Pierre-Henri Gouyon

Role of mutator alleles in adaptive evolution.

Because most newly arising mutations are neutral or deleterious, it has been argued that the mutation rate has evolved to be as low as possible, limited only by the cost of error-avoidance and error-correction mechanisms. But up to one per cent of natural bacterial isolates are ‘mutator’ clones that have high mutation rates. We consider here whether high mutation rates might playan important role in adaptive evolution. Models of large, asexual, clonal populations adapting to a new environment show that strong mutator genes (such as those that increase mutation rates by 1,000-fold) can accelerate adaptation, even if the mutator gene remains at a very low frequency (for example, 10−5). Less potent mutators (10 to 100-fold increase) can become fixed in a fraction of finite populations. The parameters of the model have been set to values typical for Escherichia coli cultures, which behave in a manner similar to the model in long-term adaptation experiments.

Metapopulation Genetics and the Evolution of Dispersal

A Markovian extinction model that takes into account age structure of local populations allows consideration of the effects of demography and successional dynamics on the evolution of migration. Analytical expressions for the evolutionarily stable (ES) rates of dispersal are given for cases in which newly recolonized sites attain carrying capacity within a single season. Using a low-fecundity numerical model, we find that an increase of the level of site saturation increases the dispersal rate. Ecological successions and unequal local extinction rates between newly colonized sites and established populations strongly affect the ES dispersal rate. The frequency of genetic modifiers that enhance the rate of dispersal evolves negative correlations with deme age, with high-migration genotypes predominant among colonizers while progressively declining in frequency as a deme ages. This suggests that between-deme selection (colonization) favors migrants while within-deme selection favors low dispersers, which allows the coexistence of types with different dispersal rates. Because of the interaction between the two levels of selection, the relation between the ES dispersal rate and the deme maximal lifetime is nonmonotone. We suggest that life-history traits other than dispersal might also experience antagonistic selective forces at the between- and within-deme levels.

Evolution of Reproductive Systems in the Genus Silene

The genus Silene contains both hermaphrodite, gynodioecious and dioecious species, dioecy being represented in three sections of the genus. To locate the events of change of reproductive systems, we compared ITS sequences of 22 species of Silene chosen throughout the whole genus, and four putative outgroup species. Gynodioecy, which is the most common reproductive system within the genus Silene and in closely related genera such as Saponaria and Dianthus, is proposed to be ancestral in the genus. Dioecy has evolved at least twice: once in the section containing S. latifolia, and once in the clade containing S. otites and S. acaulis ssp. bryoides. Evolution towards hermaphroditism, associated with evolution of selfing, has also occurred at least twice, in S. gallica and S. conica.

Persistence of oilseed rape (Brassica napus L.) outside of cultivated fields

Abstract It is widely assumed that most cultivated plants cannot persist in natural or semi-natural habitats. Most people thus assume that the plants growing outside of fields (in particular oilseed rape along roadsides) find their origins in the current or previous year’s cultivation of that crop. One consequence of this assumption is that the identity of plants growing on road verges is thought to reflect one of the cultivars currently or recently cultivated, while another consequence is the widespread belief that transgenic plants can be simply managed and controlled by stopping their cultivation. Our work shows that this assumption is false. We identify relict plants of a now unmarketable cultivar type of oilseed rape which have persisted in a semi-natural habitat (road verges) for at least 8 years according to farmer surveys in the studied area. More generally, we confirm that the dynamics of the feral oilseed rape plants of road verges is more complex than those resulting from spillage from agricultural machines or from neighbouring arable fields cultivated the previous year. Within the scope of transgenic oilseed rape cultivation, these results suggest that more studies on the dynamics of feral oilseed rape are needed in order to assess more precisely the risks of its invasiveness and its potential impact on genetic pollution between GM fields and non-GM fields.

