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  • Arnell, Matilda, et al. (författare)
  • Local distribution patterns of fleshy-fruited woody plants - testing the orchard hypothesis
  • 2021
  • Ingår i: Ecography. - 0906-7590 .- 1600-0587. ; 44:3, s. 481-492
  • Tidskriftsartikel (refereegranskat)abstract
    • Plant distribution patterns are influenced by many different factors. We examined mechanisms behind local distribution patterns of boreo-nemoral fleshy-fruited woody plants with seed dispersal mainly mediated by birds. It has been suggested that guilds of these plants develop 'orchards', i.e. locally aggregated occurrences composed of several species. We analysed spatially explicit occurrence data of different life stages of a local guild of fleshy-fruited woody plants in south-eastern Sweden, and conducted a seedling recruitment experiment for a subset of ten species. Spatial point pattern analyses showed that the guild of fleshy-fruited species was aggregated at small (< 10 m) spatial scales. Saplings were more common under canopies of heterospecific reproductive individuals than expected by chance. These results show that the local guild of fleshy-fruited species is distributed as orchards, i.e. clusters consisting of individuals of different species and life stages. We found no evidence of negative distance dependence between saplings and reproductive conspecific individuals. Results from the recruitment experiment suggest that recruitment is seed limited and generally low among the studied species. At the site-scale (circular areas with 50 m radius), there was no difference in seedling recruitment between sites with and without reproductive conspecific individuals for most species included in the recruitment experiment. This further suggests that the aggregated patterns found are not simply a result of spatial concordance in suitable habitats across life stages. Instead, we suggest that the sheer number of seeds from species in the guild deposited under the crowns of fruit bearing individuals is the main mechanism behind the build-up of orchards. Although further studies are needed to fully disentangle the processes underlying the observed patterns of local diversity, we argue that describing patterns and contrasting them to the predictions of ecologically relevant hypotheses is a useful first step.
  • Arvanitis, Leena, et al. (författare)
  • Butterfly seed predation: effects of landscape characteristics, plant ploidy level and population structure
  • 2007
  • Ingår i: Oecologia. - 0029-8549. ; 152:2, s. 275-285
  • Tidskriftsartikel (refereegranskat)abstract
    • Polyploidization has been suggested as one of the most common mechanisms for plant diversification. It is often associated with changes in several morphological, phenological and ecological plant traits, and therefore has the potential to alter insect–plant interactions. Nevertheless, studies evaluating the effect of plant polyploidy on interspecific interactions are still few. We investigated pre-dispersal seed predation by the butterfly Anthocharis cardamines in 195 populations of two ploidy levels of the herb Cardamine pratensis (tetraploid ssp. pratensis, 2n = 30 vs. octoploid ssp. paludosa, 2n = 56–64). We asked if differences in incidence and intensity of predation among populations were related to landscape characteristics, plant ploidy level and population structure. The incidence of the seed predator increased with increasing plant population size and decreasing distance to nearest population occupied by A. cardamines. The intensity of predation decreased with increasing plant population size and was not affected by isolation. Probability of attack decreased with increasing shading, and intensity of predation was higher in grazed than in non-grazed habitats. The attack intensity increased with increasing mean flower number of plant population, but was not affected by flowering phenology. Individuals in tetraploid populations suffered on average from higher levels of seed predation, had higher mean flower number, were less shaded and occurred more often in grazed habitats than octoploid populations. When accounting for differences in habitat preferences between ploidy levels there was no longer a difference in intensity of predation, suggesting that the observed differences in attack rates among populations of the two ploidy levels are mediated by the habitat. Overall, our results suggest that polyploidization is associated with differentiation in habitat preferences and phenotypic traits leading to differences in interspecific interaction among plant populations. This, in turn, may facilitate further divergence of ploidy levels.
  • Arvanitis, Leena, et al. (författare)
  • Plant ploidy level influences selection by butterfly seed predators
  • 2008
  • Ingår i: Oikos. ; 117, s. 1020-1025
  • Tidskriftsartikel (refereegranskat)abstract
    • Polyploidization is a common route to plant diversification. Polyploids often differ from their progenitors in size, flower number, flower size and flowering phenology. Such differences may translate into differences in the intensity of interactions with animals. Here we investigated the impact of the ploidy-related differences in tetraploids and octoploids of the perennial herb Cardamine pratensis on pre-dispersal seed predation by the butterfly Anthocharis cardamines. The probability of escaping attack was lower for octoploids than for tetraploids, even after accounting for the fact that octoploids were larger and had fewer flowers than tetraploids. Flower shoot size was correlated with probability of attack in tetraploids but not in octoploids. Differences in plant traits associated with polyploidization can alter interactions with animals, and animal-mediated differences in trait selection between ploidy types can contribute to their further divergence.
