The snails__ proverbial inertness makes it an ideal subject to study the patterns and processes that lead to speciation. The land snail family Chondrinidae consists of about 70 extant species in... Show moreThe snails__ proverbial inertness makes it an ideal subject to study the patterns and processes that lead to speciation. The land snail family Chondrinidae consists of about 70 extant species in six genera. They occur throughout western and central Europe, northern Africa and as far east as Pakistan. These snails share a long and interesting evolutionary history, to the knowledge of which we contribute here. Show less
Hox genes are a very important family of transcription factors during development of vertebrate and invertebrates. This family of genes contains up to 39 Hox gene members organized in 4 clusters in... Show moreHox genes are a very important family of transcription factors during development of vertebrate and invertebrates. This family of genes contains up to 39 Hox gene members organized in 4 clusters in the genome. The main function of Hox genes is the establishment of the anteroposterior axis of the embryo. During gastrulation of the frog Xenopus laevis, Hox genes start to be expressed in the mesoderm excluding the Spemann organizer mesoderm. However, a necessary interaction between the involuting mesodermal cells and the signals from the Spemann organizer center freeze the pattern of Hox expression at that time point. Thus a temporal Hox expression is converted into a spatial Hox expression during development. Moreover, Hox gene expression within the mesoderm seems to be important for Hox expression within the neural tissue. We missexpressed several Hox genes and analyzed their phenotype within the hindbrain and more posterior neural tissue. Paralogous 1 group Hox genes are important for globally pattern the hindbrain, while Hoxc6 gene seems to very important during neurogenesis in Xenopus. Axis elongation and segmentation are liked processes during development. We showed that Hoxc6 is an important gene for proper segmentation of Xenopus embryo. Show less
Plants produce a variety of secondary metabolites. In Catharanthus roseus, several have pharmaceutical applications, including the monomeric alkaloids serpentine and ajmalicine, which are used as a... Show morePlants produce a variety of secondary metabolites. In Catharanthus roseus, several have pharmaceutical applications, including the monomeric alkaloids serpentine and ajmalicine, which are used as a tranquillizer and to reduce hypertension, respectively, and the dimeric alkaloids vincristine and vinblastine, which are potent antitumour drugs. Jasmonic acid (JA) is a key defense hormone, which controls the expression of several alkaloid biosynthesis genes in Catharanthus. The JA-responsive expression is controlled by the AP2-domain transcription factors ORCA2 and ORCA3. The results in this thesis demonstrate that JA-responsive ORCA expression is controlled by an up-stream positive regulator, whose activities are affected by a family of repressors. Understanding the regulation mechanism may help to generate a very valuable tool for engineering the production of valuable secondary metabolites. Show less
Avian vocalizations function in mate attraction and territorial defence. Vocalizations can act as behavioural barriers and play an important role in speciation processes. Hybrid zones illustrate... Show moreAvian vocalizations function in mate attraction and territorial defence. Vocalizations can act as behavioural barriers and play an important role in speciation processes. Hybrid zones illustrate behavioural barriers are not always impermeable and provide a natural laboratory to examine the role of vocalizations in the causes and consequences of hybridization. This thesis examines a hybrid zone between two species of African doves: the vinaceous (Streptopelia vinacea) and ring-necked dove (S.capicola) by investigating its composition and history with molecular techniques, the mechanisms underlying the variation in dove coos and the response to hybrid signals within and outside the hybrid zone. The variation in hybrid signals and the possibility of learning which vocalizations to respond to can play an important role in facilitating further introgression between the two species. Show less
Het onderzoek beschreven in het proefschrift van B.I. Lindhout heeft zich gericht op het maken van kunstmatige eiwitten die expressie van genen be_nvloeden, zogeheten zinkvinger bevattende artifici... Show moreHet onderzoek beschreven in het proefschrift van B.I. Lindhout heeft zich gericht op het maken van kunstmatige eiwitten die expressie van genen be_nvloeden, zogeheten zinkvinger bevattende artifici_le transcriptiefactoren. Met dit type eiwitten kan worden onderzocht hoe bepaalde processen in een organisme gereguleerd worden, maar ook om op een nieuwe manier eigenschappen van een organisme te veranderen. Een speciaal type DNA-bindende zinkvingers vormt een onderdeel van deze eiwitten. Het proefschrift beschrijft experimenten die zijn gericht op de verdere uitwerking van deze techniek, vooral voor