Phylogenetic systematics and tempo of evolution of the Viverrinae (Mammalia, Carnivora, Viverridae) within feliformians: implications for faunal exchanges between Asia and Africa

We reconstructed the phylogeny of the subfamily Viverrinae (Mammalia, Carnivora, Viverridae) using a approximately 3kb data set in order to reassess timing and patterns of faunal exchanges between Asia and Africa. Maximum parsimony, maximum likelihood, and Bayesian analyses of separated and combined matrices (cytochrome b, transthyretin intron I and IRBP exon 1 [IRBP1]) recovered all the well-supported relationships within feliformian lineages. In addition, IRBP1 supported paraphyly of genus Herpestes and contributed to the resolution of equivocal hypotheses within Viverridae, including (1) the monophyly of Viverrinae, and (2) Viverricula sister-group of the other terrestrial civets (Civettictis and Viverra). The combined analysis yielded a robust phylogeny, recovering monophyly of Prionodontidae and yielding high posterior probabilities for nodes (1) (Prionodontidae, Felidae) and (2) ((Felidae, Prionodontidae), ((Hyaenidae, (Herpestidae, Eupleridae)), Viverridae)). Using a fossil cross-validation method, we estimated the emergence of Viverridae at 34.29Myr, with a separation between the three traditional subfamilies Hemigalinae, Paradoxurinae, and Viverrinae during the Late Oligocene-Early Miocene. The terrestrial civets and the splits between (1) Civettictis and Viverra and (2) Poiana and Genetta were estimated to appear during the Middle Miocene. Parsimony- and maximum likelihood-based methods yielded unambiguous ancestral area reconstructions, including the Asian origin of the family Viverridae, the subfamily Viverrinae, the terrestrial civets and the clade (Civettictis, Viverra). On the grounds of genetic distances, morphological divergence, and divergence time estimates, we propose the erection of the subfamily Genettinae (including Genetta and Poiana). Our analyses suggested two independent migration events from Asia to Africa, during the Middle Miocene (Civettictis) and between the Late Oligocene and Middle Miocene (Genettinae). These results are in agreement with the hypothesis of Miocene routes from Asia to Africa-via the Arabian microplate-that would have involved several independent events of migrations. Couched in the context of the viverrid fossil record, our study calls for a revision of the paleontological data in order to fully appreciate the complexity of Afro-Asian faunal exchanges.     

Phylogeny of the caniform carnivora: evidence from multiple genes

The monophyletic group Caniformia in the order Carnivora currently comprises seven families whose relationships remain contentious. The phylogenetic positions of the two panda species within the Caniformia have also been evolutionary puzzles over the past decades, especially for Ailurus fulgens (the red panda). Here, new nuclear sequences from two introns of the β-fibrinogen gene (β-fibrinogen introns 4 and 7) and a complete mitochondrial (mt) gene (ND2) from 17 caniform representatives were explored for their utilities in resolving higher-level relationships in the Caniformia. In addition, two previously available nuclear (IRBP exon 1 and TTR intron 1) data sets were also combined and analyzed simultaneously with the newly obtained sequence data in this study. Combined analyses of four nuclear and one mt genes (4417 bp) recover a branching order in which almost all nodes were strongly supported. The present analyses provide evidence in favor of Ailurus fulgens as the closest taxon to the procyonid-mustelid (i.e., Musteloidea sensu stricto) clade, followed by pinnipeds (i.e., Otariidae and Phocidae), Ursidae (including Ailuropoda melanoleuca), and Canidae, the most basal lineage in the Caniformia. The potential utilities of different genes in the context of caniform phylogeny were also evaluated, with special attention to the previously unexplored β-fibrinogen intron 4 and 7 genes.     

