254
hybridization. In this study, the high correspondence between leaf morphology and
genetic differentiation in the three sites strongly confirms genetic and morphological differences between the two parental species and the existence of intermediate
morphotypes, which correspond to interspecific hybrids.
9.3.2 Genetic and Morphometric Markers are Able to
Differentiate Three Morphotypes Belonging to Section
Algarobia of Genus Prosopis
Through successive field trips and observations, it was detected in Sumampa, south
of the Province of Santiago del Estero (29° 22′ S, 63° 23′ W to 29° 15′ S, 63° 10′
W), an area where P. alba and P. ruscifolia overlap and apparently hybridize producing fertile hybrids, as was suggested by the presence of morphotypes with intermediate morphology to both species. Thus, a study was conducted in that area along
a transect which represent an environmental gradient going from the foothills of the
Sumampa mountain ranges up to the salty lowlands of Laguna de Mar Chiquita
basin. This gradient means a gradual phytosociological shift from the Schinopsis
lorentzii (“quebracho”) forests in the highlands (“quebrachales”) with P. alba as a
secondary species, to a halophyte community with P. ruscifolia as the dominant
species (“vinalar”).
The evidence of hybridization between these two species is derived from the
combination of morphological and molecular analyses through RAPD molecular
markers (Random Amplified Polymorphic DNA). Both analyses allow the recognition and significant differentiation of three groups, one corresponding to P. alba,
another to P. ruscifolia and a third group to interspecific hybrids. These results indicate that the leaf morphology between these two species also constitutes a tool for
the identification of interspecific hybrids. Surprisingly, the dispersion of the phenotypic values around the average was not different between the hybrid group and the
putative parental species. This is not expected if we assume that the hybrid group is
genetically more variable as a consequence of the addition of the set of genes from
both parental species. One possible explanation would be that phenotypic variation
is caused by environmental rather than genetic factors. If this were the case, the
phenotypic variation would be the consequence of plasticity. However, a correlation
analysis performed between phenotypic and genetic distances suggests that in
almost all traits heritabilities were significant. The three groups studied showed
high genetic variability. However, the hybrids showed significantly higher values
than the determined morphotypes such as P. alba and P. ruscifolia (Table 9.1).
It is important to note that the hybrid morphotype was identified as P. vinalillo by
Burkart (1976). In fact, the author suggested that this species could be a hybrid
between P. alba and P. ruscifolia. Moreover, so far we have not detected a pure
population of P. vinalillo; this species is always associated to the presence of both
P. alba and P. ruscifolia (Ferreyra et al. 2013).
C. Vega et al.
hybridization. In this study, the high correspondence between leaf morphology and
genetic differentiation in the three sites strongly confirms genetic and morphological differences between the two parental species and the existence of intermediate
morphotypes, which correspond to interspecific hybrids.
9.3.2 Genetic and Morphometric Markers are Able to
Differentiate Three Morphotypes Belonging to Section
Algarobia of Genus Prosopis
Through successive field trips and observations, it was detected in Sumampa, south
of the Province of Santiago del Estero (29° 22′ S, 63° 23′ W to 29° 15′ S, 63° 10′
W), an area where P. alba and P. ruscifolia overlap and apparently hybridize producing fertile hybrids, as was suggested by the presence of morphotypes with intermediate morphology to both species. Thus, a study was conducted in that area along
a transect which represent an environmental gradient going from the foothills of the
Sumampa mountain ranges up to the salty lowlands of Laguna de Mar Chiquita
basin. This gradient means a gradual phytosociological shift from the Schinopsis
lorentzii (“quebracho”) forests in the highlands (“quebrachales”) with P. alba as a
secondary species, to a halophyte community with P. ruscifolia as the dominant
species (“vinalar”).
The evidence of hybridization between these two species is derived from the
combination of morphological and molecular analyses through RAPD molecular
markers (Random Amplified Polymorphic DNA). Both analyses allow the recognition and significant differentiation of three groups, one corresponding to P. alba,
another to P. ruscifolia and a third group to interspecific hybrids. These results indicate that the leaf morphology between these two species also constitutes a tool for
the identification of interspecific hybrids. Surprisingly, the dispersion of the phenotypic values around the average was not different between the hybrid group and the
putative parental species. This is not expected if we assume that the hybrid group is
genetically more variable as a consequence of the addition of the set of genes from
both parental species. One possible explanation would be that phenotypic variation
is caused by environmental rather than genetic factors. If this were the case, the
phenotypic variation would be the consequence of plasticity. However, a correlation
analysis performed between phenotypic and genetic distances suggests that in
almost all traits heritabilities were significant. The three groups studied showed
high genetic variability. However, the hybrids showed significantly higher values
than the determined morphotypes such as P. alba and P. ruscifolia (Table 9.1).
It is important to note that the hybrid morphotype was identified as P. vinalillo by
Burkart (1976). In fact, the author suggested that this species could be a hybrid
between P. alba and P. ruscifolia. Moreover, so far we have not detected a pure
population of P. vinalillo; this species is always associated to the presence of both
P. alba and P. ruscifolia (Ferreyra et al. 2013).
C. Vega et al.