Susana Guillén

Brazilian and Mexican experiences in the study of incipient domestication

BackgroundStudies of domestication enables a better understanding of human cultures, landscape changes according to peoples’ purposes, and evolutionary consequences of human actions on biodiversity. This review aimed at discussing concepts, hypotheses, and current trends in studies of domestication of plants, using examples of cases studied in regions of Mesoamerica and Brazil. We analyzed trends of ethnobiological studies contributing to document processes of domestication and to establish criteria for biodiversity conservation based on traditional ecological knowledge.MethodsBased on reviewing our own and other authors’ studies we analyzed management patterns and evolutionary trends associated to domestication occurring at plant populations and landscape levels. Particularly, we systematized information documenting: ethnobotanical aspects about plant management and artificial selection mechanisms, morphological consequences of plant management, population genetics of wild and managed plant populations, trends of change in reproduction systems of plants associated to management, and other ecological and physiological aspects influenced by management and domestication.ResultsBased on the analysis of study cases of 20 native species of herbs, shrubs and trees we identified similar criteria of artificial selection in different cultural contexts of Mexico and Brazil. Similar evolutionary trends were also identified in morphology (selection in favor of gigantism of useful and correlated parts); organoleptic characteristics such as taste, toxicity, color, texture; reproductive biology, mainly breeding system, phenological changes, and population genetics aspects, maintenance or increasing of genetic diversity in managed populations, high gene flow with wild relatives and low structure maintained by artificial selection. Our review is a first attempt to unify research methods for analyzing a high diversity of processes. Further research should emphasize deeper analyses of contrasting and diverse cultural and ecological contexts for a better understanding of evolution under incipient processes of domestication.ConclusionHigher research effort is particularly required in Brazil, where studies on this topic are scarcer than in Mexico but where diversity of human cultures managing their also high plant resources diversity offer high potential for documenting the diversity of mechanisms of artificial selection and evolutionary trends. Comparisons and evaluations of incipient domestication in the regions studied as well as the Andean area would significantly contribute to understanding origins and diffusion of the experience of managing and domesticating plants.

Differential survival and growth of wild and cultivated seedlings of columnar cacti: Consequences of domestication

PREMISE OF THE STUDY Studies of domestication of cacti in the Tehuacán Valley have identified morphophysiological divergences between wild and cultivated populations. To determine whether such divergences are associated with differential survivorship in xeric and mesic environments characterizing wild and cultivated habitats, respectively, we hypothesized that seedlings from cultivated populations are less tolerant of xeric environments and that differences between wild and cultivated populations are greater in species with higher management intensity. METHODS We compared size, survivorship, and absolute and relative growth rates (AGRs, RGRs) in shade and humidity gradients of seedlings from wild and cultivated populations of Stenocereus pruinosus, S. stellatus, Polaskia chichipe, and Escontria chiotilla. These species represent a range of management intensity, from highest to lowest, respectively. KEY RESULTS Seedlings of cultivated populations were larger than those of wild populations in all species studied. The AGRs were significantly different in P. chichipe and E. chiotilla associated with management, whereas the RGRs and seedling survival were significantly different in S. pruinosus and P. chichipe throughout the shade gradient tested. We also found significant differences in seedling survival among humidity treatments in E. chiotilla and among shade treatments in P. chichipe. CONCLUSIONS Artificial selection favoring larger fruits favors larger seeds and seedlings. Seedling survivorship and growth of managed plants are generally higher in mesic environments apparently because of natural selection associated with habitat conditions. Such differences may contribute to morphophysiological divergences between wild and cultivated populations. Interspecific differences might be associated with adaptations to the natural environments where each species occurs.

Evolutionary Ethnobotanical Studies of Incipient Domestication of Plants in Mesoamerica

Human cultures that occupied the area currently known as Mesoamerica developed a broad repertory of technologies for managing the biotic resources and ecosystems of the surrounding areas they lived. These technologies emerged from early experiences and had long time, enough for leading to the first forms of agriculture of the New World. Mesoamerica is actually recognized as one of the regions where agriculture and domestication of plants originated, with nearly 10,000 years of antiquity. This chapter summarizes ethnobotanical, ecological, and evolutionary information documented in different regions of Mexico, combining different research approaches in order to understand the human motives for managing plant resources, and the ecological and evolutionary consequences of management of plants and ecosystems. We therefore analyse those processes involving domestication as part of general design of nature according to human needs and desires, occurring at the levels of plant population of particular species, but also at the level of ecosystems and landscapes. We pay particular attention in the analysis of plant species that in the Mesoamerican area have wild and domesticated populations and maintain reproductive interactions. These interactions allow exploring practices and natural processes intervening in conforming populations in which divergence populations guided by natural and artificial selection and other evolutionary forces are occurring. Because natural processes continually weaken the human activities, the divergence is relatively slight and we have therefore called these processes incipient domestication. We analyse the cases of traditional greens called ‘quelites’ such as Anoda cristata and Crotalaria pumila in which people distinguish favourable and unfavourable morphs and practice artificial selection resulting in the abundance of the favourable morphs in areas more intensively managed. Similarly, some examples are analysed of trees (Leucaena esculenta, Crescentia spp. Spondias purpurea, S. mombin, and Sideroxylon palmeri), agaves (Agave inaequidens and A. hookeri), and columnar cacti (Escontria chiotilla, Myrtillocactus schenckii, Pachycereus hollianus, Polaskia spp., Stenocereus spp.). In the cases studied we analysed divergence in morphology, reproduction, population genetics, and germination patterns, among other features, between wild, silvicultural managed and cultivated populations. These case studies allow demonstrating that evolutionary divergence influenced by humans occurs not only under agriculture but also under silvicultural management and we hypothesize that domestication under silvicultural systems could have leaded to the origins of agriculture.

