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Last Common Ancestor (last + common_ancestor)
Selected AbstractsThe amphioxus T-box gene, AmphiTbx15/18/22, illuminates the origins of chordate segmentationEVOLUTION AND DEVELOPMENT, Issue 2 2006Laura Beaster-Jones SUMMARY Amphioxus and vertebrates are the only deuterostomes to exhibit unequivocal somitic segmentation. The relative simplicity of the amphioxus genome makes it a favorable organism for elucidating the basic genetic network required for chordate somite development. Here we describe the developmental expression of the somite marker, AmphiTbx15/18/22, which is first expressed at the mid-gastrula stage in dorsolateral mesendoderm. At the early neurula stage, expression is detected in the first three pairs of developing somites. By the mid-neurula stage, expression is downregulated in anterior somites, and only detected in the penultimate somite primordia. In early larvae, the gene is expressed in nascent somites before they pinch off from the posterior archenteron (tail bud). Integrating functional, phylogenetic and expression data from a variety of triploblast organisms, we have reconstructed the evolutionary history of the Tbx15/18/22 subfamily. This analysis suggests that the Tbx15/18/22 gene may have played a role in patterning somites in the last common ancestor of all chordates, a role that was later conserved by its descendents following gene duplications within the vertebrate lineage. Furthermore, the comparison of expression domains within this gene subfamily reveals similarities in the genetic bases of trunk and cranial mesoderm segmentation. This lends support to the hypothesis that the vertebrate head evolved from an ancestor possessing segmented cranial mesoderm. [source] Generality of vertebrate developmental patterns: evidence for a dermomyotome in fishEVOLUTION AND DEVELOPMENT, Issue 1 2006S. H. Devoto SUMMARY The somitic compartment that gives rise to trunk muscle and dermis in amniotes is an epithelial sheet on the external surface of the somite, and is known as the dermomyotome. However, despite its central role in the development of the trunk and limbs, the evolutionary history of the dermomyotome and its role in nonamniotes is poorly understood. We have tested whether a tissue with the morphological and molecular characteristics of a dermomyotome exists in nonamniotes. We show that representatives of the agnathans and of all major clades of gnathostomes each have a layer of cells on the surface of the somite, external to the embryonic myotome. These external cells do not show any signs of terminal myogenic or dermogenic differentiation. Moreover, in the embryos of bony fishes as diverse as sturgeons (Chondrostei) and zebrafish (Teleostei) this layer of cells expresses the pax3 and pax7 genes that mark myogenic precursors. Some of the pax7- expressing cells also express the differentiation-promoting myogenic regulatory factor Myogenin and appear to enter into the myotome. We therefore suggest that the dermomyotome is an ancient and conserved structure that evolved prior to the last common ancestor of all vertebrates. The identification of a dermomyotome in fish makes it possible to apply the powerful cellular and genetic approaches available in zebrafish to the understanding of this key developmental structure. [source] Geobiological analysis using whole genome-based tree building applied to the Bacteria, Archaea, and EukaryaGEOBIOLOGY, Issue 1 2003Christopher H. House ABSTRACT We constructed genomic trees based on the presence and absence of families of protein-encoding genes observed in 55 prokaryotic and five eukaryotic genomes. There are features of the genomic trees that are not congruent with typical rRNA phylogenetic trees. In the bacteria, for example, Deinococcus radiodurans associates with the Gram-positive bacteria, a result that is also seen in some other phylogenetic studies using whole genome data. In the Archaea, the methanogens plus Archaeoglobus form a united clade and the Euryarchaeota are divided with the two Thermoplasma genomes and Halobacterium sp. falling below the Crenarchaeota. While the former appears to be an accurate representation of methanogen-relatedness, the misplacement of Halobacterium may be an artefact of parsimony. These results imply the last common ancestor of the Archaea was not a methanogen, leaving sulphur reduction as the most geochemically plausible metabolism for the base of the archaeal crown group. It also suggests that methanogens were not a component of the Earth's earliest biosphere and that their origin occurred sometime during the Archean. In the Eukarya, the parsimony analysis of five Eukaryotes using the Crenarchaeota as an outgroup seems to counter the Ecdysozoa hypothesis, placing Caenorhabditis elegans (Nematoda) below the common ancestor of Drosophila melanogaster (Arthropoda) and Homo sapiens (Chordata) even when efforts are made to counter the possible effects of a faster rate of sequence evolution for the C. elegans genome. Further analysis, however, suggests that the gene loss of ,animal' genes is highest in C. elegans and is obscuring the relationships of these organisms. [source] Head structures of males of Strepsiptera (Hexapoda) with emphasis on basal splitting events within the orderJOURNAL OF MORPHOLOGY, Issue 5 2006Rolf Georg Beutel Abstract Internal and external head structures of males of Strepsiptera were examined and the head of a species of Mengenilla is described in detail. The