Reproductive assurance through selfing during colonization events or when population densities are low has often been put forward as a mechanism selecting for the evolution of self-fertilization. Such arguments emphasize on the role of both local demography and metapopulation processes. We developed a model for the evolution of self-fertilization in a structured metapopulation in which local densities are not steady because of population growth. Reproduction by selfing is density-independent (reproductive assurance) but selfed seeds endure inbreeding depression, whereas reproduction by outcrossing is density-dependent (Allee effect). First, we derived an analytical criterion for metapopulation viability as a function of the selfing rate and metapopulation parameters. We show that outcrossers can develop a viable metapopulation when they produce a high amount of dispersal seeds that counterbalances their incapacity to found new populations from low densities. Second, the model shows there is a positive feedback between demography and outcrossing rates, leading to either complete outcrossing or selfing. Specifically, we illustrate that inbreeding depression can paradoxically favor the evolution of selfing because of its negative effect on density. Also, complete outcrossing can be selected despite pollen limitation, although it does not provide a full seed set. This model underlines the influence of the mating system both on demography and gene dynamics in a metapopulation context. K E Y W O R D S :Allee effect, Baker's law, evolution of self-fertilization, metapopulation dynamic, reproductive assurance.

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Local populations are subject to recurrent extinctions, and small populations are particularly prone to extinction. Both demographic (stochasticity and the Allee effect) and genetic factors (drift load and inbreeding depression) potentially affect extinction. In fragmented populations, regular dispersal may boost population sizes (demographic rescue effect) or/and reduce the local inbreeding level and genetic drift (genetic rescue effect), which can affect extinction risks. We studied extinction processes in highly fragmented populations of the common species Crepis sancta (Asteraceae) in urban habitats exhibiting a rapid turnover of patches. A four-year demographic monitoring survey and microsatellite genotyping of individuals allowed us to study the determinants of extinction. We documented a low genetic structure and an absence of inbreeding (estimated by multilocus heterozygosity), which suggest that genetic factors were not a major cause of patch extinction. On the contrary, local population size was the main factor in extinction, whereas connectivity was shown to decrease patch extinction, which we interpreted as a demographic rescue effect that was likely due to better pollination services for reproduction. This coupling of demographic and genetic tools highlighted the importance of dispersal in local patch extinctions of small fragmented populations connected by gene flow.

Th e metapopulation framework considers that the spatiotemporal distribution of organisms results from a balance between the colonization and extinction of populations in a suitable and discrete habitat network. Recent spatially realistic metapopulation models have allowed patch dynamics to be investigated in natural populations but such models have rarely been applied to plants. Using a simple urban fragmented population system in which favourable habitat can be easily mapped, we studied patch dynamics in the annual plant Crepis sancta (Asteraceae). Using stochastic patch occupancy models (SPOMs) and multi-year occupancy data we dissected extinction and colonization patterns in our system. Overall, our data were consistent with two distinct metapopulation scenarios. A metapopulation (sensu stricto) dynamic in which colonization occurs over a short distance and extinction is lowered by nearby occupied patches (rescue eff ect) was found in a set of patches close to the city centre, while a propagule rain model in which colonization occurs from a large external population was most consistent with data from other networks. Overall, the study highlights the importance of external seed sources in urban patch dynamics. Our analysis emphasizes the fact that plant distributions are governed not only by habitat properties but also by the intrinsic properties of colonization and dispersal of species. Th e metapopulation approach provides a valuable tool for understanding how colonization and extinction shape occupancy patterns in highly fragmented plant populations. Finally, this study points to the potential utility of more complex plant metapopulation models than traditionally used for analysing ecological and evolutionary processes in natural metapopulations.Since fi rst defi ned by Levins ( 1969), the metapopulation concept has been widely accepted and developed in both theoretical and empirical ecology (Hanski 1998). Th e metapopulation framework provides a quantitative basis for analysing and predicting species distribution at the regional scale by evaluating the colonization and extinction of local populations (Hanski 1998). Initially based on Levins ' model assumptions (Levins 1969), the generalization of colonization and extinction processes integrating for instance the rescue eff ect on extinction -the decrease in the extinction rate with increasing metapopulation occupancy (Hanski 1982) -or the propagule rain model, in which colonizing propagules come from large and often unknown populations (Gotelli 1991), now provides a general framework within which to analyse various metapopulation scenarios. Moreover, the development of spatially realistic models (Ovaskainen and Hanski 2004a) coupled with extensive statistical tools (Etienne et al. 2004) allows the analysis of empirical data. Th us, stochastic patch occupancy models (hereafter ' SPOMs ' ) allow the modelling of population turnover and assessments of how population dynamics occur at large scales. Th ese models provide estimates of colonization and extinction...

