Temperature Effects on Gametophyte Life-History Traits and Geographic Distribution of Two Cryptic Kelp Species

A major determinant of the geographic distribution of a species is expected to be its physiological response to changing abiotic variables over its range. The range of a species often corresponds to the geographic extent of temperature regimes the organism can physiologically tolerate. Many species have very distinct life history stages that may exhibit different responses to environmental factors. In this study we emphasized the critical role of the haploid microscopic stage (gametophyte) of the life cycle to explain the difference of edge distribution of two related kelp species. Lessonia nigrescens was recently identified as two cryptic species occurring in parapatry along the Chilean coast: one located north and the other south of a biogeographic boundary at latitude 29–30°S. Six life history traits from microscopic stages were identified and estimated under five treatments of temperature in eight locations distributed along the Chilean coast in order to (1) estimate the role of temperature in the present distribution of the two cryptic L. nigrescens species, (2) compare marginal populations to central populations of the two cryptic species. In addition, we created a periodic matrix model to estimate the population growth rate (λ) at the five temperature treatments. Differential tolerance to temperature was demonstrated between the two species, with the gametophytes of the Northern species being more tolerant to higher temperatures than gametophytes from the south. Second, the two species exhibited different life history strategies with a shorter haploid phase in the Northern species contrasted with considerable vegetative growth in the Southern species haploid stage. These results provide strong ecological evidence for the differentiation process of the two cryptic species and show local adaptation of the life cycle at the range limits of the distribution. Ecological and evolutionary implications of these findings are discussed

Common garden experiments in the genomic era : new perspectives and opportunities

PdV was supported by a doctoral studentship from the French Ministère de la Recherche et de l’Enseignement Supérieur. OEG was supported by the Marine Alliance for Science and Technology for Scotland (MASTS)The study of local adaptation is rendered difficult by many evolutionary confounding phenomena (e.g. genetic drift and demographic history). When complex traits are involved in local adaptation, phenomena such as phenotypic plasticity further hamper evolutionary biologists to study the complex relationships between phenotype, genotype and environment. In this perspective paper, we suggest that the common garden experiment, specifically designed to deal with phenotypic plasticity has a clear role to play in the study of local adaptation, even (if not specifically) in the genomic era. After a quick review of some high-throughput genotyping protocols relevant in the context of a common garden, we explore how to improve common garden analyses with dense marker panel data and recent statistical methods. We then show how combining approaches from population genomics and genome-wide association studies with the settings of a common garden can yield to a very efficient, thorough and integrative study of local adaptation. Especially, evidence from genomic (e.g. genome scan) and phenotypic origins constitute independent insights into the possibility of local adaptation scenarios, and genome-wide association studies in the context of a common garden experiment allow to decipher the genetic bases of adaptive traits.PostprintPeer reviewe

Contrasting patterns of evolutionary constraint and novelty revealed by comparative sperm proteomic analysis in Lepidoptera

Background: Rapid evolution is a hallmark of reproductive genetic systems and arises through the combined processes of sequence divergence, gene gain and loss, and changes in gene and protein expression. While studies aiming to disentangle the molecular ramifications of these processes are progressing, we still know little about the genetic basis of evolutionary transitions in reproductive systems. Here we conduct the first comparative analysis of sperm proteomes in Lepidoptera, a group that exhibits dichotomous spermatogenesis, in which males produce a functional fertilization-competent sperm (eupyrene) and an incompetent sperm morph lacking nuclear DNA (apyrene). Through the integrated application of evolutionary proteomics and genomics, we characterize the genomic patterns potentially associated with the origination and evolution of this unique spermatogenic process and assess the importance of genetic novelty in Lepidopteran sperm biology. Results: Comparison of the newly characterized Monarch butterfly (Danaus plexippus) sperm proteome to those of the Carolina sphinx moth (Manduca sexta) and the fruit fly (Drosophila melanogaster) demonstrated conservation at the level of protein abundance and post-translational modification within Lepidoptera. In contrast, comparative genomic analyses across insects reveals significant divergence at two levels that differentiate the genetic architecture of sperm in Lepidoptera from other insects. First, a significant reduction in orthology among Monarch sperm genes relative to the remainder of the genome in non-Lepidopteran insect species was observed. Second, a substantial number of sperm proteins were found to be specific to Lepidoptera, in that they lack detectable homology to the genomes of more distantly related insects. Lastly, the functional importance of Lepidoptera specific sperm proteins is broadly supported by their increased abundance relative to proteins conserved across insects. Conclusions: Our results identify a burst of genetic novelty amongst sperm proteins that may be associated with the origin of heteromorphic spermatogenesis in ancestral Lepidoptera and/or the subsequent evolution of this system. This pattern of genomic diversification is distinct from the remainder of the genome and thus suggests that this transition has had a marked impact on lepidopteran genome evolution. The identification of abundant sperm proteins unique to Lepidoptera, including proteins distinct between specific lineages, will accelerate future functional studies aiming to understand the developmental origin of dichotomous spermatogenesis and the functional diversification of the fertilization incompetent apyrene sperm morph

