Merels in de stad blijken te verschillen van soortgenoten in naburige bossen ten aanzien van lichaamsbouw, zang, en genetica. Nederlandse stadsmerels zijn zwaarder dan hun soortgenoten in het bos.... Show moreMerels in de stad blijken te verschillen van soortgenoten in naburige bossen ten aanzien van lichaamsbouw, zang, en genetica. Nederlandse stadsmerels zijn zwaarder dan hun soortgenoten in het bos. Daarnaast zingen stadsmerels met een hogere frequentie dan bosmerels wat de hoorbaarheid bij laagtonig verkeerslawaai ten goede komt. Merelmannen merken zelf daadwerkelijk de verschillen op tussen de zang van stads- en bosmerels, zo blijkt uit experimenten waarbij de zang werd afgespeeld in merelterritoria in stad en bos. Stadsmerels reageren namelijk sterker op hogere zang en bosmerels juist meer op lagere. Variatie in zang en reactie op zang kan mogelijk de onderlinge uitwisseling tussen stad- en bospopulaties be_nvloeden. Dit wordt ondersteund door de bevinding dat populaties uit steden en naburige bossen inderdaad genetisch anders zijn. De gevonden verschillen zijn opmerkelijk omdat de studiepopulaties in stad en bos slechts 5 _ 10 km uit elkaar liggen. Het onderzoek toont dus aan dat een stedelijke omgeving invloed kan hebben op belangrijke soortskenmerken waarbij het echter nog maar de vraag is of deze evolutie ooit zal leiden tot het ontstaan van twee gescheiden merelsoorten. Show less
In view of their predominant sessile lifestyle, plants need to be able to adapt to changes in their environment. Environmental signals such as light and gravity modulate plant growth and... Show moreIn view of their predominant sessile lifestyle, plants need to be able to adapt to changes in their environment. Environmental signals such as light and gravity modulate plant growth and architecture by redirecting polar cell-to-cell transport of auxin, thus causing changes in the distribution of this plant hormone. The PIN auxin efflux carriers are key drivers of auxin transport that determine the direction of auxin flow through their asymmetric subcellular distribution. An important component in PIN polarity establishment is the plant protein kinase PINOID (PID). PID instructs apical (shoot meristem facing) PIN polarity by phosphorylating the central hydrophylic loop of PIN proteins (PINHL). In this thesis we investigated modulation of PID activity by the calcium binding proteins TCH3 and PBP1, and by the protein kinase PDK1. All three proteins were found to regulate both the enzymatic activity and the sub-cellular localisation of PID in response to calcium and phospholipids, respectively, and as such they are likely to be involved in translating environmental signals into PIN polarity changes. In addition, we show that PID and its close homologs act both redundantly and differentially in orienting plant development by instructing the subcellular distribution of PINs. Show less
Plant hybridization has been shown to have important ecological and evolutionary consequences in a number of genera, including Senecio. Here, I investigate the possible consequences of natural... Show morePlant hybridization has been shown to have important ecological and evolutionary consequences in a number of genera, including Senecio. Here, I investigate the possible consequences of natural hybridization between Senecio jacobaea and S. aquaticus. It is shown that many factors are involved in hybrid fitness, and that hybridization can alter the expression of primary and secondary metabolites in plants. Show less
What makes plant shoots grow towards the light, and plant roots grow down into the soil? This was a question that Charles Darwin asked himself, and his experiments more than a century ago to find... Show moreWhat makes plant shoots grow towards the light, and plant roots grow down into the soil? This was a question that Charles Darwin asked himself, and his experiments more than a century ago to find the answer laid the basis for the identification of the growth hormone auxin. Auxin, or indole-3-acetic acid (IAA), directs plant growth and development through its polar cell-to-cell transport-driven asymmetric distribution. Cellular IAA concentrations determine cell division, -elongation and -differentiation by facilitating the degradation of the Aux/IAA repressor proteins and thus inducing gene expression. The presumed pathway for the programmed degradation of proteins involves the attachment of a protein called ubiquitin, leading to recognition and destruction by a molecular complex called the proteasome. Here we investigated the role of protein ubiquitination and degradation in auxin action. First, we provided evidence for the longstanding paradigm that Aux/IAA proteins are ubiquitinated prior to their proteasomal degradation. At the same time we showed that ubiquitin labeling is not necessarily required for proteasomal degradation of plant proteins. Moreover, we showed that a regulator of auxin transport polarity is also involved in fine tuning auxin responses through the ubiquitin pathway. Our results place protein ubiquitination at a central position in auxin biology and thus in the movement of plants. Show less
