257
Despite this clear morphological differentiation (expressed in their home habitats separately), we wanted to explore to what extent these disjunct areas of distribution differed genetically. Moreover, we wanted to get insights into the underlying
historical process shaping this disjunct distribution. Noncoding fragments of the
chloroplast genome are the most appropriate markers for phylogeographical studies
due to their uniparental inheritance and their ability to detect neutral processes of
evolution (Avise 2000). However, previous studies had shown that chloroplast DNA
markers were not able to differentiate species of section Algarobia and used other
genetics techniques (Ramírez et al. 1999; Vázquez-Garcidueñas et al. 2003; Ferreyra
et al. 2004, 2007; Vega and Hernandez 2005; Catalano et al. 2008). Nevertheless,
we performed a screening of multiple primers (trnQ-rps16, trnH-psbA, rpl32RndhF, rpl32F-trnL, trnD-trnT; Shaw et al. 2007) and found that the noncoding chloroplastic regions ndhF-rpL32 and rpl32F-trnL retrieved enough variability at
intraspecific level. The noncoding chloroplastic region ndhF-rpL32 was sequenced
in 52 individuals from 15 localities of Argentina and 24 localities of Bolivia, obtaining eight haplotypes. Haplotype genealogy was reconstructed using the medianjoining algorithm implemented in Network v 5.0.0.1 (Bandelt et al. 1999). It showed
a typical star-like topology with two very frequent and widespread haplotypes, one
in Bolivia (H1, N = 17) and the other in Argentina (H6, N = 27), from which derived
haplotypes of very low frequency (H2, H3, H4, H5, H7 and H8), separated from the
central ones by few mutational steps (Fig. 9.5). Moreover, the presence of a past
historical barrier between the two geographical groups was evidenced using the
spatial analysis of the molecular variance implemented in SAMOVA v.2.0
(Dupanloup et al. 2002) retrieving an optimal partitioning genetic diversity with
k = 2 (FCT = 0.84; p < 0.0001).
The conclusions from both morphological and molecular analyses are consistent
and indicate that the tree species P. chilensis differs at least into two groups,
accordingly with its disjunct geographic distribution. Argentinean P. chilensis trees
have shorter and narrower leaves than the trees from Bolivia, which could be at least
partially associated to climatic differences between both geographical regions.
Also, genetic evidence reinforced that significant differences were detected between
the disjunct populations.
9.3.4 Genetic-Adaptive Studies in Populations of Prosopis alba
Genetic diversity is the basis on which natural selection acts, giving organisms the
ability to adapt to changes in their environment (Krutovsky and Neale 2005).
Populations with little genetic variation are more vulnerable to the arrival of new
pests or diseases, pollution, changes in climate, and habitat destruction due to
human activities or other catastrophic events (Krutovsky and Neale 2005).
Particularly in the face of the impact of climate change, natural populations can
survive through migration to more favorable sites, or by phenotypic plasticity or
local adaptations thus remaining in situ (Aitken et al. 2008). As plants, and more
9 Genetic Variation Patterns of “Algarrobos” from the “Great American Chaco…
Despite this clear morphological differentiation (expressed in their home habitats separately), we wanted to explore to what extent these disjunct areas of distribution differed genetically. Moreover, we wanted to get insights into the underlying
historical process shaping this disjunct distribution. Noncoding fragments of the
chloroplast genome are the most appropriate markers for phylogeographical studies
due to their uniparental inheritance and their ability to detect neutral processes of
evolution (Avise 2000). However, previous studies had shown that chloroplast DNA
markers were not able to differentiate species of section Algarobia and used other
genetics techniques (Ramírez et al. 1999; Vázquez-Garcidueñas et al. 2003; Ferreyra
et al. 2004, 2007; Vega and Hernandez 2005; Catalano et al. 2008). Nevertheless,
we performed a screening of multiple primers (trnQ-rps16, trnH-psbA, rpl32RndhF, rpl32F-trnL, trnD-trnT; Shaw et al. 2007) and found that the noncoding chloroplastic regions ndhF-rpL32 and rpl32F-trnL retrieved enough variability at
intraspecific level. The noncoding chloroplastic region ndhF-rpL32 was sequenced
in 52 individuals from 15 localities of Argentina and 24 localities of Bolivia, obtaining eight haplotypes. Haplotype genealogy was reconstructed using the medianjoining algorithm implemented in Network v 5.0.0.1 (Bandelt et al. 1999). It showed
a typical star-like topology with two very frequent and widespread haplotypes, one
in Bolivia (H1, N = 17) and the other in Argentina (H6, N = 27), from which derived
haplotypes of very low frequency (H2, H3, H4, H5, H7 and H8), separated from the
central ones by few mutational steps (Fig. 9.5). Moreover, the presence of a past
historical barrier between the two geographical groups was evidenced using the
spatial analysis of the molecular variance implemented in SAMOVA v.2.0
(Dupanloup et al. 2002) retrieving an optimal partitioning genetic diversity with
k = 2 (FCT = 0.84; p < 0.0001).
The conclusions from both morphological and molecular analyses are consistent
and indicate that the tree species P. chilensis differs at least into two groups,
accordingly with its disjunct geographic distribution. Argentinean P. chilensis trees
have shorter and narrower leaves than the trees from Bolivia, which could be at least
partially associated to climatic differences between both geographical regions.
Also, genetic evidence reinforced that significant differences were detected between
the disjunct populations.
9.3.4 Genetic-Adaptive Studies in Populations of Prosopis alba
Genetic diversity is the basis on which natural selection acts, giving organisms the
ability to adapt to changes in their environment (Krutovsky and Neale 2005).
Populations with little genetic variation are more vulnerable to the arrival of new
pests or diseases, pollution, changes in climate, and habitat destruction due to
human activities or other catastrophic events (Krutovsky and Neale 2005).
Particularly in the face of the impact of climate change, natural populations can
survive through migration to more favorable sites, or by phenotypic plasticity or
local adaptations thus remaining in situ (Aitken et al. 2008). As plants, and more
9 Genetic Variation Patterns of “Algarrobos” from the “Great American Chaco…