North American Wild Relatives of Grain Crops

The wild-growing relatives of the grain crops are useful for long-term worldwide crop improvement research. There are neglected examples that should be accessioned as living seeds in gene banks. Some of the grain crops, amaranth, barnyard millet, proso millet, quinoa, and foxtail millet, have understudied unique and potentially useful crop wild relatives in North America. Other grain crops, barley, buckwheat, and oats, have fewer relatives in North America that are mostly weeds from other continents with more diverse crop wild relatives. The expanding abilities of genomic science are a reason to accession the wild species since there are improved ways to study evolution within genera and make use of wide gene pools. Rare wild species, especially quinoa relatives in North American, should be acquired by gene banks in cooperation with biologists that already study and conserve at-risk plant populations. Many of the grain crop wild relatives are weeds that have evolved herbicide resistance that could be used in breeding new herbicide-resistant cultivars, so well-documented examples should be accessioned and also vouchered in gene banks

Genetic structure of the endangered perennial plant Eryngium alpinum (Apiaceae) in an alpine valley

International audienceWe investigated the genetic structure of Eryngium alpinum (Apiaceae) in an Alpine valley where the plant occurs in patches of various sizes. In a conservation perspective, our goal was to determine whether the valley consists of one or several genetic units. Habitat fragmentation and previous observations of restricted pollen/seed dispersal suggested pronounced genetic structure, but gene dispersal often follows a leptokurtic distribution, which may lead to weak genetic structure. We used nine microsatellite loci and two nested sampling designs (50 x 50 m grid throughout the valley and 2 x 2 m grid in two 50 x 10 m quadrats). Within the overall valley, F-statistics and Bayesian approaches indicated high genetic homogeneity. This result might be explained by: (1) underestimation of long-distance pollen/seed dispersal by in situ experiments and (2) too recent fragmentation events to build up genetic structure. Spatial autocorrelation revealed isolation by distance on the overall valley but this pattern was much more pronounced in the 50 x 10 m quadrats sampled with a 2-m mesh. This was probably associated with limited primary seed dispersal, leading to the spatial clustering of half-sibs around maternal plants. We emphasize the interest of nested sampling designs and of combining several statistical tools. (C) 2008 The Linnean Society of London

Reproductive ecology of the endangered alpine species Eryngium alpinum L. (Apiaceae): Phenology, gene dispersal and reproductive success

