Diversity and distribution of andean tubers: an agrogeographic analysis

. Andean tubers are a group of basic plants in the security and food sovereignty of Andean community for thousands of years. The conservation of the infra and interspecific diversity of these plants is a strategy for environmental adaptation rooted in the high-Andean cultural identity. Solanum tuberosum, Oxalis tuberosa, Tropaeolum tuberosum and Ullucus tuberosus, have in common that they develop edible modified stems with a wide variety of shapes, colors, and flavors, and these are cultivated in the Andean countries. The high diversity of Andean tuberous species is heterogeneously distributed and concentrated in micro-centers of diversification distributed in South American countries. The aim of this work was to determine the general distribution pattern of the four mentioned species and their agrogeographic nodes. With the coordinates of presence of these four species, registered in the GBIF platform (Global Biodiversity Information Facility), biogeographical methods were applied to model the individual traces that show the distribution pattern of each species and through the intersection of these, a generalized trace that makes visible the distribution patterns of Andean tubers, as well as their agro-geographical nodes. The greatest diversity of the four species is concentrated in these intersections, favoring domestication scenarios. Some micro-centers of diversity identified, correspond to those defined in the investigations of morphological or molecular characterizations. The main nodes were found in Peru and Ecuador between the biogeographic provinces of Puno, in the South American Transition Zone and the Yungas, from the southern Brazilian domain. The study of the geographical distribution patterns of cultivated plants allows to identify the patterns of plant exchange of the human groups involved in their management. The study of the geographical distribution patterns of cultivated plants allows to identify the patterns of plant exchange of the human groups involved in their management.

Oxalis tuberosa has been used by Andean populations for thousands of years, it has an adaptation to environments where other crops cannot survive, including tolerance to cold climates, thrives in soils with pH of 5.3 to 7.8, resistant to various pests and other phytosanitary problems (Rosero, 2010;Clavijo-P. & Pérez-M., 2014).It is probable that this species or some related ones, have been consumed and perhaps cultivated by the inhabitants of the inter-Andean valleys since the Holocene . Rosero-A. (2010) identified the south of the department of Nariño, especially the municipalities of Cumbal, Guachavéz, El Encano and Puerres, as the area of greatest diversity of this species in the department. Although the species is a material that propagates vegetatively cycle after cycle, there is evidence of variation at the phenotypic and genotypic level that should be conserved and used for the generation of new and better materials that respond to the interests of farmers, producers and consumers (Morillo et al., 2016;Clavijo-P. y Pérez-M., 2014), but conserving native germplasm to avoid its loss.
The Tropaeolum tuberosum, like O. tuberosa thrives in cold climates and is tolerant of various types of pests and diseases, but its taste is not very liked by the population due to its strong bitter taste caused by the high content of isothiocyanates derived from glucosinolates (Grau et al., 2000) which has decreased its consumption, despite presenting high nutritional and very possibly medicinal value (Leidi et al., 2018). Two possible domestication centers are proposed for this species, the highlands located between Peru and Bolivia and the Cundiboyacense savanna in Colombia, where varieties with dissimilar morphological and physiological characteristics are found (Grau et al., 2003;Tapia & Fries,2007). However, Seminario (2004), considers that the tuberization phenomenon is related to adaptations to areas with prolonged periods of drought, rare phenomena in the Colombian region. Manrique et al. (2014) identified the micro-centers of diversity by morphological characterization of 107 accessions; finding that the states of Huancavelica, Junín, Pasco and Cusco represent 62% of all Peruvian accessions (Manrique et al., 2014). In the state of Cusco, Ortega et al. (2007), analyzed the patterns of genetic diversity of cultivated and wild populations of T. tuberosum, a wide genetic diversity was found, and it was determined that wild populations are closely related to cultivated ones. These results strengthen the Cusco region as a micro center of diversity of T. tuberosum.
