Madagascan baobab trees.
The baobab or 'upside down' trees, mostly of Madagascar, are an interesting example of how species radiate and evolve to fit different available niches in their immediate environment, but the genus also contains some examples of remarkable migrations and one example of the founder effect in evolution where a new species can arise by going through a very narrow genetic bottle neck where a new population is founded on an atypical sample of the parent species genome.
The evolution of the genus also includes examples of how, as species diverge, there is a period during which they can still hybridize and how hybrids themselves can be the foundation of new species.
Tell me all about baobab trees (Andersonia) including their evolution and distribution, please. Baobab trees, belonging to the genus Andersonia, are among the most iconic and recognizable trees in the world, known for their massive trunks and unique appearance. There are nine species of baobabs, which are distributed across Africa, Madagascar, and Australia. Here's a detailed overview of their characteristics, evolution, and distribution:
Characteristics
Evolution
- Appearance:
- Trunk: Baobabs have massive, cylindrical trunks that can reach diameters of up to 10 meters. These trunks are often hollow, providing habitats for various animals and storage for water.
- Leaves: Baobabs have palmately compound leaves, which means the leaves are arranged like the fingers of a hand. They typically drop their leaves during the dry season.
- Flowers: The trees produce large, white flowers that open at night and are often pollinated by bats and moths. These flowers have a distinctive, often unpleasant smell.
- Fruit: The fruit of baobabs is large, woody, and often referred to as "monkey bread." It contains a dry, powdery pulp rich in vitamin C.
- Longevity: Baobabs are known for their long lifespan, with some individuals estimated to be over a thousand years old. However, dating the exact age of baobabs can be challenging due to their unique growth patterns.
Distribution
- Origins: The baobab genus Andersonia is believed to have originated in Africa. Genetic studies suggest that the ancestor of modern baobabs appeared around 20 million years ago.
- Diversification: The spread and diversification of baobab species are linked to continental drift and climate changes. As Africa and Madagascar separated from other landmasses, baobabs evolved into distinct species adapted to their specific environments.
- Adaptations: Baobabs have evolved several adaptations to survive in arid environments, such as their ability to store water in their trunk and thick bark, which helps protect them from fire and drought.
Ecological and Cultural Significance
- Africa:
- Species: There are two main species in mainland Africa: Andersonia digitata (the African baobab) and Andersonia kilima (the hill baobab).
- Range: A. digitata is widespread across the African savannah and can be found in countries from Senegal in the west to Kenya and Tanzania in the east.
- Madagascar:
- Species: Madagascar is home to six endemic species: Andersonia grandidieri, Andersonia suarezensis, Andersonia madagascariensis, Andersonia perrieri, Andersonia rubrostipa, and Andersonia za.
- Range: These species are mostly confined to specific regions of Madagascar, with some like A. grandidieri being found in the west and others like A. suarezensis in the north.
- Australia:
- Species: Australia has one species, Andersonia gregorii, commonly known as the boab.
- Range: A. gregorii is found in the northwestern parts of Australia, particularly in the Kimberley region.
- Ecology: Baobabs play a crucial role in their ecosystems, providing food and shelter for a variety of wildlife. The flowers, fruit, and leaves are consumed by animals and humans.
- Cultural Importance: Baobabs are deeply ingrained in the cultures of the regions where they grow. They are often featured in folklore and traditional medicine. In some African communities, baobabs are considered sacred and are used as meeting places and landmarks.
Conservation
Baobabs face threats from climate change, deforestation, and human activity. Some species, particularly in Madagascar, are listed as endangered due to habitat loss and over-exploitation. Conservation efforts are focused on protecting these unique trees through habitat preservation, legal protection, and community education initiatives.
In summary, baobabs are remarkable trees with a fascinating evolutionary history and significant ecological and cultural roles in their native regions. Their unique adaptations have allowed them to thrive in some of the harshest environments on Earth.