Times Cited: 3 Cited Reference Count: 37International audienceBackground and aims Eryngium alpinum (Apiaceae) is an endangered perennial, characteristic of the Alpine flora. Because the breeding system influences both demographic (reproductive success) and genetic (inbreeding depression. evolutionary potential) parameters that are crucial for population maintenance, the reproductive ecology of E. alpinum was investigated. Specifically, the aims of the study were (1) to determine the factors (resources and/or pollen) limiting plant fitness; and (2) to assess the potential for gene flow within a plant, within a patch of plants, and across a whole valley where the species is abundant. Methods Field experiments were performed at two sites in the Fournel valley, France, over three consecutive years. Studies included a phenological survey, observations of pollinators (visitation rates and flight distances), dispersal of a fluorescent powder used as a pollen analogue, the use of seed traps, determination of the pollen/ovule ratio. and an experiment to test whether seed production is limited by pollen and/or by resources. Key results E. alpinum is pollinated by generalist pollinators, visitation rates are very high and seed set is resource-rather than pollen-limited. The short flights of honeybees indicate a high potential for geitonogamy, and low pollen and seed dispersals suggest strong genetic structure over short distances. These results are interpreted in the light of previous molecular markers studies, which, in contrast, showed complete outcrossing and high genetic homogeneity. Conclusions. The study highlights the usefulness of adopting several complementary approaches to understanding the dynamic processes at work in natural populations. and the conservation implications for E. alpinum are emphasized. Although the studied populations do not seem threatened in the near future, long-term monitoring appears necessary to assess the impact of habitat fragmentation. Moreover, this study provides useful baseline data for future investigations in smaller and more isolated populations. (C) 2004 Annals of Botany Company

Low selfing in a mass-flowering, endangered perennial, Eryngium alpinum L. (Apiaceae)

Times Cited: 9 Cited Reference Count: 58International audienceWe investigated the reproductive ecology of an endangered alpine species, Eryngium alpinum L., to determine its selfing rate and to propose possible mechanisms that may shape its breeding system. Whereas pollinators' foraging behavior suggested a high potential for geitonogamy (70% of the flights occur within plants), microsatellite analyses of seed progenies demonstrated that plants are primarily outcrossing (outcrossing rate [tm]=0.65, 0.96, and 1 in three populations). Given the relatively long pollen viability (at least 4-5 d) and the high number of simultaneously opened flowers on each plant, protandry is not sufficient to eliminate selfing. second. controlled crosses demonstrated not only auto-fertility, but also partial self-incompatibility. Partial self-incompatibility is probably due to the competitive advantage of cross vs. self-pollen, and, together with protandry, could lead the species to selling as a reproductive assurance. These results are encouraging for the maintenance of large populations. However higher selfing was observed in a small population that could suffer inbreeding depression, as observed on experimentally selfed seeds. Thus, these populations should be carefully monitored. Finally, this study shows how molecular markers and field experiments may complement each other in our reaching a global understanding of mating patterns

Evolutionary conflict between Trollius europaeus and its seed-parasite pollinators Chiastocheta flies

Times Cited: 16 Reference Count: 35International audienceMutualisms are characterized by balanced reciprocal exploitation. This creates an evolutionary conflict in that selection will favour individuals that increase their fitness at the cost of the mutualist partner. To counter this evolutionary instability, each partner must be able to prevent over-exploitation by the other. In plant/seed-parasite pollinator mutualisms like that involving the globeflower Trollius europaeus and the globeflower fly (Chiastocheta spp.), ovipositing females can have a more or less mutualistic/antagonistic effect on plant seed output, depending on the amount of pollination achieved during oviposition, the number of eggs laid and seed predation per larva. We found that flowers with no Chiastocheta egg had a high seed set and there was no significant increase in seed set before predation with increasing egg load, suggesting that most pollination is achieved by non-ovipositing visitors (males and/or non-ovipositing females). Hence, additional eggs do not lead to higher pollination, oviposition is a non-mutualistic behaviour and, therefore, there is a conflict between T. europaeus and Chiastocheta flies for the number of eggs laid. Egg load increases throughout flower lifespan. No mechanism seems to have evolved to regulate the number of eggs laid on T. europaeus. For example, controlled pollination experiments showed that T europaeus cannot limit Chiastocheta oviposition by triggering flower senescence as soon as full pollination has been achieved. In this context, the high average number of eggs per flower observed in alpine populations is not surprising. Finally, the decrease in net seed production with increasing egg load was weak. We discuss the other factors involved in the regulation of the conflict between T europaeus and Chiastocheta flies