The research described in this thesis mainly focussed on making and refining a model that describes axial patterning during gastrulation in the frog Xenopus laevis. Chapter 2 and 3 describe that... Show moreThe research described in this thesis mainly focussed on making and refining a model that describes axial patterning during gastrulation in the frog Xenopus laevis. Chapter 2 and 3 describe that axial information arises in the mesoderm and subsequently in the neurectoderm. Also is shown that this information, under influence of the Spemann organiser and cellular movements, is translated from a time sequence into a space sequence. The function of the Spemann organiser, important for AP patterning is neural induction. In chapter 4 is described that retinoids, important for axial patterning and formed in the mesoderm, have a patterning effect on neurectoderm. An important conclusion in this chapter is that retinoids are candidates for transfer of axial information from mesoderm to neurectoderm and can, in this way, coordinate the expression of axial information between mesoderm and neurectoderm. In chapter 5 a study is described where the transcriptional targets of Hoxc6 or Antennapedia in the frog Xenopus laevis and the fruitfly Drosophila melanogaster are compared. From this comparison conclusions can be drawn about the processes that are important for the function of Hoxc6/Antp. From this study could be concluded that celldivision, cellmigration, and suppresion of head formation are processes that are important for the function of Hoxc6/Antp. Show less
Forest damselflies (family Platystictidae) are widespread in southeast Asia from Sri Lanka to New Guinea, and are also known from Central America and the northern part of South America. The larvae... Show moreForest damselflies (family Platystictidae) are widespread in southeast Asia from Sri Lanka to New Guinea, and are also known from Central America and the northern part of South America. The larvae of most species live in small streams or seepages under forest canopy. Adults are found hanging from the tips of leaves or twigs along streams. The family is thought to have evolved more than 100 million years ago. Only 213 species are known worldwide, of which the author described 46 as new to science. Although most species are remarkably similar in general appearance, they show significant variation in structural details such as wing venation, pronotum, and secondary genitalia of the male. The group is ideal for biogeographical studies, since most species have small distributional ranges. A reconstruction of the phylogeny shows that several ancient lineages occur along the margin of the Indian Plate. Although Platystictidae are not known from Africa, it is hypothesized that the family evolved on that continent. The ancestors of the subfamilies Platystictinae and Sinostictinae drifted with India to Asia between 100 and 45 Ma. A scenario of the historical biogeography of the Platystictinae is described in relation to the palaeogeography of southeast Asia since the Eocene. The subfamily Palaemnematinae most likely dispersed from Africa to the New World via Europe and the ‘North Atlantic Land Bridge’. Show less
Based on the digitized herbarium records housed at the National Herbarium of the Netherlands I developed high spatial resolution patterns of Borneo's botanical richness, endemicity, and the... Show moreBased on the digitized herbarium records housed at the National Herbarium of the Netherlands I developed high spatial resolution patterns of Borneo's botanical richness, endemicity, and the floristic regions. The patterns are derived from species distribution models which predict a species occurrence based on the identified relationships between species recorded presences and the ecological circumstances at those localities. A new statistical method was developed to test the species distribution models. Several areas of high richness and endemicity were added to the list of previous known ones. Furthermore, the lowland rain forest of Borneo, previously recognized as one floristic region, in fact harbours at least four (and possibly six) different floristic regions. Show less
Agrobacterium is the natures genetic engineer that can transfer genes across the kingdom barriers to both prokaryotic and eukaryotic host cells. The host genes which are involved in Agrobacterium... Show moreAgrobacterium is the natures genetic engineer that can transfer genes across the kingdom barriers to both prokaryotic and eukaryotic host cells. The host genes which are involved in Agrobacterium-mediated transformatiom (AMT) are not well known. Here, I studied in a systematic way to identify the whole eukaryotic host genes which are involved in this event. For this, I used a collection of around 4800 homozygous diploid deletion mutants and the cDNA libraries of yeast Saccharomyces cerevisiae as the eukaryotic host and two strains of Agrobacterium. First, a large-scale AMT protocol for the transformation of yeast mutants was developed. Then, the yeast mutant collection was screened for the mutants with an increased or a decreased AMT. 249 deletion mutant strains were found which affect AMT. Of great importance were host chromatin remodeling and histone modifying complexes. Besides, using GFP technique I showed the nuclear localization of Agrobacteriums VirD2 in yeast. Yeast two-hybrid screens also identified 12 yeast putative interaction partners of VirD2 protein. Show less
