Abstracts (first author)

Talk 

Mutualists and antagonists drive among-population variation in selection and evolution of floral display in a perennial herb

Author(s): Ågren J, Ehrlén J

Summary:

Spatial variation in the direction of selection drives the evolution of adaptive differentiation. Yet, few experimental studies have examined the relative importance of different environmental factors for variation in selection and evolutionary trajectories in natural populations. We combined 8 years of observational data and field experiments to assess the relative importance of mutualistic and antagonistic interactions for spatial variation in selection and short-term evolution of a genetically based floral display dimorphism in the short-lived perennial herb Primula farinosa. Natural populations of this species include two floral morphs: long-scaped plants that present their flowers well above the ground and short-scaped plants with flowers positioned close to the ground. The direction and magnitude of selection on scape morph varied among populations, and so did the frequency of the short morph (median 19%, range 0-100%; N = 69 populations). A field experiment replicated at four sites demonstrated that variation in the strength of interactions with grazers and pollinators were responsible for among-population differences in relative fitness of the two morphs. Selection exerted by grazers favored the short-scaped morph, whereas pollinator-mediated selection favored the long-scaped morph. Moreover, variation in selection among natural populations was associated with differences in morph frequency change, and the experimental removal of grazers at nine sites significantly reduced the frequency of the short-scaped morph over eight years. The results demonstrate that spatial variation in intensity of grazing and pollination produces a selection mosaic, and that changes in biotic interactions may trigger rapid genetic changes in natural plant populations.



Abstracts (coauthor)

Summary:

A prominent floral display may be favoured by selection because it increases attractiveness to pollinators, but may be associated with a cost in terms of an increased risk of damage from seed predators and grazers. While the benefits of a large display may be expressed through both male and female function, the negative effects of herbivore attack may often appear only after pollen dispersal, and thus predominantly influence female reproductive success. The short-lived, hermaphroditic herb Primula farinosa is dimorphic for scape length and occurs as a long-scaped and a short-scaped morph. The long-scaped morph displays its flowers well above the ground, whereas the short-scaped morph displays its flowers close to the ground. We conducted a field experiment with genotyped plants at two sites in SE Sweden to examine whether male reproductive success of the long-scaped morph is greater than that of the short-scaped morph, and whether this may compensate for a higher risk of reduced seed production caused by interactions with seed predators and grazers. Female reproductive success was assessed by quantifying seed production and male siring success by genotyping offspring. At the first site, where grazing pressure and seed predation were high, the long-scaped morph sired significantly more offspring but produced fewer seeds than did the short-scaped morph. At the second site, the two morphs did not differ significantly in siring success or seed production. The results demonstrate that interactions with mutualists and antagonists can differentially affect selection on floral display through male and female function and produce a relationship between floral display and plant functional gender. Positive effects of a large floral display on male reproductive success may at least partly compensate for an increased risk of herbivore-mediated reduction in seed production.

Pronounced maternal effect on hybrid gene expression in Arabidopsis

Author(s): Videvall, E, Sletvold N, Hagenblad J, Ågren J, Hansson B

Summary:

Understanding how hybridization influences phenotype is of major importance for evolutionary biology. Theoretically, phenotypic differences are expected to be controlled mainly by gene regulation, which can be environmentally or genetically determined. However, until recently it has been difficult to accurately measure expression levels and determine whether hybrid gene expression are caused by additive (intermediate expression levels between the parents), dominance (expression levels equal to one of the parents) or parental effects (gene expression similar to that of either the mother or the father). Here we use high throughput RNA-sequencing (Illumina) to test the different expression hypotheses and evaluate gene expression in hybrids between two differentiated populations of Arabidopsis lyrata. Our results showed (i) broad differential expression between populations (9573 significant genes) and (ii) a very strong maternal effect on hybrid gene expression (94.7% of genes followed the expression of the mother rather than the father plant). In plants, where seed dispersal is limited and the developing seedlings will experience similar environmental conditions as their mothers, such maternal effects are expected to be highly beneficial as they can facilitate local adaptation.

