246
P. hassleri, P. chilensis, and P. flexuosa belong to the Algarobia section, which
contains most economically important species (Burkart 1976).
The identification of management and conservation units of “algarrobo” (the
Spanish word for carob) is hampered by characteristics of the genus Prosopis,
which is shown as a continuum from the morphological and adaptive point of view
(Verga 1995). Furthermore, its taxonomic species have the ability to exchange
genetic information, generating high diversity in multiple points of contact and giving rise to hybrid swarms (Hunziker 1986; Saidman et al. 2000). These areas are
often active sites of evolutionary changes in which hybridization and introgression
may lead to increases in intraspecific genetic diversity, transfer of genetic adaptations, and even the emergence of new ecotypes or species (Petit et al. 1999).
Moreover, the existence of interspecific hybridization is accepted as the major
mechanism for generating evolutionary novelties in the plant kingdom (Rieseberg
and Gerber 1995; Rieseberg 1997; Arnold 1997; Rieseberg and Carney 1998;
Barton 2001).
Problems of species delimitation in the genus Prosopis occur mainly in the section Algarobia, in which it is very common the appearance of intermediate forms
originated presumably by interspecific hybridization in areas where different species come into contact. Numerous authors have presented morphological, cytological, and molecular evidences of natural hybridization between several species of the
Algarobia section that grows in the Chaco Domain (Burghardt and Palacios 1981;
Palacios and Bravo 1981; Hunziker 1986; Verga 1995; Vázquez-Garcidueñas et al.
2003; Vega and Hernandez 2005; Ferreyra et al. 2013). These authors have suggested that the absence of strong interspecific reproductive barriers and the fact that
some species are sympatric facilitate hybridization and introgression and contribute
to the great morphological and genetic variation observed in natural populations.
In Prosopis, the existence of hybrids and introgressed individuals is very common. In this chapter we will present the results that have been obtained in wild pure
populations and in zones of hybrid swarms of Prosopis together with those obtained
from installed progeny trials. This knowledge will help to understand the functioning of this complex of species and will serve as the basis for the design of intervention programs for the dynamic conservation of genetic resources, improving the
evolutionary capacity of the complex and facilitating adaptation to changing
environments.
9.1 Morphological Analyses as a First Approach to the Study
of the Algarrobos’ Genetic Resources
in the Chaco Region
Describing patterns of morphological variability among taxa and among individuals
within taxa, and unraveling the processes leading to such patterns, is one of the
fundamental questions in biology. In the Chaco region, although some Prosopis
species are easily recognized, there are great morphological leaf variability within
C. Vega et al.
P. hassleri, P. chilensis, and P. flexuosa belong to the Algarobia section, which
contains most economically important species (Burkart 1976).
The identification of management and conservation units of “algarrobo” (the
Spanish word for carob) is hampered by characteristics of the genus Prosopis,
which is shown as a continuum from the morphological and adaptive point of view
(Verga 1995). Furthermore, its taxonomic species have the ability to exchange
genetic information, generating high diversity in multiple points of contact and giving rise to hybrid swarms (Hunziker 1986; Saidman et al. 2000). These areas are
often active sites of evolutionary changes in which hybridization and introgression
may lead to increases in intraspecific genetic diversity, transfer of genetic adaptations, and even the emergence of new ecotypes or species (Petit et al. 1999).
Moreover, the existence of interspecific hybridization is accepted as the major
mechanism for generating evolutionary novelties in the plant kingdom (Rieseberg
and Gerber 1995; Rieseberg 1997; Arnold 1997; Rieseberg and Carney 1998;
Barton 2001).
Problems of species delimitation in the genus Prosopis occur mainly in the section Algarobia, in which it is very common the appearance of intermediate forms
originated presumably by interspecific hybridization in areas where different species come into contact. Numerous authors have presented morphological, cytological, and molecular evidences of natural hybridization between several species of the
Algarobia section that grows in the Chaco Domain (Burghardt and Palacios 1981;
Palacios and Bravo 1981; Hunziker 1986; Verga 1995; Vázquez-Garcidueñas et al.
2003; Vega and Hernandez 2005; Ferreyra et al. 2013). These authors have suggested that the absence of strong interspecific reproductive barriers and the fact that
some species are sympatric facilitate hybridization and introgression and contribute
to the great morphological and genetic variation observed in natural populations.
In Prosopis, the existence of hybrids and introgressed individuals is very common. In this chapter we will present the results that have been obtained in wild pure
populations and in zones of hybrid swarms of Prosopis together with those obtained
from installed progeny trials. This knowledge will help to understand the functioning of this complex of species and will serve as the basis for the design of intervention programs for the dynamic conservation of genetic resources, improving the
evolutionary capacity of the complex and facilitating adaptation to changing
environments.
9.1 Morphological Analyses as a First Approach to the Study
of the Algarrobos’ Genetic Resources
in the Chaco Region
Describing patterns of morphological variability among taxa and among individuals
within taxa, and unraveling the processes leading to such patterns, is one of the
fundamental questions in biology. In the Chaco region, although some Prosopis
species are easily recognized, there are great morphological leaf variability within
C. Vega et al.