Rejecting strictly allopatric speciation on a continental island: prolonged postdivergence gene flow between Taiwan (Leucodioptron taewanus, Passeriformes Timaliidae) and Chinese (L. canorum canorum) hwameis.
Allopatry is conventionally considered the geographical mode of speciation for continental island organisms. However, strictly allopatric speciation models that assume the lack of postdivergence gene flow seem oversimplified given the recurrence of land bridges during glacial periods since the late Pliocene. Here, to evaluate whether a continental island endemic, the Taiwan hwamei (Leucodioptron taewanus, Passeriformes Timaliidae) speciated in strict allopatry, we used weighted-regression-based approximate Bayesian computation (ABC) to analyse the genetic polymorphism of 18 neutral nuclear loci (total length: 8500 bp) in Taiwan hwamei and its continental sister species, the Chinese hwamei (L. canorum canorum). The nonallopatry model was found to fit better with observed genetic polymorphism of the two hwamei species (posterior possibility = 0.82). We also recovered unambiguous signals of nontrivial bidirectional postdivergence gene flow (N(e)m >> 1) between Chinese hwamei and Taiwan hwamei until 0.5 Ma. Divergence time was estimated to be 3.5 to 2 million years earlier than that estimated from mitochondrial cytochrome b sequences. Finally, using the inferred nonallopatry model to simulate genetic variation at 24 nuclear genes examined showed that the adiponectin receptor 1 gene may be under divergent adaptation. Our findings imply that the role of geographical barrier may be less prominent for the speciation of continental island endemics, and suggest a shift in speciation studies from simply correlating geographical barrier and genetic divergence to examining factors that facilitate and maintain divergence, e.g. differential selection and sexual selection, especially in the face of interpopulation gene flow.
Li
Jing-Wen
JW
Department of Life Science, National Taiwan Normal University, Taipei 116 Taiwan.
Yeung
Carol K L
CK
Tsai
Pi-Wen
PW
Lin
Rong-Chien
RC
Yeh
Chia-Fen
CF
Yao
Cheng-Te
CT
Han
Lianxian
L
Hung
Le Manh
le M
Ding
Ping
P
Wang
Qishan
Q
Li
Shou-Hsien
SH
D000818:Animals; D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics; D002681:China; D051456:Gene Flow; D049810:Genetic Speciation; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes; D016013:Likelihood Functions; D008957:Models, Genetic; D046109:Passeriformes / Q000235:genetics*; D011110:Polymorphism, Genetic; D012044:Regression Analysis; D017422:Sequence Analysis, DNA; D013624:Taiwan