Ullucus tuberosus and T. tuberosum have been shown to have more than 35% starch, along with high resistance to pests, low temperatures and drought (Campos et al., 2018;Naranjo et al., 2017). Tapia & Fries (2007) consider that one of the domestication centers of U. tuberosus is Colombia, since the cultivated morphotypes present wild characteristics such as creeping growth and smaller diameter of the tubers. However, Parra-Q et al. (2012) suggest that the site of origin was in the central Andes, between Peru and Bolivia, from where it was dispersed semi-domesticated towards Colombia and later the erect growth morphotypes were domesticated that had a new wave of dispersal towards the north. In Colombia, in the departments of Boyacá and Cundinamarca, 36 accessions were morphologically and molecularly characterized and it was concluded that the populations of the center of the country correspond to the subspecies in the process of domestication, given its decumbent growth and its genetic distance with the populations of the south of the country (Parra-Q. et al., 2012).
Regarding potatoes, it is widely accepted that one of the main centers of initial domestication of potatoes is in southern Peru on the border with Bolivia 10,000 years ago (Hawkes & Ruel, 1989). tuberosum and S. phureja in Nariño, Colombia; however, it was found that neither morphological nor molecular markers can clearly distinguish the evaluated species and varieties. In fact, Huamán & Spooner (2002) morphologically characterized eight species of potatoes in Latin America and concluded that given the genetic plasticity and continuous hybridization, all the evaluated potatoes could well be classified as a single species, S. tuberosum, with eight different cultivars.
As can be seen, the high varietal and intravarietal diversity of these species has been promoted and accumulated after thousands of years of selection and management by traditional Andean farmers. However, factors such as the homogenization of agroecosystems, cultural uprooting and the globalization of the diet, endanger the future maintenance of this diversity (Malice & Baudoin, 2009); in the nineties Stephen Brush (Brush et al, 1992), and those of Karl Zimmerer, carried out several studies where they identified the factors that led to the incorporation of new varieties, but they also highlighted that some groups of peasants sought the conservation of native species, almost thirty years later Velásquez-M et al. (2016). They also point out the need to apply various actions for conservation, including the identification of agrobiodiversity zones at the local, regional and national level, to avoid genetic erosion.
The distribution of the diversity of Andean tubers is not homogeneous but is identified concentrated in micro-centers of diversity and outside of them less interspecific diversity is conserved: Various authors have identified as micro centers of diversification of these: Cajamarca, Huancavelica, Huánuco and Cusco in Perú; in Bolivia the Altiplano and La Candelaria territories; in Ecuador the provinces of Carchi and Huaconas and in Colombia in the departments of Boyacá and Nariño (García & Cadima, 2003;Seminario, 2004;Ortega et al., 2007;Parra-Q. et al. 2012;Manrique et al. 2014Fonseca et al., 2014). These micro-centers of diversification share a high intravarietal diversity, both morphological and genetic, as well as an important cultural roots of these species. The latter is possibly due in part to the fact that they occupy the same agroecological niche and the farmer generally sows them in association or in very close plots with similar management (Tapia, 2000).
Panbiogeography is a geographic approach applied to contribute to the understanding of biodiversity by identifying biotic components, individual traces, generalized traces and panbiogeographic nodes, starting from the distribution of plant and animal species (Morrone, 2004) (34) were the ones that presented the highest abundance of intersection coordinates in the country.

Discussion
According to biogeographic theory, panbiogeographic nodes imply the intersection of different ecological and biogeographic histories that can have the following interpretations: presence of local endemisms, absence of widely distributed taxa, high phylogenetic diversity and geographic affinities with other areas and boundaries or geographic or phylogenetic of taxa (Miguel-T & Escalante, 2013;Morrone, 2015b;Grehan, 2020). In this analysis, the identified nodes do not correspond to panbiogeographic nodes but to agro-geographic nodes, understanding that human beings have been decisive in the flow of seeds of cultivated plants, as well as in the selection and adaptation of their varieties (Velásquez et al., 2013).
Molecular studies confirm the highlands of Peru, departments of Huánuco, Pasco, Junín, Huancavelica, Apurímac, Ayacucho, Cusco and Puno as the domestication region of S. tuberosum; where, due to temperature fluctuations, the development of plants with growth of underground propagules is favored (Morales-G., 2007).