results suggest a reinterpretation of some structures. The head of basal extant strepsipterans is subprognathous, whereas it is strictly orthognathous in the groundplan of Strepsiptera s.l. The labrum and hypopharynx are not part of the mouthfield sclerite. The labial palps are absent in all strepsipterans. A very slightly modified mandibular articulation is preserved in Eoxenos, whereas it is distinctly reduced in other extant groups. A salivary duct, salivary glands, and a cephalic aorta are absent. The cladistic analysis of 44 characters of the head results in the following branching pattern: (Protoxenos + (Mengea + (Eoxenos + (Mengenilla [Austr.] + Mengenilla) + (Elenchus + Dundoxenos + Xenos + Stylops)))). Most apomorphies of males are associated with the necessity of finding females within a short time span and with a reduced necessity to consume food: large "raspberry" eyes, flabellate antennae with numerous dome-shaped chemoreceptors, Hofeneder's organ, an ovoid sensillum of the maxillary palp, and the simplified condition of the maxilla and the labium. Strepsiptera excl. Protoxenos are supported by the dorsomedian frontal impression, the dorsally shifted antennal insertions, a reduced number of antennal segments, absence of the galea, and probably by the presence of the mouthfield sclerite, which is a unique apomorphic feature. The balloon-gut combined with an unusual air-uptake apparatus is another possible autapomorphy of this clade. It is likely that the last common ancestor of Strepsiptera excl. Protoxenos did not process food. Strepsiptera s.str. are characterized by the strongly reduced condition of the labrum and the absence of the epistomal suture. Eoxenos is the sister group of the remaining Strepsiptera s.str. Synapomorphies of Mengenilla + Stylopidia are the advanced reduction of the mandibular articulation and the secondary absence of the ovoid sensillum. The monophyly of Mengenilla is confirmed, even though a small free labrum is present in Australian species. Derived features of Stylopidia are the absence of the coronal suture and the reduced condition of the frontal suture. Apomorphies that have evolved within Stylopidia are the membranization of parts of the head, the fusion of antennal segments, the increase or decrease of the number of flabellate flagellomeres, reductions and modifications of the mandibles, and modifications of the mouthfield sclerite. The monophyly of Stylopiformia is not unambiguously supported. A position of the mandibles posterior to the mouthfield sclerite (when adducted) is a possible synapomorphy shared by Xenos, Stylops, and other "higher Stylopidia." The blade-like distal part of the mandibles suggests a closer relationship of Elenchus with these taxa. © 2004 Wiley-Liss, Inc. [source] A new neosuchian crocodylomorph (Crocodyliformes, Mesoeucrocodylia) from the Early Cretaceous of north-east BrazilPALAEONTOLOGY, Issue 5 2009DANIEL C. FORTIER Abstract:, A new neosuchian crocodylomorph, Susisuchus jaguaribensis sp. nov., is described based on fragmentary but diagnostic material. It was found in fluvial-braided sediments of the Lima Campos Basin, north-eastern Brazil, 115 km from where Susisuchus anatoceps was found, in rocks of the Crato Formation, Araripe Basin. S. jaguaribensis and S. anatoceps share a squamosal,parietal contact in the posterior wall of the supratemporal fenestra. A phylogenetic analysis places the genus Susisuchus as the sister group to Eusuchia, confirming earlier studies. Because of its position, we recovered the family name Susisuchidae, but with a new definition, being node-based group including the last common ancestor of Susisuchus anatoceps and Susisuchus jaguaribensis and all of its descendents. This new species corroborates the idea that the origin of eusuchians was a complex evolutionary event and that the fossil record is still very incomplete. [source] Evolution of centric diatoms inferred from patterns of oogenesis and spermatogenesisPHYCOLOGICAL RESEARCH, Issue 3 2008Makoto Mizuno SUMMARY Centric diatoms have three patterns of oogenesis and four patterns of spermatogenesis, yielding a combination of seven patterns. The evolution of these combinations was inferred from differences in character states of the meiotic patterns observed in oogenesis and spermatogenesis. Furthermore, we have inferred the evolutionary relationships among centric diatoms based on the evolution of these combinations, the data on occurrence of combinations and a molecular phylogenetic tree. Our results suggested that the last common ancestor of extant diatoms was a bipolar or multipolar centric diatom with the most primitive among extant oogenetic/spermatogenic combinations. Our results also suggested that ancestors of the radial centrics and pennates would have diverged, in that order, from a bipolar or multipolar centric diatom with the most primitive among extant oogenetic/spermatogenic combinations. [source] The evolution of brachiation in ateline primates, ancestral character states and historyAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2008Andrea L. Jones Abstract This study examines how brachiation locomotion evolved in ateline primates using recently-developed molecular phylogenies and character reconstruction algorithms, and a newly-collected dataset including the fossils Protopithecus, Caipora, and Cebupithecia. Fossils are added to two platyrrhine molecular phylogenies to create several phylogenetic scenarios. A generalized least squares algorithm