No abstract

The fine-scale pattern of correlated paternity was characterized within a population of the narrow-endemic model plant species, Centaurea corymbosa, using microsatellites and natural progeny arrays. We used classical approaches to assess correlated mating within sibships and developed a new method based on pairwise kinship coefficients to assess correlated paternity within and among sibships in a spatio-temporal perspective. We also performed numerical simulations to assess the relative significance of different mechanisms promoting correlated paternity and to compare the statistical properties of different estimators of correlated paternity. Our new approach proved very informative to assess which factors contributed most to correlated paternity and presented good statistical properties. Within progeny arrays, we found that about one-fifth of offspring pairs were full-sibs. This level of correlated mating did not result from correlated pollen dispersal events (i.e., pollen codispersion) but rather from limited mate availability, the latter being due to limited pollen dispersal distances, the heterogeneity of pollen production among plants, phenological heterogeneity and, according to simulations, the self-incompatibility system. We point out the close connection between correlated paternity and the "TwoGener" approach recently developed to infer pollen dispersal and discuss the conditions to be met when applying the latter.C ORRELATED paternity refers to the fact that dif-or embryo abortion, as well as resource allocation to each sex (Charnov 1982). Under limited seed dispersal, ferent offspring may be sired by the same father.where interacting individuals are likely sibs, it may also Within maternal progeny arrays it is often referred to act on the type of competitive interactions involved (e.g., as "correlated mating" and can be expressed by the kin selection; Hamilton 1964; Schuster and Mitton fraction of full-sib pairs (e.g., Ritland 1989; El-Kassaby 1991; Rousset and Billiard 2000), the average fitness and Jaquish 1996) or by the number of different fathers of competing siblings (Young 1981; Schmitt and Ehrinvolved (e.g., Campbell 1998). In this context, pure hardt 1987; Karron and Marshall 1990, 1993), or half-sib and pure full-sib families represent the extreme the success of mating events between nearby individuals alternatives of a continuum from uncorrelated to totally when inbreeding depression or self-incompatibility occorrelated mating events (e.g., polyads of mimosoid lecurs. Second, together with the outcrossing rate, the gumes and tropical figs; Nason et al. 1998). Correlated pattern of correlated mating is a key parameter of the paternity can also be considered between maternal mating system (Ritland 1988 and can provide progeny arrays, where it can be expressed by the relative valuable information on pollination biology because it proportions of (paternal) half-sibs and non-sibs.depends on a set of biological factors related in particuIn plant populations, correlated paternity is impor...

Self-incompatibility (SI) systems are widespread mechanisms that prevent self-fertilization in angiosperms. They are generally encoded by one genome region containing several multiallelic genes, usually called the S-locus. They involve a recognition step between the pollen and the pistil component and pollen is rejected when it shares alleles with the pistil. The direct consequence is that rare alleles are favored, such that the S-alleles are subject to negative frequency-dependent selection. Several theoretical articles have predicted the specific patterns of polymorphism, compared to neutral loci, expected for such genes under balancing selection. For instance, many more alleles should be maintained and populations should be less differentiated than for neutral loci. However, empirical tests of these predictions in natural populations have remained scarce. Here, we compare the genetic structure at the S-locus and microsatellite markers for five natural populations of the rare species Brassica insularis. As in other Brassica species, B. insularis has a sporophytic SI system for which molecular markers are available. Our results match well the theoretical predictions and constitute the first general comparison of S-allele and neutral polymorphism.H OMOMORPHIC self-incompatibility (SI) systems are widespread physiological mechanisms preventing self-fertilization in Angiosperms by controlling pollen germination or pollen tube growth (De Nettancourt 2001). Pollen and pistil are incompatible when they both express identical alleles. The recognition involves specificity molecules usually encoded by one genome region containing several multiallelic genes (De Nettancourt 2001). In gametophytic (GSI) systems, the pollen phenotype is encoded by its own haploid genome, whereas in sporophytic (SSI) systems, the pollen phenotype is determined by the sporophyte (diploid pollen parent) and can involve dominance interactions among alleles. For instance, two classes of alleles are known in Brassica oleracea (Nasrallah 1991). Class I alleles are dominant over the class II alleles in the pollen, while alleles within class I and class II are mutually codominant. In the pistil, all alleles are codominant. This scheme is also found in B. campestris, with the exception that alleles occur in three dominance levels in the pollen and a few alleles are recessive in the stigma (Hatakeyama et al. 1998). At the molecular level, the SSI system of the Brassicaceae is among the best known (for a recent review see Hiscock and McInnis 2003). Both pistil and pollen genes have been identified (Schopfer et al. 1999;Takayama et al. 2000). In this system, recognition proceeds through receptor-ligand interaction between S-locus cysteinerich protein (SCR), a small hypervariable ligand peptide, and S-locus receptor kinase (SRK), a transmembrane receptor with an intracellular kinase domain (Kachroo et al. 2001).SI evolutionary properties have also long aroused the population geneticist's interest because selection pressures are known a priori. C...