Phylogenetic studies of pantherine cats (Felidae) based on multiple genes, with novel application of nuclear beta-fibrinogen intron 7 to carnivores

The pantherine lineage of the cat family Felidae (order: Carnivora) includes five big cats of genus Panthera and a great many midsized cats known worldwide. Presumably because of their recent and rapid radiation, the evolutionary relationship among pantherines remains ambiguous. We provide an independent assessment of the evolutionary history of pantherine lineage using two complete mitochondrial (mt) genes (ND2 and ND4) and the nuclear beta-fibrinogen intron 7 gene, whose utility in carnivoran phylogeny was first explored. The available four mt (ND5, cytb, 12S, and 16SrRNA) and two nuclear (IRBP and TTR) sequence loci were also combined to reconstruct phylogeny of 14 closely related cat species. Our analyses of combined mt data (six genes; approximately 3750 bp) and combined mt and nuclear data (nine genes; approximately 6500 bp) obtained identical tree topologies, which were well-resolved and strongly supported for almost all nodes. Monophyly of Panthera genus in pantherine lineage was confirmed and interspecific affinities within this genus revealed a novel branching pattern, with P. tigris diverging first in Panthera genus, followed by P. onca, P. leo, and last two sister species P. pardus and P. uncia. In addition, close association of Neofelis nebulosa to Panthera, the phylogenetic redefinition of Otocolobus manul within the domestic cat group, and the relatedness of Acinonyx jubatus and Puma concolor were all important findings in the resulting phylogenies. The potential utilities of nine different genes for phylogenetic resolution of closely related pantherine species were also evaluated, with special interest in that of the novel nuclear beta-fibrinogen intron 7.     

Rates of nuclear and cytoplasmic mitochondrial DNA sequence divergence in mammals

Differential rates of nucleotide substitution among different gene segments and between distinct evolutionary lineages is well documented among mitochondrial genes and is likely a consequence of locus-specific selective constraints that delimit mutational divergence over evolutionary time. We compared sequence variation of 18 homologous loci (15 coding genes and 3 parts of the control region) among 10 mammalian mitochondrial DNA genomes which allowed us to describe different mitochondrial evolutionary patterns and to produce an estimation of the relative order of gene divergence. The relative rates of divergence of mitochondrial DNA genes in the family Felidae were estimated by comparing their divergence from homologous counterpart genes included in nuclear mitochondrial DNA (Numt, pronounced "new might"), a genomic fossil that represents an ancient transfer of 7.9 kb of mitochondrial DNA to the nuclear genome of an ancestral species of the domestic cat (Felis catus). Phylogenetic analyses of mitochondrial (mtDNA) sequences with multiple outgroup species were conducted to date the ancestral node common to the Numt and the cytoplasmic (Cymt) mtDNA genes and to calibrate the rate of sequence divergence of mitochondrial genes relative to nuclear homologous counterparts. By setting the fastest substitution rate as strictly mutational, an empirical "selective retardation index" is computed to quantify the sum of all constraints, selective and otherwise, that limit sequence divergence of mitochondrial gene sequences over time.      

Confrontation of morphological and molecular data: the Praomys group (Rodentia, Murinae) as a case of adaptive convergences and morphological stasis

Phylogenetic relationships in a group of 21 African rodent species designated as the Praomys group (Murinae) were investigated using morphological characters and sequence data from the complete mitochondrial cytochrome b gene and nuclear IRBP gene fragment (840bp). The molecular results confirm the monophyly of the Praomys group, including the species Malacomys verschureni, while the other Malacomys species appear very divergent. The basal relationships within the Praomys group are poorly resolved, suggesting a rapid radiation at about 7-9 million years ago based on genetic divergence rates calibrated from the fossil record. Discrepancies between molecular and morphological results probably reflect of numerous convergences as well as variations in the rates of morphological evolution among lineages. Reconstructions of the ancestral character states suggest a savannah origin for the Praomys group, along with some morphological traits conserved by stasis in savannah taxa. At the same time, forest taxa seem to be characterized by an accelerated morphological evolution, with acquisition of convergent adaptive characters.     

