The first part of the paper contains a short review of the image processing in early vision is static, when the eyes and the stimulus are stable, and in dynamics, when the eyes participate in fixation eye movements. In the second part, we give an interpretation of Donders' and Listing's law in terms of the Hopf fibration of the 3-sphere over the 2-sphere. In particular, it is shown that the configuration space of the eye ball (when the head is fixed) is the 2-dimensional hemisphere SL+, called Listing hemisphere, and saccades are described as geodesic segments of SL+ with respect to the standard round metric. We study fixation eye movements (drift and microsaccades) in terms of this model and discuss the role of fixation eye movements in vision. A model of fixation eye movements is proposed that gives an explanation of presaccadic shift of receptive fields.

• Keywords
• Donders’ and Listing’s law, Hopf bundle, drift, fixation eyes movements, microsaccades, neurogeometry, quaternions, remapping, shift of receptive fields,
• Publication type
• Journal Article MeSH

Genetic drift is a basic evolutionary principle describing random changes in allelic frequencies, with far-reaching consequences in various topics ranging from species conservation efforts to speciation. The conventional approach assumes that genetic drift has the same effect on all populations undergoing the same changes in size, regardless of different non-reproductive behaviors and history of the populations. However, here we reason that processes leading to a systematic increase of individuals` chances of survival, such as learning or immunological memory, can mitigate loss of genetic diversity caused by genetic drift even if the overall mortality rate in the population does not change. We further test this notion in an agent-based model with overlapping generations, monitoring allele numbers in a population of prey, either able or not able to learn from successfully escaping predators' attacks. Importantly, both these populations start with the same effective size and have the same and constant overall mortality rates. Our results demonstrate that even under these conditions, learning can mitigate loss of genetic diversity caused by drift, by creating a pool of harder-to-die individuals that protect alleles they carry from extinction. Furthermore, this effect holds regardless if the population is haploid or diploid or whether it reproduces sexually or asexually. These findings may be of importance not only for basic evolutionary theory but also for other fields using the concept of genetic drift.

• MeSH
• Alleles MeSH
• Biological Evolution * MeSH
• Diploidy MeSH
• Gene Frequency MeSH
• Genetic Drift * MeSH
• Humans MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

It is broadly assumed that polyploidy success reflects an increase in fitness associated with whole-genome duplication (WGD), due to higher tolerance to stressful conditions. Nevertheless, WGD also arises with several costs in neo-polyploid lineages, like genomic instability, or cellular mis-management. In addition to these costs, neo-polyploid individuals also face frequency dependent selection because of frequent low-fitness triploids formed by cross-ploidy pollinations when tetraploids are primarily rare in the population. Interestingly, the idea that polyploidy can be fixed by genetic drift as a neutral or deleterious mutation is currently underexplored in the literature. To test how and when polyploidy can fix in a population by chance, we built a theoretical model in which autopolyploidization occurs through the production of unreduced gametes, a trait modelled as a quantitative trait that is allowed to vary through time. We found that when tetraploid individuals are less or as fit as their diploid progenitors, fixation of polyploidy is only possible when genetic drift is stronger than natural selection. The necessity of drift for tetraploid fixation holds even when polyploidy confers a selective advantage, except for scenarios where tetraploids are much fitter than diploids. Finally, we found that self-fertilization is less beneficial for tetraploid establishment than previously thought, notably when polyploids harbour an initial decrease in fitness. Our results bring a novel, non-exclusive explanation for the unequal temporal and spatial distribution of polyploid species.

• Keywords
• genetic drift, polyploid establishment, self-fertilization, unreduced gametes,
• MeSH
• Diploidy MeSH
• Genetic Drift MeSH
• Polyploidy * MeSH
• Plants MeSH
• Tetraploidy * MeSH
• Germ Cells MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

The extracellular subunit of the major histocompatibility complex MHCIIβ plays an important role in the recognition of pathogens and the initiation of the adaptive immune response of vertebrates. It is widely accepted that pathogen-mediated selection in combination with neutral micro-evolutionary forces (e.g. genetic drift) shape the diversity of MHCIIβ, but it has proved difficult to determine the relative effects of these forces. We evaluated the effect of genetic drift and balancing selection on MHCIIβ diversity in 12 small populations of Galápagos mockingbirds belonging to four different species, and one larger population of the Northern mockingbird from the continental USA. After genotyping MHCIIβ loci by high-throughput sequencing, we applied a correlational approach to explore the relationships between MHCIIβ diversity and population size by proxy of island size. As expected when drift predominates, we found a positive effect of population size on the number of MHCIIβ alleles present in a population. However, the number of MHCIIβ alleles per individual and number of supertypes were not correlated with population size. This discrepancy points to an interesting feature of MHCIIβ diversity dynamics: some levels of diversity might be shaped by genetic drift while others are independent and possibly maintained by balancing selection.

