Causes and consequences of the rarity of plant species

The reasons why some plant species are rare, while some others are not, is a long-standing concern for biologists. A better understanding of drivers of plant rarity is central to broaden our knowledge of the distribution of species and is crucial for conservation practitioners to protect rare and threatened species. However, despite a large literature body dedicated to this question, we are lacking understanding and evidences on the effects of factors suggested to contribute to plant species rarity and factors suggested to increase success of conservation projects of threatened plants. In this thesis, I focused on investigating whether generalist herbivory and genetic processes could contribute to further plant species rarity and how genetic diversity, propagule pressure and plant origin alter reintroduction success. To achieve this, I have conducted multi-species experiments taking into account the local and regional rarity, habitat characteristics and several traits linked to life-history and resource-allocation strategies of the plant species. In the first chapter of this thesis, I investigated how the performance and preference of one below-ground and three aboveground invertebrate generalist herbivore species vary with the rarity, habitat characteristics and traits linked to resource-allocation strategies of 62 different plant species. I found that regionally and locally rare and common plant species did not generally differ in their defense against generalist herbivores. The results indicate that the hypothesis that rare plant species are less defended against herbivores does not hold for herbaceous plant species. Instead, they suggest that the ability of plants to allocate resources away from defense against herbivores to achieve a stronger competitive ability might have allowed plants to become locally and regionally common. In the second chapter, I tested whether selfing and between-population outcrossing affected five fitness-related traits for 16 species of different local and regional rarity, habitat characteristics and resource-allocation strategies. The results demonstrate that regional rarity, habitat characteristics and traits linked to resource-allocation strategies shape the outcome of selfing and between-population outcrossing in plants. This study highlights that inbreeding depression may not represent a major threat to species that are already rare. Moreover, as between-population outcrossing appears beneficial for plant fitness of many species, including rare ones, we suggest considering it for plant-conservation activities. In the last chapter, I investigated how genetic diversity, propagule pressure and population of origin alter fitness of reintroduced rare and threatened plant species. The results show that genetic diversity and population of origin interacted and were important determinants of early plant fitness. The effect of genetic diversity was positive or negative depending on how ecologically similar the populations of origin to the translocation site are. In addition, propagule pressure may affect negatively fitness of reintroduced plants, possibly due to intra-specific competition or plant antagonists. The study underlines the importance to match reintroduction and origin sites very carefully by conducting vegetation record to assess ecological similarity. Altogether, the results of this thesis challenge important hypotheses about rare plant species and suggest that plant species rarity may be driven by complex interactions between extrinsic and intrinsic factors. Finally, it highlights the importance of considering context dependency in multi-species experiments in order to disentangle patterns related to plant rarity from those related to plant habitat and resource allocation strategies

Rarity and life-history strategies shape inbreeding and outbreeding effects on early plant fitness

Local abundance and regional distribution are two aspects of a species’ rarity. They are suggested to differentially alter genetic processes in plants: Locally rare species are hypothesized to suffer less from inbreeding and outbreeding than locally common species, thanks to genetic purging through long inbreeding histories and weaker local adaptations, respectively. Regionally rare species are hypothesized to be more susceptible to outbreeding, but less to inbreeding, compared to regionally common ones, due to small and declining range size. While this has major implications for plant conservation practices, we lack evidences and general understanding on how breeding effects on a plant’s early life fitness are related to its local and regional rarity. To investigate effects of inbreeding and outbreeding on plants’ early fitness, we performed self-, within- and between-population pollinations in eight pairs of closely related species differing in regional and local rarity. To avoid biases due to context dependency, we took species competitive ability, habitat resource-richness and resource-allocation strategy into account in the analyses. We then tested how inbreeding and outbreeding affected five fruit-, seed- and seedling-related traits. Inbreeding did not generally have more negative effects on early fitness of regionally rare and non-competitive species than on regionally common and competitive ones. Outbreeding was generally beneficial to early fitness of plant species across the gradients of regional rarity, competitive ability and habitat resource-richness. Our results show that outbreeding may be beneficial to the early fitness of plant species, including rare and non-competitive ones and may be considered for conservation strategies

A common soil temperature threshold for the upper limit of alpine grasslands in European mountains