Mitogenomic analyses of caniform relationships

Extant members of the order Carnivora split into two basal groups, Caniformia (dog-like carnivorans) and Feliformia (cat-like carnivorans). In this study we address phylogenetic relationships within Caniformia applying various methodological approaches to analyses of complete mitochondrial genomes. Pinnipeds are currently well represented with respect to mitogenomic data and here we add seven mt genomes to the non-pinniped caniform collection. The analyses identified a basal caniform divergence between Cynoidea and Arctoidea. Arctoidea split into three primary groups, Ursidae (including the giant panda), Pinnipedia, and a branch, Musteloidea, which encompassed Ailuridae (red panda), Mephitidae (skunks), Procyonidae (raccoons) and Mustelidae (mustelids). The analyses favored a basal arctoid split between Ursidae and a branch containing Pinnipedia and Musteloidea. Within the Musteloidea there was a preference for a basal divergence between Ailuridae and remaining families. Among the latter, the analyses identified a sister group relationship between Mephitidae and a branch that contained Procyonidae and Mustelidae. The mitogenomic distance between the wolf and the dog was shown to be at the same level as that of basal human divergences. The wolf and the dog are commonly considered as separate species in the popular literature. The mitogenomic result is inconsistent with that understanding at the same time as it provides insight into the time of the domestication of the dog relative to basal human mitogenomic divergences.     

Patterns of Y and X chromosome DNA sequence divergence during the Felidae radiation.

The 37 species of modern cats have evolved from approximately eight phylogenetic lineages within the past 10 to 15 million years. The Felidae family has been described with multiple measures of morphologic and molecular evolutionary methods that serve as a framework for tracking gene divergence during brief evolutionary periods. In this report, we compare the mode and tempo of evolution of noncoding sequences of a large intron within Zfy (783 bp) and Zfx (854 bp), homologous genes located on the felid Y and X chromosomes, respectively. Zfy sequence variation evolves at about twice the rate of Zfx, and both gene intron sequences track feline hierarchical topologies accurately. As homoplasies are infrequent in patterns of nucleotide substitution, the Y chromosome sequence displays a remarkable degree of phylogenetic consistency among cat species and provides a highly informative glimpse of divergence of sex chromosome sequences in Felidae.     

Phylogeny of rodentia (Mammalia) inferred from the nuclear-encoded gene IRBP

The order Rodentia includes nearly half of all living mammalian species. Phylogenetic relationships among 22 species of rodents were investigated by use of a 1.2-kb region from exon 1 of the single-copy nuclear gene IRBP. IRBP has been extensively used for study of interordinal phylogeny in mammals, which allowed inclusion of 50 outgroup species, representing every eutherian order plus seven marsupials. Several clades were strongly supported, regardless of analytical method or inclusion/exclusion of data. These include a monophyletic Muroidea, with a clade including Spalax and Rhizomys as the first divergence; a clade uniting Zapus with Dipus, but excluding Sicista; a monophyletic Myodonta (Muroidea plus Dipodidae); and a clade including Aplodontidae as sister to Sciuridae. One bipartition, separating Hystricognathi and Geomyoidea from the remaining rodents, is strongly supported in all analyses that include third-position sites but almost completely absent from analyses that exclude third-position sites. A combination of nonstationary nucleotide composition and branch length effects may be causing all methods examined (including those using the LogDet distance) to support an incorrect conclusion when third-position sites are analyzed together with first- and second-position sites.     

食肉目猫科物种的系统发育学研究概述

猫科动物(Felidae)是食肉目中肉食性最强的一科, 其中许多成员是人们最熟悉、最引人注目的动物, 也是各地的顶级食肉动物。目前37个现存猫科物种中有36个已经被列为濒危和稀有对象。食肉目猫科物种的进化历史是一个快速辐射和较近时期发生的物种形成事件, 使得猫科物种之间系统发育关系的重建非常困难, 一直处于广泛争论的状态。构建可靠的猫科系统发育关系, 具有重要的进化理论意义和保护生物学价值。文章对猫科物种的系统发育学研究进展, 包括来自于形态学特征、细胞学和分子生物学方面的证据做简要概述, 并提出目前研究中存在的问题。以期对今后猫科物种的系统发育方面的进一步研究工作具有指导意义, 并为该类群的生物多样性资源保护提供科学依据。     

