“Reconstructing the geography of speciation from contemporary biodiversity data”
Alexander Skeels and Marcel Cardillo (Feb 2019)
Simulations show speciation leaves trace in ranges and phylogeny. Sympatric common mode in plants and founder in animals
The geographic origin of species
The mechanisms underlying the origin of species have been debated since both Darwin and Wallace noted that there may be different potential mechanisms that drive populations to diverge and eventually become new species. Whether geographic barriers, such as the formation of a mountain range, are more important than, for example, resource competition driving ecological divergence in co-occurring populations (such as proposed for Darwin’s finches) has been the focus of an enduring research program. Yet because speciation events have taken place in the past, trying to reconstruct their geographic context relies on secondary information from the observable geographic ranges of species in the present, which may not reflect historical ranges at the time of speciation.
To investigate this, Alex Skeels and Marcel Cardillo of the Australian National University developed a simulation model of dynamic range evolution and diversification. This model allowed the authors to modify the major drivers of geographic range movement over evolutionary time across simulated clades, to determine whether we can still detect the signal of the geographic context of speciation from contemporary biodiversity data such as species distributions and phylogeny. The simulation model suggests that the signal of speciation history can be recovered from contemporary data, and used this to infer the speciation history of a number of plant and animal groups. Animal groups, including a number of bird, mammal, reptile, and amphibian clades, showed strong support for a founder model of speciation – where a long-distance dispersal event establishes a new, isolated population that eventually becomes a new species. The speciation history of plants, on the other hand, appeared to be primarily sympatric. These results suggest that there may be distinctly different processes shaping the origin of species across taxonomic groups, and point to different roles of geography and ecology in the speciation process shaping the evolution of biodiversity around the world.
Inferring the geographic mode of speciation could help reveal the evolutionary and ecological mechanisms that underlie the generation of biodiversity. Comparative methods have sought to reconstruct the geographic speciation history of clades using data on phylogeny and species geographic ranges. However, inference from comparative methods has been limited by uncertainty over whether contemporary biodiversity data retain the historic signal of speciation. We constructed a process-based simulation model to determine the influence of speciation mode and post-speciation range evolution on current biodiversity patterns. The simulations suggest that the signal of speciation history remains detectable in species distributions and phylogeny, even when species ranges have evolved substantially through time. We extracted this signal using a combination of summary statistics that had good power to distinguish speciation modes, then used these statistics to infer the speciation history of 30 plant and animal clades. The results point to broad taxonomic patterns in the modes of speciation, with strongest support for founder speciation in mammals and birds, and strongest support for sympatric speciation in plants. Our model and analyses show that broad-scale comparative methods can be a powerful complementary approach to more focused genomic analyses in the study of the patterns and mechanisms of speciation.