het plantenbiologisch onderzoek. Er wordt aangetoond dat zinkvinger transcriptiefactoren inderdaad goed gebruikt kunnen worden om een specifiek gen te reguleren, maar ook hoe een grote verzameling daarvan gebruikt kan worden om te zoeken naar verborgen genetische eigenschappen. Deze speciale toepassing houdt in dat specifieke kenmerken die een plant in principe van zichzelf zou kunnen hebben, maar die ontbreken omdat het eigen genetische materiaal van de plant onvoldoende tot uitdrukking komt, plotseling zichtbaar kunnen worden. Zo is gebleken dat introductie van een bepaalde transcriptiefactor de plant in staat stelt zijn DNA veel nauwkeuriger te repareren. Eveneens is beschreven hoe lichtgevende zinkvingers gebruikt kunnen worden om __live__ naar het genetische materiaal van planten- en muizencellen te kunnen kijken. Show less
Mate choice by female cichlid fish from Lake Victoria plays an important role in speciation and the maintenance of species. Females are expected to select against males that are intermediate in... Show moreMate choice by female cichlid fish from Lake Victoria plays an important role in speciation and the maintenance of species. Females are expected to select against males that are intermediate in their phenotype during the process of speciation driven by sexual selection. To test this, we hybridized two species of cichlids that differ in male nuptial coloration. Male hybrids were intermediate in nuptial coloration compared to the parental species. Hybrids had a comparable fitness to the parental species and did not suffer from inviability, sterility, skewed sex ratios, reduced survival or reduced growth rates. Females preferred males of their own species over males of the other species. This implies that female mate preference can drive speciation. Females of one species were able to distinguish between males of their own species and hybrid males; females of the other species however, were not able to see this difference. When there is hybridization in nature, for instance when coloration becomes invisible by an increase in turbidity of the water, there would be asymmetrical selection against hybrids. An understanding of these processes is crucial in speciation research and for the maintenance of biodiversity. Show less
Adaptive radiation involves the rapid divergence of a single ancestral species into a group of species each occupying a different ecological niche. Differences between species are the result of... Show moreAdaptive radiation involves the rapid divergence of a single ancestral species into a group of species each occupying a different ecological niche. Differences between species are the result of trade-offs in the ability to exploit different environments to avoid competitive interactions. The many species of wildfowl and their diversity in feeding methods are believed to represent an example of adaptive radiation. Frequently used feeding methods are filtering small food items from water and terrestrial grazing. However, few if any anseriform species apply both feeding methods. I have shown that duck-species have a higher performance for filter-feeding than for grazing. Geese and swans, on the other hand, have a higher performance for grazing than for filter-feeding. Structures of the tongue and roof of the upper bill are clearly related with feeding method and the corresponding mechanisms to transport food items through the bill to the oesophagus. These adaptations for either grazing or filter-feeding are incompatible and prevent maximal performance of both feeding methods at the same time. A study on the shape of the skull revealed several adaptations to feeding method. The size of the jaw muscles is exclusively related to size of the bill and only indirectly to feeding method. Show less
Plant architecture is determined by tightly regulated developmental processes that largely depend on the action of the plant hormone auxin. A major determinant in auxin action, besides its... Show morePlant architecture is determined by tightly regulated developmental processes that largely depend on the action of the plant hormone auxin. A major determinant in auxin action, besides its signaling pathway, is its polar cell-to-cell transport (PAT) throughout the plant. The direction on this transport depends on the localization of the auxin efflux carriers, the PIN proteins. The PINOID (PID) serine/threonine protein kinase is a key regulator of the subcellular localization of the PINs, which are direct phosphorylation targets of the kinase. This thesis describes the functional analysis of three direct interacting partners of PID, two calcium-binding proteins, TOUCH3 (TCH3) and PID BINDING PROTEIN1 (PBP1), and a BTB and TAZ domain (BT) protein. Several studies have already indicated that calcium signaling is induced by auxin application and is necessary for auxin transport. With the isolation of the two calcium-binding proteins TCH3 and PBP1 as interactors of PID, a molecular link between auxin transport and calcium signaling was identified. In this thesis, we show that calcium is involved in the regulation of both the kinase activity and the subcellular localization of PID. In complement to calcium, BTB scaffold proteins are part of the PID protein complex. A detailed analysis of BT protein family in Arabidopsis indicate a functional redundancy among the five members of this family and their requirement for the female gametophyte development. Moreover the BT proteins are required scaffold components in the PID signaling pathway. The functional analyses of the PBPs described in this thesis uncover a new mechanism of protein kinase activity regulation via calcium signaling, and present novel roles for the BT proteins, not only in PID signaling, but also more in general in plant development. Show less