Open Access funding provided by Université de Lausanne. Field inventories and temperature loggers were financially supported by 5th RTD Framework Programme of the European Union, UK Centre for Ecology and Hydrology, Département de la culture et des sports du Valais, Departamento de Medio Ambiente del Gobierno de Aragón, Foundation Dr. Joachim de Giacomi, Fondation Mariétan, Italian project of strategic interest NextData, MAVA Foundation, Frignano Regional Park (Modena), Norwegian Environment Agency, Ordesa & Monte Perdido National Park, Research Commission of the Swiss National Park, Scientific Grant Agency VEGA (project Nr. 2/0132/18), Scottish Natural Heritage, Sierra Nevada National Park, Société académique de Genève, Swiss Federal Office of Education and Science, Swiss Federal Office for the Environment, Tiroler Wissenschaftsfonds, Tuscan-Emilian Apennines National Park, and Wissenschaftsförderung der Südtiroler Landesregierung.We thank the numerous collaborators in each region who participated in field inventories, S. Jordan for his preliminary analyses, and A.-L. Aeby and F. Schütz for their assistance on statistical analyses. We are particularly grateful to C. Körner and two anonymous reviewers for their helpful comments on earlier versions of the manuscript.While climatic research about treeline has a long history, the climatic conditions corresponding to the upper limit of closed alpine grasslands remain poorly understood. Here, we propose a climatic definition for this limit, the 'grassline', in analogy to the treeline, which is based on the growing season length and the soil temperature. Eighty-seven mountain summits across ten European mountain ranges, covering three biomes (boreal, temperate, Mediterranean), were inventoried as part of the GLORIA project. Vascular plant cover was estimated visually in 326 plots of 1 x 1 m. Soil temperatures were measured in situ for 2-7 years, from which the length of the growing season and mean temperature were derived. The climatic conditions corresponding to 40% plant cover were defined as the thresholds for alpine grassland. Closed vegetation was present in locations with a mean growing season soil temperature warmer than 4.9 degrees C, or a minimal growing season length of 85 days, with the growing season defined as encompassing days with daily mean >= 1 degrees C. Hence, the upper limit of closed grasslands was associated with a mean soil temperature close to that previously observed at the treeline, and in accordance with physiological thresholds to growth in vascular plants. In contrast to trees, whose canopy temperature is coupled with air temperature, small-stature alpine plants benefit from the soil warmed by solar radiation and consequently, they can grow at higher elevations. Since substrate stability is necessary for grasslands to occur at their climatic limit, the grassline rarely appears as a distinct linear feature.Universite de Lausanne5th RTD Framework Programme of the European UnionFoundation Dr. Joachim de GiacomiFondation MarietanMAVA FoundationNorwegian Environment AgencyScottish Natural HeritageSociete academique de GeneveSwiss Federal Office of Education and ScienceSwiss Federal Office for the EnvironmentTiroler WissenschaftsfondsTuscan-Emilian Apennines National ParkWissenschaftsforderung der Sudtiroler LandesregierungOrdesa & Monte Perdido National ParkResearch Commission of the Swiss National ParkVedecka grantova agentura MSVVaS SR a SAV (VEGA) 2/0132/18Italian project of strategic interest NextDataFrignano Regional Park (Modena)UK Centre for Ecology and HydrologyDepartement de la culture et des sports du ValaisGobierno de Arago

Environmental variation in sex ratios and sexual dimorphism in three wind‐pollinated dioecious plant species

Variation in plant sex ratios is often attributable to sex-specific mortality in heterogeneous environments that differentially limit male and female plant reproduction. Yet sexual dimorphism and plastic responses to environmental heterogeneity are common and may co-vary with variation in sex ratios. Here, we show that the sex ratio and the degree of sexual dimorphism for a number of plant traits varied along climatic and elevation gradients in three wind-pollinated dioecious species, Rumex lunaria, Urtica dioica and Salix helvetica. Some of the observed sex-specific responses to climatic variation are consistent with greater sensitivity of females to water scarcity, but most responses rather point to the greater sensitivity of males to ecological stress, consistent with larger male reproductive effort, as has been commonly reported for wind-pollinated plants. In contrast, we found no evidence for variation in either sex ratios or sexual dimorphism expected under sexual selection. Interestingly, sex ratios and sexual dimorphism varied both along distinct and the same ecological axes of variation, suggesting that the evolution of sexual dimorphism in the measured traits was not sufficient to prevent sex-specific mortality

Are rare plant species less resistant than common ones to herbivores? A multi-plant species study using above- and below-ground generalist herbivores.

Rare plant species are suggested to be less resistant to herbivores than common species. Their lower apparency and the fact that they often live in isolated populations, resulting in fewer herbivore encounters, might have led to the evolution of reduced defences. Moreover, their frequent lower levels of genetic diversity compared with common species could negatively affect their resistance against enemies. However, the hypothesis that plant resistance depends on plant regional and local rarity, independently of habitat and competitive and growth strategy, lacks evidence. To test this hypothesis, we assessed the performance and preference of one belowground and three aboveground generalist invertebrate herbivores from different taxonomic groups as indicators of plant resistance. Herbivores were fed a total of 62 regionally and locally rare and common plant species from Switzerland. We accounted for differences in a plant's growth and competitive strategy and habitat resource availability. We found that regionally and locally rare and common plant species did not generally differ in their resistance to most generalist herbivores. However, one herbivore species even performed better and preferred locally and regionally common plant species over rarer ones, indicating that common species are not more resistant, but tend to be less resistant. We also found that all herbivore species consistently performed better on competitive and large plant species, although different herbivore species generally preferred and performed better on different plant species. The latter indicates that the use of generalist herbivores as indicators of plant-resistance levels can be misleading. Synthesis: Our results show that rare plant species are not inherently less resistant than common ones to herbivores. Instead, our results suggest that the ability of plants to allocate resources away from defence towards enhancing their competitive ability might have allowed plants to tolerate herbivory, and to become locally and regionally common

