Direct and indirect estimates of gene flow among wild and managed populations of Polaskia chichipe, an endemic columnar cactus in Central Mexico

Microsatellite markers were used to obtain direct and indirect estimates of gene flow in populations of Polaskia chichipe under different management regimes, in order to understand the genetic consequences of gene flow in the evolutionary process of domestication. P. chichipe is a columnar cactus endemic to the Tehuacan Valley, Central Mexico, and has come under domestication for its edible fruit. Morphological, phenological, physiological, and reproductive differences, apparently attributable to artificial selection, exist between wild and managed populations, which grow sympatrically. However, strong gene flow may counteract the effects of this selection. In this study, we used paternity analysis to demonstrate that although most of the pollinations occur among individuals within the same population at distances < 40 m, pollen flow from other populations is considerable (27 +/- 5%). Heterogeneity in pollen clouds sampled by mother plants (FST = 0.12) indicated nonrandom mating, which is probably due to temporal heterogeneity in pollen movement. Spatial structure on local and regional scales is consistent with an isolation-by-distance model. The similarity of indirect, direct and demographic estimates of neighbourhood size (74-250 individuals) suggests that this genetic structure is representative of an equilibrium state. These results suggest that traditional management practices have conserved the genetic resources of this species in situ, but also that gene flow is counteracting the effect of domestication to some degree. We discuss our results in the general context of genetic exchange between cultivated and wild populations during the domestication process.     

Morphological variation and the process of domestication of Stenocereus stellatus (Cactaceae) in Central Mexico

Morphological variation was analyzed in wild, managed in situ, and cultivated populations of the columnar cactus Stenocereus stellatus in central Mexico. The purpose was to evaluate whether morphological divergence between manipulated and wild populations has resulted from domestication processes. Variation of 23 morphological characters was analyzed among 324 individuals from 19 populations of the Tehuacán Valley and La Mixteca Baja. Multivariate statistical analyses were used to group individuals and populations according to their morphological similarity. Individuals grouped according to the way of management and fruit characteristics were the most relevant for grouping. Within each region, sweet fruits with pulp colors other than red were more frequent in cultivated populations, where fruits were also larger, contained more and bigger seeds, and had thinner peel and fewer spines than fruits from wild individuals. Phenotypes common in managed in situ and cultivated populations generally occur in the wild but in lower frequencies. Artificial selection has thus operated by enhancing and maintaining desirable rare phenotypes in managed in situ and cultivated populations, causing divergent patterns of morphological variation from wild populations. Cultivation has caused the strongest level of divergence, but divergence has also been significant with management of wild populations in situ.     

Evolution under domestication: ongoing artificial selection and divergence of wild and managed Stenocereus pruinosus (Cactaceae) populations in the Tehuac��n Valley, Mexico

Background and Aims

The Tehuacán Valley in Mexico is a principal area of plant domestication in Mesoamerica. There, artificial selection is currently practised on nearly 120 native plant species with coexisting wild, silvicultural and cultivated populations, providing an excellent setting for studying ongoing mechanisms of evolution under domestication. One of these species is the columnar cactus Stenocereus pruinosus, in which we studied how artificial selection is operating through traditional management and whether it has determined morphological and genetic divergence between wild and managed populations.

Methods

Semi-structured interviews were conducted with 83 households of three villages to investigate motives and mechanisms of artificial selection. Management effects were studied by comparing variation patterns of 14 morphological characters and population genetics (four microsatellite loci) of 264 plants from nine wild, silvicultural and cultivated populations.

Key Results

Variation in fruit characters was recognized by most people, and was the principal target of artificial selection directed to favour larger and sweeter fruits with thinner or thicker peel, fewer spines and pulp colours others than red. Artificial selection operates in agroforestry systems favouring abundance (through not felling plants and planting branches) of the preferred phenotypes, and acts more intensely in household gardens. Significant morphological divergence between wild and managed populations was observed in fruit characters and plant vigour. On average, genetic diversity in silvicultural populations (H_E = 0·743) was higher than in wild (H_E = 0·726) and cultivated (H_E = 0·700) populations. Most of the genetic variation (90·58 %) occurred within populations. High gene flow (Nm_FST > 2) was identified among almost all populations studied, but was slightly limited by mountains among wild populations, and by artificial selection among wild and managed populations.

