The breeding habitat of the collared flycatcher (Ficedula albicollis) in Val Bavona, Ticino, Switzerland

by Enea Fadini

Supervisor: Prof. Yvonne Willi

The ecology of the collared flycatcher (Ficedula albicollis) south of the Alps is poorly understood. The species has declined rapidly in the last decades in this part of its range, probably because of habitat loss. To promote the species, more information on the precise breeding habitat requirements are needed.Study area was the floodplain forest at the bottom of the Bavona valley where two forest patches still accomodate several breeding pairs. In those forest patches, I investigated tree species composition as well as forest density and clearing percentage. I also compared the habitat structure where the species is breeding to adjacent areas where the species is absent. Furthermore, the birds were monitored during breeding and ringed.
The collared flycatcher once inhabited old chestnut, oak or beech forests in Ticino. Now, the species inhabits ash-alder Alnion incanae alluvional forests with clearings and little to no understorey. The two study sites had a similar diversity index for tree species, and they consisted mostly of the same species. The sites were maintained by grazing cattle. They had densities of 5.3 and 4.9 trees per 10 m² in Bolla and Sonlert, respectively. The higher density of trees in Bolla was also reflected in the percentage of clearings, which was only 9.8% compared to the 33.6% of Sonlert.
Even though the results did not give clear answers on the habitat requirements of the collared flycatcher, the fact that this species is only found in grazed woodlands suggests their importance. Conservation efforts have therefore to be firstly aimed at allowing cattle to continue to graze these forests. These wood-pastures are important habitats for a variety of organisms at multiple trophic levels. Furthermore, the restoration and maintaining of existing old forests could possibly allow the species to return to its original breeding grounds.

Species-specific drought responses in Alpine grassland species of the Swiss Alps

by Franziska Morgen

Supervisor: Prof. Yvonne Willi

Climate change is expected to alter the frequency and intensity of drought events, a development particularly significant for mountain ecosystems where climate change is projected to occur 3-4 times faster than the global average. While general patterns to drought in alpine grasslands are relatively well-studied, there is still a lack of species-specific insights. My study aimed to determine whether certain alpine species might be less affected and could emerge as "winners" under climate change-induced summer-drought conditions. Six of the most abundant alpine grassland species (Anthoxanthum alpinum, Carex curvula, Helictotrichon versicolor, Geum urbanum, Leontodon helveticus, Potentilla aurea) within a Caricetum curvulae community were grouped in monocultures and subjected to a moderate 6-week drought. Throughout the treatment and for the rest of the growing season, I measured leaf length as a proxy for above-ground growth and recorded physiological parameters, including net assimilation, stomatal conductance to water vapor, and transpiration, comparing them to control conditions. Summer-drought generally reduced above-ground growth, increased the exponential growth parameter, and decreased the decay parameter. Drought also decreased net assimilation, stomatal conductance, and transpiration. The three grass species exhibited more pronounced negative trends, while the herbs showed negative, neutral, or even positive trends. Although clear evidence of negative drought impacts can only be reported for the outstanding species Carex curvula, these findings lay the groundwork for further research into species-specific drought effects in the studied alpine grassland.

The center-margin hypothesis applied to elevational range limits

by Julia Felber

Supervisors: Prof. Yvonne Willi, Dr. Jana Flury

Rising temperatures, as a consequence of climate change, are forcing mountain plants to shift their distributions upward in elevation where temperatures are better for population persistence. Observed range shifts are associated with extinctions at the warm ends of distributions and/or expansions at the cold ends. This raises the question whether populations at both ends suffer from low genetic variation associated with small population size or demographic bottlenecks as predicted by the population-genetic extension of the centre-margin hypothesis and evolutionary theory on range expansions, respectively. The general prediction was tested by comparing low-, mid- and high-elevation populations of two mountain transects of each of six herbaceous plant species belonging to the Brassicaceae family. Results showed that populations were genetically differentiated over the elevational transects, but that genetic diversity was not significantly reduced in the low- and high-elevation populations as compared to the mid-elevation populations. This research shows that the centre-margin hypothesis is not a general rule and that so far, upward range expansions have not impacted genetic variation. Results also suggest that other evolutionary constraints than low genetic diversity must be responsible for the extinction of populations at the low-elevation margins of species distributions under climate warming.

