The odd-man-out Project

Tackling the Old Riddle of the Low Plant Diversity of Tropical Africa

The Odd-Man-Out pattern describes the presumed lower plant diversity of tropical Africa compared to other tropical regions of the world: the Neotropics, Madagascar, and tropical Asia. This pattern has been explained by historical biodiversity loss via past climatic instability and higher extinction rates, however this hypothesis has not been thoroughly tested. In this project, we aim to test this long-standing hypothesis focusing on the large angiosperm family Euphorbiaceae, which is a notable odd-man-out example with many of its genera showing lower species diversity in tropical Africa.

We will use the HybSeq target sequencing approach (hybrid enrichment with genome skimming) to sequence 431 low-copy nuclear genes. These genomic data will allow us to infer phylogenetic relationships and lineage divergence times of the selected clades. Correlations between diversification rates with clade age, major climatic and geological events, phenotypic traits, and the geographical space available to lineages over time, will be tested using time-dependent, paleoenvironmental-dependent, and trait-dependent birth-death models.

Our project will contribute to reduce the gap in floristic and phylogenetic knowledge in the Afrotropics. By focusing on a broad phylogenetic range of genera varying in species richness, growth forms, traits, and habitats, rather than on a single monophyletic group (e.g., a genus), we expect to obtain a more complete picture of the evolutionary dynamics of tropical lineages in Africa and attempt to explain the origins and drivers behind the odd-man-out pattern. We will also contribute to the alpha-taxonomy, floristic knowledge, and conservation status of many poorly known African clades and regions.

Understanding the Odd-Man-Out pattern is also relevant to understanding the global "latitudinal species gradient", a pattern that has sparked a long-standing debate among ecologists and evolutionary biologists. Our results will also contribute to overcoming two relevant scientific and societal challenges: a better understanding of the effect of environmental drivers on changes in biodiversity, and the continuing loss of plant diversity.

Extinction selectivity is expected to be based on species intrinsic characteristics. Recent studies have demonstrated that the loss of endangered species results in a disproportionate loss of Evolutionary History, because anthropogenic extinction, unlike random background extinction, often targets species-poor and geologically old taxa. These taxa typically contain unique characteristics and functions, which alone represent millions of years of trait evolution. Thus, considerable effort is being put into identifying these taxa, known as "Evolutionarily Distinct and Globally Endangered" (EDGE) species.

Tropical African Euphorbiaceae

Tropical African Euphorbiaceae harbours numerous potentially old, species-poor lineages, exhibiting remarkable variation in phenotypic characteristics, which could become a conservation EDGE priority. This situation could be repeated in other Afrotropical plant families, emphasizing the need for intensified inventorying, collection and systematic efforts in this continent. Our approach, if successful, could be used as a model in other tropical African plant lineages exhibiting, or not, the Odd-Man-Out pattern.

Acknowledgments

Funding: Project Grant PID2019-108109GB-100 funded by MCIN/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”

Funding and Participating Institutions