Conclusions

Traditional management of S. pruinosus involves artificial selection, which, despite the high levels of gene flow, has promoted morphological divergence and moderate genetic structure between wild and managed populations, while conserving genetic diversity.     

Evolution of Polaskia chichipe (Cactaceae) under domestication in the Tehuacan Valley, central Mexico: reproductive biology

Polaskia chichipe, a columnar cactus, is cultivated for its edible fruits in central Mexico. This study analyzed whether artificial selection has modified its reproduction patterns and caused barriers to pollen exchange between wild, managed in situ, and cultivated populations. Anthesis was diurnal (～16 h in winter, ～10 h in spring) as well as partly nocturnal (～12 h in winter, ～3 h in spring), and flowers were pollinated by bees, hummingbirds, and hawk moths. Manual cross-pollination was ～37-49% effective in all populations. Self-pollination was ～12% successful in the wild, but twice as successful (～22-27%) in managed and cultivated populations. Diurnal pollination was ～35-55% effective in winter and 100% in spring. Nocturnal pollination was successful only in winter (15%). Crosses among individuals were more effective within populations than among populations, including populations under a similar management regimen. The least successful crosses were between wild and cultivated populations. Flowers were produced in all populations from January to March, but flowering peaks differed by 1 mo among wild, managed, and cultivated populations and by 2 mo between wild and cultivated populations. The latter interrupted pollen exchange in May. Seeds from managed and cultivated populations germinated faster than those from wild individuals. Domestication has seemingly favored self-compatible P. chichipe plants with higher fruit yield, a longer period of fruit production, and faster seed germination, attributes that have resulted in partial reproductive barriers between wild and manipulated populations.     

Landscape management and domestication of Stenocereus pruinosus (Cactaceae) in the Tehuacan Valley: human guided selection and gene flow

ABSTRACT: BACKGROUND: Use of plant resources and ecosystems practiced by indigenous peoples of Mesoamerica commonly involves domestication of plant populations and landscapes. Our study analyzed interactions of coexisting wild and managed populations of the pitaya Stenocereus pruinosus, a columnar cactus used for its edible fruit occurring in natural forests, silviculturally managed in milpa agroforestry systems, and agriculturally managed in homegardens of the Tehuacan Valley, Mexico. We aimed at analyzing criteria of artificial selection and their consequences on phenotypic diversity and differentiation, as well as documenting management of propagules at landscape level and their possible contribution to gene flow among populations. METHODS: Semi-structured interviews were conducted to 83 households of the region to document perception of variation, criteria of artificial selection, and patterns of moving propagules among wild and managed populations. Morphological variation of trees from nine wild, silviculturally and agriculturally managed populations was analyzed for 37 characters through univariate and multivariate statistical methods. In addition, indexes of morphological diversity (MD) per population and phenotypic differentiation (PD) among populations were calculated using character states and frequencies. RESULTS: People recognized 15 pitaya varieties based on their pulp color, fruit size, form, flavor, and thorniness. On average, in wild populations we recorded one variety per population, in silviculturally managed populations 1.58 +/- 0.77 varieties per parcel, and in agriculturally managed populations 2.19 +/- 1.12 varieties per homegarden. Farmers select in favor of sweet flavor (71% of households interviewed) and pulp color (46%) mainly red, orange and yellow. Artificial selection is practiced in homegardens and 65% of people interviewed also do it in agroforestry systems. People obtain fruit and branches from different population types and move propagules from one another. Multivariate analyses showed morphological differentiation of wild and agriculturally managed populations, mainly due to differences in reproductive characters; however, the phenotypic differentiation indexes were relatively low among all populations studied. Morphological diversity of S. pruinosus (average MD = 0.600) is higher than in other columnar cacti species previously analyzed. CONCLUSIONS: Artificial selection in favor of high quality fruit promotes morphological variation and divergence because of the continual replacement of plant material propagated and introduction of propagules from other villages and regions. This process is counteracted by high gene flow influenced by natural factors (pollinators and seed dispersers) but also by human management (movement of propagules among populations), all of which determines relatively low phenotypic differentiation among populations. Conservation of genetic resources of S. pruinosus should be based on the traditional forms of germplasm management by local people.     

