200
expected, since the most distributed exotic willow clone in the study area is female
(Budde et al. 2011).
Additionally, a molecular pair-comparison was made in 15 sites of the Negro
River, where adult trees (> 20 years) and groups of juveniles (< 5 years) grow
together. It was found that the number of populations with hybrids increased twice
in the last 20 years (50% of the juvenile groups analysed had hybrids) and that the
number of hybrid individuals increased three times in the last 20 years (16% of the
regeneration) (Gallo et al. 2016, 2018). The higher proportion of hybrids at the
juvenile stage could indicate the intensification of the hybridization process.
Processes like genetic assimilation, demographic swamping and loss of genetic
integrity are some of the possible outcomes (Thomas and Leyer 2014).
To assess the genetic diversity of S. humboldtiana and to unravel the population
genetic structure along Patagonian rivers, samples were collected at four locations,
most of them along the Negro River and just a few in the confluence of its main
tributaries, the rivers Limay and Neuquén. By genotyping at five nuclear microsatellites (Bozzi et al. 2015), a lower genetic diversity was found (Ho = 0.568;
He = 0.555) as compared with other riparian species (e.g. Lin et al. 2009; Mosner
et al. 2012). A trend of increasing genetic diversity was observed downstream along
the Negro River, which is in line with some other studies of riparian species indicating unidirectional gene flow mediated by water dispersal (Huang et al. 2015;
Schleuning et al. 2011). However, no structuring was detected among the 34 analysed sites.
The genetic diversity of the main North Patagonian rivers and a subtropical population was also compared with some of the same markers used in the previous
analysis of the Negro River genetic diversity (Pomponio et al. 2018). Samples of
leaves from typical trees in Victoria (Province of Entre Ríos, 32°37′S) and on the
banks of the rivers Neuquén (38°30′S), Negro (39°S) and Chubut (42°30′S) in North
Patagonia were collected. Samples of introduced species of Salix inhabiting the
same region were also included to estimate the existence of hybridization.
Preliminary molecular studies were carried out from a total of 178 samples belonging to four populations using five microsatellite markers: Shum_49, Shum_71
(Bozzi et al. 2015), gSIMCO24, ORPM_446 and PMGC-223 (http://www.ornl.gov/
sci/ipgc/ssr_resource.htm); the latter was used as taxa diagnostic for hybrid estimation (Bozzi et al. 2012).
The sampled trees were selected phenotypically according to leaves, buds,
bark, architecture and phenological traits. The exotic species that inhabit the natural distribution of S. humboldtiana, such as S. alba, S. euxina (ex S. fragilis) and
S. babylonica in North Patagonia and S. nigra, S. alba and S. babylonica in Entre
Ríos (NE of Argentina) were analysed with the same SSRs markers as a control.
Only two putative hybrids were found, indicating that phenotypical selection of
pure individuals can be done with minimum bias. When both analysed regions
were compared, a notable difference was found in all genetic diversity parameters. Patagonian populations showed a low genetic diversity over loci (Ho = 0.180;
He = 0.236), whereas the subtropical population at Victoria (Province of Entre
Ríos) presented moderate values (Ho = 0.515; He = 0.612) (Table 7.4). The
P. Marchelli et al.
expected, since the most distributed exotic willow clone in the study area is female
(Budde et al. 2011).
Additionally, a molecular pair-comparison was made in 15 sites of the Negro
River, where adult trees (> 20 years) and groups of juveniles (< 5 years) grow
together. It was found that the number of populations with hybrids increased twice
in the last 20 years (50% of the juvenile groups analysed had hybrids) and that the
number of hybrid individuals increased three times in the last 20 years (16% of the
regeneration) (Gallo et al. 2016, 2018). The higher proportion of hybrids at the
juvenile stage could indicate the intensification of the hybridization process.
Processes like genetic assimilation, demographic swamping and loss of genetic
integrity are some of the possible outcomes (Thomas and Leyer 2014).
To assess the genetic diversity of S. humboldtiana and to unravel the population
genetic structure along Patagonian rivers, samples were collected at four locations,
most of them along the Negro River and just a few in the confluence of its main
tributaries, the rivers Limay and Neuquén. By genotyping at five nuclear microsatellites (Bozzi et al. 2015), a lower genetic diversity was found (Ho = 0.568;
He = 0.555) as compared with other riparian species (e.g. Lin et al. 2009; Mosner
et al. 2012). A trend of increasing genetic diversity was observed downstream along
the Negro River, which is in line with some other studies of riparian species indicating unidirectional gene flow mediated by water dispersal (Huang et al. 2015;
Schleuning et al. 2011). However, no structuring was detected among the 34 analysed sites.
The genetic diversity of the main North Patagonian rivers and a subtropical population was also compared with some of the same markers used in the previous
analysis of the Negro River genetic diversity (Pomponio et al. 2018). Samples of
leaves from typical trees in Victoria (Province of Entre Ríos, 32°37′S) and on the
banks of the rivers Neuquén (38°30′S), Negro (39°S) and Chubut (42°30′S) in North
Patagonia were collected. Samples of introduced species of Salix inhabiting the
same region were also included to estimate the existence of hybridization.
Preliminary molecular studies were carried out from a total of 178 samples belonging to four populations using five microsatellite markers: Shum_49, Shum_71
(Bozzi et al. 2015), gSIMCO24, ORPM_446 and PMGC-223 (http://www.ornl.gov/
sci/ipgc/ssr_resource.htm); the latter was used as taxa diagnostic for hybrid estimation (Bozzi et al. 2012).
The sampled trees were selected phenotypically according to leaves, buds,
bark, architecture and phenological traits. The exotic species that inhabit the natural distribution of S. humboldtiana, such as S. alba, S. euxina (ex S. fragilis) and
S. babylonica in North Patagonia and S. nigra, S. alba and S. babylonica in Entre
Ríos (NE of Argentina) were analysed with the same SSRs markers as a control.
Only two putative hybrids were found, indicating that phenotypical selection of
pure individuals can be done with minimum bias. When both analysed regions
were compared, a notable difference was found in all genetic diversity parameters. Patagonian populations showed a low genetic diversity over loci (Ho = 0.180;
He = 0.236), whereas the subtropical population at Victoria (Province of Entre
Ríos) presented moderate values (Ho = 0.515; He = 0.612) (Table 7.4). The
P. Marchelli et al.