Sostdc1 Plays an Essential Role in Mammalian Tooth Patterning : Insight into the Rodent Dental Evolution

This thesis work focuses on the role of TGF-beta family antagonists during the development of mouse dentition. Tooth develops through an interaction between the dental epithelium and underlying neural crest derived mesenchyme. The reciprocal signaling between these tissues is mediated by soluble signaling molecules and the balance between activatory and inhibitory signals appears to be essential for the pattern formation. We showed the importance of Sostdc1 in the regulation of tooth shape and number. The absence of Sostdc1 altered the molar cusp patterning and led to supernumerary tooth formation both in the molar and incisor region. We showed that initially, Sostdc1 expression is in the mesenchyme, suggesting that dental mesenchyme may limit supernumerary tooth induction. We tested this in wild-type incisors by minimizing the amount of mesenchymal tissue surrounding the incisor tooth germs prior to culture in vitro. The cultured teeth phenocopied the extra incisor phenotype of the Sostdc1-deficient mice. Furthermore, we showed that minimizing the amount of dental mesenchyme in cultured Sostdc1-deficient incisors caused the formation of additional de novo incisors that resembled the successional incisor development resulting from activated Wnt signaling. Sostdc1 seemed to be able to inhibit both mesenchymal BMP4 and epithelial canonical Wnt signaling, which thus allows Sostdc1 to restrict the enamel knot size and regulate the tooth shape and number. Our work emphasizes the dual role for the tooth mesenchyme as a suppressor as well as an activator during tooth development. We found that the placode, forming the thick mouse incisor, is prone to disintegration during initiation of tooth development. The balance between two mesenchymal TGF-beta family signals, BMP4 and Activin is essential in this regulation. The inhibition of BMP4 or increase in Activin signaling led to the splitting of the large incisor placode into two smaller placodes resulting in thin incisors. These two signals appeared to have different effects on tooth epithelium and the analysis of the double null mutant mice lacking Sostdc1 and Follistatin indicated that these TGF-beta inhibitors regulate the mutual balance of BMP and Activin in vivo. In addition, this work provides an alternative explanation for the issue of incisor identity published in Science by Tucker et al. in 1998 and proposes that the molar like morphology that can be obtained by inhibiting BMP signaling is due to partial splitting of the incisor placodes and not due to change in tooth identity from the incisor to the molar. This thesis work presents possible molecular mechanisms that may have modified the mouse dental pattern during evolution leading to the typical rodent dentition of modern mouse. The rodent dentition is specialized for gnawing and consists of two large continuously growing incisors and toothless diastema region separating the molars and incisors. The ancestors of rodents had higher number of more slender incisors together with canines and premolars. Additionally, murine rodents, which include the mouse, have lost their ability for tooth replacement. This work has revealed that the inhibitory molecules appear to play a role in the tooth number suppression by delineating the spatial and temporal action of the inductive signals. The results suggest that Sostdc1 plays an essential role in several stages of tooth development through the regulation of both the BMP and Wnt pathway. The work shows a dormant sequential tooth forming potential present in wild type mouse incisor region and gives a new perspective on tooth suppression by dental mesenchyme. It reveals as well a novel mechanism to create a large mouse incisor through the regulation of mesenchymal balance between inductive and inhibitory signals.

Population structure and evolution in the ant Plagiolepis pygmaea and its two social parasites Plagiolepis xene and Plagiolepis grassei

