Adaptations and evolution of a heritable leaf nodule symbiosis between Dioscorea sansibarensis and Orrella dioscoreae

Various plant species establish intimate symbioses with bacteria within their aerial organs. The bacteria are contained within nodules or glands often present in distinctive patterns on the leaves in what is commonly referred to as leaf nodule symbiosis. We describe here a highly specific symbiosis between a wild yam species from Madagascar, Dioscorea sansibarensis and bacteria of the species Orrella dioscoreae. Using whole-genome sequencing of plastids and bacteria from wild-collected samples, we show phylogenetic patterns consistent with a dominant vertical mode of transmission of the symbionts. Unique so far among leaf nodule symbioses, the bacteria can be cultured and are amenable to comparative transcriptomics, revealing a potential role in complementing the host’s arsenal of secondary metabolites. We propose a recent establishment of a vertical mode of transmission in this symbiosis which, together with a large effective population size explains the cultivability and apparent lack of genome reductive evolution in O. dioscoreae. We leverage these unique features to reveal pathways and functions under positive selection in these specialized endophytes, highlighting the candidate mechanisms enabling a permanent association in the phyllosphere

The yams (Dioscorea spp.) of Madagascar: wild endemic and cultivated species; diversity, perception, nutritional value, and sustainable management

Endemic and introduced species of Malagasy yams (Dioscorea spp.) have been studied in the dry western area (Menabe central, near Morondava) where diversity is high, taking into account the occurrence of new species recently described. A comparison with a humid area of the eastern slopes of the country (around Brickaville) shows a striking difference in terms of diversity. However, in the humid area, the cultivated yams (especially Dioscorea alata) introduced by the fi rst Indo-Malay settlers are abundant in shifting cultivations, together with the wild species, and the various cultivars have been maintained thanks to a sociocultural system that implies an obligation of replanting the head of the tuber after cropping. Such an agro-ecosystem has a global production of the same order of magnitude as those of central Africa. Densities of the different species of yams have been measured on plots of the study areas. The sustainable utilization of the various yam species may differ, especially in the dry area, where regeneration occurs when pieces of broken tubers are left after harvesting, and the soil is subject to important restructuration due to frequent digging of holes for cropping. Local knowledge and traditions related to yams have been studied in villages of the two study areas. The yam tubers have been analysed to determine nutritional value, and comparative tests related to taste (hedonic value) conducted in various places, including Antananarivo, for cross-cultural and sensory comparisons. The results of this study, implying a possible introduction of new cultivated yam species, are discussed in terms of species differentiation in various bioclimatic areas and according to the specificity of the agro-ecosystemNous comparons la richesse en espèces endémiques d'ignames (Dioscorea spp.) d'une région de Madagascar au climat sec (Menabe central, prés de Morondava), où les formes sauvages sont particulièrement diversifiées et incluent des espèces nouvellement décrites, avec celle du versant oriental humide (région de Brickaville). Si, dans la zone humide, on observe une moindre diversité des formes endémiques que dans la zone sèche, en revanche l'introduction ancienne d'espèces cultivées (en particulier Dioscorea alata, par les premiers migrants indo-malais ) et la diversité des cultivars actuels dont le système social exige la remise en terre de la tête du tubercule après récolte, aboutit à des agro-écosystèmes ayant une production du même ordre de grandeur que ceux d'Afrique centrale. Les densités des différentes espèces d'ignames ont été mesurées afin de pouvoir évaluer, en fonction de leur mode d'utilisation, les possibilités de gestion durable des peuplements naturels des régions sèches et de ceux des jachères des régions humides où les formes introduites sont maintenues en parallèle avec des peuplements d'espèces indigènes. Dans les forêts sèches, la récolte des tubercules des espèces endémiques entraîne une restructuration du sol et une régénération des ignames lorsque des morceaux des tubercules restent en terre ; toutefois l'impact des prélèvements dans le milieu naturel diffère considérablement selon les espèces. Les connaissances locales et les utilisations de ces différentes formes d'ignames ont été comparées en fonction des résultats d'enquêtes participatives. Les tubercules des différentes espèces de ces deux régions ont été analysés pour déterminer leur valeur nutritionnelle. Enfin des tests de dégustation ont permis de comparer, en fonction de la sensibilité gustative, les valeurs hédoniques attribuées à ces tubercules dans différents contextes socioculturels incluant celui de la capitale, Antananarivo. Les possibilités d'introduction ou de mises en culture d'espèces qui, jusqu'à présent, ne faisaient l'objet que de ramassage dans les milieux naturels ou transformés, ont été examinées en fonction de ces résultats et des modes de gestion propres à chaque agro-écosystème

