A new sociobiological theory of homosexuality applicable to societies with universal marriage

Several sociobiological theories have tried to explain human homosexuality. Adaptationally orthodox theories view it as a specific instance of reproductive altruism, in which the homosexual orientation in combination with a cross-gender identity is the emotional motivator of a nonreproductive role, leading to higher inclusive fitness for the individual displaying the trait in a particular environment. The nonreproduction is typically assumed to be plete—a large reproductive sacrifice. A new model is proposed in which human homosexuality remains a reproductively altruistic, trait, but in which the magnitude of the altruism is much reduced, and so presumably is more likely to result in a net increase in inclusive fitness. The theory applies to societies in which social pressures require marriage of essentially all reproductively able individuals, and does not require gender nonconformity. Hence, the new theoy fills some of the gaps left by the earlier orthodox theories, and in combination with them offers a consolidated set of hypothesis for testing.     

A novel empirical free energy function that explains and predicts protein-protein binding affinities

A free energy function can be defined as a mathematical expression that relates macroscopic free energy changes to microscopic or molecular properties. Free energy functions can be used to explain and predict the affinity of a ligand for a protein and to score and discriminate between native and non-native binding modes. However, there is a natural tension between developing a function fast enough to solve the scoring problem but rigorous enough to explain and predict binding affinities. Here, we present a novel, physics-based free energy function that is computationally inexpensive, yet explanatory and predictive. The function results from a derivation that assumes the cost of polar desolvation can be ignored and that includes a unique and implicit treatment of interfacial water-bridged interactions. The function was parameterized on an internally consistent, high quality training set giving R2=0.97 and Q2=0.91. We used the function to blindly and successfully predict binding affinities for a diverse test set of 31 wild-type protein-protein and protein-peptide complexes (R2=0.79, rmsd=1.2 kcal mol(-1)). The function performed very well in direct comparison with a recently described knowledge-based potential and the function appears to be transferable. Our results indicate that our function is well suited for solving a wide range of protein/peptide design and discovery problems.     

Genealogical theory for random mating populations with two sexes

Consider a random mating population that has N(m) males and N(f) females in each generation. Let us assume that at time 0 a random sample of n copies of a gene is taken from this population. Then, for models introduced by Wright [Evolution in Mendelian populations, Genetics 16 (1931) 97; Inbreeding and homozygosis, Proc. Nat. Acad. Wash. 19 (1933) 420; Evolution and the Genetics of Populations, The Theory of Gene Frequencies, vol. II, The University of Chicago, Chicago and London, 1969.], it is possible to obtain generalizations of the haploid theory of genealogical processes developed by Felsenstein . It is conjectured that these hold generally, regardless of the effective population size, if n相似文献   

A taxonomic distance applicable to paleontology

A general Hausdorff-like metric on sets is presented with applications to paleontological “dissimilarity measures.” The distances between taxa represented by living organisms and/or fossil material are obtainable simply and independently of the nature of the characteristics used to define the taxonomic units. In particular, linear independence of the measured anatomical characters is not required.     

A nonparametric approach to the discrimination of two cell populations

An approach to the statistical testing of differences between two cell populations the elements of which are characterized by multivariate data is described. The approach is based on the Fisher discriminant and the Kruskal-Wallis test. The method, which is sufficient but not necessary, makes no assumptions about the normality of the data or about the equality of the covariance matrices for each population.     

