No link between population isolation and speciation rate in squamate reptiles

Abstract

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.

Anti-predator defenses are linked with high levels of genetic differentiation in frogs

“…A positive link between genetic differentiation and speciation rates has been shown in lineages such as birds and fish [13,76]. However, despite being extensively predicted by theory, there is no evidence of such link in orchids, sea snakes or reptiles in general [77][78][79][80], suggesting that in some lineages, other processes independent of genetic differentiation might promote or limit reproductive isolation. To our knowledge, no studies have explicitly tested for a link between genetic differentiation and speciation rates in amphibians, but our results offer indirect evidence.…”

Speciation rates are unrelated to the formation of population structure in Malagasy gemsnakes

“…Previous studies (Harvey et al, 2017;Singhal et al, 2022) showed high variation in the estimation of speciation rates across a F I G U R E 5 Scatterplots showing the relationship between log slope (β IBD for GBS and genetic distance over space for mtDNA) for log speciation rate estimates from CLaDS and DR for taxa with more than four samples. The former two methods model rates of speciation using the entire tree structure and therefore may be detecting overall trends better than the DR method.…”

Do the species with large geographic ranges diversify faster?

“…Potentially powerful approach for disentangling incipient from exhausted radiations would comprise integrating phylogenetic and range data with information on genetic structure of individual species. Past efforts in this direction were often limited by the resolution of population genetic data 21,64 or by spatial and phylogenetic extent they were covering 65 . However, the fast development of genomics promises the future possibility of identifying centres of incipient diversification globally, using the population-level genetic data.…”