Evolution of Migration Rate and Other Traits: The Metapopulation Effect

Publisher Summary This chapter focuses on metapopulation evolutionary models and metapopulation effect. Metapopulation evolutionary models focus on the evolutionary consequences of population extinctions and recolonizations. In these models, the emphasis is on the selective pressures created by population turnover within a metapopulation. The focus is on the evolution of particular traits, whose genetic determinism is usually unknown. Metapopulation evolutionary models are mostly used to study the evolution of migration rate. It is shown that the demographic functioning of metapopulations creates intrinsic emergent properties that influence the evolution of major biological traits, such as migration rate. This chapter also shows that the processes determining the migration rate in a metapopulation are specific to the very functioning of the metapopulation (the metapopulation effect) and interacting with the processes determining the evolution of most significant life-history traits. These processes result in a partial adaptation of the metapopulation to its landscape. This adaptation is incomplete because the processes involved act between genes at both the population and the metapopulation levels. Thus, they necessarily involve frequency dependence; and therefore, Fishers fundamental theorem of natural selection does not apply at the metapopulation level.

The genetics of transient populations: Research at the metapopulation level

The metapopulation concept allows us to generate new models, in which each single local population is in disequilibrium (from both demographic and genetic points of view) but the whole is stable. We review recent empirical and theoretical results showing the relevance of the metapopulation level, in particular for understanding the evolution of those traits that do not experience the same selective forces during the different demographic stages of each local population.

The Ecological Consequences of Flowering Asynchrony in Monoecious Figs: A Simulation Study

For plants with temporally separate sexual phases to outcross, population- level flowering asynchrony is necessary, but this can decrease the resource base available for pollinators. We developed a simulation model to examine the consequences of such asynchrony for individual reproductive success and long-term pollinator maintenance with- in monoecious fig populations. In figs, flowering is synchronous within a tree and the specialist pollinators/seed predators can only survive briefly away from trees. Consequently, population-level flowering asynchrony must extend year-round for pollinators to persist locally. In repeated stochastic simulations using phenological traits of one well-studied species (Ficus natalensis), a median of 95 trees was required to produce an asynchronous sequence that could maintain local pollinator populations for 4 yr. However, many trees in those simulated populations were either male-sterile (10%) or both male- and female- sterile (35%), because their sexual phases were not well timed with the opposite phases of other trees. Sterility within a population approached zero at 2-3 times the critical population size. Both the predicted critical population size and frequency of success of the trees within it depended strongly on the duration of reproductive episodes and the intervals between episodes. The level of within-tree reproductive synchrony was also critical: doubling the length of time over which individuals could donate pollen resulted in a 39% decrease in critical population size and a 27% increased likelihood that individuals would achieve at least some reproductive success. These results point to the need for precise phenological data for estimating plant fitness and population structure both in models and in the field.

Models of sexual and asexual coexistence in aphids based on constraints

Two models are presented to test the hypothesis that in aphids, a particular constraint (the necessity to resist frost) could be the proximal cause for the maintenance of sex. Both models are based on temporal variability in winter survival of asexuals.

Evolution of pollen morphology

Over evolutionary time, the morphology of angiosperm pollen has evolved toward an increasing number of apertures, among other things. From a neo-Darwinian point of view, this means that (i) some polymorphism for aperture number must exist and (ii) there must be some fitness increase associated with increasing the aperture number. Pollen types with different aperture numbers often occur in the same species. Such is the case in Viola diversifolia. Comparison of pollen with three and four apertures in this species showed that four-apertured grains germinated faster than three-apertured ones but that the four-apertured ones experienced other disadvantages. These results obtained on the gametophyte can be interpreted in terms of strategies of the sporophyte

Complex determination of male sterility in Thymus vulgaris L.: genetic and molecular analysis

SummaryNucleocytoplasmic determination of male sterility in Thymus vulgaris L. has been assumed in all papers attempting to explain the remarkably high frequencies of male steriles found in natural populations of this species. This paper provides strong evidence that both nuclear and cytoplasmic genes are involved in the determination of male sterility of this species, giving a complex inheritance. Interpopulation and intrapopulation crosses have shown that the ratio of females versus hermaphrodites among offsprings varied widely from 1∶0 to 1∶1. Furthermore, interpopulation crosses consistently yielded a higher frequency of females than intrapopulation crosses. Nucleocytoplasmic inheritance was demonstrated by an absence of male fertiles in backcrosses and asymmetrical segregation in reciprocal crosses. Molecular analysis of the mitochondrial DNA of some of the parents used in crosses suggested the involvement of different cytoplasms in the inheritance of male steriliy.