Social behaviour affects dispersal of animals and is an important modifier of genetic population structures. The female sex is often philopatric, which maintains coancestry within the breeding groups and promotes cooperative behaviours. This enables also inclusive fitness returns from altruism and explains why some individuals sacrifice personal reproduction for the good of others in social insects such as ants. However, reduced dispersal and population substructuring at the level of colonies may also entail inbreeding, loss of genetic diversity, and vulnerability. In addition, the most vulnerable ants are species that are evolved to parasitize colonies of other ants, and which compromise between abilities to disperse and the efficiency to parasitize the host. On the other hand, certain social organisations of ant colonies may facilitate a species to disperse outside its natural range and become a pest. Altogether, knowledge on genetic structuring of ant populations, as well as the evolution of their life histories can contribute to conservation biology and population management. The aim of this thesis was to investigate population structures and phylogenetic evolution of the ant Plagiolepis pygmaea and its two obligatory, workerless social parasites (inquilines) P. xene and P. grassei with genetic markers and DNA sequence data. The results support the general assumption that populations of inquiline parasites are highly fragmented and genetically vulnerable. Comparison of the two parasites suggests that differences in their relative abundance may follow from their interaction with the host, i.e. how well the species is adapted to reproduce in the host colonies. The results also indicate that the most recent free living ancestor to these two parasite species is their common host. This is considered to provide evidence for the controversial issue of sympatric speciation. Further, given that the level of adaptations to parasitic life history depends on the evolutionary time since the free-living ancestor, the results establish a link between species rarity and its evolutionary age. The populations of the host species P. pygmaea displayed significantly reduced dispersal both among the females (queens) and males, and high levels of inbreeding which may enhance worker altruism. In addition, the queens were found to mate with multiple males. Given the high relatedness between the queens and their mates, this occurs probably for non-genetic reasons, e.g. without benefits associated in genetically more diverse offspring. The results hence caution that the contribution of non-genetic factors to the prevailing mating patterns and genetic population structures should not be underestimated.

Mutations as molecular tools : The metabolic-rate dependent molecular clock and DNA barcoding of allied species

Mutation and recombination are the fundamental processes leading to genetic variation in natural populations. This variation forms the raw material for evolution through natural selection and drift. Therefore, studying mutation rates may reveal information about evolutionary histories as well as phylogenetic interrelationships of organisms. In this thesis two molecular tools, DNA barcoding and the molecular clock were examined. In the first part, the efficiency of mutations to delineate closely related species was tested and the implications for conservation practices were assessed. The second part investigated the proposition that a constant mutation rate exists within invertebrates, in form of a metabolic-rate dependent molecular clock, which can be applied to accurately date speciation events. DNA barcoding aspires to be an efficient technique to not only distinguish between species but also reveal population-level variation solely relying on mutations found on a short stretch of a single gene. In this thesis barcoding was applied to discriminate between Hylochares populations from Russian Karelia and new Hylochares findings from the greater Helsinki region in Finland. Although barcoding failed to delineate the two reproductively isolated groups, their distinct morphological features and differing life-history traits led to their classification as two closely related, although separate species. The lack of genetic differentiation appears to be due to a recent divergence event not yet reflected in the beetles molecular make-up. Thus, the Russian Hylochares was described as a new species. The Finnish species, previously considered as locally extinct, was recognized as endangered. Even if, due to their identical genetic make-up, the populations had been regarded as conspecific, conservation strategies based on prior knowledge from Russia would not have guaranteed the survival of the Finnish beetle. Therefore, new conservation actions based on detailed studies of the biology and life-history of the Finnish Hylochares were conducted to protect this endemic rarity in Finland. The idea behind the strict molecular clock is that mutation rates are constant over evolutionary time and may thus be used to infer species divergence dates. However, one of the most recent theories argues that a strict clock does not tick per unit of time but that it has a constant substitution rate per unit of mass-specific metabolic energy. Therefore, according to this hypothesis, molecular clocks have to be recalibrated taking body size and temperature into account. This thesis tested the temperature effect on mutation rates in equally sized invertebrates. For the first dataset (family Eucnemidae, Coleoptera) the phylogenetic interrelationships and evolutionary history of the genus Arrhipis had to be inferred before the influence of temperature on substitution rates could be studied. Further, a second, larger invertebrate dataset (family Syrphidae, Diptera) was employed. Several methodological approaches, a number of genes and multiple molecular clock models revealed that there was no consistent relationship between temperature and mutation rate for the taxa under study. Thus, the body size effect, observed in vertebrates but controversial for invertebrates, rather than temperature may be the underlying driving force behind the metabolic-rate dependent molecular clock. Therefore, the metabolic-rate dependent molecular clock does not hold for the here studied invertebrate groups. This thesis emphasizes that molecular techniques relying on mutation rates have to be applied with caution. Whereas they may work satisfactorily under certain conditions for specific taxa, they may fail for others. The molecular clock as well as DNA barcoding should incorporate all the information and data available to obtain comprehensive estimations of the existing biodiversity and its evolutionary history.

