Population Genetics of Escontria chiotilla in Wild and Silvicultural Managed Populations in the Tehuacán Valley, Central Mexico

Abstract

Escontria chiotilla is a columnar cactus that grows in the arid and semiarid lands of Central Mexico and produces edible fruit with economic. In the wild, this plant species is distributed as part of thorn-scrub and tropical deciduous forests, but in the Tehuaca´n Valley also occurs in silvicultural managed in situ populations, in which people practise artificial selection enhancing phenotypes with larger fruits. The population genetics of wild and managed populations was studied to analyse the effects of management on genetic structure of E. chiotilla. A total of 150 individuals from six populations were studied, analysing 13 loci for eight enzymes by starch gel electrophoresis. The genetic variation in wild populations was significantly higher than in managed populations (H o = 0.079, H e = 0.134, H T = 0.370, and H o = 0.052, H e = 0.110, H T = 0.298, respectively), indicating that silvicultural management has caused a reduction of the genetic variation in populations. Most of the genetic variation in both wild and managed populations occurs within populations (D ST = 0.027 in the wild and 0.018 in managed populations). The genetic distance coefficients were slightly different for silvicultural managed populations than in wild ones, illustrating an incipient effect of management on the genetic structure of populations. However, values of Nm GST = 3.845 and Nm FST = 3.848 indicate that a high gene flow counteracts the effects of human selection on the differentiation of populations.

Agroforestry systems and biodiversity conservation in arid zones: the case of the Tehuacán Valley, Central México

“…Agricultural management involves clearing from the fields tolerating individuals of Escontria chiotilla and other 35 species of useful plants (Arellano and Casas 2003;Vivar 2004). Morphological and population genetics studies (Arellano and Casas 2003;Tinoco et al 2005) revealed patterns of artificial selection and gene flow similar to those referred to above for Polaskia spp. (3) Garambullal, a forest type dominated by Myrtillocactus schenckii (370 ind./ha) occurring at elevations from 600 to 2,100 m on volcanic soils, in the territory of Santiago Coatepec.…”

“…Also noteworthy is the capability of agroforestry systems studied to maintain or even enhance the abundance of some endemic species of high cultural values, such as Escontria chiotilla, Polaskia chende, and P. chichipe. In addition, it is remarkable that, on average, nearly 94% of genetic diversity of wild populations of the main columnar cacti species composing natural forests is maintained within agroforestry systems (Tinoco et al 2005, Parra et al 2008.…”

Traditional Knowledge and Useful Plant Richness in the Tehuacán–Cuicatlán Valley, Mexico

“…Recent studies have documented that some of these management practices have had some effect on the populations of various species, which can be interpreted as forms of incipient domestication. Among these species are the columnar cacti Escontria chiotilla, Pachycereus hollianus, Polaskia chende, P. chichipe, Stenocereus stellatus, S. pruinosus (Casas et al 1997b(Casas et al , 1999b(Casas et al , 1999cCruz and Casas 2002;Arellano and Casas 2003;Otero-Arnaíz et al 2003, 2005a, 2005bCarmona and Casas 2005;Tinoco et al 2005;Oaxaca-Villa et al 2006;Rodríguez-Arévalo et al 2006;Ruíz-Duran 2007), as well as species of other plant groups such as Sideroxylon palmeri (Sapotaceae) (González-Soberanis and Casas 2004), Ceiba aesculifolia ssp. parvifolia (Bombacaceae) (Avendaño et al 2006), and Proboscidea louisianica spp.…”

High levels of genetic variability and inbreeding in two Neotropical dioecious palms with contrasting life histories

“…In addition, heterozygote deficits in tropical plants have been found in populations of Piper amalago (Heywood and Fleming, 1986), Austromyrtus spp. (Shapcott and Playford, 1996), Syzygium nervosum (Shapcott, 1998), Ancistrocladus korupensis (Foster and Sork, 1997), Capsicum annuum (Hernández-Verdugo et al, 2001), Escontria chiotilla (Tinoco et al, 2005) and the dioecious species Chamaedorea tuerckheimii, Carica papaya and Carica cauliflora (Oyama et al, unpublished data). Inbreeding was also detected in populations of the trees Pithecellobium pedicellare (O'Malley and Bawa, 1987) and Bertholletia excelsa (O'Malley et al, 1988).…”