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ArnaudHaond, S., Stoeckel, S., & Bailleul, D. (2020). New insights into the population genetics of partially clonal organisms: When seagrass data meet theoretical expectations. Mol. Ecol., 29(17), 3248–3260.
Résumé: Seagrass meadows are among the most important coastal ecosystems in terms of both spatial extent and ecosystem services, but they are also declining worldwide. Understanding the drivers of seagrass meadow dynamics is essential for designing sound management, conservation and restoration strategies. However, poor knowledge of the effect of clonality on the population genetics of natural populations severely limits our understanding of the dynamics and connectivity of meadows. Recent modelling approaches have described the expected distributions of genotypic and genetic descriptors under increasing clonal rates, which may help us better understand and interpret population genetics data obtained for partial asexuals. Here, in the light of these recent theoretical developments, we revisited population genetics data for 165 meadows of four seagrass species. Contrasting shoot lifespan and rhizome turnover led to the prediction that the influence of asexual reproduction would increase along a gradient fromZostera noltiitoZostera marina, Cymodocea nodosaandPosidonia oceanica, with increasing departure from HardyWeinberg equilibrium (Fis), mostly towards heterozygote excess, and decreasing genotypic richness (R). This metaanalysis provides a nested validation of this hypothesis at both the species and meadow scales through a significant relationship betweenF(is)andRwithin each species. By empirically demonstrating the theoretical expectations derived from recent modelling approaches, this work calls for the use of HardyWeinberg equilibrium (Fis) rather than only the strongly samplingsensitiveRto assess the importance of clonal reproduction (c), at least when the impact of selfing onF(is)can be neglected. The results also emphasize the need to revise our appraisal of the extent of clonality and its influence on the dynamics, connectivity and evolutionary trajectory of partial asexuals in general, including in seagrass meadows, to develop the most accurate management strategies.

Reichel, K., Masson, J.  P., Malrieu, F., ArnaudHaond, S., & Stoeckel, S. (2016). Rare sex or out of reach equilibrium? The dynamics of FIS in partially clonal organisms. BMC Genet., 17, 76.
Résumé: Background: Partially clonal organisms are very common in nature, yet the influence of partial asexuality on the temporal dynamics of genetic diversity remains poorly understood. Mathematical models accounting for clonality predict deviations only for extremely rare sex and only towards mean inbreeding coefficient (FIS) over bar < 0. Yet in partially clonal species, both FIS < 0 and FIS > 0 are frequently observed also in populations where there is evidence for a significant amount of sexual reproduction. Here, we studied the joint effects of partial clonality, mutation and genetic drift with a stateandtime discrete Markov chain model to describe the dynamics of FIS over time under increasing rates of clonality. Results: Results of the mathematical model and simulations show that partial clonality slows down the asymptotic convergence to FIS = 0. Thus, although clonality alone does not lead to departures from HardyWeinberg expectations once reached the final equilibrium state, both negative and positive FIS values can arise transiently even at intermediate rates of clonality. More importantly, such “transient” departures from Hardy Weinberg proportions may last long as clonality tunes up the temporal variation of FIS and reduces its rate of change over time, leading to a hyperbolic increase of the maximal time needed to reach the final mean (FIS,Finfinity) over bar value expected at equilibrium. Conclusion: Our results argue for a dynamical interpretation of FIS in clonal populations. Negative values cannot be interpreted as unequivocal evidence for extremely scarce sex but also as intermediate rates of clonality in finite populations. Complementary observations (e.g. frequency distribution of multiloci genotypes, population history) or time series data may help to discriminate between different possible conclusions on the extent of clonality when mean (FIS) over bar values deviating from zero and/or a large variation of FIS over loci are observed.
