304
outcrossing rate (tm) was high (≥0.957) in all populations, indicating that this species is predominantly an outcrosser. Moreover, this study showed a high probability
that the individuals within each progeny array are half sibs. On the other hand, a
similar study on three populations of A. aroma also using isozymes, similarly
revealed a high multilocus outcrossing rate tm ≥ 0.914, although with a high probability that individuals within progeny arrays are full rather than half sibs (Casiva
et al. 2004). These last results should be taken carefully due to a reduced sample
size. In the case of A. visco, a study of the mating system was assessed by means of
the AFLP technique in three different natural scenarios. The estimate of multilocus
outcrossing rate (tm) was high (≥0.971) in all populations. Moreover, in the three
populations studied, the progenies of open pollination were constituted mainly by
half-sibs (94.3%) (Pometti et al. 2013). Nowadays, seeds of all South American
Acacia species are mainly dispersed by cattle, so they likely have a long-distance
dispersal rate (Aronson 1992).
Prosopis affinis is pollinated by insects (primarily bees) and has endozoochory
dispersion through wild and domestic mammals (Burkart 1976; Abraham de Noir
et al. 2002; Martín 2014). There are no specific data about its mating system; however, the species of Algarobia section are considered mostly cross-pollinated
(Simpson 1977; Simpson et al. 1977), having been reported low levels of autogamy
in some species of the genus (Bessega et al. 2000; Saidman et al. 2000). There are
few studies about distances of seed and pollen dispersal for the genus. It has been
estimated that the seeds can be dispersed about 50 m by small rodents or may be
dispersed by cattle at greater distances (between 4 and 6 km) (Reynolds 1954; Keys
1993; Keys and Smith 1994). On the other hand, the entomophilic condition of
Prosopis species determines that pollen is usually unable to migrate large distances
(Bessega et al. 2000), but it is estimated that can be dispersed among 5.36 and
30.92 m (Bessega et al. 2012).
Very little is known about the reproduction of Gonopterodendron sarmientoi.
There is only a mention of a Meliponini bee species, Geotrigona argentina (Vossler
2014) pollinating the species. The fruit, dispersed by autochory, consists of a threewinged capsule where each mericarp contains one seed (Abraham de Noir et al.
2002). Regarding the reproduction by seeds, information related to the germination
requirements is scarce (but see de Viana et al. 2014). Field observations (Camps
et al. unpublished information) revealed asexual reproduction by sprouting roots,
being this kind of reproduction very frequent in the monospecific forests
(“palosantales”).
11.4 Population Structure and Landscape Genetic Structure
Plant populations are not randomly arranged assemblages of genotypes but are usually structured in space and time. Diverse approaches implemented in computer
programmes like STRUCTURE, GENELAND and BAPS allow studying the
C. Pometti et al.
outcrossing rate (tm) was high (≥0.957) in all populations, indicating that this species is predominantly an outcrosser. Moreover, this study showed a high probability
that the individuals within each progeny array are half sibs. On the other hand, a
similar study on three populations of A. aroma also using isozymes, similarly
revealed a high multilocus outcrossing rate tm ≥ 0.914, although with a high probability that individuals within progeny arrays are full rather than half sibs (Casiva
et al. 2004). These last results should be taken carefully due to a reduced sample
size. In the case of A. visco, a study of the mating system was assessed by means of
the AFLP technique in three different natural scenarios. The estimate of multilocus
outcrossing rate (tm) was high (≥0.971) in all populations. Moreover, in the three
populations studied, the progenies of open pollination were constituted mainly by
half-sibs (94.3%) (Pometti et al. 2013). Nowadays, seeds of all South American
Acacia species are mainly dispersed by cattle, so they likely have a long-distance
dispersal rate (Aronson 1992).
Prosopis affinis is pollinated by insects (primarily bees) and has endozoochory
dispersion through wild and domestic mammals (Burkart 1976; Abraham de Noir
et al. 2002; Martín 2014). There are no specific data about its mating system; however, the species of Algarobia section are considered mostly cross-pollinated
(Simpson 1977; Simpson et al. 1977), having been reported low levels of autogamy
in some species of the genus (Bessega et al. 2000; Saidman et al. 2000). There are
few studies about distances of seed and pollen dispersal for the genus. It has been
estimated that the seeds can be dispersed about 50 m by small rodents or may be
dispersed by cattle at greater distances (between 4 and 6 km) (Reynolds 1954; Keys
1993; Keys and Smith 1994). On the other hand, the entomophilic condition of
Prosopis species determines that pollen is usually unable to migrate large distances
(Bessega et al. 2000), but it is estimated that can be dispersed among 5.36 and
30.92 m (Bessega et al. 2012).
Very little is known about the reproduction of Gonopterodendron sarmientoi.
There is only a mention of a Meliponini bee species, Geotrigona argentina (Vossler
2014) pollinating the species. The fruit, dispersed by autochory, consists of a threewinged capsule where each mericarp contains one seed (Abraham de Noir et al.
2002). Regarding the reproduction by seeds, information related to the germination
requirements is scarce (but see de Viana et al. 2014). Field observations (Camps
et al. unpublished information) revealed asexual reproduction by sprouting roots,
being this kind of reproduction very frequent in the monospecific forests
(“palosantales”).
11.4 Population Structure and Landscape Genetic Structure
Plant populations are not randomly arranged assemblages of genotypes but are usually structured in space and time. Diverse approaches implemented in computer
programmes like STRUCTURE, GENELAND and BAPS allow studying the
C. Pometti et al.