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Stem Lineage (stem + lineage)
Selected AbstractsTHE IMPORTANCE OF PREADAPTED GENOMES IN THE ORIGIN OF THE ANIMAL BODYPLANS AND THE CAMBRIAN EXPLOSIONEVOLUTION, Issue 5 2010Charles R. Marshall The genomes of taxa whose stem lineages branched early in metazoan history, and of allied protistan groups, provide a tantalizing outline of the morphological and genomic changes that accompanied the origin and early diversifications of animals. Genome comparisons show that the early clades increasingly contain genes that mediate development of complex features only seen in later metazoan branches. Peak additions of protein-coding regulatory genes occurred deep in the metazoan tree, evidently within stem groups of metazoans and eumetazoans. However, the bodyplans of these early-branching clades are relatively simple. The existence of major elements of the bilaterian developmental toolkit in these simpler organisms implies that these components evolved for functions other than the production of complex morphology, preadapting the genome for the morphological differentiation that occurred higher in metazoan phylogeny. Stem lineages of the bilaterian phyla apparently required few additional genes beyond their diploblastic ancestors. As disparate bodyplans appeared and diversified during the Cambrian explosion, increasing complexity was accommodated largely through changes in cis -regulatory networks, accompanied by some additional gene novelties. Subsequently, protein-coding genic richness appears to have essentially plateaued. Some genomic evidence suggests that similar stages of genomic evolution may have accompanied the rise of land plants. [source] Early evolution of a homeobox gene: the parahox gene Gsx in the Cnidaria and the BilateriaEVOLUTION AND DEVELOPMENT, Issue 4 2003John R. Finnerty Summary Homeobox transcription factors are commonly involved in developmental regulation in diverse eukaryotes, including plants, animals, and fungi. The origin of novel homeobox genes is thought to have contributed to many evolutionary innovations in animals. We perform a molecular phylogenetic analysis of cnox2, the best studied homeobox gene from the phylum Cnidaria, a very ancient lineage of animals. Among three competing hypotheses, our analysis decisively favors the hypothesis that cnox2 is orthologous to the gsx gene of Bilateria, thereby establishing the existence of this specific homeobox gene in the eumetazoan stem lineage, some 650,900 million years ago. We assayed the expression of gsx in the planula larva and polyp of the sea anemone Nematostella vectensis using in situ hybridization and reverse transcriptase polymerase chain reaction. The gsx ortholog of Nematostella, known as anthox2, is expressed at high levels in the posterior planula and the corresponding "head" region of the polyp. It cannot be detected in the anterior planula or the corresponding "foot" region of the polyp. We have attempted to reconstruct the evolution of gsx spatiotemporal expression in cnidarians and bilaterians using a phylogenetic framework. Because of the surprisingly high degree of variability in gsx expression within the Cnidaria, it is currently not possible to infer unambiguously the ancestral cnidarian condition or the ancestral eumetazoan condition for gsx expression. [source] A NEW SEA SPIDER (ARTHROPODA: PYCNOGONIDA) WITH A FLAGELLIFORM TELSON FROM THE LOWER DEVONIAN HUNSRÜCK SLATE, GERMANYPALAEONTOLOGY, Issue 5 2006MARKUS POSCHMANN Abstract:, A new Lower Devonian sea spider (Arthropoda: Pycnogonida) from the Hunsrück Slate, Germany, is described as Flagellopantopus blocki gen. et sp. nov. This is only the sixth fossil pycnogonid species to be described. Its most remarkable and unique aspect is the long, flagelliform telson. Although our fossil apparently lacks chelifores (an apomorphy), the retained telson and the segmented trunk end behind the last pair of legs resolve F. blocki to a fairly basal position in the pycnogonid stem lineage. It probably lies between Palaeoisopus problematicus Broili, which has a lanceolate telson and the most trunk segments of any sea spider, and all other Silurian,Recent Pycnogonida. Our new material shows that at least two fossil pycnogonids retained a telson, albeit with very different morphologies, and further supports the idea that a greater diversity of body plans existed among the Palaeozoic pycnogonid taxa. [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] THE IMPORTANCE OF PREADAPTED GENOMES IN THE ORIGIN OF THE ANIMAL BODYPLANS AND THE CAMBRIAN EXPLOSIONEVOLUTION, Issue 5 2010Charles R. Marshall The genomes of taxa whose stem lineages branched early in metazoan history, and of allied protistan groups, provide a tantalizing outline of the morphological and genomic changes that accompanied the origin and early