Phylogenetic relationships of the endemic malagasy carnivoreCryptoprocta ferox (Aeluroidea): DNA/DNA hybridization experiments

A molecular and morphological study of several living aeluroid Carnivora was completed to evaluate the evolutionary relationships of the endemicCryptoprocta ferox, a carnivore living on the island of Madagascar. The molecular analysis, based on DNA/DNA hybridization experiments, suggests thatCryptoprocta is more closely related to the Herpestidae (as represented byMungos andIchneumia) than it is to the Viverrinae (Genetta), Paradoxurinae (Paguma, Paradoxurus), Felidae (Felis, Panthera), or Hyaenidae (Crocuta). Based on bootstrapping procedures applied to the individual DNA/DNA results, three branching patterns were observed which differ only by the relative position of the Felidae within the Aeluroidea. The amounts of genetic divergence measured between pairs of compared taxa have been transformed into millions years datings by the molecular clock concept, and this was done by establishing a molecular time scale based on the fossil record of the aeluroid Carnivora.     

A molecular perspective on mammalian evolution from the gene encoding interphotoreceptor retinoid binding protein, with convincing evidence for bat monophyly.

The evolutionary relationships of the various orders of placental mammals remain an issue of uncertainty and controversy. Molecular studies of mammalian phylogeny at the DNA level that include more than just a few orders are still relatively meager. Here we report results on mammalian phylogeny deduced from the coding sequence of the single-copy nuclear gene for the interphotoreceptor retinoid binding protein (IRBP). Analysis of 13 species representing eight eutherian orders and one marsupial yielded results that falsify the hypothesis that megachiropteran bats are "flying primates," only convergently resembling microchiropteran bats. Instead, in agreement with more traditional views, as well as those from other recent molecular studies, the results strongly support a monophyletic Chiroptera (micro- and megabats grouped together). The IRBP results also offer some rare molecular support for the Glires concept, in which rodents and lagomorphs form a superordinal grouping. Also in congruence with other recent molecular evidence, IRBP sequences do not support the view of a superorder Archonta that includes Chiroptera along with Dermoptera (flying lemur), Scandentia (tree shrew), and Primates. IRBP was not however, without its shortcomings as a molecular phylogenetic system: high levels of homoplasy, evident in the marsupial outgroup, did not allow us to properly root the tree, and several of the higher level eutherian clades were only weakly supported (e.g., a Carnivora/Chiroptera clade and an Artiodactyla/Carnivora/Chiroptera clade). We suggest that these shortcomings may be diminished as the phylogenetic density of the data set is increased.     

Phylogenetic relationships and divergence times among mustelids (Mammalia: Carnivora) based on nucleotide sequences of the nuclear interphotoreceptor retinoid binding protein and mitochondrial cytochrome b genes

Phylogenetic relationships among 20 species-group taxa of Mustelidae, representing Mustelinae (Mustela, Martes, Gulo), Lutrinae (Enhydra), and Melinae (Meles), were examined using nucleotide sequences of the nuclear interphotoreceptor retinoid binding protein (IRBP) and mitochondrial cytochrome b genes. Neighbor-joining and maximum-parsimony phylogenetic analyses on these genes separately and combined were conducted. While IRBP performed better than cytochrome b in recovering more-inclusive clades, cytochrome b demonstrated more resolving power in recovering less-inclusive clades. Strong support was found for a close affinity of Enhydra with Mustela to the exclusion of Martes and Gulo (causing Mustelinae to be paraphyletic); the most-basal position of Mustela vison within Mustela, followed by Mustela erminea; an association of Mustela lutreola, Mustela itatsi, Mustela sibirica, and the subgenus Putorius (including Mustela putorius and Mustela eversmanii), to the exclusion of Mustela nivalis and Mustela altaica; and a basal position of Mustela itatsi to a clade containing Mustela sibirica and Putorius. Whereas cytochrome b strongly supported Mustela lutreola as the sister species to Putorius, IRBP strongly supported its basal placement to the Mustela itatsi-Mustela sibirica-Putorius clade. The low level of sequence divergence in cytochrome b between Mustela lutreola and Putorius is therefore a result of interspecific mitochondrial introgression between these taxa, rather than a recent origin of Mustela lutreola in a close relationship to Putorius. Time estimates inferred from IRBP and cytochrome b for mustelid divergence events are mostly in agreement with the fossil record.     

