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