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Rates of species formation vary widely across the tree of life and contribute to massive disparities in species richness among clades. This variation can emerge from differences in metapopulation-level processes that affect the rates at which lineages diverge, persist, and evolve reproductive barriers and ecological differentiation. For example, populations that evolve reproductive barriers quickly should form new species at faster rates than populations that acquire reproductive barriers more slowly. This expectation implicitly links microevolutionary processes (the evolution of populations) and macroevolutionary patterns (the profound disparity in speciation rate across taxa). Here, leveraging extensive field sampling from the Neotropical Cerrado biome in a biogeographically controlled natural experiment, we test the role of an important microevolutionary process—the propensity for population isolation—as a control on speciation rate in lizards and snakes. By quantifying population genomic structure across a set of codistributed taxa with extensive and phylogenetically independent variation in speciation rate, we show that broad-scale patterns of species formation are decoupled from demographic and genetic processes that promote the formation of population isolates. Population isolation is likely a critical stage of speciation for many taxa, but our results suggest that interspecific variability in the propensity for isolation has little influence on speciation rates. These results suggest that other stages of speciation—including the rate at which reproductive barriers evolve and the extent to which newly formed populations persist—are likely to play a larger role than population isolation in controlling speciation rate variation in squamates.
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Speciation rates are unrelated to the formation of population structure in Malagasy gemsnakes
Abstract Speciation rates vary substantially across the tree of life. These rates should be linked to the rate at which population structure forms if a continuum between micro and macroevolutionary patterns exists. Previous studies examining the link between speciation rates and the degree of population formation in clades have been shown to be either correlated or uncorrelated depending on the group, but no study has yet examined the relationship between speciation rates and population structure in a young group that is constrained spatially to a single‐island system. We examine this correlation in 109 gemsnakes (Pseudoxyrhophiidae) endemic to Madagascar and originating in the early Miocene, which helps control for extinction variation across time and space. We find no relationship between rates of speciation and the formation rates of population structure over space in 33 species of gemsnakes. Rates of speciation show low variation, yet population structure varies widely across species, indicating that speciation rates and population structure are disconnected. We suspect this is largely due to the persistence of some lineages not susceptible to extinction. Importantly, we discuss how delimiting populations versus species may contribute to problems understanding the continuum between shallow and deep evolutionary processes.
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- PAR ID:
- 10441500
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 13
- Issue:
- 8
- ISSN:
- 2045-7758
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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