Population Genetic Structure of Two Columnar Cacti with a Patchy Distribution in Eastern Brazil

Abstract

The genetic variability and population genetic structure of six populations of Praecereus euchlorus and Pilosocereus machrisii were investigated. The genetic variability in single populations of Pilosocereus vilaboensis, Pilosocereus aureispinus, and Facheiroa squamosa was also examined. All of these cacti species have a patchy geographic distribution in which they are restricted to small areas of xeric habitats in eastern Brazil. An analysis of genetic structure was used to gain insights into the historical mechanisms responsible for the patchy distribution of P. euchlorus and P. machrisii. High genetic variability was found at the populational level in all species (P=58.9-92.8%, A(p)=2.34-3.33, H(e)=0.266-0.401), and did not support our expectations of low variability based on the small population size. Substantial inbreeding was detected within populations (F(IS)=0.370-0.623). In agreement with their insular distribution patterns, P. euchlorus and P. machrisii had a high genetic differentiation (F(ST)=0.484 and F(ST)=0.281, respectively), with no evidence of isolation by distance. Accordingly, estimates of gene flow (N(m)) calculated from F(ST) and private alleles were below the level of N(m)=1 in P. machrisii and P. euchlorus. These results favored historical fragmentation as the mechanism responsible for the patchy distribution of these two species. The genetic distance between P. machrisii and P. vilaboensis was not compatible with their taxonomic distinction, indicating a possible local speciation event in this genus, or the occurrence of introgression events.

Esterase Polymorphism and the Analysis of Genetic Diversity and Structure in Cactus Populations Descended from Cereus peruvianus Plants Regenerated In Vitro

“…On the other hand, the negative values of F is observed in the F 1 populations contrast with moderate to high levels of endogamy in other Cactaceae species (Nassar et al 2003;Clark-Tapia and Molina-Freaner 2003;Moraes et al 2005;Lambert et al 2006). The low values of F is indicating excess of heterozygous individuals could be the result of human selection (domestication) in the F 1 parent (C 1 -C 14 cultivated plants).…”

“…This result contrasts with the low or moderate genetic structure reported for most cactus species analyzed so far. Only 35% of these cactus species had high levels of genetic structure (Nason et al 2002;Moraes et al 2005;Lambert et al 2006). Small F st values have been justified as a result of long-distance pollen dispersal that has a homogenizing influence at the regional level (OteroArnaiz et al 2005).…”

Genetic diversity and structure of populations in Pilosocereus gounellei (F.A.C.Weber ex K.Schum. ) (Cactaceae) in the Caatinga biome as revealed by heterologous microsatellite primers

“…The level of heterozygosity in samples of P. grounellei growing in areas of natural occurrence in three Brazilian states (PI, RN, and BA) is higher than those reported for the following other species of the Pilosocereus genus, distributed in South America, using isozyme markers: P. lanuginosus (H e ¼ 0.274), P. aureispinus (H e ¼ 0.284), P. viloboensis (H e ¼ 0.292), P. machrissii (H e ¼ 0.380), and Pilosocereus tillianus (H e ¼ 0.352) (Nassar et al, 2003;Moraes et al, 2005;Figueredo et al, 2010). The microsatellite transferability proved to be an interesting approach that was used to i) reveal both the highest genetic polymorphism in P. gounellei and how the plants are genetically related in three parts of the Caatinga biome; ii) select SSR loci candidates (mEgR98, Pichi44, and mEgR63) to investigate genetic diversity in xiqueexique plants from others regions of the Caatinga; iii) indicate the need of broader the genetic base of the species to obtain most genetically divergent plant groups with potential for use in breeding programs.…”

Population genetic diversity and structure of Pilosocereus tillianus (Cactaceae, Cereeae), a columnar cactus endemic to the Venezuelan Andes

“…Besides being one of the most conspicuous and abundant cactus growth forms, many columnar cacti are considered keystone species in arid ecosystems (Nassar et al, 1997;Valiente-Banuet et al, 2002) and several species have been used by indigenous people in Mesoamerica for thousands of years, and even today are important food sources in several regions (Casas and Barbera, 2002). Historically, the majority of genetic studies with columnar cacti have been conducted in Mexico (Clark-Tapia et al, 2005;Casas et al, 2007;Parra et al, 2008), USA and Venezuela (Nassar et al, 2003); but more recently, information from species in other countries such as Brazil (Moraes et al, 2005) has become available. Additional information is considerably valuable, since habitats of columnar cacti vary notably among different geographic regions.…”