Limitations of Species Delimitation Based on Phylogenetic Analyses: A Case Study in the Hypogymnia hypotrypa Group (Parmeliaceae, Ascomycota).
Delimiting species boundaries among closely related lineages often requires a range of independent data sets and analytical approaches. Similar to other organismal groups, robust species circumscriptions in fungi are increasingly investigated within an empirical framework. Here we attempt to delimit species boundaries in a closely related clade of lichen-forming fungi endemic to Asia, the Hypogymnia hypotrypa group (Parmeliaceae). In the current classification, the Hypogymnia hypotrypa group includes two species: H. hypotrypa and H. flavida, which are separated based on distinctive reproductive modes, the former producing soredia but absent in the latter. We reexamined the relationship between these two species using phenotypic characters and molecular sequence data (ITS, GPD, and MCM7 sequences) to address species boundaries in this group. In addition to morphological investigations, we used Bayesian clustering to identify potential genetic groups in the H. hypotrypa/H. flavida clade. We also used a variety of empirical, sequence-based species delimitation approaches, including: the "Automatic Barcode Gap Discovery" (ABGD), the Poisson tree process model (PTP), the General Mixed Yule Coalescent (GMYC), and the multispecies coalescent approach BPP. Different species delimitation scenarios were compared using Bayes factors delimitation analysis, in addition to comparisons of pairwise genetic distances, pairwise fixation indices (FST). The majority of the species delimitation analyses implemented in this study failed to support H. hypotrypa and H. flavida as distinct lineages, as did the Bayesian clustering analysis. However, strong support for the evolutionary independence of H. hypotrypa and H. flavida was inferred using BPP and further supported by Bayes factor delimitation. In spite of rigorous morphological comparisons and a wide range of sequence-based approaches to delimit species, species boundaries in the H. hypotrypa group remain uncertain. This study reveals the potential limitations of relying on distinct reproductive strategies as diagnostic taxonomic characters for Hypogymnia and also the challenges of using popular sequence-based species delimitation methods in groups with recent diversification histories.
State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
Xinli
X
Wei
Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, United States of America.
Bruce
B
McCune
Science & Education, The Field Museum, Chicago, Illinois, United States of America.
H Thorsten
HT
Lumbsch
State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.|University of Chinese Academy of Sciences, Beijing, China.
Hui
H
Li
Department of Biology, Brigham Young University, Provo, Utah, United States of America.
Steven
S
Leavitt
Department of Bioproduction Science, Faculty of Bioresource Sciences, Akita Prefectural University, Akita, Japan.
Yoshikazu
Y
Yamamoto
Sakhalin Botanical Garden, Yuzhno-Sakhalinsk, Russia.
Svetlana
S
Tchabanenko
State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
Jiangchun
J
Wei
D000531:Altitude; D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics; D002681:China; D016000:Cluster Analysis; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics*; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D005843:Geography; D007564:Japan; D064168:Minichromosome Maintenance Complex Component 7; D000068837:Parmeliaceae / Q000145:classification / Q000235:genetics*; D010641:Phenotype; D010802:Phylogeny; D011110:Polymorphism, Genetic; D012426:Russia; D017422:Sequence Analysis, DNA / Q000379:methods*; D013045:Species Specificity
D004271:DNA, Fungal; D021903:DNA, Ribosomal Spacer; D005656:Fungal Proteins; D064168:Minichromosome Maintenance Complex Component 7