Distinct viral populations differentiate and evolve independently in a single perennial host plant

The complex structure of virus populations has been the object of intensive study in bacteria, animals, and plants for over a decade. While it is clear that tremendous genetic diversity is rapidly generated during viral replication, the distribution of this diversity within a single host remains an obscure area in this field of science. Among animal viruses, only Human immunodeficiency virus and Hepatitis C virus populations have recently been thoroughly investigated at an intrahost level, where they are structured as metapopulations, demonstrating that the host cannot be considered simply as a "bag" containing a homogeneous or unstructured swarm of mutant viral genomes. In plants, a few reports suggested a possible heterogeneous distribution of virus variants at different locations within the host but provided no clues as to how this heterogeneity is structured. Here, we report the most exhaustive study of the structure and evolution of a virus population ever reported at the intrahost level through the analysis of a Prunus tree infected by Plum pox virus for over 13 years following a single inoculation event and by using analysis of molecular variance at different hierarchical levels combined with nested clade analysis. We demonstrate that, following systemic invasion of the host, the virus population differentiates into several distinct populations that are isolated in different branches, where they evolve independently through contiguous range expansion while colonizing newly formed organs. Moreover, we present and discuss evidence that the tree harbors a huge "bank" of viral clones, each isolated in one of the myriad leaves.     

A stochastic step model of replicative senescence explains ROS production rate in ageing cell populations

Increases in cellular Reactive Oxygen Species (ROS) concentration with age have been observed repeatedly in mammalian tissues. Concomitant increases in the proportion of replicatively senescent cells in ageing mammalian tissues have also been observed. Populations of mitotic human fibroblasts cultured in vitro, undergoing transition from proliferation competence to replicative senescence are useful models of ageing human tissues. Similar exponential increases in ROS with age have been observed in this model system. Tracking individual cells in dividing populations is difficult, and so the vast majority of observations have been cross-sectional, at the population level, rather than longitudinal observations of individual cells.One possible explanation for these observations is an exponential increase in ROS in individual fibroblasts with time (e.g. resulting from a vicious cycle between cellular ROS and damage). However, we demonstrate an alternative, simple hypothesis, equally consistent with these observations which does not depend on any gradual increase in ROS concentration: the Stochastic Step Model of Replicative Senescence (SSMRS). We also demonstrate that, consistent with the SSMRS, neither proliferation-competent human fibroblasts of any age, nor populations of hTERT overexpressing human fibroblasts passaged beyond the Hayflick limit, display high ROS concentrations. We conclude that longitudinal studies of single cells and their lineages are now required for testing hypotheses about roles and mechanisms of ROS increase during replicative senescence.     

A simple theoretical model explains dynein's response to load

Recent experiment showed that cytoplasmic dynein 1, a molecular motor responsible for cargo transport in cells, functions as a gear in response to external load. In the presence of vanishing or small external load, dynein walks with 24- or 32-nm steps, whereas at high external load, its step size is reduced to 8 nm. A simple model is proposed to account for this property of dynein. The model assumes that the chemical energy of ATP hydrolysis is used through a loose coupling between the chemical reaction and the translocation of dynein along microtubule. This loose chemomechanical coupling is represented by the loosely coupled motions of dynein along two different reaction coordinates. The first reaction coordinate is tightly coupled to the chemical reaction and describes the protein conformational changes that control the chemical processes, including ATP binding and hydrolysis, and ADP-Pi release. The second coordinate describes the translocation of dynein along microtubule, which is directly subject to the influence of the external load. The model is used to explain the experimental data on the external force dependence of the dynein step size as well as the ATP concentration dependence of the stall force. A number of predictions, such as the external force dependence of speed of translocation, ATP hydrolysis rate, and dynein step sizes, are made based on this theoretical model. This model provides a simple understanding on how a variable chemomechanical coupling ratio can be achieved and used to optimize the biological function of dynein.     