Molecular Phylogeny of Mitochondrial Cytochrome b and 12S rRNA Sequences in the Felidae: Ocelot and Domestic Cat Lineages

Molecular phylogeny of the cat family Felidae is derived using two mitochondrial genes, cytochrome b and 12S rRNA. Phylogenetic methods of weighted maximum parsimony and minimum evolution estimated by neighbor-joining are employed to reconstruct topologies among 20 extant felid species. Sequence analyses of 363 bp of cytochrome b and 376 bp of the 12S rRNA genes yielded average pair-wise similarity values between felids ranging from 94 to 99% and from 85 to 99%, respectively. Phylogenetic reconstruction supports more recent, intralineage associations but fails to completely resolve interlineage relationships. Both genes produce a monophyletic group ofFelisspecies but vary in the placement of the pallas cat. The ocelot lineage represents an early divergence within the Felidae, with strong associations between ocelot and margay, Geoffroy's cat and kodkod, and pampas cat and tigrina. Implications of the relative recency of felid evolution, presence of ancestral polymorphisms, and influence of outgroups in placement of the topological root are discussed.     

Tandemly repeated satellite DNA ofDolichopoda schiavazzii: A test for models on the evolution of highly repetitive DNA

The evolutionary relationships among the Carnivora were studied in a phylogenetic analysis based on the complete mitochondrial cytochromeb gene. The study, which addressed primarily the relationships among the Caniformia, included 4 feliform and 26 caniform species, with 9 pinnipeds. The analysis identified five caniform clades: Canidae, Ailuridae (with the monotypic lesser panda), Musteloidea (Mustelidae+Procyonidae), Ursidae (including the giant panda), and Pinnipedia. The closest relatives of the Pinnipedia among terrestrial caniforms were not identified conclusively. Our analysis shows that the skunks are only distantly related to remaining mustelids (Mustelidae sensu stricto) and that the family Mustelidae, including the skunks, is paraphyletic. The relationship among the five caniform clades was unresolved, suggesting an evolutionary separation within a relatively short period of time. Based on distance values, we propose that this primary diversification took place 45 million years ago.     

Building large trees by combining phylogenetic information: a complete phylogeny of the extant Carnivora (Mammalia)

One way to build larger, more comprehensive phylogenies is to combine the vast amount of phylogenetic information already available. We review the two main strategies for accomplishing this (combining raw data versus combining trees), but employ a relatively new variant of the latter: supertree construction. The utility of one supertree technique, matrix representation using parsimony analysis (MRP), is demonstrated by deriving a complete phylogeny for all 271 extant species of the Carnivora from 177 literature sources. Beyond providing a 'consensus' estimate of carnivore phylogeny, the tree also indicates taxa for which the relationships remain controversial (e.g. the red panda; within canids, felids, and hyaenids) or have not been studied in any great detail (e.g. herpestids, viverrids, and intrageneric relationships in the procyonids). Times of divergence throughout the tree were also estimated from 74 literature sources based on both fossil and molecular data. We use the phylogeny to show that some lineages within the Mustelinae and Canidae contain significantly more species than expected for their age, illustrating the tree's utility for studies of macroevolution. It will also provide a useful foundation for comparative and conservational studies involving the carnivores.     

