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The rate of adaptive evolution of a population ultimately depends on the rate of incorporation of beneficial mutations. Even beneficial mutations may, however, be lost from a population since mutant individuals may, by chance, fail to reproduce. In this paper, we calculate the probability of fixation of beneficial mutations that occur in populations of changing size. We examine a number of demographic models, including a population whose size changes once, a population experiencing exponential growth or decline, one that is experiencing logistic growth or decline, and a population that fluctuates in size. The results are based on a branching process model but are shown to be approximate solutions to the diffusion equation describing changes in the probability of fixation over time. Using the diffusion equation, the probability of fixation of deleterious alleles can also be determined for populations that are changing in size. The results developed in this paper can be used to estimate the fixation flux, defined as the rate at which beneficial alleles fix within a population. The fixation flux measures the rate of adaptive evolution of a population and, as we shall see, depends strongly on changes that occur in population size.

INTRODUCTION The importance of recombination is usually discussed in the context of its significance for the success of sexual systems over asexual ones. Most arguments hold that independent segregation of [...]

Whether in sexual or asexual organisms, selection among cell lineages during development is an effective way of eliminating deleterious mutations. Using a mathematical analysis, we find that relatively small differences in cell replication rates during development can translate into large differences in the proportion of mutant cells within the adult, especially when development involves a large number of cell divisions. Consequently, intraorganismal selection can substantially reduce the deleterious mutation rate observed among offspring as well as the mutation load within a population, because cells rather than individuals provide the selective 'deaths' necessary to stem the tide of deleterious mutations. The reduction in mutation rate among offspring is more pronounced in organisms with plastic development than in those with structured development. It is also more pronounced in asexual organisms that produce multicellular rather than unicellular offspring. By effecting the mutation rate, intraorganismal selection may have broad evolutionary implications; as an example, we consider its influence on the evolution of ploidy levels, finding that cell-lineage selection is more effective in haploids and tends to favor their evolution.

A two-locus model was used to analyse the factors involved in the evolution of a dominant diploid state in organisms undergoing an alternation of generations. The results of the analysis showed that dipoidy will be favored whenever masking of deleterious mutations occur. However, this masking effect is highly dependent on the degree of free recombination. When the level of recombination is low, diploidy is less favored. The analysis revealed that even when the masking effect is strong, significant levels of recombination are still neccessary for diploidy to have evolved.

Selection acts upon genes linked together on chromosomes. This physical connection reduces the efficiency by which selection can act because, in the absence of sex, alleles must rise and fall together in frequency with the genome in which they are found. This selective interference underlies such phenomena as clonal interference and Muller's Ratchet and is broadly termed Hill-Robertson interference. In this review, I examine the potential for selective interference to account for the evolution and maintenance of sex, discussing the positive and negative evidence from both theoretical and empirical studies, and highlight the gaps that remain. [ABSTRACT FROM AUTHOR]

• Doping with samarium increased radiosensitising effects of TiO 2 NPs in cancer cells. • ROS levels increased by doped samarium in X-ray irradiated cells. • No alterations in cellular uptake and cytotoxicity by doped samarium were observed. • Samarium doped NPs showed higher CT values than undoped NPs. Titanium dioxide nanoparticles (TiO 2 NPs) have been investigated for their role as radiosensitisers for radiation therapy. The study aims to increase the efficiency of these NPs by synthesising them with samarium. Samarium-doped TiO 2 NPs (Ti(Sm)O 2 NPs) were synthesised using a solvothermal method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS) were performed for characterising of the Ti(Sm)O 2 NPs. The intracellular uptake and cytotoxicity were assessed in vitro using A549 and DU145 cancer cell lines. Furthermore, the effect of dose enhancement and generation of reactive oxygen species (ROS) in response to 6 MV X-rays was evaluated. Additionally, the image contrast properties were investigated using computed tomography (CT) images. The synthesised Ti(Sm)O 2 NPs were about 13 nm in diameter as determined by TEM. The XRD pattern of Ti(Sm)O 2 NPs was consistent with that of anatase-type TiO 2. EDS confirmed the presence of samarium in the nanoparticles. At 200 μg/ml concentration, no differences in cellular uptake and cytotoxicity were observed between TiO 2 NPs and Ti(Sm)O 2 NPs in both A549 and DU145 cells. However, the combination of Ti(Sm)O 2 NPs and X-rays elicited higher cytotoxic effect and ROS generation in the cells than that with TiO 2 NPs and X-rays. The CT numbers of Ti(Sm)O 2 NPs were systematically higher than that of TiO 2 NPs. The Ti(Sm)O 2 NPs increased the dose enhancement of MV X-ray beams than that elicited by TiO 2 NPs. Samarium improved the efficiency of TiO 2 NPs as potential radiosensitising agent. [ABSTRACT FROM AUTHOR]

Pacific oyster Crassostrea gigas, endemic to coastal Asia, has been translocated globally throughout the past century, resulting in self‐sustaining introduced populations (naturalized). Oyster aquaculture industries in many parts of the world depend on commercially available seed (hatchery‐farmed) or naturalized/wild oysters to move onto a farm (naturalized‐farmed). It is therefore important to understand genetic variation among populations and farm types. Here, we genotype naturalized/wild populations from France, Japan, China, and most extensively in coastal British Columbia, Canada. We also genotype cultured populations from throughout the Northern Hemisphere to compare with naturalized populations. In total, 16,942 markers were identified using double‐digest RAD‐sequencing in 182 naturalized, 112 hatchery‐farmed, and 72 naturalized‐farmed oysters (n = 366). Consistent with previous studies, very low genetic differentiation was observed around Vancouver Island (mean FST = 0.0019) and low differentiation between countries in the Japan–Canada–France historical translocation lineage (France–Canada FST = 0.0024; Japan–Canada FST = 0.0060). Chinese populations were more differentiated (China–Japan FST = 0.0241). Hatchery‐propagated populations had higher interindividual relatedness suggesting family structure. Within‐population inbreeding was not detected on farms, but nucleotide diversity and polymorphism rate were lower in one farm population. Moving oysters from nature onto farms did not result in strong within‐generation selection. Private alleles at substantial frequency were identified in several hatchery populations grown in BC, suggesting nonlocal origins. Tests of selection identified outlier loci consistent with selective differences associated with domestication, in some cases consistently identified in multiple farms. Top outlier candidates were nearby genes involved in calcium signaling and calmodulin activity. Implications of potential introgression from hatchery‐farmed oysters depend on whether naturalized populations are valued as a locally adapted resource or as an introduced, invasive species. Given the value of the industry in BC and the challenges the industry faces (e.g., climate change, crop losses, biotic stressors), this remains an important question. [ABSTRACT FROM AUTHOR]

Author(s): Leithen K. M'Gonigle (corresponding author) [1, 3]; Rupert Mazzucco [2]; Sarah P. Otto [1]; Ulf Dieckmann [2] Empirical data indicate that sexual preferences are critical for maintaining species boundaries [...]

A model of mate choice among sexual individuals and asexual gynogens was used to explore the mating preference favored by the males of the sexual species with sexual females over gynogenetic females to determine if such mating preferences could stably maintain both gynogenetic and sexual individuals within a community. The model revealed that stable coexistence of gynogens and their sexual hosts possibly occurs when there is variation among males in the degree of preference for mating with sexual females and when pickier males pay a higher cost of preference.