A diffusion-based theory of organism dispersal in heterogeneous populations

We develop a general theory of organism movement in heterogeneous populations that can explain the leptokurtic movement distributions commonly measured in nature. We describe population heterogeneity in a state-structured framework, employing advection-diffusion as the fundamental movement process of individuals occupying different movement states. Our general analysis shows that population heterogeneity in movement behavior can be defined as the existence of different movement states and among-individual variability in the time individuals spend in these states. A presentation of moment-based metrics of movement illustrates the role of these attributes in general dispersal processes. We also present a special case of the general theory: a model population composed of individuals occupying one of two movement states with linear transitions, or exchange, between the two states. This two-state "exchange model" can be viewed as a correlated random walk and provides a generalization of the telegraph equation. By exploiting the main result of our general analysis, we characterize the exchange model by deriving moment-based metrics of its movement process and identifying an analytical representation of the model's time-dependent solution. Our results provide general and specific theoretical explanations for empirical patterns in organism movement; the results also provide conceptual and analytical bases for extending diffusion-based dispersal theory in several directions, thereby facilitating mechanistic links between individual behavior and spatial population dynamics.     

A morphological study of two populations of Bosmina longispina exposed to different predation

Two populations of Bosmina longispina existing in two similarand closely situated Norwegian mountain lakes were investigatedwith respect to morphological variations. The two lakes areinhabited by different predators, Lake Gopollen is dominatedby whitefish and Lake Djupen by a sparse population of browntrout and invertebrate predators. The B. longispina in LakeDjupen were both larger and also longer at maturation than theB. longispina of Lake Gopollen. In Lake Djupen the mucronesof B. longispina were twice as long and their relative antennulalength was also larger than in Lake Gopollen. However, the relativeeye size did not differ between the two populations. The observationsfit the present hypothesis on morphological predator avoidanceadaptations in B. longispina, fairly well. Invertebrate predatorsfavour large B. longispina with long protuberances, body sizeand length of mucro being the most important features.     

A unified kinetic mechanism applicable to multiple DNA polymerases

After extensive studies spanning over half a century, there is little consensus on the kinetic mechanism of DNA polymerases. Using stopped-flow fluorescence assays for mammalian DNA polymerase beta (Pol beta), we have previously identified a fast fluorescence transition corresponding to conformational closing, and a slow fluorescence transition matching the rate of single-nucleotide incorporation. Here, by varying pH and buffer viscosity, we have decoupled the rate of single-nucleotide incorporation from the rate of the slow fluorescence transition, thus confirming our previous hypothesis that this transition represents a conformational event after chemistry, likely subdomain reopening. Analysis of an R258A mutant indicates that rotation of the Arg258 side chain is not rate-limiting in the overall kinetic pathway of Pol beta, yet is kinetically significant in subdomain reopening. We have extended our kinetic analyses to a high-fidelity polymerase, Klenow fragment (KF), and a low-fidelity polymerase, African swine fever virus DNA polymerase X (Pol X), and showed that they follow the same kinetic mechanism as Pol beta, while differing in relative rates of single-nucleotide incorporation and the putative conformational reopening. Our data suggest that the kinetic mechanism of Pol beta is not an exception among polymerases, and furthermore, its delineated kinetic mechanism lends itself as a platform for comparison of the kinetic properties of different DNA polymerases and their mutants.     

Pivoting plant immunity from theory to the field

<正>Plants live in complex environments and are constantly exposed to potential pathogens with different lifestyles and infection strategies.The evolutionary arms race between plants and their attackers has provided plants with a highly sophisticated and multi-layered defense system,which recognizes pathogen molecules and responds by activating defense pathways in order to resist the invaders.Here,we discuss recent developments in plant immunity,summarize conserved anti-microbial defense outputs and pathways,and     

A model for genetic relationship in areally continuous plant populations

Representations are based on plant populations, continuously distributed over their habitats according to specified density patterns. Migration of genetic material takes place via pollen and seed dispersal. Monoecious plants with arbitrary rates of self-fertilization and dioecious plants are considered. The model was constructed with the intention of determining coefficients of inbreeding and kinship for all locations within the seed population after its dispersal over the habitat, assuming the respective genetic relationships of the parental generation to be known. To display the consequences of single components hidden in the general result, the following specifications have been treated: finite population size combined with random dispersal of seed, equilibrium states for hypothetically infinite population size with “limited” dispersal of pollen and seed, random dispersal of pollen, and random dispersal of seed.