• Keywords
• Mimus, genetic diversity, major histocompatibility complex, population size, trans-species polymorphism,
• MeSH
• Genetic Variation MeSH
• Genetic Drift * MeSH
• Genotype MeSH
• Genes, MHC Class II * MeSH
• Population Density MeSH
• Islands MeSH
• Passeriformes genetics   MeSH
• Genetics, Population MeSH
• Selection, Genetic * MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Ecuador MeSH
• Islands MeSH

Phenotypic invariance-the outcome of purifying selection-is a hallmark of biological importance. However, invariant phenotypes might be controlled by diverged genetic systems in different species. Here, we explore how an important and invariant phenotype-the development of sexually differentiated individuals-is controlled in over two dozen species in the frog family Pipidae. We uncovered evidence in different species for 1) an ancestral W chromosome that is not found in many females and is found in some males, 2) independent losses and 3) autosomal segregation of this W chromosome, 4) changes in male versus female heterogamy, and 5) substantial variation among species in recombination suppression on sex chromosomes. We further provide evidence of, and evolutionary context for, the origins of at least seven distinct systems for regulating sex determination among three closely related genera. These systems are distinct in their genomic locations, evolutionary origins, and/or male versus female heterogamy. Our findings demonstrate that the developmental control of sexual differentiation changed via loss, sidelining, and empowerment of a mechanistically influential gene, and offer insights into novel factors that impinge on the diverse evolutionary fates of sex chromosomes.

• Keywords
• developmental systems drift, recombination suppression, sex chromosomes, sexual antagonism,
• MeSH
• Biological Evolution MeSH
• Phenotype MeSH
• Genetic Drift MeSH
• Evolution, Molecular MeSH
• Pipidae genetics   physiology   MeSH
• Sex Chromosomes genetics   MeSH
• Sex Determination Processes MeSH
• Recombination, Genetic MeSH
• Selection, Genetic MeSH
• Sex Differentiation MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Discussions of the survival determinism concept have previously focused on its primary role in the evolution of early unicellular organisms in the light of findings which have been reported on a number of diseases. The rationale for such parallel was in the view according to which multicellular organisms could be regarded as sophisticated colonies of semi-autonomous, single-celled entities, whereby various diseases were described as conditions arising upon the activation of the respective survival mechanisms in a milieu unsuitable for such robust stress response. The cellular mechanisms that were discussed in these contexts have been known to play various roles in other biological processes. The proposed notion could thereby be further extended to discussion on mechanisms for the implementation of the respective survival pathways in the development of metazoa, considering that they would have been propagated in their evolution for so long. This manuscript first presents a concise overview of the model previously discussed, followed by the discussion on the role of respective mechanism(s) in origins and development of metazoa. Finally, a reflection on the concept in relation to the prominent evolutionary models is put forward to illustrate a broader context of what is being discussed.

• Keywords
• Drifts, Evolutionary leaps, Selection, Survival determinism,
• MeSH
• Biological Evolution * MeSH
• Cell Lineage MeSH
• Caenorhabditis elegans MeSH
• Drosophila melanogaster MeSH
• Phylogeny * MeSH
• Genetic Variation MeSH
• Genetic Drift MeSH
• Genomics MeSH
• Models, Genetic MeSH
• Mutation MeSH
• Mutagenesis MeSH
• Genetics, Population MeSH
• Saccharomyces cerevisiae MeSH
• Selection, Genetic * MeSH
• Stochastic Processes MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH

The interactions of evolutionary forces are difficult to analyse in free-living populations. However, when properly understood, they provide valuable insights into evolutionary biology and conservation genetics. This is particularly important for the interplay of genetic drift and natural selection in immune genes that confer resistance to disease. The Galápagos Islands are inhabited by four closely related species of mockingbirds (Mimus spp.). We used 12 different-sized populations of Galápagos mockingbirds and one population of their continental relative northern mockingbird (Mimus polyglottos) to study the effects of genetic drift on the molecular evolution of immune genes, the Toll-like receptors (TLRs: TLR1B, TLR4 and TLR15). We found that neutral genetic diversity was positively correlated with island size, indicating an important effect of genetic drift. However, for TLR1B and TLR4, there was little correlation between functional (e.g., protein) diversity and island size, and protein structural properties were largely conserved, indicating only a limited effect of genetic drift on molecular phenotype. By contrast, TLR15 was less conserved and even its putative functional polymorphism correlated with island size. The patterns observed for the three genes suggest that genetic drift does not necessarily dominate selection even in relatively small populations, but that the final outcome depends on the degree of selection constraint that is specific for each TLR locus.