Hybridization upon secondary contact – Lycaena hippothoe in the Swiss Alps

by Elias Trachsel

Supervisors: Prof. Yvonne Willi, Prof. Kay Lucek

Zones of secondary contact between closely related taxa are considered natural laboratories to study the processes that drive reproductive isolation and ultimately speciation. In these systems, hybridization can occasionally lead to the emergence of novel hybrid lineages. Here, I study a secondary contact zone of two Lycaena hippothoe subspecies in the Swiss Alps by combining genomic, morphological, and ecological analyses. Using whole-genome data, I inferred ancestries and whether gene flow occurred. Further, I quantified morphological differences by making use of a machine-learning approach to detect wing patterns. Genomic analyses revealed a hybrid swarm in the contact zone that locally displaced its parental subspecies, with additional zones of hybridization dispersed across the Swiss Alps. Interestingly, the morphologically distinct parental subspecies contributed unequally to the hybrid genomes, with the largest difference in gene flow lying on the Z chromosome. The Z chromosome might pose a reproductive barrier in this system, as sex chromosome linked traits have been observed to impact ecological adaptation and mate choice in other butterflies. Lastly, ecological inferences suggested that the two subspecies and the hybrid lineage differ in the elevational range of occurrences and potentially in the thermal niche. Taken together, this study detected strong gene flow between two phenotypically distinct Lycaena hippothoe subspecies, highlighted by a hybrid swarm in a zone of secondary contact, placing it at an early stage along the speciation continuum despite the Z chromosome being a potential reproductive barrier.

Population modelling to predict the spread and eradication success of the alien species Triturus carnifex

by Svenja Zehnder

Supervisors: Prof. Yvonne Willi, Dr. Benedikt Schmidt

Invasive species can have detrimental effects on native species and therefore conservation measures may be necessary to protect the native species. Such measures should be evaluated for their effectiveness, e.g., by predictive modelling of the population dynamics of the invading species in the presence of various eradication plans. In this thesis, an age-structured population dynamics model was used to simulate the spread of the invasive Italian crested newt, Triturus carnifex, in the pond network in Basel, where the native Triturus cristatus occurs. The model incorporated the complexity of a pond-breeding amphibian life cycle, dispersal characteristics, and the connectivity of the pond network. Several eradication strategies were explored for their effectiveness. Their comparison revealed that the removal efforts do not have to be equally high in all ponds; an effective strategy is to focus the removal to ponds with the highest density of T. carnifex, and to also remove individuals from nearby ponds. Furthermore, the amount of removed individuals determined the speed until the population collapsed, whereas the duration of removal influenced when and if the population recovered from a collapse. The sensitivity analysis revealed that the model was more sensitive to demographic than behavioural traits. In summary, the simulations suggest that removal efforts over approximately ten years may be sufficient to eradicate T. carnifex in its introduced range.

Elevational gradient in herbivory and plant defence in wild Brassicaceae

by Janisse Deluigi

Supervisor: Prof. Yvonne Willi, Alessio Maccagni

An important open question in ecology is what drives species spatial distribution and species diversity (Gaston, 2003). While the importance of climate is well known and supported by many studies (Lee-Yaw et al., 2016), the role of biotic factors and the interaction between abiotic and biotic factors is still unclear (Sexton, 2010; Wisz et al., 2013; Louthan et al., 2015). Here, I investigated herbivore abundance, diversity and herbivore damage on an elevational gradient. At the same time, I studied differences in plant defence strategies among plant species with different elevational distribution, as plant defence is predicted to depend both on the herbivory regime and other stressors. The aim was to evaluate how elevation and herbivory pressure interact to shape plant defence strategies in species with different elevational distribution.
I performed two separate experiments, one in the field to assess herbivory over an elevational gradient, and one in climate chambers to assess plant defence under manipulated temperature conditions. The first was a transplant experiment on Calanda mountain (Chur, Switzerland) involving 30 Brassicaceae plant species differing in elevational distribution. Seeds were sown and plants raised at 5 sites over an elevational gradient of 1400m a.s.l. Variation in herbivore abundance, diversity and herbivore damage was assessed and tested for an association with the elevational gradient. The climate chamber experiment included 12 Brassicaceae species, which were subjected to one of three temperature treatments (cold, mid, warm) and one of two defence induction treatments (with or without application of jasmonic acid; 3x2 factorial design). I tested whether there was a relationship between defence strategy (physical or chemical defence) and elevational distribution of the species (high-elevation vs. mid-elevation vs. low-elevation) and whether temperature and defence induction treatment affected the type and amount of defence. In addition, I investigated the relationship between plant growth, plant defence, and herbivore resistance estimated in a bioassay with a generalist caterpillar (Spodoptera littoralis).
Although we did not find evidence for an elevational gradient in herbivore abundance and diversity and in herbivore damage, we observed an association between herbivory and temperature and their interaction in shaping plant defence. In the field experiment, increasing mean temperature at site was associated with increased damage. In the controlled-conditions experiment (climate chamber), plant defence traits were mostly affected by the warm temperature and the induction treatments, both generally increasing plant defences. In both approaches however, variability across plant species was high, suggesting different degrees of response across plant species. Interactions between both abiotic and biotic factors seem therefore to play an important role in shaping plant defence and therefore plant-herbivore interactions. Further studies are needed to better understand the influence of these interactions on the species-specific traits.