Madagascar’s extraordinary biodiversity: Threats and opportunities

Madagascar's unique biota is heavily affected by human activity and is under intense threat. Here, we review the current state of knowledge on the conservation status of Madagascar's terrestrial and freshwater biodiversity by presenting data and analyses on documented and predicted species-level conservation statuses, the most prevalent and relevant threats, ex situ collections and programs, and the coverage and comprehensiveness of protected areas. The existing terrestrial protected area network in Madagascar covers 10.4% of its land area and includes at least part of the range of the majority of described native species of vertebrates with known distributions (97.1% of freshwater fishes, amphibians, reptiles, birds, and mammals combined) and plants (67.7%). The overall figures are higher for threatened species (97.7% of threatened vertebrates and 79.6% of threatened plants occurring within at least one protected area). International Union for Conservation of Nature (IUCN) Red List assessments and Bayesian neural network analyses for plants identify overexploitation of biological resources and unsustainable agriculture as themost prominent threats to biodiversity. We highlight five opportunities for action at multiple levels to ensure that conservation and ecological restoration objectives, programs, and activities take account of complex underlying and interacting factors and produce tangible benefits for the biodiversity and people of Madagascar

Madagascar’s extraordinary biodiversity: Evolution, distribution, and use

Madagascar's biota is hyperdiverse and includes exceptional levels of endemicity. We review the current state of knowledge on Madagascar's past and current terrestrial and freshwater biodiversity by compiling and presenting comprehensive data on species diversity, endemism, and rates of species description and human uses, in addition to presenting an updated and simplified map of vegetation types. We report a substantial increase of records and species new to science in recent years; however, the diversity and evolution of many groups remain practically unknown (e.g., fungi and most invertebrates). Digitization efforts are increasing the resolution of species richness patterns and we highlight the crucial role of field- and collections-based research for advancing biodiversity knowledge and identifying gaps in our understanding, particularly as species richness corresponds closely to collection effort. Phylogenetic diversity patterns mirror that of species richness and endemism in most of the analyzed groups. We highlight humid forests as centers of diversity and endemism because of their role as refugia and centers of recent and rapid radiations. However, the distinct endemism of other areas, such as the grassland-woodland mosaic of the Central Highlands and the spiny forest of the southwest, is also biologically important despite lower species richness. The documented uses of Malagasy biodiversity are manifold, with much potential for the uncovering of new useful traits for food, medicine, and climate mitigation. The data presented here showcase Madagascar as a unique living laboratory for our understanding of evolution and the complex interactions between people and nature. The gathering and analysis of biodiversity data must continue and accelerate if we are to fully understand and safeguard this unique subset of Earth's biodiversity

Les ignames (Dioscorea spp.) de Madagascar : espèces endémiques et formes introduites ; diversité, perception, valeur nutritionnelle et systèmes de gestion durable

