The Evolution of Self-Fertilization in Density-Regulated Populations

We study the evolution of selfing in hermaphrodites to reveal the demographic conditions that lead to intermediate selfing rates. Using a demographic model based on Ricker-type density regulation we first assume that independent of population density, inbred individuals survive less well than outbred individuals and, second, that inbred and outbred individuals differ in their competitive abilities in density-regulated populations. The evolution of selfing, driven by inbreeding depression and the cost of outcrossing, is then analyzed for three fundamentally different demographic scenarios: stable population densities, deterministically varying population densities (resulting from cyclical or chaotic population dynamics), and stochastic fluctuations of carrying capacities (resulting from environmental noise). We show that even under stable demographic conditions evolutionary outcomes are not confined to either complete selfing or full outcrossing. Instead, intermediate selfing rates arise under a wide range of conditions, depending on the nature of competitive interactions between inbred and outbred individuals. We also explore the evolution of selfing under deterministic and stochastic density fluctuations to demonstrate that such environmental conditions can evolutionarily stabilize intermediate selfing rates. This is the first study to consider in detail the effect of density regulation on the evolution of selfing rates

Urbanization alters plastic responses in the common dandelion Taraxacum officinale

Urban environments expose species to contrasting selection pressures relative to rural areas due to altered microclimatic conditions, habitat fragmentation, and changes in species interactions. To improve our understanding on how urbanization impacts selection through biotic interactions, we assessed differences in plant defense and tolerance, dispersal, and flowering phenology of a common plant species (Taraxacum officinale) along an urbanization gradient and their reaction norms in response to a biotic stressor (i.e., herbivory). We raised plants from 45 lines collected along an urbanization gradient under common garden conditions and assessed the impact of herbivory on plant growth (i.e., aboveground biomass), dispersal capacity (i.e., seed morphology), and plant phenology (i.e., early seed production) by exposing half of our plants to two events of herbivory (i.e., grazing by locusts). Independent from their genetic background, all plants consistently increased their resistance to herbivores by which the second exposure to locusts resulted in lower levels of damage suffered. Herbivory had consistent effects on seed pappus length, with seeds showing a longer pappus (and, hence, increased dispersal capacities) regardless of urbanization level. Aboveground plant biomass was neither affected by urbanization nor herbivore presence. In contrast to consistent responses in plant defenses and pappus length, plant fitness did vary between lines. Urban lines had a reduced early seed production following herbivory while rural and suburban lines did not show any plastic response. Our results show that herbivory affects plant phenotypes but more importantly that differences in herbivory reaction norms exist between urban and rural populations

No Evolutionary Shift in the Mating System of North American Ambrosia artemisiifolia (Asteraceae) Following Its Introduction to China

The mating system plays a key role during the process of plant invasion. Contemporary evolution of uniparental reproduction (selfing or asexuality) can relieve the challenges of mate limitation in colonizing populations by providing reproductive assurance. Here we examined aspects of the genetics of colonization in Ambrosia artemisiifolia, a North American native that is invasive in China. This species has been found to possess a strong self-incompatibility system and have high outcrossing rates in North America and we examined whether there has been an evolutionary shift towards the dependence on selfing in the introduced range. Specifically, we estimated outcrossing rates in one native and five invasive populations and compared levels of genetic diversity between North America and China. Based on six microsatellite loci we found that, like the native North American population, all five Chinese populations possessed a completely outcrossing mating system. The estimates of paternity correlations were low, ranging from 0.028–0.122, which suggests that populations possessed ∼8–36 pollen donor parents contributing to each maternal plant in the invasive populations. High levels of genetic diversity for both native and invasive populations were found with the unbiased estimate of gene diversity ranging from 0.262–0.289 for both geographic ranges based on AFLP markers. Our results demonstrate that there has been no evolutionary shift from outcrossing to selfing during A. artemisiifolia's invasion of China. Furthermore, high levels of genetic variation in North America and China indicate that there has been no erosion of genetic variance due to a bottleneck during the introduction process. We suggest that the successful invasion of A. artemisiifolia into Asia was facilitated by repeated introductions from multiple source populations in the native range creating a diverse gene pool within Chinese populations

Breeding systems in Tolpis (Asteraceae) in the Macaronesian islands: the Azores, Madeira and the Canaries

