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Audrey C. Heppleston

Bio: Audrey C. Heppleston is an academic researcher from McGill University. The author has contributed to research in topics: Evolution of sexual reproduction & Genetic load. The author has an hindex of 3, co-authored 3 publications receiving 84 citations.

Papers
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Journal ArticleDOI
TL;DR: Despite the similarities of early events related to development of the branchial region and initial outgrowth of the fins, later stages are increasingly characterized by taxon‐specific morphologies making a universal staging table for chondrichthyans less applicable.
Abstract: The ontogeny of the northwestern Atlantic batoid, Leucoraja ocellata, is described with special focus on the development of skate specific morphologies and the development of the fins. The results show that the sequence of events involving the early outgrowth of the paired fins and the initial development of the pharyngeal region is remarkably constant in skates, holocephalians, and sharks. However, differences exist in timing of the reshaping of the mandibular arch region, development of branchial filaments, median fins, denticles, and the order of branchial cleft formation. Despite the similarities of early events related to development of the branchial region and initial outgrowth of the fins, later stages are increasingly characterized by taxon-specific morphologies making a universal staging table for chondrichthyans less applicable. The staging table presented in this study represents an important resource for future studies on batoid embryology.

61 citations

Journal ArticleDOI
TL;DR: It is suggested that sexual populations at equilibrium with selection in a benign environment may be mixtures of several or many epistatic genotypes with nearly equal fitness, and Recombination between these genotypes reduces mean fitness and creates genetic variance for fitness.
Abstract: We measured the mean fitness of populations of Chlamydomonas reinhardtii maintained in the laboratory as obligately sexual or asexual populations for about 100 sexual cycles and about 1000 asexual generations. Sexuality (random gamete fusion followed by meiosis) is expected to reduce mutational load and increase mean fitness by combining deleterious mutations from different lines of descent. We found no evidence for this process of mutation clearance: the mean fitness of sexual populations did not exceed that of asexual populations, whether measured through competition or in pure culture. We found instead that sexual progeny suffer an immediate loss in fitness, and that sexual lines maintain genetic variance for fitness. We suggest that sexual populations at equilibrium with selection in a benign environment may be mixtures of several or many epistatic genotypes with nearly equal fitness. Recombination between these genotypes reduces mean fitness and creates genetic variance for fitness. This may provide fuel for continued selection should the environment change.

23 citations

Journal ArticleDOI
TL;DR: A developmental series of Alligator mississippiensis forelimb buds reveal only five digital anlagen, supports a pentadactyl ground state for the archosaurian manus, and rejects portions of the evolutionary developmental trajectories proposed, lending further support to the contribution of a homeotic transformation during digit reduction in avian ancestry.
Abstract: The three-fingered state of the avian manus poses intriguing questions about the evolution of digit reduction. Although digit reduction in most tetrapods appears to be the product of straightforward digit loss, avian digit reduction may have occurred with a dissociation of digit position from digit identity. The three digits of birds have the ancestral identities of I, II, and III but develop from an early pentadactyl ground state from digital anlage 2, 3, and 4. A series of hypotheses have been proposed in an attempt to explain this disparity, including a recent suggestion that the anteriormost condensation visible in the avian limb bud is in fact a vestigial structure from a hexadactyl ancestral ground state. We investigated this proposal by presenting sets of compatible evolutionary developmental trajectories starting from a hexadactyl state to test hypotheses of digit reduction. The development of skeletogenic mesenchymal condensations in a crocodylian, the closest extant relative to birds, is used to identify any extra precartiloginous digital vestiges. A developmental series of Alligator mississippiensis forelimb buds reveal only five digital anlagen, supports a pentadactyl ground state for the archosaurian manus, and rejects portions of the evolutionary developmental trajectories proposed. This condition lends further support to the contribution of a homeotic transformation during digit reduction in avian ancestry to account for the dissociation between digital identity and developmental position.

20 citations

Journal ArticleDOI
TL;DR: The EDESIA programme will allow the translation of science into guidelines for healthy eating and the production of nutritionally improved food crops, leading to innovative food products, particularly for prevention and treatment of chronic diseases where age is a major risk factor.
Abstract: Abstract In an era where preventive medicine is increasingly important due to an ageing population and rising obesity, optimised diets are key to improving health and reducing risk of ill health. The Wellcome Trust‐funded, EDESIA: Plants, Food and Health: a cross‐disciplinary PhD programme from Crop to Clinic (218 467/Z/19/Z) focuses on investigating plant‐based nutrition and health, from crop to clinic, drawing on the world‐class interdisciplinary research expertise of partner institutions based on the Norwich Research Park (University of East Anglia, John Innes Centre, Quadram Institute and Earlham Institute). Through a rotation‐based programme, EDESIA PhD students will train in a wide range of disciplines across the translational pathway of nutrition research, including analyses of epidemiological datasets, assessment of nutritional bioactives, biochemical, genetic, cell biological and functional analyses of plant metabolites, in vitro analyses in tissue and cell cultures, investigation of efficacy in animal models of disease, investigation of effects on composition and functioning of the microbiota and human intervention studies. Research rotations add a breadth of knowledge, outside of the main PhD project, which benefits the students and can be brought into project design. This comprehensive PhD training programme will allow the translation of science into guidelines for healthy eating and the production of nutritionally improved food crops, leading to innovative food products, particularly for prevention and treatment of chronic diseases where age is a major risk factor. In this article, we summarise the programme and showcase the experiences of the first cohort of students as they start their substantive PhD projects after a year of research rotations.

