Deleterious mutations are of fundamental importance to all aspects of organismal biology. Evolutionary geneticists have expended tremendous effort to estimate the genome-wide rate of mutation and the effects of new mutations on fitness, but the degree to which genomic mutational properties vary within and between taxa is largely unknown, particularly in multicellular organisms. Beginning with two highly inbred strains from each of three species in the nematode family Rhabditidae (Caenorhabditis briggsae, Caenorhabditis elegans, and Oscheius myriophila), we allowed mutations to accumulate in the relative absence of natural selection for 200 generations. We document significant variation in the rate of decay of fitness because of new mutations between strains and between species. Estimates of the per-generation mutational decay of fitness were very consistent within strains between assays 100 generations apart. Rate of mutational decay in fitness was positively associated with genomic mutation rate and negatively associated with average mutational effect. These results provide unambiguous experimental evidence for substantial variation in genome-wide properties of mutation both within and between species and reinforce conclusions from previous experiments that the cumulative effects on fitness of new mutations can differ markedly among related taxa.Caenorhabditis briggsae ͉ Caenorhabditis elegans ͉ deleterious mutation ͉ mutation accumulation ͉ Oscheius myriophila F ew topics in evolutionary biology have generated as much controversy in recent years as spontaneous mutation, considered at the level of the entire genome (1-4). It is widely accepted that the great majority of new mutations are either neutral or deleterious (refs. 1 and 5-7; also see refs. 3 and 8-13), and the importance of deleterious mutations to a wide variety of biological processes and phenomena is well appreciated (7). The source of the controversy stems from uncertainty in the rate at which new mutations accrue in the genome and the distribution of effects of those mutations on fitness.Beginning in the early 1960s, Mukai, Ohnishi, and their colleagues (14-18) conducted several large mutation accumulation (MA) experiments with Drosophila melanogaster that were designed to estimate the rate and average effect of new mutations on fitness. By the early 1970s, the results seemed clear: averaged over experiments, egg-to-adult viability declined rapidly, on the order of 1% per genome per generation, with the implication that the diploid genomic mutation rate (U) was on the order of 0.6 per generation or greater and the average homozygous effect on fitness of a new mutation (2a ) was Ϸ0.05 or less. The typical newborn fly was thus expected to harbor one new mutation that could be expected to reduce its viability by Ϸ5% when homozygous.Several additional lines of evidence supported the results from the early f ly MA experiments. First, the considerable inbreeding depression in Drosophila implied either a high rate of deleterious mutation or considerable...
We carried out a geologic survey and a preliminary archaeological survey of four fossil‐spring tufa localities in Kharga Oasis, Egypt, to constrain the timing of pluvial episodes in the Western Desert, and to document prehistoric occupation contemporaneous with times of increased rainfall. Uranium‐series dating of the tufas confirms that at least five episodes of tufa deposition are represented in Kharga, although not every event is represented at each locality. Across the region studied, tufas were most frequently deposited as part of a fluvial barrage system, characterized by terraced, vegetated pools impounded by arcuate tufa dams and separated by small waterfalls. Available water resources during pluvial phases would have included not only spring‐fed streams but also small freshwater lakes. While Earlier Stone Age (ESA) and Middle Stone Age (MSA) lithic artifacts may be found either as surficial lags on tufas, or, less commonly, encased within tufas, Epipalaeolithic and Neolithic artifacts are generally found in or on silts within surface deflation depressions in the tufas, principally at Wadi Midauwara. © 2004 Wiley Periodicals, Inc.
Lake Ontario once supported a large complex of Atlantic Salmon (Salmo salar) populations that became extinct prior to scientific study. Since the 1860s, research efforts to conserve and reintroduce a sustainable population of Atlantic Salmon have focused on determining whether Lake Ontario’s original salmon populations had migrated to the Atlantic Ocean as part of their lifecycle (anadromy), stayed in the lake year-round (potamodromy), or both. We used stable carbon, nitrogen, and sulfur isotope analyses of archaeological bones and historical museum-archived salmon scales to show that the original salmon populations from Lake Ontario completed their entire lifecycle without migrating to the Atlantic Ocean. With a time depth of more than 500 years, our findings provide a unique baseline with significant potential for informing modern restocking and conservation efforts.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.