Traditional management and morphological variation inLeucaena Esculenta (Fabaceae: Mimosoideae) in the mixtec region of Guerrero,Mexico

Ethnobotanical information about uses, management and traditional classification ofLeucaena esculenta by the Mixtec in Guerrero, Mexico, is presented. This plant is mainly used as human food. Buds of leaves and flowers as well as seeds and young pods are the main edible parts. Size, flavor and digestibility of seeds and pods are shown to be important in the Mixtec classification ofLeucaena species and in selection of trees to harvest during gathering. Artificial selection inL. esculenta subsp.esculenta by the Mixtec occurs not only under cultivation, but also in wild populations where people eliminate some individuals while promoting the growth of others with favorable phenotypes. Morphological characters of seeds and pods of individual trees of this subspecies were measured in order to compare phenotypic variation in populations subject to different regimes of management. Samples of trees were analyzed from a) a wild population not affected by intentional disturbances; b) a wild population selectively managed in situ; and c) a sample of cultivated individuals. Ordination methods and analysis of variance were used to examine differences between populations. A marked divergence between the three samples was found, especially between the wild populations managed and unmanaged. The frequency of the phenotypes preferred by people was found to be higher in the wild populationin situ managed. Our study confirms that through in situ forms of management, people are able to modify the phenotypic structure of plant populations. Possible routes of plant domestication within plant populationsin situ are suggested.     

Genetic variation and evolution of Polaskia chichipe (Cactaceae) under domestication in the Tehuacán Valley, central Mexico

Polaskia chichipe is a columnar cactus under artificial selection in central Mexico because of its edible fruits. Our study explored the effect of human manipulation on levels and distribution of genetic variation in wild, silviculturally managed and cultivated sympatric populations. Total genetic variation, estimated in nine populations with five microsatellite loci, was H(T) = 0.658 +/- 0.026 SE, which was mainly distributed within populations (H(S) = 0.646) with low differentiation among them (F(ST) = 0.015). Fixation index (F(IS)) in all populations was positive, indicating a deficit of heterozygous individuals with respect to Hardy-Weinberg expectations. When populations were pooled by management type, the highest expected heterozygosity (H(E) = 0.631 +/- 0.031 SE) and the lowest fixation index (F(IS) = 0.07) were observed in wild populations, followed by cultivated populations (H(E) = 0.56 +/- 0.03 SE, F(IS) = 0.14), whereas the lowest variation was found in silviculturally managed populations (H(E) = 0.51 +/- 0.05 SE, F(IS) = 0.17). Low differentiation among populations under different management types (F(ST) 0.005, P < 0.04) was observed. A pattern of migration among neighbouring populations, suggested from isolation by distance (r2 = 0.314, P < 0.01), may have contributed to homogenizing populations and counteracting the effects of artificial selection. P. chichipe, used and managed for at least 700 generations, shows morphological differentiation, changes in breeding system and seed germination patterns associated with human management, with only slight genetic differences detected by neutral markers.     

Wildlife uses and hunting patterns in rural communities of the Yucatan Peninsula, Mexico

Background

Use of plant resources and ecosystems practiced by indigenous peoples of Mesoamerica commonly involves domestication of plant populations and landscapes. Our study analyzed interactions of coexisting wild and managed populations of the pitaya Stenocereus pruinosus, a columnar cactus used for its edible fruit occurring in natural forests, silviculturally managed in milpa agroforestry systems, and agriculturally managed in homegardens of the Tehuacán Valley, Mexico. We aimed at analyzing criteria of artificial selection and their consequences on phenotypic diversity and differentiation, as well as documenting management of propagules at landscape level and their possible contribution to gene flow among populations.

Methods

Semi-structured interviews were conducted to 83 households of the region to document perception of variation, criteria of artificial selection, and patterns of moving propagules among wild and managed populations. Morphological variation of trees from nine wild, silviculturally and agriculturally managed populations was analyzed for 37 characters through univariate and multivariate statistical methods. In addition, indexes of morphological diversity (MD) per population and phenotypic differentiation (PD) among populations were calculated using character states and frequencies.