Plants on oceanic islands often originate from self-compatible (SC) colonizers capable of seed set by self fertilization. This fact is supported by empirical studies, and is rooted in the hypothesis that one (or few) individuals could find a sexual population, whereas two or more would be required if the colonizers were self-incompatible (SI). However, a SC colonizer would have lower heterozygosity than SI colonizers, which could limit radiation and diver sification of lineages following establishment. Limited evidence suggests that several species-rich island lineages in the family Asteraceae originated from SI colonizers with some ‘‘leakiness’’ (pseudo-self-compatibility, PSC) such that some self-seed could be produced. This study of Tolpis (Asteraceae) in Macaronesia provides first reports of the breeding system in species from the Azores and Madeira, and additional insights into variation in Canary Islands. Tolpis from the Azores and Madeira are predominately SI but with PSC. This study suggests that the breeding sys tems of the ancestors were either PSC, possibly from a single colonizer, or from SI colonizers by multiple dis seminules either from a single or multiple dispersals. Long distance colonists capable of PSC combine the advantages of reproductive assurance (via selfing) in the establishment of sexual populations from even a single colonizer with the higher heterozygosity resulting from its origin from an outcrossed source population. Evolution of Tolpis on the Canaries and Madeira has generated diversity in breeding systems, including the origin of SC. Macaronesian Tolpis is an excellent system for studying breeding system evolution in a small, diverse lineage.info:eu-repo/semantics/publishedVersio

Persistence of butterfly populations in fragmented habitats along urban density gradients: motility helps

In a simulation study of genotypes conducted over 100 generations for more than 1600 butterfly’s individuals, we evaluate how the increase of anthropogenic fragmentation and reduction of habitat size along urbanisation gradients (from 7% to 59% of impervious land cover) influences genetic diversity and population persistence in butterfly species. We show that in areas characterised by a high urbanisation rate (> 56% impervious land cover), a large decrease of both genetic diversity (loss of 60-80% of initial observed heterozygosity) and population size (loss of 70-90% of individuals) is observed over time. This is confirmed by empirical data available for the mobile butterfly species Pieris rapae in a sub-part of the study area. Comparing simulated data for P. rapae with its normal dispersal ability and with a reduced dispersal ability, we also show that a higher dispersal ability can be an advantage to survive in an urban or highly fragmented environment. The results obtained here suggest that it is of high importance to account for population persistence, and confirm that it is crucial to maintain habitat size and connectivity in the context of land-use planning

Does the evolution of self-fertilization rescue populations or increase the risk of extinction?

International audienceBackground and aims-As a major evolutionary transition in seed plants, the evolution of plant mating systems has been much debated in evolutionary ecology. Over the last ten years, well-established patterns of evolution have emerged. On the one hand, experimental studies have shown that self-fertilization is likely to evolve in a few generations (microevolution) as a response to rapid environmental change (e.g. pollinator a decline), eventually rescuing a population. On the other, phylogenetic studies have demonstrated that repeated evolution towards self-fertilization (macroevolution) leads to a higher risk of lineage extinction and is thus likely to be disadvantageous in the long term. Scope-In either casethe short-term or long-term evolution of self-fertilization (selfing)these findings indicate that a mating system is not neutral with respect to population or lineage persistence. They also suggest that selfing can have contrasting effects depending on timescale. This raises the question of whether mating system evolution can rescue populations facing environmental change. In this review, empirical and theoretical evidence of the direct and indirect effects of mating systems on population demography and lineage persistence was analysed. A simple theoretical evolutionary rescue model was also developed to investigate the potential for evolutionary rescue through selfing. Key findings-Demographic studies consistently show a short-term advantage of selfing provided by reproductive assurance, but a long-term disadvantage for selfing lineages, suggesting indirect genomic consequences of selfing (e.g. mutation load and lower adaptability). However, our theoretical evolutionary rescue model found that even in the short 2 term, while mating system evolution can lead to evolutionary rescue, it can also lead to evolutionary suicide, due to the inherent frequency-dependent selection of mating system traits. Conclusions-These findings point to the importance of analyzing the demographic consequences of self-fertilization in order to predict the effect of selfing on population persistence as well as take into account the indirect genomic consequences of selfing. The pace at which processes such as inbreeding depression, purging, reproductive assurance and genomic rearrangements occur after the selfing transition is the key to clarifying whether selfing will result in evolutionary rescue or not

Does the evolution of self-fertilization rescue populations or increase the risk of extinction?

International audienc

Sidewalk plants as a model for studying adaptation to urban environments

International audienceAs a widespread human-altered-habitat, urban environment represents a potentially interesting model for evolutionary ecologists to study contemporary adaptation face to global change. For plants, one of the most obvious characteristics of urban environment is fragmentation. Small patches around planted trees on sidewalks have been colonized by wild plants and represent a typical fragmented urban habitat. It also represents a geometrical and homogeneous habitat to study plant adaptation to fragmentation. Based on a ten year research program in French Mediterranean (Montpellier), we will discuss how plants have adapted to urban patches in the annual weed Crepis sancta (Asteraceae). While the most obvious traits expected to respond to fragmentation is seed dispersal traits, we will present results showing how urban patch have actually selected for a battery of life history traits and ecophysiological traits. The striking result is that adaptation is rapid in urban environment and can be detected in less than 15 generations. We will discuss to what extent such adaptation can be generalized to adaptation urban environment and how the comparison between rural and urban populations provides a powerful method to study how plants adapt to various facets of global change. Overall, urban environments has proved to be a manageable and relevant ecological model to study contemporary adaptation