Biology subjects

Hardy, O. J.

Publications and source records attributed to Hardy, O. J..

4 recordsLinked to original sources

bioRxiv2025

Phylogenetic biome niche conservatism underlies the evolution of forest paleoendemic legume trees in tropical Africa

Niche conservatism is prevalent during the evolution of plant lineages. However, inferring biome niche lability and its impact on tropical tree species diversification is currently limited. To better understand biome niche lability and its effect on diversification rates, we analyzed an endemic lineage of African tropical trees, testing whether biome niche type (forest vs savanna) and biome lability are non-randomly distributed. We reconstructed a time-calibrated phylogeny of the Berlinia clade (16 genera, ca 201 species) using 140 nuclear genes, 75% of its extant species, and eight fossil calibrations. We also analyzed the phylogenetic signal of biome shifts across the group and its effect on diversification and extinction rates. We found the forest biome as the ancestral condition and a directional shift from forest to savanna (no reversals). The forest biome type is conserved in the Berlinia clade, but the lability to shift biomes is randomly distributed in the group. We did not find evidence that biome shift was associated with higher diversification or lower extinction rates. Our analyses identified five paleoendemic genera that have persisted solely in the forest biome since the Eocene. These paleoendemic and forest-restricted lineages are potentially more susceptible to habitat alterations of human related activities and future climate change, due to perhaps an innate limitation to adapt to new habitat types.

evolutionary biology↗

bioRxiv2024

How fast are viruses spreading in the wild?

Genomic data collected from viral outbreaks can be exploited to reconstruct the dispersal history of viral lineages in a two-dimensional space using continuous phylogeographic inference. These spatially explicit reconstructions can subsequently be used to estimate dispersal metrics allowing to unveil the dispersal dynamics and evaluate the capacity to spread among hosts. Heterogeneous sampling intensity of genomic sequences can however impact the accuracy of dispersal insights gained through phylogeographic inference. In our study, we implement a simulation framework to evaluate the robustness of three dispersal metrics -- a lineage dispersal velocity, a diffusion coefficient, and an isolation-by-distance signal metric -- to the sampling effort. Our results reveal that both the diffusion coefficient and isolation-by-distance signal metrics appear to be robust to the number of samples considered for the phylogeographic reconstruction. We then use these two dispersal metrics to compare the dispersal pattern and capacity of various viruses spreading in animal populations. Our comparative analysis reveals a broad range of isolation-by-distance patterns and diffusion coefficients mostly reflecting the dispersal capacity of the main infected host species but also, in some cases, the likely signature of rapid and/or long-distance dispersal events driven by human-mediated movements through animal trade. Overall, our study provides key recommendations for the lineage dispersal metrics to consider in future studies and illustrates their application to compare the spread of viruses in various settings.

evolutionary biology↗

bioRxiv2019

Contrasting dates of rainforest fragmentation in Africa inferred from trees with different dispersal abilities

The rainforests of Tropical Africa have fluctuated over time. Although today the forest cover is continuous in Central Africa this may have not always been the case, as the scarce fossil record in this region suggests that more arid conditions might have significantly reduced the density of trees during the Ice Ages. Our aim was to investigate whether the dry ice-age periods left a genetic signature on tree species that can be used to date the past fragmentation of the rainforest. We sequenced reduced representation libraries of 182 samples representing five Legume tree species that are widespread in African rainforests and seven outgroups. Phylogenetic analyses identified an early divergent lineage for all species in West Africa (Upper Guinea), and two clades in Central Africa: Lower Guinea-North and Lower Guinea-South. As the structure separating the Northern and Southern clades cannot be explained by geographic barriers, we tested other hypotheses using demographic model testing. The best estimates recovered using {partial}a{partial}I indicate that the two clades split between the Upper Pliocene and the Pleistocene, a date compatible with forest fragmentation driven by ice-age climatic oscillations. Furthermore, we found remarkably older split dates for the shade-tolerant tree species with non-assisted seed dispersal than for light-demanding long-distance wind-dispersed trees. We also show that the genetic diversity significantly declines with the distance from ice-age refugia in the two long-distance dispersed species only. Different recolonisation abilities after recurrent cycles of forest fragmentation seem to explain why we observe congruent genetic spatial structures across species with contrasted timescales.\n\nSIGNIFICANCE STATEMENTAlthough today the rainforest cover is continuous in Central Africa, the scarce fossil record suggests that arid conditions during the Ice Ages might have reduced the density of trees during the Ice Ages. However, the vast majority of the fossil pollen records preserved in Tropical Africa is too young to inform about this period. Investigating whether the past climate change left a genetic signature on trees can thus be useful to date past forest fragmentation. However, most genetic studies available to date lack resolution as they use limited numbers of loci. In this study we use modern DNA technology to study five Legume trees. Our results show significant differentiation of the populations of each species at a date compatible with forest fragmentation driven by ice-age climatic oscillations. Contrasted timescales were obtained for each species, which probably reflects their different recolonisation abilities after forest fragmentation.

evolutionary biology↗

bioRxiv2019

Population genomics of the widespread African savannah trees Afzelia africana and Afzelia quanzensis (Caesalpinioideae, Fabaceae) reveals no significant past fragmentation of their distribution ranges

Few studies have addressed the evolutionary history of tree species from African savannahs at large geographic scales, particularly in the southern hemisphere (Zambezian region). Afzelia (Fabaceae: Caesalpinioideae) contains economically important timber species, including two species widely distributed in African savannahs: A. africana in the Sudanian region and A. quanzensis in the Zambezian region. To characterize the population genetic diversity and structure of these two species across their distribution ranges, we used nuclear microsatellites (simple sequence repeats, SSRs) and genotyping-by-sequencing (GBS) markers. Six SSR loci were genotyped in 241 A. africana and 113 A. quanzensis individuals, while 2,800 and 3,841 high-quality single nucleotide polymorphisms (SNPs) were identified in 30 A. africana and 12 A. quanzensis individuals, respectively. Both species appeared to be outcrossing (selfing rate ~ 0%). The spatial genetic structure was consistent with isolation-by-distance expectations based on both SSR and SNP data, suggesting that gene dispersal is spatially restricted in both species (bLd (SSR)= -0.005 and -0.007 and bLd (SNP)= -0.008 and -0.006 for A. africana and A. quanzensis, respectively). Bayesian clustering of SSR genotypes failed to identify genetic structure within species. In contrast, SNP data resolved intraspecific genetic clusters in both species, illustrating the higher resolving power of GBS at shallow levels of divergence. However, the clusters identified by SNPs revealed low levels of differentiation and no clear geographical entities. These results suggest that, although gene flow has been restricted over short distances in both species, populations have remained connected throughout the large, continuous Savannah landscapes. The absence of clear phylogeographic discontinuities, also found in a few other African savannah trees, indicates that their distribution ranges have not been significantly fragmented during past climate changes, in contrast to patterns commonly found in African rainforest trees.

plant biology↗