Recurrent gene flow versus incomplete lineage sorting: allele sharing between two hybridizing pines with overlapping distributions
Author(s): Zhou, Y, Duvaux, L, Liu, J, Savolainen, O
When closely related species occur with parapatric or sympatric distributions, allele sharing between them might due to retention of ancestral polymorphism because of incomplete lineage sorting and/or recurrent gene flow following secondary contact. One difficulty for studying speciation is to distinguish between the two. Here, genetic polymorphisms at multiple intronic sequences of two closely related pines (Pinus massoniana Lamb. and P. hwangshanensis Hisa) with overlapping distributions were employed to address this issue. First, we compared the patterns of genetic diversity, linkage disequilibrium (LD), differentiation and population structure in parapatric and allopatric populations of the two pines. Approximate Bayesian Computation (ABC) was then employed in defining demographic and speciation models. Parapatric populations harbored higher levels of intraspecific genetic diversity, lower levels of interspecific differentiation and more rapid decay of LD than allopatric populations. Population structure analyses revealed more introgression in parapatric populations than that in allopatric populations. Model selection based on ABC suggested that the two species came into secondary contact about 10000 generations ago and gradually spread to reach the current patterns of overlapping distributions. Taken together, allele sharing between these two closely related parapatric pines might due to secondary introgression rather than incomplete lineage sorting.
School of Life Sciences
The phylogeography of a wide-ranging bird in Asia, the common pheasant Phasianus colchicus
Author(s): Liu, Y, Liu, X, Zhang, Z
The common pheasant, Phasianus colchicus is distributed throughout temperate regions in East and Central Asia, and had been widely introduced into Europe and North America as a game bird. This species is well adapted to a wide range of environmental and climate conditions. Thirty-one subspecies have been identified based on substantial variation in male morphological ornaments. We investigated the phylogeography and genetic diversity patterns of common pheasant in Asia using mitochondrial and nuclear genes, and male morphological characters. Our analyses revealed five highly divergent evolutionary lineages and the affinity of subspecies to evolutionary lineages corresponds with four pre-defined morphological groups and a previously undescribed group. The distribution of these lineages reflects geographical breaks of mountains, plains and deserts, and the estimates for the divergence times between these lineages probably predate the last glacial maximum. We further found evidence of extensive genetic introgression between contiguous subspecies within lineages. Taken together, these results suggest that the phylogeographic patterns of common pheasant had been shaped by ancient colonization events and population expansions during postglacial periods. We are currently investigating genome-wide variation related to adaptation and radiation of common pheasant using a RAD-sequencing approach. Furthermore, our study system provides a favorable framework to study the speciation processes under biogeography, local adaptation and sex selection.