Gynodioecy, the co-occurrence of females and hermaphrodites, is often due to conflicting interactions between cytoplasmic male sterility genes and nuclear restorers. Although gynodioecy often occurs in self-compatible species, the effect of self-pollination, inbreeding depression, and pollen limitation acting differently on females and hermaphrodites remains poorly known in the case of nuclear-cytoplasmic gynodioecy (NCG). In this study, we model NCG in an infinite population and we study the effect of selfing rate, inbreeding depression, and pollen limitation on the maintenance of gynodioecy and on sex ratios at equilibrium. We found that selfing and inbreeding depression have a strong impact, which depends on whether restorer cost acts on male or female fitness. When cost affects male fitness, the strength of cost has no effect, whereas selfing and inbreeding depression only impact gynodioecy by modifying the value of the female advantage. When cost affects female fitness, selfing facilitates NCG and reduces the role of strength of the cost, even when no inbreeding depression occurs, whereas inbreeding depression globally restricts the maintenance of the polymorphism. Finally, we found that pollen limitation could additionally strongly modify the dynamic of gynodioecy. We discuss our findings in the light of empirical data available in gynodioecious species. K E Y W O R D S :Cost of restorer, cytoplasmic male sterility, female advantage, gynodioecy, inbreeding depression, pollen limitation, self-fertilization.

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We describe nine new variable di‐ and trinucleotide microsatellites in the plant Crepis sancta, as well as conditions for multiplexing and simultaneous genotyping sets of loci. Their variability was assessed in four populations. Four to 33 alleles were detected per locus; two to 23 alleles per population. Significant deviations from Hardy–Weinberg equilibrium could be attributed either to a mating system involving partial selfing or to null alleles. Genetic differentiation over all loci was significant among the four populations studied. These markers will constitute an efficient tool for investigating dispersal patterns in fragmented landscapes. Cross‐species amplification provided few loci variability in three other Crepis species (C. pulcra, C. foetida and C. rubra).

A Dornier and P-O CheptouAnalyzing population dynamics in changing habitats is a prerequisite for population dynamics forecasting. The recent development of metapopulation modeling allows the estimation of dispersal kernels based on the colonization pattern but the accuracy of these estimates compared with direct estimates of the seed dispersal kernel has rarely been assessed. In this study, we used recent genetic methods based on parentage analysis (spatially explicit mating models) to estimate seed and pollen dispersal kernels as well as seed and pollen immigration in fragmented urban populations of the plant species Crepis sancta with contrasting patch dynamics. Using two independent networks, we documented substantial seed immigration and a highly restricted dispersal kernel. Moreover, immigration heterogeneity among networks was consistent with previously reported metapopulation dynamics, showing that colonization was mainly due to external colonization in the first network (propagule rain) and local colonization in the second network. We concluded that the differences in urban patch dynamics are mainly due to seed immigration heterogeneity, highlighting the importance of external population source in the spatio-temporal dynamics of plants in a fragmented landscape. The results show that indirect and direct methods were qualitatively consistent, providing a proper interpretation of indirect estimates. This study provides attempts to link genetic and demographic methods and show that patch occupancy models may provide simple methods for analyzing population dynamics in heterogeneous landscapes in the context of global change.