Abstract
Background
Accurate inference of demographic histories of temperate tree species can aid our understanding of current climate change as a driver of evolution. Microsatellites are more suitable for reflecting recent historical events due to their high mutation rates. However, most programs analyze microsatellite data following a strict stepwise mutation model (SMM), which could cause false detection of population shrinkage when microsatellite mutation is not according with SMM.
Results
This study aims to reconstruct the recent demographic histories of five cool-temperate tree species, Quercus mongolica, Q. liaotungensis, Juglans cathayensis, J. mandshurica and J. ailantifolia, in eastern Asia by using 19 microsatellite markers and two methods considering generalized stepwise mutation model (GSM) (MIGRAINE and VarEff). Both types of software revealed that all populations experienced expansions after the Last Glacial Maximum (LGM). In particular, J. cathayensis experienced a more serious bottleneck in its history than the other species, leading to a smaller effective population of ancestors, while Q. mongolica showed only a moderate increase in population size and remained stable after the expansion. In addition, the point estimates of the multistep mutation proportion in the generalized stepwise mutation model (pGSM) in all populations were between 0.50 and 0.65, which indicates that when inferring population demographic history of the above forest species using microsatellite molecular markers, it is better to assume a GSM rather than a SMM.
Conclusions
This study provides the first direct evidence that five cool-temperate tree species in East Asia have experienced expansions after the LGM using microsatellites data. Moreover, since the mutation model of microsatellite have a vital influence on demographic inference, combining multiple software programs such as MIGRAINE and VarEff can effectively reduce unnecessary errors caused by inappropriate model selection and prior setting.