Although theory predicts that females should prefer the highest quality male, female mating preferences within populations often show pronounced variation. What causes and maintains this variation... Show moreAlthough theory predicts that females should prefer the highest quality male, female mating preferences within populations often show pronounced variation. What causes and maintains this variation remains poorly understood. This thesis addresses the influence of rearing conditions both on female mating preferences and male advertising signals in the zebra finch Taeniopygia guttata. It reconciles earlier apparently contradicting findings on the relative importance of visual versus acoustic signals by comparing females__ preferences across three commonly used testing contexts. It then goes on using brood size manipulations and operant conditioning tests to ask for the effects of developmental condition on sexual traits and preferences. Birds that were raised in small or large broods differed in adult morphology and physiology and adult behaviour: male advertising song and female mating preferences reflected developmental condition. Moreover, the mating behaviour of poor condition females provides the first experimental evidence of self-perceived attractiveness in animals influencing their partner choice. The results provide strong empirical support for theoretical models of state-dependent mate choice. Show less
Aspergillus niger produces a wide variety of carbohydrate hydrolytic enzymes which have potential applications in the baking, starch, textile, food and feed industries. The goal of this thesis is... Show moreAspergillus niger produces a wide variety of carbohydrate hydrolytic enzymes which have potential applications in the baking, starch, textile, food and feed industries. The goal of this thesis is to unravel the molecular mechanisms of starch and inulin modifying network of A. niger, in order to improve the enzyme production and substrate utilization as well as to find novel enzyme activities. The research described in this thesis shows how we identify genes which encode enzymes involved in starch and inulin catabolism, how they are transcriptionally regulated, as well as how the expressed enzymes react to the carbon sources and what are their physiological roles in A. niger. Important findings are outlined as follows. We have identified inulin pathway activator InuR. The activation of InuR is thought to be triggered by the pathway inducer, sucrose or its derivative, but not previously known fructose. The activated InuR induces the expression of genes encoding inulin modifying enzymes and related sugar transporters in inulin metabolism. In addition, using the tightly regulated inuE promoter combined with racA(G12V) and GFP reporter genes, we set up a novel screening method for isolation of mutants involved in inulin signaling pathway. Show less
The great Lakes of East Africa are inhabited by a great number of haplochromine cichlid species, which form a diverse group in both ecology and nuptial coloration. The large number of sympatrically... Show moreThe great Lakes of East Africa are inhabited by a great number of haplochromine cichlid species, which form a diverse group in both ecology and nuptial coloration. The large number of sympatrically occuriring closely related species has raised questions about the underlying mechanism for reproductive isolation. In this thesis I describe experiments that test for the effects of early experience on their species assortative behaviour in the contexts of mate choice and male territorial interactions. The maternal care in haplochromine cichlids provides the opportunity for early learning, but do the young cichlids take this opportunity to learn:? And, if so, can this promote reproductive isolation under sympatric conditions? With cross-fostering experiments, I found that young female cichlid fish are affected by experiences with their mothers__ phenotype in their later mate preferences. Maternal imprinting proved to be a mechanism favourable for sympatric speciation in a mathematical comparison of female preference development. This indicates that the propensity that the Lake Victoria cichlid fish appear to have for assortative mating may be fuelled by learning. The behaviour of the males, in contrast, was not affected by learning about their mothers__ phenotype, but male-male interactions were influenced by experiences with siblings. Show less