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.

Evolutionary Ecology and Ethnobiology

Evolutionary ethnobiology studies the evolutionary processes derived from interactions between humans and biotic elements (mainly plants, animals, fungi, and some micro-organisms) that form part of the ecosystems the manage. Such interactions may have evolutionary consequences on: (1) the organisms interacting with humans, (2) the humans themselves, their culture and societies, and (3) the managed ecosystems and landscapes. This perspective indicates that questions of evolutionary ethnobiology are eminently social-ecological complex problems, and their understanding therefore require interdisciplinary research approaches combining perspectives from a broad spectrum of social and ecological disciplines. We summarise in this chapter conceptual and methodological approaches for analysing the interactions between humans and plants and animals, their domestication and forms to evaluate their morphological, physiological, and genetic consequences. In addition, we analyse the repercussion of domestication on settled life and the arising of civilisation, and their current influence on social organisation and culture. Finally, we analyse the process of modelling of landscapes that predominate on most of the surface of the Earth, particularly those intentional forms that conform what we call landscape domestication. We conclude that evolution on each of these dimensions influence the others and, therefore, the integrated view is necessary for a holistic comprehension of evolutionary processes influenced by humans. In addition, we conclude that the theoretical construction in this field may substantially help in designing sustainable management strategies. Concepts and methods referred to are those adopted and constructed by our own research group for analysing main problems in relation to the main aspects mentioned of evolutionary ethnobiology.

Consequences of domestication of Stenocereus stellatus in seed size and germination in a water stress gradient

Stenocereus stellatus is a columnar cactus species of cultural and ecological importance in the TehuacanValley; their fruits are collected from wild populations but plants of this species are also silviculturally managed and cultivated in agroforestry systems. Previous studies documented morpho-physiological and genetic divergences between wild and managed populations caused by artifi cial selection and limitations to gene fl ow; nevertheless, the documented divergences could also be infl uenced by differences in germination and survivorship patterns of wild and cultivated seedlings in forests and managed environments. We hypothesized that artifi cial selection in favor of larger fruits may in turn favor larger seeds in cultivated plants that also could have higher germination rates in high humidity conditions, but more susceptible to water stress than seeds from wild plants. We evaluated fruit and seed weight and germination rates in a water stress gradient (0.0, -0.2, -0.4, -0.6, -0.8, and -1.0 Megapascals) in wild and cultivated populations. Cultivated fruits and seeds were signifi cantly heavier (54.616 ± 1.547 g, 0.190 ± 0.017 g, respectively) than wild fruits and seeds (37.023 ± 1.122 g, 0.153 ± 0.005 g, respectively). Deviance analysis showed signifi cant differences in starting germination (X2 = 1639.0, df = 4; X2 = 236.31, df = 1, respectively) and velocity (X2 = 20.91, df = 4) associated to management and water potential (cultivated seeds were more susceptible to water stress than wild ones). Artifi cial selection favoring larger fruits has apparently infl uenced indirectly seed size and differences; in wild and managed environments could have infl uenced differences of seed susceptibility to water stress.

Ethnobotany in Mexico: History, Development, and Perspectives

Ethnobotany is defined as the study of the traditional botanical knowledge of different cultures, the techniques utilized in the use and management of plant resources, and the place they have in their cultural Cosmo vision. This study aimed to review the development and perspectives of ethnobotany in Mexico, based on an extensive review of all ethnobotanical studies showed at the Mexican Botanical Congress (MBC), the main forum of ethnobotanical studies in Mexico, between 1963 and 2010. We systematized a total of 897 works, identifying their progressive increase in the generation of investigative papers up until 1990, then a decrease until 1995 and a new increase from 1995 to the present. The main Mexican institutions studying ethnobotany are the Universidad Nacional Autonoma de Mexico, Universidad Autonoma Chapingo, Instituto Politecnico Nacional, Universidad Autonoma Metropolitana, and the Universidad Autonoma de Nuevo Leon, which produced nearly half of all the studies recorded. The best represented cultural groups studied were the Maya, Nahua, Otomi, Totonac, and Mixtec, studied under the predominant approach of descriptive ethnobotany. Ethnobotany in Mexico is in a stage of growth and therefore in the phase of consolidating its approaches, particularly in the areas of ecological, economic, quantitative, and evolutionary ethnobotany. In order to achieve the development of sustainable management strategies of plant resources, it is of the highest priority to consolidate ethnobotanical research and direct it towards the analysis of environmental degradation and solutions.