Mathematical analysis of the transmission dynamics of the liver fluke, Opisthorchis viverrini

We develop and analyse two population-based models of the transmission dynamics of the worm parasit e Opisthorchis viverrini . The life cycle of  O. viverrini includes humans, cats and dogs as definitive hosts; and snails and fish as intermediate hosts. The first model has only one definitive host (humans) while the second model has two additional hosts: the reservoir hosts, cats and dogs. We define reproduction numbers and endemic equilibrium points for the two models. We use prevalence data for the five hosts from two islands in Lao People’s Democratic Republic to estimate distributions of parameter values. We use these distributions to compute the sensitivity index and the partial rank correlation coefficient of the basic reproduction number and the endemic equilibrium point to the parameters. We calculate distributions of the host-specific type-reproduction number to show that humans are necessary to maintain transmission and can sustain transmission without additional reservoir hosts. Therefore interventions targeting humans could be sufficient to interrupt transmission of  O. viverrin

Targeting the Ets Binding Site of the HER2/neu Promoter with Pyrrole-Imidazole Polyamides

Three DNA binding polyamides (1-3) were synthesized that bind with high affinity (Ka = 8.7·10^9 M^-1 to 1.4·10^10 M^-1) to two 7-base pair sequences overlapping the Ets DNA binding site (EBS; GAGGAA) within the regulatory region of the HER2/neu proximal promoter. As measured by electrophoretic mobility shift assay, polyamides binding to flanking elements upstream (1) or downstream (2 and 3) of the EBS were one to two orders of magnitude more effective than the natural product distamycin at inhibiting formation of complexes between the purified EBS protein, epithelial restricted with serine box (ESX), and the HER2/neu promoter probe. One polyamide, 2, completely blocked Ets-DNA complex formation at 10 nM ligand concentration, whereas formation of activator protein-2-DNA complexes was unaffected at the activator protein-2 binding site immediately upstream of the HER2/neu EBS, even at 100 nM ligand concentration. At equilibrium, polyamide 1 was equally effective at inhibiting Ets/DNA binding when added before or after in vitro formation of protein-promoter complexes, demonstrating its utility to disrupt endogenous Ets-mediated HER2/neu preinitiation complexes. Polyamide 2, the most potent inhibitor of Ets-DNA complex formation by electrophoretic mobility shift assay, was also the most effective inhibitor of HER2/neu promoter-driven transcription measured in a cell-free system using nuclear extract from an ESX- and HER2/neu-overexpressing human breast cancer cell line, SKBR-3

Mathematical Analysis of the Transmission Dynamics of the Liver Fluke, Opisthorchis viverrini

We develop and analyse two population-based models of the transmission dynamics of the worm parasite Opisthorchis viverrini. The life cycle of O. viverrini includes humans, cats and dogs as definitive hosts; and snails and fish as intermediate hosts. The first model has only one definitive host (humans) while the second model has two additional hosts: the reservoir hosts, cats and dogs. We define reproduction numbers and endemic equilibrium points for the two models. We use prevalence data for the five hosts from two islands in Lao People’s Democratic Republic to estimate distributions of parameter values. We use these distributions to compute the sensitivity index and the partial rank correlation coefficient of the basic reproduction number and the endemic equilibrium point to the parameters. We calculate distributions of the host-specific type-reproduction number to show that humans are necessary to maintain transmission and can sustain transmission without additional reservoir hosts. Therefore interventions targeting humans could be sufficient to interrupt transmission of O. viverrini

Age dependency in the transmission dynamics of the liver fluke, Opisthorchis viverrini and the effectiveness of interventions

We introduce a population-based model of the transmission dynamics of the liver fluke Opisthorchis viverrini, that allows the mean worm burden in humans to depend on the host age. We parameterise the model using data on intensity of infection in humans and prevalence data for cats, dogs, fish and snails from two island communities in Lao People’s Democratic Republic. We evaluate the steady state solution using a fixed point iteration and estimate the basic reproductive number. We optimise the coverage level of MDA in an adapted model of five age groups to compare varying coverages across age groups. Our results suggest that although adults have the strongest contribution to transmission and campaigns should target adults, if such targeting is operationally infeasible, achieving moderate coverage levels in all age groups can still have a substantial impact on reducing worm burden

Analysis of interventions against the liver fluke, Opisthorchis viverrini

We adapt a population-based model of Opisthorchis viverrini transmission dynamics to determine the effectiveness of three different interventions. The model includes the definitive hosts, humans; the reservoir hosts, dogs and cats; and the intermediate hosts, snails and fish. We consider the interventions: education campaigns to reduce the consumption of raw or undercooked fish, improved sanitation and treatment through mass drug administration. We fit model parameters to a data set from two islands in southern Lao PDR. We calculate the control reproduction number, simulate different scenarios and optimise the interventions with optimal control. We look at the potential of the interventions to eliminate transmission within 20 years. The model shows that education and improved sanitation need a very high coverage to fulfil the goal of elimination, whereas annual drug distribution at medium coverage is sufficient. The best solution is a combination of drug distribution at a medium level of coverage and as high as possible coverage of education and improved sanitation