Phylogenetic relationships of the Cobitoidea (Teleostei: Cypriniformes) inferred from mitochondrial and nuclear genes with analyses of gene evolution

The superfamily Cobitoidea of the order Cypriniformes is a diverse group of fishes, inhabiting freshwater ecosystems across Eurasia and North Africa. The phylogenetic relationships of this well-corroborated natural group and diverse clade are critical to not only informing scientific communities of the phylogeny of the order Cypriniformes, the world's largest freshwater fish order, but are key to every area of comparative biology examining the evolution of traits, functional structures, and breeding behaviors to their biogeographic histories, speciation, anagenetic divergence, and divergence time estimates. In the present study, two mitochondrial gene sequences (COI, ND4+5) and four single-copy nuclear gene segments (RH1, RAG1, EGR2B, IRBP) were used to infer the phylogenetic relationships of the Cobitoidea as reconstructed from maximum likelihood (ML) and partitioned Bayesian Analysis (BA). Analyses of the combined mitochondrial/nuclear gene datasets revealed five strongly supported monophyletic Cobitoidea families and their sister-group relationships: Botiidae+(Vaillantellidae+(Cobitidae+(Nemacheilidae+Balitoridae))). These recovered relationships are in agreement with previous systematic studies on the order Cypriniformes and/or those focusing on the superfamily Cobitoidea. Using these relationships, our analyses revealed pattern lineage- or ecological-group-specific evolution of these genes for the Cobitoidea. These observations and results corroborate the hypothesis that these group-specific-ancestral ecological characters have contributed in the diversification and/or adaptations within these groups. Positive selections were detected in RH1 of nemacheilids and in RAG1 of nemacheilids and genus Vaillantella, which indicated that evolution of RH1 (related to eye's optic sense) and RAG1 (related to immunity) genes appeared to be important for the diversification of these groups. The balitorid lineage (those species inhabiting fast-flowing riverine habitats) had, as compared with other cobitoid lineages, significantly different dN/dS, dN and dS values for ND4 and IRBP genes. These significant differences are usually indicative of weaker selection pressure, and lineage-specific evolution on genes along the balitorid lineage. Furthermore, within Cobitoidea, excluding balitorids, species living in subtropics had significantly higher dN/dS values in RAG1 and IRBP genes than those living in temperate and tropical zones. Among tropical cobitoids, genes COI, ND5, EGR2B, IRBP and RH1, had a significantly higher mean dS value than those species in subtropical and temperate groups. These findings suggest that the evolution of these genes could also be ecological-group-specific and may have played an important role in the adaptive evolution and diversification of these groups. Thus, we hypothesize that the genes included in the present study were actively involved in lineage- and/or ecological-group-specific evolutionary processes of the highly diverse Cobitoidea. These two evolutionary patterns, both subject to further testing, are hypothesized as integral in the diversification with this major clade of the world's most diverse group of freshwater fishes.     

New DNA data from a transthyretin nuclear intron suggest an Oligocene to Miocene diversification of living South America opossums (Marsupialia: Didelphidae)

Phylogenetic relationships of 19 species of didelphid marsupials were studied using two nuclear markers, the non-coding transthyretin intron 1 (TTR) and the coding interphotoreceptor retinoid binding protein exon 1 (IRBP), and two mitochondrial genes, the protein-coding cytochrome b (cyt-b) and the structural 12S ribosomal DNA (12S rDNA). Evolutionary dynamics of these four markers were compared to each other, revealing the appropriate properties presented by TTR intron 1 together with its well supported and resolved phylogenetic signal. Nuclear markers supported the monophyly of medium and large-sized opossums Metachirus+(Chironectes, Lutreolina, Didelphis, Philander), and the paraphyly of mouse-sized opossums, with the genera Gracilinanus, Thylamys, and Marmosops as a sister group to medium and large-sized didelphids. Conflicting branching patterns between mitochondrial and nuclear data involved the phylogenetic position of Marmosa-Micoureus-Monodelphis relative to other mouse-sized opossums. Nuclear phylogenetic inferences among genera were confirmed by the presence of synapomorphic indels observed in TTR intron 1. A Bayesian relaxed molecular clock dating of didelphid evolution using nuclear markers estimated their origin in the Middle Eocene (39.8 million years ago), with subsequent diversification during the Oligocene (Deseadan) and Miocene.     