Phylogeny of a taxonomically difficult group and evolution of host location mechanism

The parasitic wasps are one of the largest insect groups and their life histories are remarkably variable. Common to all parasitic wasps is that they kill their hosts, which are usually beetles, butterflies and sometimes spiders. Hosts are often at a larval or pupal stage and live in concealed conditions, such as in plant tissue. Parasitic wasps have two main ways of finding their host. 1) They can detect chemical compounds emitted by damaged plant material or released by larvae living in plant tissue, and 2) detect the larvae by sound vibrations. Even though pupae are immobile and silent, and therefore do not cause vibration, parasitoids have, however, adapted to find passive developmental stages by producing vibration themselves by knocking the substrate with their antennae, and then detecting the echoes with their legs. This echolocation allows a parasitoid to locate its potential hosts that are deeply buried in wood. This study focuses on the relationships of the subfamily Cryptinae (Hymenoptera: Ichneumonidae) and related taxa, and the evolution of host location mechanism. There are no earlier studies of the phylogeny of the Cryptinae, and the position of related taxa are unclear. According to the earlier classification, which is entirely intuitional, the Cryptinae is divided into three tribes: Cryptini, Hemigasterini and Phygadeuontini. Further, these tribes are subdiveded into numerous subtribes. This work, based on molecular characters, shows that the cryptine tribes Cryptini, Phygadeuon¬tini and Hemigasterini come out largely as monophyletic groups, thus agreeing with the earlier classification. The earlier subtribal classification had no support. In addition, it is shown that modified antennal structures are associated with host usage of wood-boring coleopteran hosts. The cryptines have a clear modification series on their antennal tips from a simply tip to a hammer-like structure. The species with strongly modified antennae belong mostly to the tribe Cryptini and they utilise wood-boring beetles as hosts. Also, field observations on insect behaviour support this result.

Joseph A. Schumpeter's Theory of Social and Economic Evolution : a Reconstruction and Critique

The book presents a reconstruction, interpretation and critical evaluation of the Schumpeterian theoretical approach to socio-economic change. The analysis focuses on the problem of social evolution, on the interpretation of the innovation process and business cycles and, finally, on Schumpeter s optimistic neglect of ecological-environmental conditions as possible factors influencing social-economic change. The author investigates how the Schumpeterian approach describes the process of social and economic evolution, and how the logic of transformations is described, explained and understood in the Schumpeterian theory. The material of the study includes Schumpeter s works written after 1925, a related part of the commentary literature on these works, and a selected part of the related literature on the innovation process, technological transformations and the problem of long waves. Concerning the period after 1925, the Schumpeterian oeuvre is conceived and analysed as a more or less homogenous corpus of texts. The book is divided into 9 chapters. Chapters 1-2 describe the research problems and methods. Chapter 3 is an effort to provide a systematic reconstruction of Schumpeter's ideas concerning social and economic evolution. Chapters 4 and 5 focus their analysis on the innovation process. In Chapters 6 and 7 Schumpeter's theory of business cycles is examined. Chapter 8 evaluates Schumpeter's views concerning his relative neglect of ecological-environmental conditions as possible factors influencing social-economic change. Finally, chapter 9 draws the main conclusions.