  • Arvanitis, Leena, 1959- (författare)
  • Plant polyploidy and interactions with insect herbivores
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Polyploidization has been suggested to be a common mechanism for plant speciation. Polyploidy is associated with changes in plant traits and altered habitat preference. Antagonistic and mutualistic animals are known to discriminate between plants based on variation in such plant traits, suggesting that interactions may have an important role in divergence of plant polyploids after the polyploidization. In this thesis, I investigated the effect of insect herbivores on divergence of plant polyploids in a system consisting of the predispersal seed predator butterfly Anthocharis cardamines, the bud gall forming midge Dasineura cardaminis, and tetraploids and octoploids of the herb Cardamine pratensis. Octoploid populations occurred more often in shaded and nongrazed habitats than tetraploids. Octoploid plants were larger and had fewer but larger flowers than tetraploids. Butterfly attack rates were higher in tetraploid than in octoploid populations, whereas the gall midge attacked only octoploids. These differences were associated with higher abundance of butterflies in sunny habitats and gall midges in shaded habitats. In contrast to the pattern at the population level, octoploid flower shoots were more likely to be attacked by the butterfly in sympatric populations. Also trait selection differed between ploidy levels, both in the absence and in the presence of herbivores. In a field experiment, butterfly preference did not alter the trait selection in tetraploids. In octoploids, the two herbivores did not change selection considered separately. However, their joint effect resulted in significant selection for smaller flower shoots and reduced selection on number of flowers. This thesis demonstrates that differences in habitat preference and phenotypic plant traits between polyploid cytotypes can lead to altered interactions with herbivores. Such differences in interactions with animals may alter not only the relative fitness of cytotypes but also trait selection within the respective ploidy type.
  • Bisang, Irene, et al. (författare)
  • Family affiliation, sexratio and sporophyte frequency in unisexual mosses
  • 2014
  • Ingår i: Botanical journal of the Linnean Society. - 0024-4074 .- 1095-8339. ; 174, s. 163-172
  • Tidskriftsartikel (refereegranskat)abstract
    • Patterns of sex expression and sex ratios are key features of the life histories of organisms. Bryophytes are the only haploid-dominant land plants. In contrast with seed plants, more than half of bryophyte species are dioecious, with rare sexual expression and sporophyte formation and a commonly female-biased sex ratio. We asked whether variation in sex expression, sex ratio and sporophyte frequency in ten dioecious pleurocarpous wetland mosses of two different families was best explained by assuming that character states  evolved: (1) in ancestors within the respective families or (2) at the species level as a response to recent habitat conditions. Lasso regression shrinkage identified relationships between family membership and sex ratio and sporophyte frequency, whereas environmental conditions were not correlated with any investigated reproductive trait. Sex ratio and sporophyte frequency were correlated with each other. Our results suggest that ancestry is more important than the current environment in explaining reproductive patterns at and above the species level in the studied wetland mosses, and that mechanisms controlling sex ratio and sporophyte frequency are phylogenetically conserved. Obviously, ancestry should be considered in the study of reproductive character state variation in plants.
  • Bisang, Irene, et al. (författare)
  • No evidence of sexual niche partitioning in a dioecious moss with raresexual reproduction
  • 2015
  • Ingår i: Annals of Botany. - 0305-7364 .- 1095-8290.
