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- Boberg, Elin, 1980-, et al.
(author)
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Phenotypic selection on floral traits in divergent populations of the moth-pollinated orchid Platanthera bifolia
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Other publication (other academic/artistic)abstract
- Among-population differences in flower morphology is commonly attributed to divergent natural selection mediated by pollinators, but comparisons of current selection in populations growing in contrasting environments are scarce. In the moth-pollinated orchid Platanthera bifolia, floral morphology and flowering phenology differ between grassland and woodland populations on the island Öland, SE Sweden. To examine whether among-population variation in floral morphology is consistent with differences in current selection, we documented phenotypic selection through female and male function on flowering phenology, plant height, flower production and spur length in three populations. One grassland and one woodland population were studied in three years, and one population bimodal for spur length and occurring in a mixed habitat was studied in one year. There was evidence of disruptive selection on spur length in the population in the mixed habitat. In one of three years, there was evidence of divergent selection on plant height between the grassland and woodland population. In all three years selection favoured longer nectar spurs; selection gradients were statistically significant in the short-spurred grassland population, but not in the long-spurred woodland population. In both populations, there was directional selection for earlier flowering and more flowers through female function. Seed production was pollen limited in the grassland population. The results support the hypothesis that disruptive selection through female reproductive success contributes to the maintenance of a bimodal distribution of spur length in P. bifolia in mixed habitats, but provides very limited evidence of divergent selection on plant morphology and flowering phenology in grassland and woodland populations of P. bifolia. The results are discussed in relation to the evolution of floral traits and the challenges associated with detecting stabilizing selection in natural populations.
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- Boberg, Elin, 1980-, et al.
(author)
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Reproductive isolation among divergent populations of the moth-pollinated orchid Platanthera bifolia
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Other publication (other academic/artistic)abstract
- Differentiation in floral traits has been documented between populations in contrasting habitats in several species of flowering plants, but few studies have investigated whether barriers to reproduction contribute to the maintenance of this variation. We investigated components of prezygotic reproductive isolation between short-spurred and long-spurred populations of the moth-pollinated orchid Platanthera bifolia on the island of Öland, SE Sweden. Short-spurred and long-spurred populations were reproductively isolated due to spatial isolation, and differences in flowering time, pollinator morphology and behaviour. The index of reproductive isolation due to pollinators and flowering time was higher for the early-flowering long-spurred plants than it was for the late-flowering short-spurred plants. In addition, we documented a postpollination isolation mechanism manifested as reduced fruit formation in short-spurred plants when pollinated with pollen from long-spurred plants. The results indicate that strong reproductive isolation contribute to the maintenance of population differentiation in morphology and phenology between long-spurred and short-spurred populations of P. bifolia.
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- Lehndal, Lina, et al.
(author)
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Herbivory influences the relative fitness of three native Lythrum salicaria populations, but no evidence of local adaptation along a latitudinal gradient
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Other publication (other academic/artistic)abstract
- Local adaptation along environmental gradients has been documented in many plant species, but the extent to which biotic interactions influence the relative fitness of local and non-local genotypes has rarely been examined experimentally. Previous common-garden experiments detected clinal variation in life history, phenology and resistance to herbivory in the perennial herb Lythrum salicaria along a latitudinal gradient in Sweden, which coincides with a decrease in the length of the growing season and intensity of herbivory from south to north. Here, we included a herbivore-removal treatment in a reciprocal transplant experiment to test whether three populations sampled along the latitudinal gradient are locally adapted, whether differences in resistance and tolerance are consistent across sites and whether herbivory influences the relative performance of the study populations. The results did not reveal any evidence of local adaptation. Instead the southernmost population had the highest relative fitness at all three sites and was consistently less damaged by herbivores than were the other populations. The intensity of herbivory was greatest at the southern site and very low at the northernmost site. The removal of insect herbivores positively affected plant growth and fecundity at the southern and central sites. Herbivore removal also affected the relative fitness of the study populations at the southern site, and tended to do so at the central site. However, the relative ranking of the three populations did not change, indicating that herbivores influenced the strength but not the direction of selection. Genetic drift, recent climatic warming and intermittent strong selection against southern genotypes at northern latitudes may all contribute to the documented patterns of among-population variation in fitness, while similarity in the behaviour and preferences of herbivore populations along the studied gradient may explain the consistent differences in resistance.