African Baobab, Adansonia digitata
How baobab trees evolved and diversified is the subject of a research paper by an international group of scientists which included husband and wife, Professor Andrew Leitch of Queen Mary University, London, UK and Dr. Ilia Leitch of the Royal Botanic Garden, Kew, Surrey, UK, and scientists from Wuhan Botanical Garden, China, the University of Antananarivo, Madagascar, the Technical University of Denmark, Lyngby, Denmark and the East African Herbarium, National Museums of Kenya, Nairobi, Kenya. Their research findings are the subject of an open access paper, in Nature and a new release from Queen Mary University:
The iconic baobabs, also known as upside-down trees, or the tree of life, have much cultural significance, inspiring innumerable arts, folklore, and traditions. The new research published in Nature reveals a remarkable example of species radiation in Madagascar followed by long distance dispersal to Africa and Australia. With speciation, an astonishing divergence of pollination mechanisms evolved, that exploit hawkmoths, bats and lemurs for a simple nectar reward.Technical details are in the team's open access paper in Naature:
The charismatic baobabs have astonishing growth forms, reaching huge sizes with massive trunks, but apparently diminutive crowns, giving them their iconic appearance as upside-down trees. The team first assembled the genomes of the eight recognised species and worked out their patterns of speciation. They then analysed the genomes themselves and discovered that the ancestor of all eight species most likely radiated in Madagascar, where they made hybrids, before two species underwent astonishing long-distance travels, one to Africa and another to Australia. In that radiation the species evolved different flower structures to attract hawkmoths, lemurs and bats.
We were delighted to be involved in this project uncovering patterns of baobab speciation in Madagascar followed by the astonishing long-distance dispersal of two species, one to Africa and another to Australia. This was accompanied by the evolution of some fascinating pollination syndromes involving hawkmoths, lemurs and bats.
Professor Andrew R. Leitch, co-lead author
School of Biological and Chemical Sciences
Queen Mary University of London, London, UK.This work has uncovered new insights into the patterns of speciation in baobabs and shows how climate change has influenced baobab distribution and speciation patterns over millions of years.
Dr. Ilia J. Leitch, co-lead author
Royal Botanic Garden, Kew, Surrey, UK.The study was carried by international collaboration between Wuhan Botanical Garden (China), Royal Botanic Gardens (Kew, UK), University of Antananarivo (Madagascar) and Queen Mary University of London (UK).We were delighted to be involved in this project uncovering patterns of baobab speciation in Madagascar before the astonishing long-distance dispersal of two species, one to Africa and another to Australia. The work also provides new insights into how climate change has influenced baobab distribution and speciation patterns over millions of years.
Professor Andrew R and Dr Ilia J Leitch.
AbstractWhat we have illustrated in these baobab trees are a number of the basic principles evolution. We have radiation into vacant niches, we have diversification under the influence of environmental factors such as climate change; we have an example of a new species arising by hybridization; we have the predictable inter breeding between species in the process of diversifying before barriers to hybridization has evolved. We also have an example of the narrow genetic bottleneck and the founder effect of a long-distance dispersal by ocean-born seed and lastly we have examples of co-evolution between flowering plants and pollinators.
The baobab trees (genus Adansonia) have attracted tremendous attention because of their striking shape and distinctive relationships with fauna1. These spectacular trees have also influenced human culture, inspiring innumerable arts, folklore and traditions. Here we sequenced genomes of all eight extant baobab species and argue that Madagascar should be considered the centre of origin for the extant lineages, a key issue in their evolutionary history2,3. Integrated genomic and ecological analyses revealed the reticulate evolution of baobabs, which eventually led to the species diversity seen today. Past population dynamics of Malagasy baobabs may have been influenced by both interspecific competition and the geological history of the island, especially changes in local sea levels. We propose that further attention should be paid to the conservation status of Malagasy baobabs, especially of Adansonia suarezensis and Adansonia grandidieri, and that intensive monitoring of populations of Adansonia za is required, given its propensity for negatively impacting the critically endangered Adansonia perrieri.
