Evidence for hawkmoth pollination in the chiropterophilous African baobab ( Adansonia digitata )

Insect-flower interactions, ecosystem functions, and restoration ecology in the northern Sahel: current knowledge and perspectives

Actions for ecological restoration under the Great Green Wall (GGW) initiative in the northern Sahel have been plant focused, paying scant attention to plant-animal interactions that are essential to ecosystem functioning. Calls to accelerate implementation of the GGW make it timely to develop a more solid conceptual foundation for restoration actions. As a step towards this goal, we review what is known in this region about an important class of plant-animal interactions, those between plants and flower-visiting insects. Essential for pollination, floral resources also support insects that play important roles in many other ecosystem processes. Extensive pastoralism is the principal subsistence mode in the region, and while recent analyses downplay the impact of livestock on vegetation dynamics compared to climatic factors, they focus primarily on rangeland productivity, neglecting biodiversity, which is critical for long-term sustainability. We summarise current knowledge on insect-flower interactions, identify information gaps, and suggest research priorities. Most insect-pollinated plants in the region have open-access flowers exploitable by diverse insects, an advantageous strategy in environments with low productivity and seasonal and highly variable rainfall. Other plant species have diverse traits that constrain the range of visitors, and several distinct flower types are represented, some of which have been postulated to match classical "pollination syndromes". As in most ecosystems, bees are among the most important pollinators. The bee fauna is dominated by ground-nesting solitary bees, almost all of which are polylectic. Many non-bee flower visitors also perform various ecosystem services such as decomposition and pest control. Many floral visitors occupy high trophic levels, and are indicators of continued functioning of the food webs on which they depend. The resilience of insect-flower networks in this region largely depends on trees, which flower year-round and are less affected by drought than forbs. However, the limited number of abundant tree species presents a potential fragility. Flowering failure of a crucial "hub" species during exceptionally dry years could jeopardise populations of some flower-visiting insects. Furthermore, across Sahelian drylands, browsers are increasingly predominant over grazers. Although better suited to changing climates, browsers exert more pressure on trees, potentially weakening insect-flower interaction networks. Understanding the separate and combined effects of climate change and land-use change on biotic interactions will be key to building a solid foundation to facilitate effective restoration of Sahelian ecosystems.

Chromosome-level baobab genome illuminates its evolutionary trajectory and environmental adaptation

Baobab (Adansonia digitata) is a long-lived tree endemic to Africa with economic, ecological, and cultural importance, yet its genomic features are underexplored. Here, we report a chromosome-level reference genome anchored to 42 chromosomes for A. digitata, alongside draft assemblies for a sibling tree, two trees from distinct locations in Africa, and A. za from Madagascar. The baobab genome is uniquely rich in DNA transposons, which make up 33%, while LTR retrotransposons account for 10%. A. digitata experienced whole genome multiplication (WGM) around 30 million years ago (MYA), followed by a second WGM event 3-11 MYA, likely linked to autotetraploidy. Resequencing of 25 trees identify three subpopulations, with gene flow across West Africa distinct from East Africa. Gene enrichment and fixation index (Fst) analyses show baobab retained multiple circadian, flowering, and light-responsive genes, which likely support longevity through the UV RESISTANCE LOCUS 8 (UVR8) pathway. In sum, we provide genomic resources and insights for baobab breeding and conservation.

Pollination syndromes and the origins of floral traits

BACKGROUND

A general view in the study of pollination syndromes is that floral traits usually represent convergent floral adaptations to specific functional pollinator groups. However, the definition of convergence is elusive and contradictory in the literature. Is convergence the independent evolution of either the same trait or similar traits with the same function? A review of the concept of convergence in developmental biology and phylogenetic systematics may shed new light in studies of pollination syndromes.

SCOPE

The aims of this article are (1) to explore the notion of convergence and other concepts (analogy, homoplasy and parallelism) within the theory and practice of developmental evolution and phylogenetic systematics; (2) to modify the definitions of syndromes in order to embrace the concepts of analogy and convergence; (3) to revisit the bat pollination syndrome in the context of angiosperm phylogeny, with focus on the showy 'petaloid' organs associated with the syndrome; (4) to revisit the genetic-developmental basis of flower colour; (5) to raise evolutionary hypotheses of floral evolution associated with the bat pollination syndrome; and (6) to highlight some of the current frontiers of research on the origin and evolution of flowers and its impact on pollination syndrome studies in the 21st century.

CONCLUSIONS

The inclusion of the concepts of analogy and convergence within the concept of syndromes will constitute a new agenda of inquiry that integrates floral biology, phylogenetic systematics and developmental biology. Phyllostomid and pteropodid bat pollination syndrome traits in eudicots and monocots represent cases of analogous and convergent evolution. Pollination syndromes are a multivariate concept intrinsically related to the understanding of flower organogenesis and evolution. The formulation of hypotheses of pollination syndromes must consider the phylogenetic levels of universality for both plant and animal taxa, flower development, genetics, homology and evolution, and a clear definition of evolutionary concepts, including analogy, convergence, homoplasy and parallelism.