251
been largely replaced by more informative molecular markers (such as direct DNA
sequencing, single-nucleotide polymorphisms and microsatellites), they are still
among the fastest and cheapest marker systems and are an excellent choice to identify high levels of genetic differentiation, e.g., incipient speciation. These initial
studies provided the first clues about the genetic relationships between the main
species of the Algarobia section, of great environmental and productive importance
for the Chaco region.
Palacios and Bravo (1981) performed morphological and chromatographic studies on some species of Prosopis (P. alba, P. fiebrigii, P. hassleri, P. nigra, P. ruscifolia, P. vinalillo) and natural hybrids of the Algarobia section. They postulated that
from a biological point of view, each taxonomic species would be equivalent to a
semi-species, and the sympatric semi-species community would constitute a syngameon (sensu Grant 1981). Isozyme studies in these and other species of the
Algarobia section showed high variability and low genetic differentiation (Saidman
1985, 1986, 1988, 1993; Saidman and Vilardi 1987, 1993; Verga 1995; Saidman
et al. 1998; Joseau et al. 2013) which would support the hypothesis proposed by
Palacios and Bravo (1981).
As a reference we can mention the study carried out by Saidman and Vilardi
(1987) where they analyzed the genetic similarities between seven Prosopis species
(P. alba, P. nigra, P. alpataco, P. caldenia, P. flexuosa, P. ruscifolia, and P. hassleri).
The study was based on data from 25 enzyme loci encoding seven enzymes
(Saidman 1985, 1986; Saidman and Naranjo 1982). Only six out of 25 loci showed
alleles that characterized different groups of species. Prosopis caldenia is the most
identifiable species based on the pattern retrieved in two loci, and P. ruscifolia can
be identified by the band corresponding to a locus. The rest of the species could not
be identified because their zymograms were very similar. However, groups of species were retrieved such as P. alpataco-P. flexuosa or P. alba-P. hassleri. Prosopis
nigra was similar to the P. alpataco-P. flexuosa group for one of the locus but differed from them for another locus. The genetic distances between the studied species were very low, with the exception of P. caldenia, which was the most easily
identifiable species through the isoenzyme technique, probably because it is the
only species in the Algarobia section that presents an isolation mechanism.
Although there are clear morphological differences that allowed Burkart (1976)
to consider the taxa analyzed here as taxonomically different, discrepancies have
been observed between morphological (through classical taxonomy) and molecular
data. Saidman and Vilardi (1987) concluded that this disagreement can be explained
by the high genetic similarity as a consequence of the weak reproductive barriers.
This hypothesis is supported by an extensive hybridization of species that occurs in
overlapping regions. However, from subsequent studies an alternative hypothesis
was proposed: the high genetic similarity found in the genus is probably due to the
relatively recent origin of these species (Bessega et al. 2000; Catalano et al. 2008).
Another study aimed to characterize the variability of the genus by combining
morphological characters (through numerical taxonomy) and isozyme analysis was
carried out by Joseau et al. (2007) in natural populations where four Prosopis
9 Genetic Variation Patterns of “Algarrobos” from the “Great American Chaco…
been largely replaced by more informative molecular markers (such as direct DNA
sequencing, single-nucleotide polymorphisms and microsatellites), they are still
among the fastest and cheapest marker systems and are an excellent choice to identify high levels of genetic differentiation, e.g., incipient speciation. These initial
studies provided the first clues about the genetic relationships between the main
species of the Algarobia section, of great environmental and productive importance
for the Chaco region.
Palacios and Bravo (1981) performed morphological and chromatographic studies on some species of Prosopis (P. alba, P. fiebrigii, P. hassleri, P. nigra, P. ruscifolia, P. vinalillo) and natural hybrids of the Algarobia section. They postulated that
from a biological point of view, each taxonomic species would be equivalent to a
semi-species, and the sympatric semi-species community would constitute a syngameon (sensu Grant 1981). Isozyme studies in these and other species of the
Algarobia section showed high variability and low genetic differentiation (Saidman
1985, 1986, 1988, 1993; Saidman and Vilardi 1987, 1993; Verga 1995; Saidman
et al. 1998; Joseau et al. 2013) which would support the hypothesis proposed by
Palacios and Bravo (1981).
As a reference we can mention the study carried out by Saidman and Vilardi
(1987) where they analyzed the genetic similarities between seven Prosopis species
(P. alba, P. nigra, P. alpataco, P. caldenia, P. flexuosa, P. ruscifolia, and P. hassleri).
The study was based on data from 25 enzyme loci encoding seven enzymes
(Saidman 1985, 1986; Saidman and Naranjo 1982). Only six out of 25 loci showed
alleles that characterized different groups of species. Prosopis caldenia is the most
identifiable species based on the pattern retrieved in two loci, and P. ruscifolia can
be identified by the band corresponding to a locus. The rest of the species could not
be identified because their zymograms were very similar. However, groups of species were retrieved such as P. alpataco-P. flexuosa or P. alba-P. hassleri. Prosopis
nigra was similar to the P. alpataco-P. flexuosa group for one of the locus but differed from them for another locus. The genetic distances between the studied species were very low, with the exception of P. caldenia, which was the most easily
identifiable species through the isoenzyme technique, probably because it is the
only species in the Algarobia section that presents an isolation mechanism.
Although there are clear morphological differences that allowed Burkart (1976)
to consider the taxa analyzed here as taxonomically different, discrepancies have
been observed between morphological (through classical taxonomy) and molecular
data. Saidman and Vilardi (1987) concluded that this disagreement can be explained
by the high genetic similarity as a consequence of the weak reproductive barriers.
This hypothesis is supported by an extensive hybridization of species that occurs in
overlapping regions. However, from subsequent studies an alternative hypothesis
was proposed: the high genetic similarity found in the genus is probably due to the
relatively recent origin of these species (Bessega et al. 2000; Catalano et al. 2008).
Another study aimed to characterize the variability of the genus by combining
morphological characters (through numerical taxonomy) and isozyme analysis was
carried out by Joseau et al. (2007) in natural populations where four Prosopis
9 Genetic Variation Patterns of “Algarrobos” from the “Great American Chaco…