Summary:

Timing of germination is expected to influence plant fitness strongly, because it determines not only the environmental conditions for the emerging seedling but also sets the context for all subsequent life stages. We studied the genomic architecture and adaptive significance of differentiation in seed dormancy and germination timing between two natural populations of the annual herb Arabidopsis thaliana located close to the geographic limits of the native range (northern Sweden and central Italy). With recombinant inbred lines (RILs) derived from a cross between the two focal populations, we mapped QTL for germination traits. First, seed dormancy was estimated for more than 400 RILs and the two parental lines using seeds that had matured in the greenhouse. Second, the timing of germination at the Swedish field site and seedling establishment at both field sites were documented for 220 RILs and the two parental lines using seeds matured at the respective field site and planted at the time of seed dispersal in spring. The Italian genotype produced seeds with a markedly stronger dormancy and germinated later at the Swedish field site than did the Swedish genotype. At both field sites, the local genotype outperformed the non-local genotype in terms of seedling establishment. In Italy, seed dormancy was positively correlated with RIL establishment success, while in Sweden this relationship was negative. Of the 11 QTL identified, one affected all three germination traits (dormancy, timing, establishment). This QTL had a huge effect size compared to the other detected QTL, and co-locates with the known dormancy gene DOG1. The results demonstrate that genetically based differences in seed dormancy are associated with differences in timing of germination and successful seedling establishment at the sites of the source populations, and thereby contribute to adaptive differentiation among natural populations of A. thaliana.

Summary:

Trichomes are hair-like epidermal structures on plant surfaces that may contribute to herbivore deterrence, UV protection, and tolerance to drought. In the annual plant Arabidopsis thaliana, leaf trichome density varies considerably among populations. We examined the genetic basis of differences in trichome density between two populations located close to the northern (Sweden) and southern (Italy) margin of the native range. We planted parental lines and 400 recombinant inbred lines (RILs) derived from a cross between the two populations at the sites of both source populations. Seedlings were planted at the time of natural seedling establishment in the autumn, and trichome density was scored on leaves before flowering in spring. We mapped QTL for trichome density using a linkage map based on 360 SNPs spaced at ca. 1 cM intervals. We asked how many QTL contribute to differences in trichome density and what is the magnitude of their effects? Do QTL for trichome density co-locate with candidate genes known to influence trichome density? Can QTL effects be linked to mutations in these genes? Preliminary analyses detected 11 QTL influencing trichome density. Of these, one QTL on chromosome 2 was consistently detected across years and at both study sites, and explained between 19% and 44% of the variation in RIL means. This QTL was located in a genomic region harbouring two genes known to influence trichome density: ETC2 and TCL1. Sequence differences between the two parental lines in these two candidate genes corresponded to four and one amino acid, respectively. We will present an analysis of the functional significance of the sequence differences detected and of their geographic distribution. In ongoing work, we explore the adaptive significance of trichome density by connecting variation in trichome density to variation in other putatively adaptive traits and to fitness in the field.

Summary:

Reciprocal transplant experiments can be used to determine the magnitude of adaptive differentiation among natural populations and to help identify putative adaptive traits and selective agents. In reciprocal transplant experiments, we quantified local adaptation between Scandinavian and Spanish populations of the alpine perennial herb Arabis alpina. At the Scandinavian field site, survival and fruit production of Scandinavian populations were higher than those of Spanish populations, while the opposite was true in Spain. The magnitude of the home advantage varied among years and was highest in a drought year in Spain and after a cold winter in Sweden. The results suggest that differences in tolerance to drought and cold contribute to adaptive differentiation between populations from the two regions. They further suggest that these A. alpina populations represent a highly suitable model system for examining the functional and genetic basis of plant adaptation in alpine environments.

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Address

XIV Congress of the European Society for Evolutionary Biology

Organization Team
Department of Animal Biology (DBA)
Faculty of Sciences of the University of Lisbon
P-1749-016 Lisbon
Portugal

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