Phylogeny of the bears (Ursidae) based on nuclear and mitochondrial genes

The taxomic classification and phylogenetic relationships within the bear family remain argumentative subjects in recent years. Prior investigation has been concentrated on the application of different mitochondrial (mt) sequence data, herein we employ two nuclear single-copy gene segments, the partial exon 1 from gene encoding interphotoreceptor retinoid binding protein (IRBP) and the complete intron 1 from transthyretin (TTR) gene, in conjunction with previously published mt data, to clarify these enigmatic problems. The combined analyses of nuclear IRBP and TTR datasets not only corroborated prior hypotheses, positioning the spectacled bear most basally and grouping the brown and polar bear together but also provided new insights into the bear phylogeny, suggesting the sister-taxa association of sloth bear and sun bear with strong support. Analyses based on combination of nuclear and mt genes differed from nuclear analysis in recognizing the sloth bears as the earliest diverging species among the subfamily ursine representatives while the exact placement of the sun bear did not resolved. Asiatic and American black bears clustered as sister group in all analyses with moderate levels of bootstrap support and high posterior probabilities. Comparisons between the nuclear and mtDNA findings suggested that our combined nuclear dataset have the resolving power comparable to mtDNA dataset for the phylogenetic interpretation of the bear family. As can be seen from present study, the unanimous phylogeny for this recently derived family was still not produced and additional independent genetic markers were in need.     

Differential enzyme targeting as an evolutionary adaptation to herbivory in carnivora

Not all members of the order Carnivora are carnivorous. Some are omnivorous, and a few, such as the giant panda, Ailuropoda melanoleuca, are almost exclusively herbivorous. Although a number of adaptations to increased plant-eating are recognized within Carnivora, few have been studied at the molecular level. One molecular adaptation to diet that is spread widely across Mammalia is the differential intracellular targeting of the intermediary metabolic enzyme alanine:glyoxylate aminotransferase (AGT), which tends to be mitochondrial in carnivores, peroxisomal in herbivores, and both mitochondrial and peroxisomal in omnivores. In the present study, we have analyzed the targeting of AGT in Carnivora in relation to species' natural diets. We show not only that there has been an adaptive shift in AGT targeting from the mitochondrion toward the peroxisome as diets have shifted from being mainly carnivorous to ones that are more omnivorous and herbivorous but also that in one lineage, namely that of the giant panda, there is evidence for positive selection pressure at the molecular level on the AGT mitochondrial targeting sequence to decrease its efficiency, thereby allowing more AGT to be targeted to the peroxisomes.     

An early origin of plastids within the cyanobacterial divergence is suggested by evolutionary trees based on complete 16S rRNA sequences

It is generally accepted that the plastids arose from a cyanobacterial ancestor, but the exact phylogenetic relationships between cyanobacteria and plastids are still controversial. Most studies based on partial 16S rRNA sequences suggested a relatively late origin of plastids within the cyanobacterial divergence. In order to clarify the exact relationship and divergence order of cyanobacteria and plastids, we studied their phylogeny on the basis of nearly complete 16S rRNA gene sequences. The data set comprised 15 strains of cyanobacteria from different morphological groups, 1 prochlorophyte, and plastids belonging to 8 species of plants and 12 species of diverse algae. This set included three cyanobacterial sequences determined in this study. This is the most comprehensive set of complete cyanobacterial and plastidial 16S rRNA sequences used so far. Phylogenetic trees were constructed using neighbor joining and maximum parsimony, and the reliability of the tree topologies was tested by different methods. Our results suggest an early origin of plastids within the cyanobacterial divergence, preceded only by the divergence of two cyanobacterial genera, Gloeobacter and Pseudanabaena.