Pollen dispersal was characterized within a population of the narrowly endemic perennial herb, Centaurea corymbosa, using exclusion-based and likelihood-based paternity analyses carried out on microsatellite data. Data were used to fit a model of pollen dispersal and to estimate the rates of pollen flow and mutation/genotyping error, by developing a new method. Selfing was rare (1.6%). Pollen dispersed isotropically around each flowering plant following a leptokurtic distribution, with 50% of mating pairs separated by less than 11 m, but 22% by more than 40 m. Estimates of pollen flow lacked precision (0-25%), partially because mutations and/or genotyping errors (0.03-1%) could also explain the occurrence of offspring without a compatible candidate father. However, the pollen pool that fertilized these offspring was little differentiated from the adults of the population whereas strongly differentiated from the other populations, suggesting that pollen flow rate among populations was low. Our results suggest that pollen dispersal is too extended to allow differentiation by local adaptation within a population. However, among populations, gene flow might be low enough for such processes to occur.

No abstract

Centaurea corymbosa is an endemic plant species restricted to a 3‐km2 area in southern France. This species is known from only six small populations that are highly differentiated genetically. Matrix models based on eight years of data (1994–2001) were used to assess the pattern of variation in the demographic vital rates of this species, and to investigate the causes of their variation. Asymptotic growth rates λ varied widely between years and populations (0.613–1.424). Randomization tests were developed to test for spatial and temporal variation in the asymptotic growth rates. These tests rely on individual data on both survival and fecundity. As our demographic survey only allowed us to estimate average fecundities, additional fecundity data collected from 1994 to 1996 were used to assess the distribution of individual fecundity expected within populations under demographic stochasticity or sampling error. Randomization tests showed that asymptotic growth rates were significantly different between populations and between years in C. corymbosa. In contrast, log‐linear analysis performed only on transition data (i.e., excluding fecundity) suggested that the observed variations in transition probabilities were mostly explained by sampling error or demographic stochasticity rather than environmental stochasticity. This suggested that variations in fecundity among populations and among years may play a key role to explain temporal and spatial differences in λ. Life‐table response experiment analysis revealed that variations in fecundity and especially in the number of just‐emerged seedlings per plant explained most of the observed variance in λ. Spatial and temporal variations were detected for most lower‐level vital rates, but causal factors that may account for these patterns are still unknown: no effect of genetic diversity was detected on the dynamics of the species, and correlation between lower‐level vital rates and climatic data did not reveal any clear trends. Our study emphasizes the need to conduct long‐term demographic surveys and to collect individual fecundity data to get more insights into the causes of variation of the demographic behavior of C. corymbosa.

Summary 1.In a context of increasing human impact on ecosystems and species distributions, population restoration (introductions, reintroductions, reinforcements) is an essential management tool, especially for plant species with limited colonization ability. However, detailed demographic surveys following restoration and comparisons of demographic rates between restored and natural populations, although essential for identifying the key factors of restoration success, are lacking. 2. We compared the demography over 10 years of six natural and two experimentally introduced populations of the narrowly endemic, cliff-dwelling, self-incompatible plant species Centaurea corymbosa . We analysed the fate of two cohorts of individuals that emerged simultaneously from seed introduction and natural germination. We then built a matrix model of population dynamics (using 6 years of data) and compared the demographic rates and asymptotic growth rate between the natural and introduced populations. 3. Overall, survival rates were higher in the introduced than in the natural populations, either due to better habitat conditions at the cliff scale or to better conditions in microsites selected for seed introduction compared to those reached by chance following natural seed dispersal. 4. In contrast, introduced populations exhibited lower fecundity than natural populations, probably due to the introduction protocol which led, in combination with self-incompatibility, to severely reduced mate availability. 5. Despite clear differences in population dynamics between introduced and natural populations, no significant difference in the asymptotic growth rates could be detected, because the higher survival compensated for the lower fecundity in introduced populations. 6. Synthesis and applications . Creating new populations of C. corymbosa in suitable unoccupied sites seems straightforward, provided that the introduction protocol allows sufficiently high fecundity. This key parameter for restoration success can be optimized by sowing seeds from several sources at high density and in several consecutive years, which should increase mate availability for selfincompatible flowering individuals. We suggest that population introduction might be successful for many (endemic) plant species whose geographical range is mainly limited by low colonization ability, especially in Mediterranean landscapes. We show that the simultaneous monitoring of restored and natural populations enables identification of the key parameters to be targeted for management optimization of restored populations.

Summary 1The phenology of temperate woody plants is commonly assumed to be locally adapted to climate. 2 However, the high gene¯ow expected in forest tree species, the high between year variance of thermal conditions at a given place and the high plasticity of phenology regarding temperature, lead us to hypothesize that genetic variation of phenology between populations is likely to be insigni®cant for many lowland tree species.3 Using phenological models, we investigated variation in the timing of¯owering between locations for four European clonal trees and between dierent populations of a further ®ve species. 4 Models were also used to study the responses of the dierent populations to climate change by simulating transfers of each population to dierent locations. 5 While clinal variations can be observed in the phenological response to temperature between populations, only one species (Corylus avellana) showed signi®cantly dierent responses between populations and even then only one of three populations could be separated from the others. 6 Hypothetical transfers show that the dierences observed between populations depend on the thermal conditions at the location of transfer, and that these dierences are less marked in warmer conditions. 7 Our results indicate that local adaptation will probably not be a serious constraint in predicting the phenological responses of temperate lowland tree species to global warming.