262
proportional to the distance that separates them, and directly proportional to the
dispersal capacity of the pollen. The difference between the estimates generated by
the two algorithms is related to additional parameters required by both methods,
such as the density of the study area, that in one case is predicted and the other has
to be provided by the researcher and some assumptions such as floral asynchrony,
uniformity in male fertility rates, etc. (see Austerlitz and Smouse 2002).
Mating system and pollen dispersal parameters were studied in a wild P. alba
population (Bessega et al. 2011) and in a preserved P. flexuosa population (Bessega
et al. 2017) using the indirect methods described above. These studies based on
microsatellite markers showed that both species are mainly outcrossers (tm = 1 in
P. alba and tm = 0.996 in P. flexuosa). However, in both populations inbreeding was
detected (from the difference tm-ts) at low but significant frequency, which is the
result of crosses between related individuals. The results showed that the number of
pollen donors per mother plant (i.e., the number of trees that act as male parents of
each family) was on average 6 individuals for P. alba and 3 for P. flexuosa (Table 9.2).
Additionally, studies that evaluated the internal constitution of each family,
defined as the set of seeds collected from each mother plant, were carried out. This
is equivalent to determining the proportion of half-sibs and full-sibs present in each
fraternal group as a whole and considering the seeds that belongs to the same or
different pods. In this case, the kinship was estimated according to the proportion of
alleles shared among all the pairs of individuals of each fraternal group. In this way,
it could be established that the proportion of full-sibs in P. alba is 64% when considering seeds from the same fruit, while this proportion drops to 10% when seeds
of different fruits are compared. In P. flexuosa, the estimates were similar and vary
between 71% and 24%, respectively. This information can be interpreted on the
basis of the behavior of the pollinators and the anatomy of the inflorescence. The
pollinating insects associated with these species usually focus their efforts on plants
with higher floral density and limit their movement between plants to the nearest
neighbors. As a consequence, each pollination event involves the pollen of a single
or a few pollen donors fertilizing each inflorescence favoring the occurrence of fullsibs in each fruit.
The dispersal analysis allowed the description of the average dispersion distance
of pollen in P. alba and P. flexuosa that ranges between 4 and 31 m, as estimated
using the Kindist or TwoGener algorithms. Indirect estimation in these Prosopis
species indicates that the dispersion of pollen and seeds would be limited. These
results can be discussed in reference to the algarrobo management program as they
provide valuable information to be considered in order to avoid the effects of
inbreeding and genetic drift within populations as a consequence of the intensive
use of these resources.
C. Vega et al.
proportional to the distance that separates them, and directly proportional to the
dispersal capacity of the pollen. The difference between the estimates generated by
the two algorithms is related to additional parameters required by both methods,
such as the density of the study area, that in one case is predicted and the other has
to be provided by the researcher and some assumptions such as floral asynchrony,
uniformity in male fertility rates, etc. (see Austerlitz and Smouse 2002).
Mating system and pollen dispersal parameters were studied in a wild P. alba
population (Bessega et al. 2011) and in a preserved P. flexuosa population (Bessega
et al. 2017) using the indirect methods described above. These studies based on
microsatellite markers showed that both species are mainly outcrossers (tm = 1 in
P. alba and tm = 0.996 in P. flexuosa). However, in both populations inbreeding was
detected (from the difference tm-ts) at low but significant frequency, which is the
result of crosses between related individuals. The results showed that the number of
pollen donors per mother plant (i.e., the number of trees that act as male parents of
each family) was on average 6 individuals for P. alba and 3 for P. flexuosa (Table 9.2).
Additionally, studies that evaluated the internal constitution of each family,
defined as the set of seeds collected from each mother plant, were carried out. This
is equivalent to determining the proportion of half-sibs and full-sibs present in each
fraternal group as a whole and considering the seeds that belongs to the same or
different pods. In this case, the kinship was estimated according to the proportion of
alleles shared among all the pairs of individuals of each fraternal group. In this way,
it could be established that the proportion of full-sibs in P. alba is 64% when considering seeds from the same fruit, while this proportion drops to 10% when seeds
of different fruits are compared. In P. flexuosa, the estimates were similar and vary
between 71% and 24%, respectively. This information can be interpreted on the
basis of the behavior of the pollinators and the anatomy of the inflorescence. The
pollinating insects associated with these species usually focus their efforts on plants
with higher floral density and limit their movement between plants to the nearest
neighbors. As a consequence, each pollination event involves the pollen of a single
or a few pollen donors fertilizing each inflorescence favoring the occurrence of fullsibs in each fruit.
The dispersal analysis allowed the description of the average dispersion distance
of pollen in P. alba and P. flexuosa that ranges between 4 and 31 m, as estimated
using the Kindist or TwoGener algorithms. Indirect estimation in these Prosopis
species indicates that the dispersion of pollen and seeds would be limited. These
results can be discussed in reference to the algarrobo management program as they
provide valuable information to be considered in order to avoid the effects of
inbreeding and genetic drift within populations as a consequence of the intensive
use of these resources.
C. Vega et al.