Intraspecific differentiation upon secondary contact between two subspecies of the Erebia euryale (Esper, 1804) species complex

by Selim Bouaouina

Supervisor: Dr. Kay Lucek, Prof. Yvonne Willi

Zones of secondary contact between closely related species or lineages are a common legacy of the Quaternary ice ages. Despite the abundance of such contact zones, little is known about the factors that shape interspecific gene flow and hybridization. In this study the two closely related subspecies Erebia euryale adyte (Huebner, 1818) and Erebia euryale isarica (Heyne, 1895), which are known to form zones of secondary contact in the Swiss Alps, are tested for genomic differentiation in sympatry and for morphological differentiation in both sympatry and allopatry. The formation of zones of secondary contact and previous studies suggesting strong phenotypic segregation in the contact zones, propose reinforcement as a driver of speciation between the two subspecies. Reinforcement is the process through which prezygotic reproductive isolation evolves in response to selection against costly hybridization in secondary contact zones. I analyzed morphological data of wing patterns and male valves between individuals from sympatric and allopatric populations of the two subspecies to assess the degree of morphological difference between the two subspecies. Furthermore, based on genomic data, gathered through restriction site associated DNA sequencing (RADseq), of sympatric populations I estimated the population structure across secondary contact zones. My study shows high occurrence of morphological hybrids and provides evidence for a high level of gene flow between the two subspecies in secondary contact and therefore the lack of strong prezygotic barriers.

Understanding reduced sensitivity of Phakopsora pachyrhizi towards demethylation-inhibitors on Glycine max

by Fabian Lörtscher

Co-Supervisor: Prof. Yvonne Willi

Soybean (Glycine max L. Merr.) is one of the most important crops worldwide, just behind wheat (Triticum aestivum L.), corn (Zea mays L.) and rice (Oryza sativa L.). It is used in many ways, for example as a food source for humans, in livestock feeding or for industrial purposes (ASA 2019). It is cultivated in large scale, led by the United States as the biggest producer, followed by Brazil and Argentina. Soybean farmers must deal with several biotic and abiotic factors, which can drastically reduce yield. One of the most important threats of soybean is Phakopsora pachyrhizi Syd. & P. Syd., also known as Asian soybean rust (ASR). Originating from Asia, the fungus spread to the American continents and now causes vast yield damages for soybean farmers. There are many approaches to counter ASR such as late sowing, elimination of secondary hosts, breeding for resistant soybean cultivars, introduction of a host free period and the application of fungicides. The most efficient way of managing ASR are fungicides and foremost, quinone-outside-inhibitors (Qols), succinate dehydrogenase inhibitors (SDHIs) and demethylation-inhibitors (DMIs). Where fungicides are applied, they may impose selection for fungicide resistance in the pathogen population and result in reduced sensitivity to the applied substance. As shown in previous studies, DMIs, Qols and SDHIs have become less effective in recent years. DMIs target the sterol biosynthesis pathway and inhibit particularly the enzyme C14-demethylase, which is encoded by the gene cyp51. While resistance to Qols seems to be qualitative, with few mutations leading to fungicide resistance, resistance to DMIs is based on small changes in sensitivity, resulting in quantitative resistance. It is thought that the effect of different resistance mechanisms combined form the resistant phenotype observed in the field today. Resistance mechanism against DMIs are highly variable and involve point mutations, over-expression of cyp51, alterations in the sterol biosynthesis pathway and up-regulation of efflux transporters. Even though some resistance mechanisms against DMIs were investigated in P. pachyrhizi, it is still unclear how such high DMI resistance levels are aquired. This study is dedicated to further characterize the loss of sensitivity against DMIs and to identify responsible mechanisms of DMI resistance, especially in the target gene cyp51.

Comparative morphology of the perianth in the tribe Sanguisorbeae (Rosaceae)

by Joao Felipe Ginefra Toni

Co-Supervisor: Prof. Yvonne Willi

Within larger taxonomic groups of the Angiosperms, considerable variation exists in the presence, number and arrangment of the basic organs of a flower, such as the perianth, and a main question is what the underlying developmental differences are. This thesis tackles this question from two sides: first, a synthesis on the parallels between the conceptual frameworks of Floral Evolutionary Development and Floral Morphology is made, and second, the developmental morphology of the perianth of seven species in the tribe of Sanguisorbeae is compared by Scanning Electron Microscopy (SEM) in order to understand petal loss and perianth evolution in Rosaceae. Three alternative hypotheses were tested: (1) homeotic replacement of petals by stamesn; (2) abortion of petal primordia; and (3) the total loss of petals by means of floral reduction. In the genera Marcetella and Polylepis, the narrow definition of homeosis was supported by the presence of petal primordia that were transformed into stamens during late development. In Sanguisorba and Acaena, no trace of rudiments or primordia in alternisepalous positions was found, thus refuting the hypothesis of homeotic transformation or abortion of petals and confirming the total loss of these organs. Moreover, a pronounced petaloidy was observed in the remaining floral whorls in these last two genera. In this case, petal loss would be explained both by reduction and developmental introgression of petal attributes into the other whorls, as a case of developmental trade-off linked with a shift from wind pollination back to insect pollination. This study emphasizes how comparative morphology is not only descriptive but also explanatory, and complements molecular approaches in the study of Floral Evolutionary Development.