
ARNAUDHAOND, S., MOALIC, Y., HERNANDEZGARCIA, E., EGUILUZ, V. M., ALBERTO, F., SERRAO, E. A., et al. (2014). Disentangling the Influence of Mutation and Migration in Clonal Seagrasses Using the Genetic Diversity Spectrum for Microsatellites. Journal Of Heredity, 105(4), 532–541.
Résumé: The recurrent lack of isolation by distance reported at regional scale in seagrass species was recently suggested to stem from stochastic events of largescale dispersal. We explored the usefulness of phylogenetic information contained in microsatellite loci to test this hypothesis by using the Genetic Diversity Spectrum (GDS) on databases containing, respectively, 7 and 9 microsatellites genotypes for 1541 sampling units of Posidonia oceanica and 1647 of Cymodocea nodosa. The simultaneous increase of microsatellite and geographic distances that emerges reveals a coherent pattern of isolation by distance in contrast to the chaotic pattern previously described using allele frequencies, in particular, for the longlived P. oceanica. These results suggest that the lack of isolation by distance, rather than the resulting from rare events of largescale dispersal, reflects at least for some species a stronger influence of mutation over migration at the scale of the distribution range. The global distribution of genetic polymorphism may, therefore, result predominantly from ancient events of stepbystep (re)colonization followed by local recruitment and clonal growth, rather than contemporary gene flow. The analysis of GDS appears useful to unravel the evolutionary forces influencing the dynamics and evolution at distinct temporal and spatial scales by accounting for phylogenetic information borne by microsatellites, under an appropriate mutation model. This finding adds nuance to the generalization of the influence of largescale dispersal on the dynamics of seagrasses.



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.

