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Assessing the genetic variation in fitness and lifespan in Daphnia magna

Titel Englisch Assessing the genetic variation in fitness and lifespan in Daphnia magna
Gesuchsteller/in Haag Christoph
Nummer 138203
Förderungsinstrument Projektförderung (Abt. I-III)
Forschungseinrichtung
Unité d'Ecologie et Evolution Département de Biologie Université de Fribourg
CNRS UMR 5175 Dépt. Dynamique des Systèmes Ecologiques Centre d'Ecologie Fonctionnelle et Evolutive
Hochschule Universität Freiburg - FR
Hauptdisziplin Zoologie
Beginn/Ende 01.11.2011 - 30.04.2015
Bewilligter Betrag 526'867.12
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Keywords (8)

Daphnia; Small populations; Structured populations; Genetic drift; Genetic basis of variation in fitness; Lifespan; Ageing; Deleterious mutations

Lay Summary (Englisch)

Lead
Lay summary
Evolution occurs because individuals in natural populations differ in fitness and because these fitness differences are heritable. However, the genetic basis of this heritable variation in fitness is not well understood. Theory predicts that the genetic basis of variation in fitness depends on population size, mainly because small populations experience increased levels of genetic drift, that is, random changes in the frequencies of genetic variants. This is predicted to shift the balance between strongly and weakly selected variants, but this prediction has rarely been tested. In this project, we will test this prediction using small and large populations of the water flea Daphnia magna (a small crustacean). We will use specific crosses that lead, in the absence of selection, to known proportions of different genotypes (so-called Mendelian ratios). Therefore, we can infer selection directly from deviations from these expected proportions. In order to do so, we choose marker genes, which are not themselves influenced by selection, but which represent selection in the chromosomal region around these genes. In fact, this method is closely related to the breeding designs that are used to construct “genetic maps”, which specify the order of different genes on chromosomes of species such as Drosophila and mouse. The difference is that, in our case, we map the naturally occurring genetic variation for fitness. This project will thus yield much needed empirical data to evaluate the above-mentioned theoretical models. A consequence of the predicted differences in the genetic basis of fitness variation, is that individuals from small populations are predicted to have a shorter lifespan than individuals from large populations because of increased accumulation of the alleles that are believed to lead to ageing. Indeed, our preliminary data suggest that individuals from small Daphnia populations live only about half as long as individuals from large Daphnia populations. In the current project, these preliminary data will be verified and it will be tested if these life-span differences are indeed due to differences in the genetic basis of variation in fitness (rather than for instance due to environmental differences). Both parts of the project thus address direct genetic consequences of increased genetic drift in small populations, and thus will advance our understanding of evolution in such environments. This is not only important for a wide range of conceptual issues in evolutionary biology, but also for conservation biology. Finally advancing our understanding of the evolution of lifespan and ageing may have important implications also for our own species.
Direktlink auf Lay Summary Letzte Aktualisierung: 21.02.2013

Verantw. Gesuchsteller/in und weitere Gesuchstellende

Mitarbeitende

Publikationen

Publikation
Automixis in Artemia: solving a century-old controversy.
Nougué O, Rode N O, Jabbour-Zahab R, Ségard A, Chevin L-M, Haag C R, Lenormand T (2015), Automixis in Artemia: solving a century-old controversy., in Journal of evolutionary biology, 28(12), 2337-48.
Genes mirror geography in Daphniamagna
Fields Peter D., Reisser Celine, Dukic Marinela, Haag Christoph R., Ebert Dieter (2015), Genes mirror geography in Daphniamagna, in MOLECULAR ECOLOGY, 24(17), 4521-4536.
Genetic load, inbreeding depression, and hybrid vigor covary with population size: An empirical evaluation of theoretical predictions.
Lohr Jennifer N, Haag Christoph R (2015), Genetic load, inbreeding depression, and hybrid vigor covary with population size: An empirical evaluation of theoretical predictions., in Evolution; international journal of organic evolution, 69(12), 3109-22.
Quantitative genetics of learning ability and resistance to stress in Drosophila melanogaster
Nepoux Virginie, Babin Aurelie, Haag Christoph, Kawecki Tadeusz J., Le Rouzic Arnaud (2015), Quantitative genetics of learning ability and resistance to stress in Drosophila melanogaster, in ECOLOGY AND EVOLUTION, 5(3), 543-556.
Uncovering Cryptic Asexuality in Daphnia magna by RAD Sequencing
Svendsen Nils, Reisser Celine M. O., Dukic Marinela, Thuillier Virginie, Segard Adeline, Liautard-Haag Cathy, Fasel Dominique, Huerlimann Evelin, Lenormand Thomas, Galimov Yan, Haag Christoph R. (2015), Uncovering Cryptic Asexuality in Daphnia magna by RAD Sequencing, in GENETICS, 201(3), 1143-1143.
REDUCED LIFESPAN AND INCREASED AGEING DRIVEN BY GENETIC DRIFT IN SMALL POPULATIONS
Lohr Jennifer N., David Patrice, Haag Christoph R. (2014), REDUCED LIFESPAN AND INCREASED AGEING DRIVEN BY GENETIC DRIFT IN SMALL POPULATIONS, in EVOLUTION, 68(9), 2494-2508.