1 citations


Cited by
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Journal ArticleDOI
TL;DR: In experiments with a facultatively sexual rotifer, populations adapting to novel environments evolve higher rates of sex because sexual mixing quickly assembles well-adapted genotypes.
Abstract: Both theory and experiments have demonstrated that sex can facilitate adaptation, potentially yielding a group-level advantage to sex. However, it is unclear whether this process can help solve the more difficult problem of the maintenance of sex within populations. Using experimental populations of the facultatively sexual rotifer Brachionus calyciflorus, we show that rates of sex evolve to higher levels during adaptation but then decline as fitness plateaus. To assess the fitness consequences of genetic mixing, we directly compare the fitnesses of sexually and asexually derived genotypes that naturally occur in our experimental populations. Sexually derived genotypes are more fit than asexually derived genotypes when adaptive pressures are strong, but this pattern reverses as the pace of adaptation slows, matching the pattern of evolutionary change in the rate of sex. These fitness assays test the net effect of sex but cannot be used to disentangle whether selection on sex arises because highly sexual lineages become associated with different allele combinations or with different allele frequencies than less sexual lineages (i.e., “short-” or “long-term” effects, respectively). We infer which of these mechanisms provides an advantage to sex by performing additional manipulations to obtain fitness distributions of sexual and asexual progeny arrays from unbiased parents (rather than from naturally occurring, and thereby evolutionarily biased, parents). We find evidence that sex breaks down adaptive gene combinations, resulting in lower average fitness of sexual progeny (i.e., a short-term disadvantage to sex). As predicted by theory, the advantage to sex arises because sexually derived progeny are more variable in fitness, allowing for faster adaptation. This “long-term advantage” builds over multiple generations, eventually resulting in higher fitness of sexual types.

145 citations

Journal ArticleDOI
01 May 2008-Heredity
TL;DR: It is shown that, while experimental evolution has helped us to begin to understand the evolutionary dynamics of traits that affect evolvability, many interesting questions remain to be answered.
Abstract: The suggestion that there are characteristics of living organisms that have evolved because they increase the rate of evolution is controversial and difficult to study. In this review, we examine the role that experimental evolution might play in resolving this issue. We focus on three areas in which experimental evolution has been used previously to examine questions of evolvability; the evolution of mutational supply, the evolution of genetic exchange and the evolution of genetic architecture. In each case, we summarize what studies of experimental evolution have told us so far and speculate on where progress might be made in the future. We show that, while experimental evolution has helped us to begin to understand the evolutionary dynamics of traits that affect evolvability, many interesting questions remain to be answered.

70 citations

Journal ArticleDOI
08 Feb 2018-Cell
TL;DR: It is shown that the neural substrates of bipedalism are present in the little skate Leucoraja erinacea, whose common ancestor with tetrapods existed ∼420 million years ago, and this indicates that the circuits that are essential for walking evolved through adaptation of a genetic regulatory network shared by all vertebrates with paired appendages.

68 citations

Journal ArticleDOI
TL;DR: The evidence from natural populations and from laboratory experiments point to antagonistic coevolution as a potent and possibly ubiquitous force of selection favouring cross‐fertilization and recombination.
Abstract: Sexual reproduction is widely regarded as one of the major unexplained phenomena in biology. Nonetheless, while a general answer may remain elusive, considerable progress has been made in the last few decades. Here, we first review the genesis of, and support for, the major ecological hypotheses for biparental sexual reproduction. We then focus on the idea that host-parasite coevolution can favour cross-fertilization over uniparental forms of reproduction, as this hypothesis currently has the most support from natural populations. We also review the results from experimental evolution studies, which tend to show that exposure to novel environments can select for higher levels of sexual reproduction, but that sex decreases in frequency after populations become adapted to the previously novel conditions. In contrast, experimental coevolution studies suggest that host-parasite interactions can lead to the long-term persistence of sex. Taken together, the evidence from natural populations and from laboratory experiments point to antagonistic coevolution as a potent and possibly ubiquitous force of selection favouring cross-fertilization and recombination.

63 citations

Journal ArticleDOI
TL;DR: It is demonstrated that the principal dorsal and ventral endoskeletal segments of the jaw, hyoid and gill arches of the skate Leucoraja erinacea derive from molecularly equivalent mesenchymal domains of combinatorial Dlx gene expression.
Abstract: It is generally believed that jaws evolved from a gill arch, but this is unsupported by palaeontological or developmental data. Gillis et al. study three gnathostome taxa and identify a conserved molecular mechanism that delineates the dorsal and ventral skeletal segments of the jaw, hyoid and gill arches.

61 citations