Results

People recognized 15 pitaya varieties based on their pulp color, fruit size, form, flavor, and thorniness. On average, in wild populations we recorded one variety per population, in silviculturally managed populations 1.58 ± 0.77 varieties per parcel, and in agriculturally managed populations 2.19 ± 1.12 varieties per homegarden. Farmers select in favor of sweet flavor (71% of households interviewed) and pulp color (46%) mainly red, orange and yellow. Artificial selection is practiced in homegardens and 65% of people interviewed also do it in agroforestry systems. People obtain fruit and branches from different population types and move propagules from one another. Multivariate analyses showed morphological differentiation of wild and agriculturally managed populations, mainly due to differences in reproductive characters; however, the phenotypic differentiation indexes were relatively low among all populations studied. Morphological diversity of S. pruinosus (average MD = 0.600) is higher than in other columnar cacti species previously analyzed.

Conclusions

Artificial selection in favor of high quality fruit promotes morphological variation and divergence because of the continual replacement of plant material propagated and introduction of propagules from other villages and regions. This process is counteracted by high gene flow influenced by natural factors (pollinators and seed dispersers) but also by human management (movement of propagules among populations), all of which determines relatively low phenotypic differentiation among populations. Conservation of genetic resources of S. pruinosus should be based on the traditional forms of germplasm management by local people.     

Plant management among the Nahua and the Mixtec in the Balsas River Basin,Mexico: An ethnobotanical approach to the study of plant domestication

Different forms of management of wild, weedy, and domesticated plants carried out by the Nahua and the Mixtec in the Balsas River Basin, Mexico, are described. Along with cultivation of domesticated plants, these forms of plant management include gathering from wild populations; in situtolerance of plant individuals during clearings of natural vegetation; in situenhancement and protection of particular plants among populations of some species; as well as sowing or planting of propagules and transplantation of complete individuals of weedy and wild plants in controlled ex situenvironments. Processes of artificial selection and possible routes of domestication occurring in these forms of plant management are discussed.     

Reproductive biology and the process of domestication of the columnar cactus Stenocereus Stellatus in Central Mexico

Pollination biology, breeding system, and floral phenology of the columnar cactus Stenocereus stellatus were studied in wild, wild managed in situ and cultivated populations of central Mexico, in order to examine whether these aspects have been modified under domestication and whether they determine reproductive barriers between wild and manipulated individuals. Individuals of both wild and manipulated populations are self-incompatible, indicating that artificial selection has not modified the breeding system. Their pollination biology is also similar. Anthesis is mainly nocturnal, with a peak of nectar production between 0200 and 0400 when the stigma presents maximum turgidity. Nocturnal visitors are the effective pollinators. Nearly 75% of flowers exposed for nocturnal pollination set fruit, while none of the flowers exposed for diurnal pollination produced fruits. The bats Leptonycteris curasoae, L. nivalis, and Choeronycteris mexicana (Glossophaginae) are the most likely pollinators, and their time of foraging is synchronized with the time of nectar production and stigma receptivity in S. stellatus. Bats potentially move pollen over a considerable distance, so there is apparently no spatial isolation to prevent pollen exchange between wild and cultivated populations. Phenological studies showed that there are also no apparent temporal barriers. However, manual cross pollination failed between some domesticated and wild phenotypes, suggesting that gene flow between wild and cultivated populations might be limited by pollen incompatibility.     

Effectiveness of bats as pollinators of Stenocereus stellatus (Cactaceae) in wild, managed in situ, and cultivated populations in La Mixteca Baja, central Mexico

Stenocereus stellatus is an endemic, self-incompatible, columnar cactus found in central Mexico where many of its wild populations have been fragmented. As an economically important species of fruit-producing cactus, S. stellatus occurs in wild, managed in situ, and cultivated populations. The objectives of this study were to determine the effective pollinators of S. stellatus, to compare pollinator visits and reproductive parameters among the three types of populations, and to determine if nectar feeding-bats are moving among populations. Effective pollinators were the nectarivorous bats Choeronycteris mexicana, Leptonycteris curasoae, and L. nivalis. Fewer total visits per flower per night and fewer visits by Choeronycteris were observed in cultivated populations, while the opposite pattern was observed for Leptonycteris. One aggressive interaction was filmed in which Choeronycteris was physically displaced by Leptonycteris, and Choeronycteris visits were significantly affected by Leptonycteris visits. Cultivated populations received more pollen grains and had more fruit set. Variation in pollinator visits between different populations and the consequent effects on reproductive success were likely a result of competition between bat species, and differences in foraging and in sensitivity of bat species to human populations. Three marked L. curasoae traveled 15 km from their roosting site to their foraging area, and one visited cultivated and managed populations, suggesting that this species may be particularly important in moving pollen among populations.     

