolution of the species and for
defining conservation and management actions.
3.3 Adaptive Genetic Variation: Patterns of Variation
Among Populations at Quantitative Traits
Neutral markers cannot unravel genetic variation resulting from adaptive processes.
Instead, classic provenance and progeny trials are appropriate to analyse variation
in quantitative traits, which due to their expression on the phenotype are potentially
adaptive. The seedling and sapling phases of plant development are the most important and acute selective stages in the life span of a tree species (Moles and Westoby
2004). Therefore, knowing selection drivers at these phases is crucial to understand
the natural processes of extinction or persistence and to take management decisions
in afforestation programmes.
In order to study genetic variation at juvenile stages, a nursery trial (Trial 1,
Table 3.1) was conducted with potted seedlings of 74 open-pollinated families corresponding to 7 Argentine natural populations (Duboscq-Carra et al. 2018). Several
shoot and root traits were measured at the end of the first growing season (Table 3.1),
and mixed linear models were applied to perform variance analysis on these traits.
Intra-population variation resulted to be quite variable among populations and traits
P. Marchelli et al.