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- Madec, Camille, et al.
(author)
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Differential effects of floral display on female and male reproductive success in the hermaphroditic herb Primula farinosa
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Other publication (other academic/artistic)abstract
- A prominent floral display increases attractiveness to pollinators, but may be associated with a cost in terms of increased risk of damage from antagonists. If damage to reproductive parts by grazers and seed predators mostly occurs after pollen dispersal, a large floral display may benefit both female and male reproductive functions, while costs may predominantly be expressed through female function. The hermaphroditic herb Primula farinosa is dimorphic for floral display with a long-scaped morph, which displays its flowers well above the ground, and a short-scaped morph, which displays its flowers close to the ground. We conducted a field experiment with genotyped plants at two sites to examine whether scape morph differentially affects female and male reproductive success and whether the two scape morphs mate assortatively. Female reproductive success was assessed by quantifying seed production and male siring success by genotyping offspring. The intensity of seed predation differed between experimental sites (59% vs. 9% of fruits attacked), whereas differences in grazing damage were smaller and not statistically significant (9% vs. 6%). At the site where seed predation was high, the long-scaped morph produced significantly fewer seeds, but sired more offspring than did the short-scaped morph. At the other site, the two morphs did not differ significantly in seed production or siring success. The scape morphs did not mate assortatively. The results indicate that interactions with pollinators and antagonists can differentially affect selection on floral display through male and female function and could potentially lead to a relationship between floral display and plant functional gender. They further demonstrate that a full understanding of selection on floral traits requires that selection through both male and female reproductive success is considered.
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- Madec, Camille, et al.
(author)
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Genetic differentiation in flowering time of a short-lived perennial herb driven by divergent selection
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Other publication (other academic/artistic)abstract
- Because flowering time influences the time available for fruit maturation, the optimal flowering time should vary among environments that differ in the length of the growing season. With field surveys and a common-garden experiment, we documented variation in flowering time among 20 populations of the perennial herb Primula farinosa growing on soils of different water availability within an 8 x 5 km area on the island Öland, SE Sweden. We tested the hypotheses that (a) among-population variation in flowering time in the field reflects genetic differentiation, (b) among-population differentiation in flowering time is larger than that at putatively neutral marker loci, and (c) genetic differentiation in flowering time is related to water availability at the sites of origin. Among-population variation in a common-garden experiment was positively correlated with variation observed among populations at their sites of origin, and among-population differentiation for start of flowering was significantly higher than at putatively neutral marker loci. In the field, flowering start tended to be positively related to soil moisture. However, among-population differentiation observed in the common-garden experiment was not related to variation in measures of water availability at the sites of origin, suggesting that factors other than soil characteristics influence the evolution of flowering time in this system of populations. The results indicate that variation in flowering time observed among natural populations of P. farinosa is the result of both genetic differentiation and phenotypic plasticity, and are consistent with divergent selection on flowering time.
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- Madec, Camille, et al.
(author)
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Genetic diversity and structure of the declining herb Primula farinosa across different spatial scales
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Other publication (other academic/artistic)abstract
- Habitat fragmentation and reduced population sizes are important threats to biodiversity. These changes increase the influence of genetic drift and are therefore expected to lead to reduced genetic diversity and increased population differentiation. We analysed patterns of genetic variation in the declining herb Primula farinosa in Sweden. On the mainland, P. farinosa has scattered, isolated occurrences due to habitat fragmentation, whereas on the island of Öland, southeast Sweden, the species remains common. On Öland, populations were sampled on both shallow soils, where fluctuations in population size are substantial, and on deep soils, where populations are more stable. Genetic diversity was investigated at 12 putatively neutral microsatellite loci and at a floral display locus influencing plant fitness. Genetic diversity was found to be lower and more strongly structured on the mainland than on Öland, which is consistent with lower gene flow and increased influence of genetic drift in mainland than in Öland populations. On Öland, genetic diversity was not related to soil depth, suggesting that differences in the magnitude of fluctuations in population size are less important for the structuring of genetic variation in P. farinosa. Moreover, population differentiation was stronger at the floral display locus compared to microsatellite loci, consistent with divergent selection acting on floral display on Öland. Taken together, our findings indicate that to maintain genetic diversity in P. farinosa, management should promote gene flow among populations and variation in the direction of selection on floral display.
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