Ethnobotany and domestication in Xoconochtli,Stenocereus stellatus (Cactaceae), in the Tehuacán Valley and La Mixteca Baja, México

Ethnobotanical information is presented on use, management, folk nomenclature and classification of the “xoconochtli” (Stenocereus stellatus) as well as on the role of this plant in subsistence of the Nahua, Mixtec and Popoloca peoples from the Tehuacán Valley and La Mixteca Baja in Central Mexico. Among all three groups, S. stellatus was used for various purposes but mainly for its edible fruits. Different variants of this species were distinguished, named and classified by indigenous people according to characteristics of the fruit; particularly size, color and flavor of the pulp, spininess and thickness of the peel. Wild plants characteristically had small red sour fruits with many spines and thick peel, while individuals selected for cultivation usually differed in one or more of these characters. Three general forms of interaction between people and this species were found: 1) gathering of useful products from the wild; 2) management of wild populations in situ which involves the sparing and enhancing of individuals with more desirable characteristics and the removal of others during clearance of the land for agriculture; and 3) cultivation, mainly in home gardens, by propagation of vegetative parts from desirable individuals. Fruit yields per individual and per population were measured and compared in wild, managed in situ and cultivated populations from the Tehuacán Valley and La Mixteca Baja. Wild and cultivated individuals from La Mixteca Baja yielded more than wild and cultivated individuals from the Tehuacán Valley. Within each region, fruit yields were similar in wild and managed in situ populations but significantly larger in cultivated populations. Forms of management of this plant species are discussed in terms of availability of products and demand for them in the local economy.     

Managing diversity: Domestication and gene flow in Stenocereus stellatus Riccob. (Cactaceae) in Mexico

Microsatellite markers (N = 5) were developed for analysis of genetic variation in 15 populations of the columnar cactus Stenocereus stellatus, managed under traditional agriculture practices in central Mexico. Microsatellite diversity was analyzed within and among populations, between geographic regions, and among population management types to provide detailed insight into historical gene flow rates and population dynamics associated with domestication. Our results corroborate a greater diversity in populations managed by farmers compared with wild ones (H_E = 0.64 vs. 0.55), but with regional variation between populations among regions. Although farmers propagated S. stellatus vegetatively in home gardens to diversify their stock, asexual recruitment also occurred naturally in populations where more marginal conditions have limited sexual recruitment, resulting in lower genetic diversity. Therefore, a clear‐cut relationship between the occurrence of asexual recruitment and genetic diversity was not evident. Two managed populations adjacent to towns were identified as major sources of gene movement in each sampled region, with significant migration to distant as well as nearby populations. Coupled with the absence of significant bottlenecks, this suggests a mechanism for promoting genetic diversity in managed populations through long distance gene exchange. Cultivation of S. stellatus in close proximity to wild populations has led to complex patterns of genetic variation across the landscape that reflects the interaction of natural and cultural processes. As molecular markers become available for nontraditional crops and novel analysis techniques allow us to detect and evaluate patterns of genetic diversity, genetic studies provide valuable insights into managing crop genetic resources into the future against a backdrop of global change. Traditional agriculture systems play an important role in maintaining genetic diversity for plant species.     

Effects of natural and artificial selection on survival of columnar cacti seedlings: the role of adaptation to xeric and mesic environments

