Revision of the systematics of the cardinalfishes (Percomorpha: Apogonidae) based on molecular analyses and comparative reevaluation of morphological characters.

Molecular analyses were conducted based on 120 of the estimated 358 species of the family Apogonidae with 33 of 40 genera and subgenera, using three gobioids and one kurtid as collective outgroups. Species of Amioides, Apogon, Apogonichthyoides, Apogonichthys, Archamia, Astrapogon, Brephamia, Cercamia, Cheilodipterus, Fibramia n. gen., Foa, Fowleria, Glossamia, Gymnapogon, Jaydia, Lachneratus, Nectamia, Ostorhinchus, Paroncheilus, Phaeoptyx, Pristiapogon, Pristicon, Pseudamia, Pterapogon, Rhabdamia, Siphamia, Sphaeramia, Taeniamia, Verulux, Vincentia, Yarica, Zapogon and Zoramia were present in the molecular analyses; species of Bentuviaichthys, Holapogon, Lepidamia, Neamia, Paxton, Pseudamiops and Quinca were absent from the analyses. Maximum-likelihood (ML), Bayesian (BA), and Maximum parsimony (MP) analyses based on two mitochondrial (12S rRNA-tRNAVal-16S rRNA, ca. 1500 bp; COI, ca. 1500 bp) and two nuclear DNA (RAG1, ca. 1300 bp; ENC1, ca. 800 bp) fragments reproduced two basal clades within the monophyletic family: one including a single species, Amioides polyacanthus, and the other comprising species of Pseudamia. All the other apogonid species formed a large well-established monophyletic group, in which almost identical 12 major clades were reproduced, with phylogenetic positions of four species (Glossamia aprion, Ostorhinchus margaritophorus, Pterapogon kauderni, and Vincentia novaehollandiae) left unsettled. Apogon sensu lato and recent Ostorhinchus (excepting O. margaritophorus) were divided into six and three major clades, respectively. Each of the recognized clades in the family was then evaluated for morphological characters to identify synapomorphies. Based on the results of the molecular analyses and the reevaluation of morphological characters, four subfamilies were proposed within the family: Apogoninae (including most of the species in the family), Amioidinae new subfamily (including Amioides, and based on morphology, Holapogon), Paxtoninae new subfamily (including Paxton, based only on morphology) and Pseudamiinae (including Pseudamia). Within the largest subfamily Apogoninae, twelve new tribes were proposed based on the 12 molecular clades and associated morphology: Apogonichthyini, Apogonini (mainly including species of Apogon sensu stricto), Archamiini, Cheilodipterini, Gymnapogonini, Ostorhinchini (including striped species of recent Ostorhinchus), Pristiapogonini, Rhabdamiini, Sphaeramiini (mainly including barred species of traditional Ostorhinchus, such as Apogonichthyoides, Jaydia and Nectamia), Siphamiini, Veruluxini, and Zoramiini. Two additional tribes are proposed based only on morphology: Glossamiini and Lepidamiini. For each of the 14 tribes, morphological characters were described. One new genus, Fibramia, type species Apogon thermalis, recently in Ostorhinchus, was described supported by morphology and molecular trees. A key to all genera is provided and all valid and uncertain status species are allocated to tribes and genera.

Divergence time of the two regional medaka populations in Japan as a new time scale for comparative genomics of vertebrates.

The southern and northern Japanese populations of the medaka fish provide useful tools to gain insights into the comparative genomics and speciation of vertebrates, because they can breed to produce healthy and fertile offspring despite their highly divergent genetic backgrounds compared with those of human-chimpanzee. Comparative genomics analysis has suggested that such large genetic differences between the two populations are caused by higher molecular evolutionary rates among the medakas than those of the hominids. The argument, however, was based on the assumption that the two Japanese populations diverged approximately at the same time (4.0-4.7 Myr ago) as the human-chimpanzee lineage (5.0-6.0 Myr ago). This can be misleading, because the divergence time of the two populations was calculated based on estimated, extremely higher molecular evolutionary rates of other fishes with an implicit assumption of a global molecular clock. Here we show that our estimate, based on a Bayesian relaxed molecular-clock analysis of whole mitogenome sequences from 72 ray-finned fishes (including 14 medakas), is about four times older than that of the previous study (18 Myr). This remarkably older estimate can be reconciled with the vicariant events of the Japanese archipelago, and the resulting rates of molecular evolution are almost identical between the medaka and hominid lineages. Our results further highlight the fact that reproductive isolation may not evolve despite a long period of geographical isolation.

Mitogenomic evaluation of the historical biogeography of cichlids toward reliable dating of teleostean divergences.

BACKGROUND: Recent advances in DNA sequencing and computation offer the opportunity for reliable estimates of divergence times between organisms based on molecular data. Bayesian estimations of divergence times that do not assume the molecular clock use time constraints at multiple nodes, usually based on the fossil records, as major boundary conditions. However, the fossil records of bony fishes may not adequately provide effective time constraints at multiple nodes. We explored an alternative source of time constraints in teleostean phylogeny by evaluating a biogeographic hypothesis concerning freshwater fishes from the family Cichlidae (Perciformes: Labroidei). RESULTS: We added new mitogenomic sequence data from six cichlid species and conducted phylogenetic analyses using a large mitogenomic data set. We found a reciprocal monophyly of African and Neotropical cichlids and their sister group relationship to some Malagasy taxa (Ptychochrominae sensu Sparks and Smith). All of these taxa clustered with a Malagasy + Indo/Sri Lankan clade (Etroplinae sensu Sparks and Smith). The results of the phylogenetic analyses and divergence time estimations between continental cichlid clades were much more congruent with Gondwanaland origin and Cretaceous vicariant divergences than with Cenozoic transmarine dispersal between major continents. CONCLUSION: We propose to add the biogeographic assumption of cichlid divergences by continental fragmentation as effective time constraints in dating teleostean divergence times. We conducted divergence time estimations among teleosts by incorporating these additional time constraints and achieved a considerable reduction in credibility intervals in the estimated divergence times.

Independent evolution of the specialized pharyngeal jaw apparatus in cichlid and labrid fishes.

BACKGROUND: Fishes in the families Cichlidae and Labridae provide good probable examples of vertebrate adaptive radiations. Their spectacular trophic radiations have been widely assumed to be due to structural key innovation in pharyngeal jaw apparatus (PJA), but this idea has never been tested based on a reliable phylogeny. For the first step of evaluating the hypothesis, we investigated the phylogenetic positions of the components of the suborder Labroidei (including Pomacentridae and Embiotocidae in addition to Cichlidae and Labridae) within the Percomorpha, the most diversified (> 15,000 spp) crown clade of teleosts. We examined those based on 78 whole mitochondrial genome sequences (including 12 newly determined sequences) through partitioned Bayesian analyses with concatenated sequences (13,933 bp). RESULTS: The resultant phylogenies indicated that the Labridae and the remaining three labroid families have diverged basally within the Percomorpha, and monophyly of the suborder was confidently rejected by statistical tests using Bayes factors. CONCLUSION: The resultant phylogenies indicated that the specified PJA evolved independently at least twice, once in Labridae and once in the common ancestor of the remaining three labroid families (including the Cichlidae). Because the independent evolution of pharyngeal jaws appears to have been followed by trophic radiations, we consider that our result supports, from the aspect of historical repeatability, the idea that the evolution of the specialized PJA provided these lineages with the morphological potential for their spectacular trophic radiations. The present result will provide a new framework for the study of functional morphology and genetic basis of their PJA.