reconstructs ateline and atelin ancestral character states for 17 characters that differentiate between ateline brachiators and nonbrachiators. Histories of these characters are mapped out on these phylogenies, producing two scenarios of ateline brachiation evolution that have four commonalities: First, many characters change towards the Ateles condition on the ateline stem lineage before Alouatta splits off from the atelins, suggesting that an ateline energy-maximizing strategy began before the atelines diversified. Second, the ateline last common ancestor is always reconstructed as an agile quadruped, usually with suspensory abilities. It is never exactly like Alouatta and many characters reverse and change towards the Alouatta condition after Alouatta separates from the atelins. Third, most characters undergo homoplastic change in all ateline lineages, especially on the Ateles and Brachyteles terminal branches. Fourth, ateline character evolution probably went through a hindlimb suspension with tail-bracing phase. The atelines most likely diversified via a quick adaptive radiation, with bursts of punctuated change occurring in their postcranial skeletons, due to changing climatic conditions, which may have caused competition among the atelines and between atelines and pitheciines. Am J Phys Anthropol, 2008. © 2008 Wiley-Liss, Inc. [source] Primate sociality in evolutionary contextAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2005Alexandra E. Müller Abstract Much work has been done to further our understanding of the mechanisms that underlie the diversity of primate social organizations, but none has addressed the limits to that diversity or the question of what causes species to either form or not form social networks. The fact that all living primates typically live in social networks makes it highly likely that the last common ancestor of living primates already lived in social networks, and that sociality formed an integral part of the adaptive nature of primate origins. A characterization of primate sociality within the wider mammalian context is therefore essential to further our understanding of the adaptive nature of primate origins. Here we determine correlates of sociality and nonsociality in rodents as a model to infer causes of sociality in primates. We found sociality to be most strongly associated with large-bodied arboreal species that include a significant portion of fruit in their diet. Fruits and other plant products, such as flowers, seeds, and young leaves, are patchily distributed in time and space and are therefore difficult to find. These food resources are, however, predictable and dependable when their location is known. Hence, membership in a social unit can maximize food exploitation if information on feeding sites is shared. Whether sociality evolved in the primate stem lineage or whether it was already present earlier in the evolution of Euarchontoglires remains uncertain, although tentative evidence points to the former scenario. In either case, frugivory is likely to have played an important role in maintaining the presence of a social lifestyle throughout primate evolution. Am J Phys Anthropol, 2005. © 2005 Wiley-Liss, Inc. [source] Frontal Fusion: Collapse of Another Anthropoid SynapomorphyTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 3 2008Alfred L. Rosenberger Abstract We test the hypothesis that the fused interfrontal suture of anthropoids is a uniquely distinguishing feature and a derived characteristic indicative of their monophyletic origin. Our survey of nonanthropoid primates and several archontan families indicates frontal fusion is widespread. It is most variable (fused, open or partially fused) inter- and intra-specifically among strepsirhines. The frontal bone is more commonly fused in living lemuroids and indrioids than among lorisoids. It appears to be fused regularly among Eocene adapids. Among nonanthropoid haplorhines, the interfrontal is fused in Tarsius, even in neonates and invariably in adults, probably also in all fossil tarsiiforms preserving the frontal bone, and in the late Eocene protoanthropoid Rooneyia. The plesiadapiform pattern remains uncertain, but fusion is ubiquitous among living tree shrews, colugos and bats. Distributional evidence implies that interfrontal fusion was present in the last common ancestor (LCA) of haplorhine primates and possibly in the LCA of euprimates as well. Anthropoids, therefore, cannot be defined cladistically by interfrontal fusion, not out of concern for homoplasy but because it is probably a primitive feature inherited from other taxa related to anthropoids. Fusion of the large anthropoid frontal bone, which was extended anteriorly to roof the orbits and expanded laterally in connection with a wide forebrain in the LCA of anthropoids and protoanthropoids, may have been preadaptive to the evolution of the postorbital septum. The zygomatico-frontal suture of the septum may provide an alternative mechanism for dissipating the calvarial strains of mastication formerly taken up by an open interfrontal suture. Anat Rec, 291:308,317, 2008. © 2008 Wiley-Liss, Inc. [source] Opsin gene polymorphism predicts trichromacy in a cathemeral lemurAMERICAN JOURNAL OF PRIMATOLOGY, Issue 1 2009Carrie C. Veilleux Abstract Recent research has identified polymorphic trichromacy in three diurnal strepsirrhines: Coquerel's sifaka (Propithecus coquereli), black and white ruffed lemurs (Varecia variegata), and red ruffed lemurs (V. rubra). Current