Verbundene Projekte

Nummer Titel Start Förderungsinstrument
118185 The genetics of inbreeding depression, hybrid vigour, and genetic load in structured populations 01.02.2008 Projektförderung (Abt. I-III)

Abstract

The genetic basis of variation in fitness among individuals of the same species is one of the most important still partly unresolved questions in evolutionary genetics. Theory predicts that the genetic basis of variation in fitness depends on population size and population structure, mainly because under increase levels of genetic drift, strongly deleterious alleles may be removed, but mildly deleterious alleles may reach higher frequencies, under some conditions even fixation. In addition, overdominance may break down if one of the alleles becomes fixed by genetic drift. In a precursor project (my current SNF project), we have started to investigate inbreeding depression and its genetic basis in Daphnia magna populations that strongly differ in population size and population structure. Here I propose to use the data produced by this precursor project as well as new data to estimate selection coefficients and dominance coefficients of alleles at fitness-relevant loci that segregate in these different populations in order to test above theory. We use a marker-based approach, exploiting several specific advantages of the Daphnia life cycle for such an approach (which include the possibility to detect genes of moderate fitness effects and to strongly reduce the problem of multiple testing). This marker-based approach involves breeding of families obtained from natural populations in a way similar to QTL-mapping and allows detection of fitness-associated QTLs. To estimate selection and dominance coefficients at the QTLs involved will require breeding of additional families (while still being able to use data on families of the precursor project), as well as typing of additional markers in the QTL regions. The latter has become possible due to the forthcoming high-density genetic SNP map of D. magna, which allows mapping of the scaffolds of the draft genome sequence that can be used to identify these markers. Using these data we will test for differences in the genetic basis of variation in fitness between populations differing in population size and population structure. The effects of population size and population structure on the genetic basis of fitness variation have implications for the evolution of several traits, including lifespan: If mildly deleterious alleles have elevated frequencies in small or strongly structured populations, individuals from these populations may show reduced lifespan and increased rates of ageing. This is because deleterious alleles that are expressed quite late in life, but not so late as to have negligible effect on overall fitness, may accumulate in these populations but not in larger populations. In a pilot study, we have found that the lifespan of D. magna differs considerably among populations (ranging from an average of 50 days to an average of 90 days), and that average lifespan is correlated with genetic diversity, an inverse surrogate of the strength of genetic drift. Here we propose experiments to test whether the among-population variation in lifespan is indeed due to different levels of genetic drift, which includes a series of experiments to test alternative explanations, such as decreased lifespan in small populations being an adaptation to some (unknown) environmental covariates. The most important of these tests will assess the lifespan of hybrid individuals between nearby populations: if decreased lifespan in small populations is an adaptation, hybrids between nearby small populations should still show this adaptation, but if it is an effect of genetic drift, hybridization should result in a longer-lived rescue phenotype.Both parts of the proposal thus address direct genetic consequences of increased genetic drift in small and structured populations, and thus will advance our understanding of evolution in such environments. This is not only important for a wide range of conceptual issues in evolutionary biology, but also for conservation biology (e.g., for the question how species in fragmented landscapes may adapt to environmental change). Finally advancing our understanding of the evolution of lifespan and ageing may have important implications also for our own species.
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