The yams (Dioscorea spp.) of Madagascar : wild endemic and cultivated species ; diversity, perception, nutritional value, and sustainable management. — Endemic and introduced species of Malagasy yams (Dioscorea spp.) have been studied in the dry western area (Menabe central, near Morondava) where diversity is high, taking into account the occurrence of new species recently described. A comparison with a humid area of the eastern slopes of the country (around Brickaville) shows a striking difference in terms of diversity. However, in the humid area, the cultivated yams (especially Dioscorea alata) introduced by the fi rst Indo-Malay settlers are abundant in shifting cultivations, together with the wild species, and the various cultivars have been maintained thanks to a sociocultural system that implies an obligation of replanting the head of the tuber after cropping. Such an agro-ecosystem has a global production of the same order of magnitude as those of central Africa. Densities of the different species of yams have been measured on plots of the study areas. The sustainable utilization of the various yam species may differ, especially in the dry area, where regeneration occurs when pieces of broken tubers are left after harvesting, and the soil is subject to important restructuration due to frequent digging of holes for cropping. Local knowledge and traditions related to yams have been studied in villages of the two study areas. The yam tubers have been analysed to determine nutritional value, and comparative tests related to taste (hedonic value) conducted in various places, including Antananarivo, for cross-cultural and sensory comparisons. The results of this study, implying a possible introduction of new cultivated yam species, are discussed in terms of species differentiation in various bioclimatic areas and according to the specificity of the agro-ecosystem.Nous comparons la richesse en espèces endémiques d’ignames (Dioscorea spp.) d’une région de Madagascar au climat sec (Menabe central, près de Morondava), où les formes sauvages sont particulièrement diversifiées et incluent des espèces nouvellement décrites, avec celle du versant oriental humide (région de Brickaville). Si, dans la zone humide, on observe une moindre diversité des formes endémiques que dans la zone sèche, en revanche l’introduction ancienne d’espèces cultivées (en particulier Dioscorea alata, par les premiers migrants indo-malais) et la diversité des cultivars actuels dont le système social exige la remise en terre de la tête du tubercule après récolte, aboutit à des agro-écosystèmes ayant une production du même ordre de grandeur que ceux d’Afrique centrale. Les densités des différentes espèces d’ignames ont été mesurées afin de pouvoir évaluer, en fonction de leur mode d’utilisation, les possibilités de gestion durable des peuplements naturels des régions sèches et de ceux des jachères des régions humides où les formes introduites sont maintenues en parallèle avec des peuplements d’espèces indigènes. Dans les forêts sèches, la récolte des tubercules des espèces endémiques entraîne une restructuration du sol et une régénération des ignames lorsque des morceaux des tubercules restent en terre ; toutefois l’impact des prélèvements dans le milieu naturel diffère considérablement selon les espèces. Les connaissances locales et les utilisations de ces différentes formes d’ignames ont été comparées en fonction des résultats d’enquêtes participatives. Les tubercules des différentes espèces de ces deux régions ont été analysés pour déterminer leur valeur nutritionnelle. Enfin des tests de dégustation ont permis de comparer, en fonction de la sensibilité gustative, les valeurs hédoniques attribuées à ces tubercules dans différents contextes socioculturels incluant celui de la capitale, Antananarivo. Les possibilités d’introduction ou de mises en culture d’espèces qui, jusqu’à présent, ne faisaient l’objet que de ramassage dans les milieux naturels ou transformés, ont été examinées en fonction de ces résultats et des modes de gestion propres à chaque agro-écosystème.Harimanga Jeannoda Vololoniaina, Razanamparany Julia, Rajaonah Mamy Tiana, Monneuse Marie-Odile, Hladik Annette, Hladik C.M. Les ignames (Dioscorea spp.) de Madagascar : espèces endémiques et formes introduites ; diversité, perception, valeur nutritionnelle et systèmes de gestion durable. In: Revue d'Écologie (La Terre et La Vie), tome 62, n°2-3, 2007. pp. 191-207

Dioscoreaccae, yams, ovy, oviala, angona

A new description of the Dioscoreaceae of Madagascar including several recently discovered species

Wild edible yams from Madagascar: New insights into nutritional composition support their use for food security and conservation.

Yams ( species) are an important food resource in Madagascar, where both cultivated winged yam ( ) and wild edible yams are consumed. However, there is limited knowledge on the nutrient composition of wild edible yams in Madagascar, and on how they compare with the cultivated winged yam. Therefore, in this study, nine wild edible yam species, one with two subspecies from Madagascar ( , , , , , , subsp. and subsp. , , and species Ovy valiha), were analyzed for their nutrient composition, compared with cultivated . They include 6/6 of the most favored wild edible yam species in Madagascar. New nutrient composition data (protein, carbohydrate/starch, energy, lipid, β‐carotene, and minerals) are presented for these nine wild edible yam species. The results show that they contain comparable levels of lipids and starch to , but none are better sources of protein than . The results show that contains a significantly higher β‐carotene content when compared to all other edible yams analyzed, and that , , and subsp. have a higher calcium content than cultivated , while all nine wild edible yam species analyzed contain a higher iron content, compared to cultivated . The nutrient composition data presented could provide new incentives to conserve wild edible yams and inform on strategies to select species for sustainable cultivation and use, providing opportunities to enhance future food security in Madagascar