  • Tidskriftsartikel (refereegranskat)abstract
    • Background and Aims. Roughly half of the species of bryophytes have separate sexes (dioecious) and half are hermaphroditic (monoecious). This variation has major consequences for the ecology and evolution of the different species. In some sexually reproducing dioecious bryophytes, sex ratio has been shown to vary with environmental conditions. This study focuses on the dioecious wetland moss Drepanocladus trifarius, which rarely produces sexual branches or sporophytes and lacks apparent secondary sex characteristics, and examines whether genetic sexes exhibit different habitat preferences, i.e. whether sexual niche partitioning occurs.Methods. A total of 277 shoots of D. trifarius were randomly sampled at 214 locations and 12 environmental factors were quantified at each site. Sex was assigned to the individual shoots collected in the natural environments, regardless of their reproductive status, using a specifically designed molecular marker associated with female sex.Key Results. Male and female shoots did not differ in shoot biomass, the sexes were randomly distributed with respect to each other, and environmental conditions at male and female sampling locations did not differ. Collectively, this demonstrates a lack of sexual niche segregation. Adult genetic sex ratio was female-biased, with 28 females for every male individual.Conclusions. The results show that although the sexes of D. trifarius did not differ with regard to annual growth, spatial distribution or habitat requirements, the genetic sex ratio as nevertheless significantly female-biased. This supports the notion that factors other than sex-related differences in reproductive costs and sexual dimorphism can also drive the evolution of biased sex ratios in plants
  • Bisang, Irene, et al. (författare)
  • Sex expression and genotypic sex ratio vary with region and environment in the wetland moss Drepanocladus lycopodioides
  • 2020
  • Ingår i: Botanical journal of the Linnean Society. - 0024-4074 .- 1095-8339. ; 192:2, s. 421-434
  • Tidskriftsartikel (refereegranskat)abstract
    • Sex ratio variation is common among organisms with separate sexes. In bryophytes, sex chromosome segregation at meiosis suggests a balanced progeny sex ratio. However, most bryophyte populations exhibit female-biased phenotypic sex ratios based on the presence of reproductive structures on gametophytes. Many bryophyte populations do not form sexual organs, and genotypic sex ratio variation in such populations is mostly unknown. We tested sex expression, and phenotypic and genotypic sex ratios against environmental parameters in natural populations of the unisexual wetland moss Drepanocladus lycopodiodes at 11 sites in each of three regions in southern Sweden. We identified sex in 660 individual ramets, based on sexual structures, when present, or with a specifically designed molecular marker, when absent. All regions exhibited a female bias in phenotypic and genotypic sex ratios. Sex ratio biases and sex expression differed between regions. Sex ratios were less female-biased in larger patches. Wetter patches exhibited a stronger female bias in genotypic sex ratio and lower sex expression. This is the first evidence of environmental effects on genotypic sex ratio in mosses. A higher frequency of females in wet patches could be due to higher female resource demands for sporophyte production or higher male sensitivity to wetness. A higher incidence of females than males in moister sites aligns with female flowering plants, but differs from reproductive bryophytes in drier environments. Taken together with previous results, our data indicate that sex ratio variation and its drivers differ among species, their life histories and environments.
  • Boalt, Elin, 1976- (författare)
  • Ecology and evolution of tolerance in two cruciferous species
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Tolerance to herbivory is the ability of plants to maintain fitness in spite of damage. The goal of this thesis is to investigate the genetic variation and expression of tolerance within species, determine whether and in what conditions tolerance has negative side-effects, and how tolerance is affected by different ecological factors. Tolerance is investigated with special focus on the effects of different damage types, competitive regimes, history of herbivory, and polyploidization in plants. Studies are conducted as a literature review and three experiments on two cruciferous species Raphanus raphanistrum and Cardamine pratensis.In the tolerance experiments, plants are subjected to artificial damage solely, or in a combination with natural damage. A literature review was conducted in order to investigate the effects of damage method. We found that traits related to tolerance, such as growth and fitness were not as sensitive in regard to damage method as measures of induced chemical traits, or measures of secondary herbivory.Genetic variation of tolerance was demonstrated within populations of R. raphanistrum and between subspecies of C. pratensis. In R. raphanistrum, traits involved in floral display and male fitness were positively associated with plant tolerance to herbivore damage. A potential cost of tolerance was demonstrated as a negative correlation between levels of tolerance in high and low competitive regimes. I found no evidence of other proposed costs of tolerance in terms of highly tolerant plants suffering of reduced fitness in the absence of herbivores or trade-offs in terms of a negative association between tolerance to apical and leaf damage, or between tolerance and competitive ability. In C. pratensis, higher ploidy level in plants involved higher levels of tolerance measured as clonal reproduction. Furthermore, populations exposed to higher levels of herbivory had better tolerance than populations exposed to lower levels of herbivory. In this thesis, I demonstrate evidence of different components for the evolution of tolerance in plants: genotypic variation, selective factors in terms of costs and ploidization, and selective agents in terms of changing environment or herbivore pressure.
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