diversifications of animals. Genome comparisons show that the early clades increasingly contain genes that mediate development of complex features only seen in later metazoan branches. Peak additions of protein-coding regulatory genes occurred deep in the metazoan tree, evidently within stem groups of metazoans and eumetazoans. However, the bodyplans of these early-branching clades are relatively simple. The existence of major elements of the bilaterian developmental toolkit in these simpler organisms implies that these components evolved for functions other than the production of complex morphology, preadapting the genome for the morphological differentiation that occurred higher in metazoan phylogeny. Stem lineages of the bilaterian phyla apparently required few additional genes beyond their diploblastic ancestors. As disparate bodyplans appeared and diversified during the Cambrian explosion, increasing complexity was accommodated largely through changes in cis -regulatory networks, accompanied by some additional gene novelties. Subsequently, protein-coding genic richness appears to have essentially plateaued. Some genomic evidence suggests that similar stages of genomic evolution may have accompanied the rise of land plants. [source] Phylogeny of Dicranophoridae (Rotifera: Monogononta) , a maximum parsimony analysis based on morphological charactersJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 1 2009O. Riemann Abstract This study presents the first phylogenetic analysis of Dicranophoridae (Rotifera: Monogononta), a species rich rotifer family of about 230 species currently recognized. It is based on a maximum parsimony analysis including 77 selected ingroup and three outgroup taxa and a total of 59 phylogenetically informative morphological characters. Character coding is based on personal investigation of material collected by the authors and an extensive survey of the literature. Apart from covering general body organization, character coding primarily relies on scanning electron microscopic preparations of the mastax jaw elements. Our study suggests monophyly of Dicranophoridae with a clade of Dicranophorus and Dorria as the sister taxon of all other dicranophorid species. Monophyly of Encentrum, the most species rich genus within Dicranophoridae, cannot be demonstrated. Within Dicranophoridae our study identifies the monophyletic taxa Caudosubbasifenestrata, Intramalleata, Praeuncinata and Proventriculata, each based on unambiguous character transformations evolved in their stem lineages. However, resolution within Praeuncinata and Proventriculata is very limited. Although some terminal clades within Praeuncinata and Proventriculata are recognized, basal splits remain obscure. Probably, other characters such as DNA sequence data are needed to further our understanding of phylogenetic relationships within these poorly resolved taxa. Zusammenfassung Die hier vorgelegte Studie stellt die erste phylogenetische Analyse des Taxons Dicranophoridae (Rotifera: Monogononta) dar, einer artenreichen Familie der Rotiferen mit zurzeit etwa 230 validen Arten. Die resultierenden phylogenetischen Verwandtschaftsbeziehungen fußen auf einer Maximum Parsimonie Analyse mit 77 ausgewählten Vertretern der Innen, und 3 Vertretern der Außengruppe bei insgesamt 59 Parsimonie,informativen Merkmalen. Die Kodierung der Merkmale basiert einerseits auf Material, das von den Autoren selbst gesammelt und bestimmt wurde und andererseits auf einem ausgedehnten Studium der relevanten Literatur. Neben der Erfassung von Merkmalen zur allgemeinen Körperorganisation stützt sich die Merkmalskodierung vor allem auf rasterelektronenmikroskopische Präparationen der Hartelemente des Mastax. Das Ergebnis der Analyse stützt die Monophylie der Dicranophoridae. Innerhalb der Dicranophoridae stellt ein monophyletisches Taxon, das die Gattungen Dicranophorus und Dorria umfasst, die Schwestergruppe aller übrigen Dicranophoridae dar. Die bei weitem artenreichste Gattung Encentrum lässt sich nicht als Monophylum begründen. Als monophyletische Teilgruppen innerhalb der Dicranophoridae identifiziert unsere Analyse die Taxa Caudosubbasifenestrata, Intramalleata, Praeuncinata und Proventriculata, die jeweils durch mindestens eine unzweideutige Merkmalstransformation in ihren Stammlinien begründet werden. Innerhalb der Taxa Praeuncinata und Proventriculata bietet unsere Analyse nur sehr begrenzte Auflösung. Obgleich sich einzelne Teilgruppen über unzweideutige Merkmalstransformationen als Monophyla begründen lassen, fehlen Merkmale für die Auflösung der basalen Verzweigungen innerhalb der Praeuncinata und Proventriculata. Es ist zu erwarten, dass andere Merkmalssysteme, wie zum Beispiel DNA Sequenzdaten, bei der Aufklärung der Verwandtschaftsbeziehungen innerhalb dieser Teilgruppen Klärung erbringen. [source] | ||||||||||