• Keywords
• conservation genetics, innate immunity, island birds, molecular phenotype, purifying selection,
• MeSH
• Genetic Drift MeSH
• Population Density MeSH
• Passeriformes * genetics   MeSH
• Genetics, Population MeSH
• Selection, Genetic MeSH
• Toll-Like Receptor 4 * genetics   MeSH
• Toll-Like Receptors genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Toll-Like Receptor 4 * MeSH
• Toll-Like Receptors MeSH

Mixotrophic plants combine photosynthesis and heterotrophic nutrition. Recent research suggests mechanisms explaining why mixotrophy is so common in terrestrial ecosystems. First, mixotrophy overcomes nutrient limitation and/or seedling establishment constraints. Second, although genetic drift may push mixotrophs to full heterotrophy, the role of photosynthesis in reproduction stabilizes mixotrophy.

• Keywords
• evolutionary metastability, heterotrophy, mycoheterotrophy, mycorrhizae, plant parasitism,
• MeSH
• Biological Evolution MeSH
• Ecosystem MeSH
• Photosynthesis * MeSH
• Genetic Drift MeSH
• Heterotrophic Processes * MeSH
• Reproduction MeSH
• Embryophyta physiology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH

Pt-based materials are widely used as heterogeneous catalysts, in particular for pollutant removal applications. The state of Pt has often been proposed to differ depending on experimental conditions, for example, metallic Pt poisoned with CO being present at lower temperature before light-off, while an oxidized Pt surface prevails above light-off temperature. In stark contrast to all previous reports, we show herein that both metallic and oxidized Pt are present in similar proportions under reaction conditions at the surface of ca. 1 nm nanoparticles showing high activity at 30 °C. The simultaneous presence of metallic and oxidized Pt enables a synergy between these phases. The main role of the metallic Pt phase is to provide strong adsorption sites for CO, while that of oxidized Pt supposedly supplies reactive oxygen. Our results emphasize the complex dual oxidic-metallic nature of supported Pt catalysts and platinum's evolving nature under reaction conditions.

• Keywords
• NAP-XPS, operando DRIFTS, platinum, room temperature CO oxidation, structure-reactivity relationship,
• Publication type
• Journal Article MeSH

Our understanding of population history in deep time has been assisted by fitting admixture graphs (AGs) to data: models that specify the ordering of population splits and mixtures, which along with the amount of genetic drift and the proportions of mixture, is the only information needed to predict the patterns of allele frequency correlation among populations. The space of possible AGs relating populations is vast, and thus most published studies have identified fitting AGs through a manual process driven by prior hypotheses, leaving the majority of alternative models unexplored. Here, we develop a method for systematically searching the space of all AGs that can incorporate non-genetic information in the form of topology constraints. We implement this findGraphs tool within a software package, ADMIXTOOLS 2, which is a reimplementation of the ADMIXTOOLS software with new features and large performance gains. We apply this methodology to identify alternative models to AGs that played key roles in eight publications and find that in nearly all cases many alternative models fit nominally or significantly better than the published one. Our results suggest that strong claims about population history from AGs should only be made when all well-fitting and temporally plausible models share common topological features. Our re-evaluation of published data also provides insight into the population histories of humans, dogs, and horses, identifying features that are stable across the models we explored, as well as scenarios of populations relationships that differ in important ways from models that have been highlighted in the literature.

• Keywords
• admixture graphs, dogs, evolutionary biology, f-statistics, genetics, genomics, horses, human, humans, population genetics,
• MeSH
• Gene Frequency MeSH
• Genetic Drift MeSH
• Hominidae * MeSH
• Horses MeSH
• Humans MeSH
• Models, Genetic MeSH
• Genetics, Population * MeSH
• Dogs MeSH
• Software MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Dogs MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH