Search results for "Biological Evolution"

Evidence for Natural Horizontal Transfer of the pcpB Gene in the Evolution of Polychlorophenol-Degrading Sphingomonads

2002

ABSTRACT The chlorophenol degradation pathway in Sphingobium chlorophenolicum is initiated by the pcpB gene product, pentachlorophenol-4-monooxygenase. The distribution of the gene was studied in a phylogenetically diverse group of polychlorophenol-degrading bacteria isolated from contaminated groundwater in Kärkölä, Finland. All the sphingomonads isolated were shown to share pcpB gene homologs with 98.9 to 100% sequence identity. The gene product was expressed when the strains were induced by 2,3,4,6-tetrachlorophenol. A comparative analysis of the 16S rDNA and pcpB gene trees suggested that a recent horizontal transfer of the pcpB gene was involved in the evolution of the catabolic pat…

Molecular evolution: Evidence for the monophyletic origin of multicellular animals

1995

New insights into non-avian dinosaur reproduction and their evolutionary and ecological implications: linking fossil evidence to allometries of extan…

2013

It has been hypothesized that a high reproductive output contributes to the unique gigantism in large dinosaur taxa. In order to infer more information on dinosaur reproduction, we established allometries between body mass and different reproductive traits (egg mass, clutch mass, annual clutch mass) for extant phylogenetic brackets (birds, crocodiles and tortoises) of extinct non-avian dinosaurs. Allometries were applied to nine non-avian dinosaur taxa (theropods, hadrosaurs, and sauropodomorphs) for which fossil estimates on relevant traits are currently available. We found that the reproductive traits of most dinosaurs conformed to similar-sized or scaled-up extant reptiles or birds. The …

Oldest Homo and Pliocene biogeography of the Malawi Rift

1993

The Malawi Rift and Pliocene palaeofaunas, which include a hominid mandible attributed to Homo rudolfensis, provide a biogeographical link between the better known Plio-Pleistocene faunal records of East and Southern Africa. The Malawi Rift is in a latitudinal position suitable for recording any hominid and faunal dispersion towards the Equator that was brought on by increased aridity of the Late Pliocene African landscape. The evidence suggests that Pliocene hominids originated in the eastern African tropical domain and dispersed to southern Africa only during more favourable ecological circumstances.

Diminishing Returns of Population Size in the Rate of RNA Virus Adaptation

2000

ABSTRACT Whenever an asexual viral population evolves by adapting to new environmental conditions, beneficial mutations, the ultimate cause of adaptation, are randomly produced and then fixed in the population. The larger the population size and the higher the mutation rate, the more beneficial mutations can be produced per unit time. With the usually high mutation rate of RNA viruses and in a large enough population, several beneficial mutations could arise at the same time but in different genetic backgrounds, and if the virus is asexual, they will never be brought together through recombination. Thus, the best of these genotypes must outcompete each other on their way to fixation. This c…

Distribution of Fitness Effects Caused by Single-Nucleotide Substitutions in Bacteriophage f1

2010

Empirical knowledge of the fitness effects of mutations is important for understanding many evolutionary processes, yet this knowledge is often hampered by several sources of measurement error and bias. Most of these problems can be solved using site-directed mutagenesis to engineer single mutations, an approach particularly suited for viruses due to their small genomes. Here, we used this technique to measure the fitness effect of 100 single-nucleotide substitutions in the bacteriophage f1, a filamentous single-strand DNA virus. We found that approximately one-fifth of all mutations are lethal. Viable ones reduced fitness by 11% on average and were accurately described by a log-normal dist…

Progreso, complejidad y evolución

2020

Ensayos en honor de Eloy Rada. [ES]: El progreso biológico es un tema ampliamente debatido en biología evolutiva que tiene partidarios y detractores. Sin embargo, no es una cuestión, a pesar de su importancia, de la que podamos afirmar que está resuelta desde el punto de vista científico. En este trabajo presento un análisis del concepto basado en la teoría de la evolución por selección natural, sus paralelismos con el también debatido concepto de “progreso” en la historia de la humanidad y, finalmente, se intenta orientarlo hacia formas accesibles a la investigación científica. Para ello, en lugar del concepto de progreso, recurro al de “complejidad biológica”. Si tenemos formas de medirla…

The evolution and changing ecology of the African hominid oral microbiome

2021

Significance The microbiome plays key roles in human health, but little is known about its evolution. We investigate the evolutionary history of the African hominid oral microbiome by analyzing dental biofilms of humans and Neanderthals spanning the past 100,000 years and comparing them with those of chimpanzees, gorillas, and howler monkeys. We identify 10 core bacterial genera that have been maintained within the human lineage and play key biofilm structural roles. However, many remain understudied and unnamed. We find major taxonomic and functional differences between the oral microbiomes of Homo and chimpanzees but a high degree of similarity between Neanderthals and modern humans, incl…

The columnar gene vnd is required for tritocerebral neuromere formation during embryonic brain development of Drosophila.

2006

International audience; In Drosophila, evolutionarily conserved transcription factors are required for the specification of neural lineages along the anteroposterior and dorsoventral axes, such as Hox genes for anteroposterior and columnar genes for dorsoventral patterning. In this report, we analyse the role of the columnar patterning gene ventral nervous system defective (vnd) in embryonic brain development. Expression of vnd is observed in specific subsets of cells in all brain neuromeres. Loss-of-function analysis focussed on the tritocerebrum shows that inactivation of vnd results in regionalized axonal patterning defects, which are comparable with the brain phenotype caused by mutatio…

Are dendrites in Drosophila homologous to vertebrate dendrites?

2005

AbstractDendrites represent arborising neurites in both vertebrates and invertebrates. However, in vertebrates, dendrites develop on neuronal cell bodies, whereas in higher invertebrates, they arise from very different neuronal structures, the primary neurites, which also form the axons. Is this anatomical difference paralleled by principal developmental and/or physiological differences? We address this question by focussing on one cellular model, motorneurons of Drosophila and characterise the compartmentalisation of these cells. We find that motorneuronal dendrites of Drosophila share with typical vertebrate dendrites that they lack presynaptic but harbour postsynaptic proteins, display c…