Escontria chiotilla, Polaskia chichipe, and Stenocereus pruinosus are species of Mexican columnar cacti that are economically important because of their edible fruits. These species are managed by gathering fruits from the wild, silvicultural management in agroforestry systems, and cultivation in home gardens. Previous studies reported that artificial selection favored individuals that produced larger fruits, which indirectly led to the production of larger seeds and seedlings, with possible effects on survival. We hypothesized that seedlings from managed populations would be larger but more susceptible to xeric conditions than those from wild populations. We evaluated the effects of artificial and natural selection on seedling survival of the three species in wild and managed populations, which were managed with low and high intensity, respectively. We tested seedling performance in gradients of shade (0, 40, and 80%) and humidity (low and high). A GLM of seedling survival showed significant differences among species, shade, and humidity treatments, with each species having environmental requirements associated with their particular adaptations. High humidity decreased seedling survival of all species, and high solar radiation decreased survival of S. pruinosus and P. chichipe. The effect of management type was significant only in S. pruinosus. Significant differences in the initial growth of seedlings among species were detected with ANOVA. In optimal conditions, the hypocotyl and the cotyledons decreased in size and the epicotyl grew, whereas under stress, these structures remained unchanged. The optimum conditions of shade and humidity varied among species and management types. The seedlings of S. pruinosus were the largest and the most susceptible, but in all species, seedlings from managed populations were more susceptible to environmental conditions. Thus, artificial selection influenced the susceptibility of these cacti to xeric environments.     

Genetic diversity, structure, gene flow and evolutionary relationships within the Sorghum bicolor wild�Cweedy�Ccrop complex in a western African region

Gene flow between domesticated plants and their wild relatives is one of the major evolutionary processes acting to shape their structure of genetic diversity. Earlier literature, in the 1970s, reported on the interfertility and the sympatry of wild, weedy and cultivated sorghum belonging to the species Sorghum bicolor in most regions of sub-Saharan Africa. However, only a few recent surveys have addressed the geographical and ecological distribution of sorghum wild relatives and their genetic structure. These features are poorly documented, especially in western Africa, a centre of diversity for this crop. We report here on an exhaustive in situ collection of wild, weedy and cultivated sorghum assembled in Mali and in Guinea. The extent and pattern of genetic diversity were assessed with 15 SSRs within the cultivated pool (455 accessions), the wild pool (91 wild and weedy forms) and between them. F (ST) and R (ST) statistics, distance-based trees, Bayesian clustering methods, as well as isolation by distance models, were used to infer evolutionary relationships within the wild-weedy-crop complex. Firstly, our analyses highlighted a strong racial structure of genetic diversity within cultivated sorghum (F (ST) = 0.40). Secondly, clustering analyses highlighted the introgressed nature of most of the wild and weedy sorghum and grouped them into two eco-geographical groups. Such closeness between wild and crop sorghum could be the result of both sorghum's domestication history and preferential post-domestication crop-to-wild gene flow enhanced by farmers' practices. Finally, isolation by distance analyses showed strong spatial genetic structure within each pool, due to spatially limited dispersal, and suggested consequent gene flow between the wild and the crop pools, also supported by R (ST) analyses. Our findings thus revealed important features for the collection, conservation and biosafety of domesticated and wild sorghum in their centre of diversity.     

Genetics and evolution of weedy Helianthus annuus populations: adaptation of an agricultural weed

Agricultural weeds are a major cost to economies throughout the world, and have evolved from numerous plant species in many different plant families. Despite their ubiquity, we do not yet know how easily or often weeds evolve from their wild ancestors or the kinds of genes underlying their evolution. Here we report on the evolution of weedy populations of the common sunflower Helianthus annuus. We analysed 106 microsatellites in 48 individuals from each of six wild and four weed populations of the species. The statistical tests lnRV and lnRH were used to test for significant reductions in genetic variability at each locus in weedy populations compared to nearby wild populations. Between 1% and 6% of genes were significant outliers with reduced variation in weedy populations, implying that a small but not insignificant fraction of the genome may be under selection and involved in adaptation of weedy sunflowers. However, there did not appear to be a substantial reduction in variation across the genome, suggesting that effective population sizes have remained very large during the recent evolution of these weedy populations. Additional analyses showed that weedy populations are more closely related to nearby wild populations than to each other, implying that weediness likely evolved multiple times within the species, although a single origin followed by gene flow with local populations cannot be ruled out. Together, our results point to the relative ease with which weedy forms of this species can evolve and persist despite the potentially high levels of geneflow with nearby wild populations.     