The first presence of potatoes in Peru dates back to 6900 years ago in the department of Lima and towards the beginning of the Formative period (3,800 years ago) in the department of Junín (Morales-G, 2007). Spooner et al. (2005) suggest that the domesticated potato comes from the wild species of the S. brevicaule complex from southern Peru, although this complex extends from Huánuco to Puno. Currently in the region of Cusco, Apurímac and Huancavelica it is common to find conservationist farmers for whom biodiversity is their lifestyle and therefore they grow 50, 100 or 300 varieties of potatoes in plots smaller than one hectare (Fonseca et al., 2014).
The Cusco region is also an important area for the conservation of the other Andean tubers. T. tuberosum registers a greater genetic and morphological diversity in the agroecosystems of this area than that conserved in the collection of the International Potato Center (Manrique et al., 2014). O. tuberosa it also presents a high diversity in the departments described, as well as in Cajamarca, Ancash and Puno (Pissard et al., 2008). Currently, the exchange between Andean tuber seed farmers has been reported between the Peruvian departments of Huánuco, Huancayo, Huancavelica, Ayacucho, Cajamarca and Cusco (Velásquez et al., 2013).
In Bolivia, the departments of La Paz and Cochabamba have been reported as micro-centers of diversity of Andean tubers in this country (García & Cadima 2003). Cochabamba is one of the regions with the greatest morphological and molecular diversity of O. tuberosa (Emshwiller & Doyle, 1998), T. tuberosum (Grau et al., 2003) and U. tuberosus (Parra-Q., 2012).
The Ecuadorian departments of Carchi, Cañar, Bolívar, Chimborazo, Cañar, and Loja, present a wide diversity of potatoes (Morales-G 2007), ullucos (Vimos et al., 1993) and Mashuas (Grau et al., 2003). In Colombia, the use of lithic tools has been reported for more than 5000 years as hoes, the edges of which have residues of starch from tubers (Aceituno-B & Rojas-M, 2012). The southeastern part of the country, mainly the municipality of Cumbal and others in the department of Nariño, are recognized micro-centers of potato diversity (Tinjacá-R. & Rodríguez-M., 2015) and ullucos (Parra-Q., 2012). In the department of Boyacá, the municipality of Ventaquemada has been identified  as one of the Colombian micro-centers. However, in our analysis the municipality of Samacá was also identified as the administrative unit where the intersection coordinates in the department concur with greater abundance. Biological diversity is concomitant to areas where there is also a high cultural diversity as a whole, they make up biocultural diversity, a key diversity in the processes of plant domestication in Mesoamerica and the Andes (Casas et al., 2017). In this sense, the identified nodes concur in areas of indigenous predominance: Quechua (Bolivia, Peru, Ecuador, and Colombia), Aimara (Peru and Bolivia), Pastos (Ecuador and Colombia), Nasa, Misak and Coconucos (Colombia); With the exception of the node in central Colombia where only remnants of the Muisca indigenous group remain (Albo et al., 2009).
The panbiographic analysis of Andean tubers offers two benefits, namely: First, it allows the identification of the geographic areas with the greatest agrobiodiversity and this in turn is important to direct protection and recovery strategies for plant genetic resources. On the other hand, it also provides evidence in the reconstruction of the history and diffusion of domestication in America, allowing temporal trans-scalarity, that is, connecting the interpretation of past events with current processes (Casas et al., 2017). The results support the hypothesis that Andean tubers were domesticated in the Peruvian highlands, from where they dispersed to the south and north following the patterns of pre-Columbian human occupations. In this sense, the history of the Andean tubers can be understood as the history and future of the Andean peoples (Viteri et al., 2020;Devaux et al., 2021;Montes et al., 2021).

Financing
This study was supported by the "Corporación Universitaria Minuto de Dios (Dirección General de Investigaciones y Centro Regional Zipaquirá)" by funding this research within the framework of the project C116-085 "Andean tubers back home: participatory conservation of tuberous species in Cundinamarca".