hypotheses suggest that the transitions to diurnality experienced by Propithecus and Varecia were necessary precursors to their independent acquisitions of trichromacy. Accordingly, cathemeral lemurs are thought to lack the M/L opsin gene polymorphism necessary for trichromacy. In this study, the M/L opsin gene was sequenced in ten cathemeral blue-eyed black lemurs (Eulemur macaco flavifrons). This analysis identified a polymorphism identical to that of other trichromatic strepsirrhines at the critical amino acid position 285 in exon 5 of the M/L opsin gene. Thus, polymorphic trichromacy is likely present in at least one cathemeral Eulemur species, suggesting that strict diurnality is not necessary for trichromacy. The presence of trichromacy in E. m. flavifrons suggests that a re-evaluation of current hypotheses regarding the evolution of strepsirrhine trichromacy may be necessary. Although the M/L opsin polymorphism may have been independently acquired three times in the lemurid,indriid clade, the distribution of opsin alleles in lemurids and indriids may also be consistent with a common origin of trichromacy in the last common ancestor of either the lemurids or the lemurid,indriid clade. Am. J. Primatol. 71:86,90, 2009. © 2008 Wiley-Liss, Inc. [source] Molecular Phylogeny and Surface Morphology of Colpodella edax (Alveolata): Insights into the Phagotrophic Ancestry of ApicomplexansTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 5 2003BRIAN S. LEANDER ABSTRACT. The molecular phylogeny of colpodellids provides a framework for inferences about the earliest stages in apicomplexan evolution and the characteristics of the last common ancestor of apicomplexans and dinoflagellates. We extended this research by presenting phylogenetic analyses of small subunit rRNA gene sequences from Colpodella edax and three unidentified eukaryotes published from molecular phylogenetic surveys of anoxic environments. Phylogenetic analyses consistently showed C. edax and the environmental sequences nested within a colpodellid clade, which formed the sister group to (eu)apicomplexans. We also presented surface details of C. edax using scanning electron microscopy in order to supplement previous ultrastructural investigations of this species using transmission electron microscopy and to provide morphological context for interpreting environmental sequences. The microscopical data confirmed a sparse distribution of micropores, an amphiesma consisting of small polygonal alveoli, flagellar hairs on the anterior flagellum, and a rostrum molded by the underlying (open-sided) conoid. Three flagella were present in some individuals, a peculiar feature also found in the microgametes of some apicomplexans. [source] The evolutionary history of krill inferred from nuclear large subunit rDNA sequence analysisBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2001SIMON N. JARMAN Early events in the speciation history of krill (Malacostraca: Euphausiacea), an abundant group of extant pelagic crustaceans, were studied with slowly evolving nuclear DNA sequences (large subunit ribosomal DNA, 28S rDNA). Krill have no fossil record, so very little is known about their paleobiology. The timing of past speciation events in krill was estimated by comparing change in their 28S rDNA to change in the 28S rDNA of their close relatives that do have a fossil record. Relationships between krill genera were also studied by phylogenetic analysis of partial 28S rDNA sequences. The analyses estimated the time that the last common ancestor of the krill family Euphausiidae lived to be the lower Cretaceous about 130 million years ago (Mya). Two lineages of krill survived the end Cretaceous extinctions 65 Mya and the modern genera of krill were established before the end of the Palaeogene 23 Mya. [source] Evolutionary and comparative anatomical investigations of the autonomic cardiac nervous system in the African cercopithecidaeJOURNAL OF MORPHOLOGY, Issue 9 2007Tomokazu Kawashima Abstract The purpose of this study was to clarify the general architecture and morphological variations of the autonomic cardiac nervous system (ACNS) in the African Cercopithecidae (Old World monkeys), and to discuss the evolutionary changes between this system in African/Asian Cercopithecidae and humans. A detailed macroscopic comparative morphological investigation of the ACNS was performed by examining the left and right sides of 11 African cercopithecid specimens, including some previously unreported species (Abyssinian colobus, Angola pied colobus, Savanna monkey, and lesser white-nosed guenon). The common characteristics of the ACNS in the African Cercopithecidae are described in detail. Consequently, homologies of the ACNS between Asian (macaques) and African Cercopithecidae, and differences between the Asian/African Cercopithecidae and humans, were found. In particular, differences in the sympathetic (cardiac) systems of the Cercopithecidae and humans were recognized, despite the similar morphology of the parasympathetic vagal (cardiac) system. These differences include the composition of the cervicothoracic ganglion, the lower positions of the middle cervical and cervicothoracic ganglia, and the narrow range for the origin of the cardiac nerves in the Cercopithecidae, compared with that in humans. In conclusion, these findings are considered with regard to the morphology of the last common ancestors of the Cercopithecidae. J. Morphol., 2007 © 2007 Wiley-Liss, Inc. [source] | |||||||||||||