252
species (P. chilensis, P. flexuosa, P. alba, P. nigra, and intermediate individuals,
considered as possible hybrids between these four species) coexist, in the semi-arid
Chaco. Six isozyme systems were analyzed. Numerical taxonomy constituted a fundamental tool for the morphological analysis and the correct identification of the
materials used in that study. They found five morphological and genetically differentiated groups. The high genetic diversity that characterized all morphological
groups was related to the fact that they are species with a wide geographical distribution, open crossing system, and with animal-mediated seed dispersion (Hamrick
and Murawski 1991). Three morphogenetic groups were considered as representatives of pure species: group 1 = P. alba, group 2 = P. chilensis, and group 5 = P
nigra. In addition, it was possible to identify two groups of intermediate morphology that at the same time had the greatest genetic diversity and the lowest differentiation with respect to the rest of the groups. The two groups with intermediate
morphology were also the groups with the highest morphological and genetic variability, while group 1 (P. alba) was the least morphologically and genetically
diverse.
The great diversity of this “species complex” would come from processes of
introgression with more “specific” species adapted to narrower niches. In this way,
the complex would maintain a high potential evolutionary capacity through the conservation of high variation in certain species and in hybrid swarms. At the same
time, some species that conform the complex are highly adapted with capacity to
occupy much more restricted niches. Thus, the complex as a whole should be considered as an evolutionary unit and the taxonomic species as part of it. The cohesion
of this species complex is maintained through the genetic exchange among species,
mediated by hybrid swarms.
9.3 Natural Interspecific Hybridization Processes Evaluated
Through Morphological Traits and Molecular Markers
The capacity of algarrobos’ species to exchange genetic information makes the
study of these contact areas of great interest, both for taxonomic, evolutionary, and
ecological studies. On one hand, they could lead to the formation of new species
and on the other, these new genetic combinations could colonize new habitats
allowing a rapid selective response to natural or anthropized unstable environments (open or hybridized environments) (Grant 1989; Arnold 1997). In this context, the hybridization processes that operate in secondary contact areas between
species would be the key to understand the evolutionary mechanisms of the complex. Their study offers the basic knowledge necessary for the development of
strategies in forest improvement and for the dynamic conservation (sensu
Namkoong et al. 2000) of these genetic resources. Below, we present some studies
carried out in contact areas of different algarrobos species characterizing morphological and genetic variation.
C. Vega et al.
species (P. chilensis, P. flexuosa, P. alba, P. nigra, and intermediate individuals,
considered as possible hybrids between these four species) coexist, in the semi-arid
Chaco. Six isozyme systems were analyzed. Numerical taxonomy constituted a fundamental tool for the morphological analysis and the correct identification of the
materials used in that study. They found five morphological and genetically differentiated groups. The high genetic diversity that characterized all morphological
groups was related to the fact that they are species with a wide geographical distribution, open crossing system, and with animal-mediated seed dispersion (Hamrick
and Murawski 1991). Three morphogenetic groups were considered as representatives of pure species: group 1 = P. alba, group 2 = P. chilensis, and group 5 = P
nigra. In addition, it was possible to identify two groups of intermediate morphology that at the same time had the greatest genetic diversity and the lowest differentiation with respect to the rest of the groups. The two groups with intermediate
morphology were also the groups with the highest morphological and genetic variability, while group 1 (P. alba) was the least morphologically and genetically
diverse.
The great diversity of this “species complex” would come from processes of
introgression with more “specific” species adapted to narrower niches. In this way,
the complex would maintain a high potential evolutionary capacity through the conservation of high variation in certain species and in hybrid swarms. At the same
time, some species that conform the complex are highly adapted with capacity to
occupy much more restricted niches. Thus, the complex as a whole should be considered as an evolutionary unit and the taxonomic species as part of it. The cohesion
of this species complex is maintained through the genetic exchange among species,
mediated by hybrid swarms.
9.3 Natural Interspecific Hybridization Processes Evaluated
Through Morphological Traits and Molecular Markers
The capacity of algarrobos’ species to exchange genetic information makes the
study of these contact areas of great interest, both for taxonomic, evolutionary, and
ecological studies. On one hand, they could lead to the formation of new species
and on the other, these new genetic combinations could colonize new habitats
allowing a rapid selective response to natural or anthropized unstable environments (open or hybridized environments) (Grant 1989; Arnold 1997). In this context, the hybridization processes that operate in secondary contact areas between
species would be the key to understand the evolutionary mechanisms of the complex. Their study offers the basic knowledge necessary for the development of
strategies in forest improvement and for the dynamic conservation (sensu
Namkoong et al. 2000) of these genetic resources. Below, we present some studies
carried out in contact areas of different algarrobos species characterizing morphological and genetic variation.
C. Vega et al.