Main
The genus Adansonia, better known as the baobabs and ‘mother of the forest’1, has captivated botanists, tourists, naturalists and passers-by for centuries. Probably the earliest record of humans marvelling at these amazing trees can be traced back to the Ancient Egyptians, around 2,300 BC (ref. 1). With their grotesque appearance, enormous size1, reputed longevity4 and diverse uses5, baobabs have become one of the most charismatic species on our planet. Embedded in folklore and tradition, baobabs have inspired innumerable pieces of art and have been associated with human settlements and cultures over millennia6,7.
Adansonia (family Malvaceae, subfamily Bombacoideae) comprises eight morphologically distinct species8,9. The extant geographic distribution of baobabs is unusual, with one tetraploid species, Adansonia digitata (2n = 4x = 168), which is widespread across continental Africa, one diploid species, Adansonia gregorii (2n = 2x = 88), restricted to Northwestern Australia, and six diploid species (2n = 2x = 84, 88) which are endemic to Madagascar3 (Fig. 1a). A substantial body of research has detailed the natural history of Adansonia, including its taxonomy, ethnobotany, ecology and physiology1,8. All but A. digitata are listed in The IUCN Red List of Threatened Species, 2023, with three of the Malagasy species threatened with extinction (Adansonia perrieri classified as critically endangered and Adansonia grandidieri and Adansonia suarezensis as endangered). The remaining Malagasy species are now listed as being of least concern but their declining populations indicate that more rigorous conservation strategies are required to ensure the long-term survival of these culturally and globally important species. For that to happen, a detailed understanding of the genetics of baobabs is urgently needed.Here we present high-quality, chromosomal-level genome assemblies for all eight baobab species (Supplementary Fig. 1). Using these data together with ecological analyses, we uncover the evolutionary history of this genus, including its origin, diversification, population history and patterns of interspecific hybridization. Our findings provide valuable insights for developing effective and biologically informed conservation strategies for these spectacular trees in a changing world10.Fig. 1: Geographic distribution and phylogenetic relationships between species of Adansonia.
a, The distribution of eight baobab species and their conservation status in IUCN. The coloured patches represent the occurrence of each baobab species. b, A maximum-likelihood tree from the concatenation of 999 SCN genes. Median ages of the nodes are shown and a timescale is provided at the bottom; grey horizontal bars show 95% CIs of estimated divergence dates between lineages. The geographic occurrence of the Adansonia species is designated: Af, African lineage; Au, Australian lineage and Malagasy species. c, Coalescence analyses of 999 concatenated SCN genes. Summary of the proportion of gene tree topologies using either SCN genes (that is, gene-based) or synteny-guided genomic blocks. d, Maximum-likelihood phylogenetic relationships of Adansonia inferred from analysing concatenated synteny-guided genomic blocks. e, The Adansonia phylogeny based on CNVs (calculated as a pairwise edit distance of duplications and deletions). A. gregorii was selected for the identification of CNVs to circumvent any potential bias caused by using species with a closer phylogenetic relationship as the reference. f, The proportions of conflicting maximum-likelihood gene tree topologies. The acronyms used for the species are as in a. Numbers represent the percentage of trees with the given topology (SCN gene dataset/synteny-guided genomic blocks). The topologies are sketched to show the different placements of each lineage, regardless of the branch length.
Wan, JN., Wang, SW., Leitch, A.R. et al.
The rise of baobab trees in Madagascar. Nature (2024). https://doi.org/10.1038/s41586-024-07447-4
Copyright: © 2024 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
And all happening over a period of some 21 million years from an original species of the Malvaceae family on a large island which arose some 21 million years before creationists believe Earth existed.
So, plenty there for creationists to misrepresent, lie about or ignore...
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