Traditional Management and Morphological Patterns of <Emphasis Type="Italic">Myrtillocactus schenckii</Emphasis> (Cactaceae) in the Tehuacán Valley,Central Mexico<Superscript>1</Superscript>

Traditional Management and Morphological Patterns of Myrtillocactus schenckii (Cactaceae) in the Tehuacán Valley, Central Mexico Myrtillocactus schenckii is a columnar cactus endemic to central México and appreciated for its edible fruit. In the Tehuacán Valley it occurs wild in thorn-scrub forests, but it is also under silviculture management—tolerate in agroforestry systems and cultivated in home gardens. Ethnobotanical and morphometric studies were conducted to document its use and management forms, as well as consequences of artificial selection on morphological patterns in managed populations. In silviculture populations artificial selection occurs through selective tolerance of the phenotypes producing more, larger, and sweeter fruits, whereas in home gardens people plant branches of the preferred phenotypes. Morphological differences were found especially in fruit size and production, the main targets of artificial selection. The highest average values of fruit size and production were found in cultivated populations (0.993 cm³ and 204.45 fruits per branch, respectively), intermediate in silviculture populations (0.819 cm³ and 70.63 fruits per branch), and the lowest in the wild (0.68 cm³ and 59.75 fruits per branch). Multivariate statistical analyses differentiated populations according to their management type. Morphological diversity was higher in managed populations (0.703 ± 0.029 and 0.679 ± 0.019 in silviculture and cultivated populations, respectively) than in the wild (0.652 ± 0.016). Managed plants of M. schenckii do not show signs of depending on humans for survival and reproduction and, therefore, domestication should be considered incipient.     

Evolution under domestication of correlated traits in two edible columnar cacti in Mexico

Evolutionary Ecology - Stenocereus pruinosus and S. stellatus are columnar cacti from central Mexico, distributed in the Valle de Tehuacán and the Mixteca Baja regions. Both species have...     

Microsatellite variation in cassava (Manihot esculenta, Euphorbiaceae) and its wild relatives: further evidence for a southern Amazonian origin of domestication

Genetic variation at five microsatellite loci was used to investigate the evolutionary and geographical origins of cassava (Manihot esculenta subsp. esculenta) and the population structure of cassava's wild relatives. Two hundred and twelve individuals were sampled, representing 20 crop accessions, 27 populations of cassava's closest wild relative (M. esculenta subsp. flabellifolia), and six populations of a potentially hybridizing species (M. pruinosa). Seventy-three alleles were observed across all loci and populations. These data indicate the following on cassava's origin: (1) genetic variation in the crop is a subset of that found in the wild M. esculenta subspecies, suggesting that cassava is derived solely from its conspecific wild relative. (2) Phenetic analyses group cassava with wild populations from the southern border of the Amazon basin, indicating this region as the likely site of domestication. (3) Manihot pruinosa, while closely related to M. esculenta (and possibly hybridizing with it where sympatric), is probably not a progenitor of the crop. Genetic differentiation among the wild populations is moderately high (F:(ST) = 0.42, rho(ST) = 0.54). This differentiation has probably arisen primarily through random genetic drift (rather than mutation) following recent population divergence.     

REDUCED DROUGHT TOLERANCE DURING DOMESTICATION AND THE EVOLUTION OF WEEDINESS RESULTS FROM TOLERANCE–GROWTH TRADE‐OFFS

The increased reproductive potential, size, shoot allocation, and growth rate of weedy plants may result from reduced resource allocation to other aspects of plant growth and defense. To investigate whether changes in resource allocation occurred during domestication or the evolution of weediness, we compared the mycorrhizal responsiveness, growth, and drought tolerance of nine native ruderal, nine agriculturally weedy (four U.S. weedy and five Australian weedy), and 14 domesticated populations (eight ancient landraces and six improved cultivars) of the common sunflower (Helianthus annuus). Domesticated sunflower cultivars were less drought tolerant, but had higher plant growth and fecundity and coarser roots than wild populations. There were no changes in level of drought tolerance between improved cultivars and ancient landrace plants, but there was an increase in allocation to flowers with recent selection. Weedy populations were intermediate between domesticated cultivars and native ruderal populations for plant growth rate, root architecture, and drought tolerance. Weedy populations benefited most from mycorrhizal inoculation by having fewer wilted leaves and wetter soil. Overall, we found that trade‐offs between drought tolerance and several aspects of plant growth, including growth rate, allocation to flowering, and root architecture, govern evolution during sunflower domestication and the invasion of disturbed habitat.