Evolution of the Neckeraceae (Bryophyta): resolving the backbone phylogeny

Earlier phylogenetic studies, including species belonging to the Neckeraceae, have indicated that this pleurocarpous moss family shares a strongly supported sister group relationship with the Lembophyllaceae, but the family delimitation of the former needs adjustment. To test the monophyly of the Neckeraceae, as well as to redefine the family circumscription and to pinpoint its phylogenetic position in a larger context, a phylogenetic study based on molecular data was carried out. Sequence data were compiled, combining data from all three genomes: nuclear ITS1 and 2, plastid trnS-rps4-trnT-trnL-trnF and rpl16, and mitochondrial nad5 intron. The Neckeraceae have sometimes been divided into the two families, Neckeraceae and Thamnobryaceae, a division rejected here. Both parsimony and Bayesian analyses of molecular data revealed that the family concept of the Neckeraceae needs several further adjustments, such as the exclusion of some individual species and smaller genera as well as the inclusion of the Leptodontaceae. Within the family three well-supported clades (A, B and C) can be distinguished. Members of clade A are mainly non-Asiatic and nontropical. Most species have a weak costa and immersed capsules with reduced peristomes (mainly Neckera spp.) and the teeth at the leaf margins are usually unicellular. Clade B members are also mainly non-Asiatic. They are typically fairly robust, distinctly stipilate, having a single, at least relatively strong costa, long setae (capsules exserted), and the peristomes are well developed or only somewhat reduced. Members of clade C are essentially Asiatic and tropical. The species of this clade usually have a strong costa and a long seta, the seta often being mammillose in its upper part. The peristome types in this clade are mixed, since both reduced and unreduced types are found. Several neckeraceous genera that were recognised on a morphological basis are polyphyletic (e.g. Neckera, Homalia, Thamnobryum, Porotrichum). Ancestral state reconstructions revealed that currently used diagnostic traits, such as the leaf asymmetry and costa strength are highly homoplastic. Similarly, the reconstructions revealed that the 'reduced' sporophyte features have evolved independently in each of the three clades.

From One Segment to a Segment of One - The Evolution of Market Segmentation Theory

The purpose of this study was to deepen the understanding of market segmentation theory by studying the evolution of the concept and by identifying the antecedents and consequences of the theory. The research method was influenced by content analysis and meta-analysis. The evolution of market segmentation theory was studied as a reflection of evolution of marketing theory. According to this study, the theory of market segmentation has its roots in microeconomics and it has been influenced by different disciplines, such as motivation research and buyer behaviour theory. Furthermore, this study suggests that the evolution of market segmentation theory can be divided into four major eras: the era of foundations, development and blossoming, stillness and stagnation, and the era of re-emergence. Market segmentation theory emerged in the mid-1950’s and flourished during the period between mid-1950’s and the late 1970’s. During the 1980’s the theory lost its interest in the scientific community and no significant contributions were made. Now, towards the dawn of the new millennium, new approaches have emerged and market segmentation has gained new attention.

Branding: The Past, Present, and Future: A Study of the Evolution and Future of Branding

Branding, as any other concept, has evolved over time: from the days when sheep of one herd started to be branded to distinguish them from another herd to the current era when everything, from water and flowers to clothes and food, is branded. Throughout these times, there have been numerous theories to describe and understand the underlying nuances. This paper finds the relationships in previous literature and reveals how these theories see branding from various perspectives and how they can be integrated to form a coherent view. It is also discussed how branding and society affect each other. Based on the knowledge of how branding theories have been developed as dependent variables of each other and the society, we are able to form a better understanding of the past, the present, and the future of branding.

Late Pleistocene and Holocene environmental evolution of the Murchisonfjorden area, Nordaustlandet, Svalbard

The purpose of this study was to establish the palaeoenvironmental conditions during the late Quaternary in Murchisonfjorden, Nordaustlandet, based on foraminiferal assemblage compositions, and to determine the onset and termination of the Weichselian glaciations. The foraminiferal assemblage compositions were studied in marine sediments from three different archives, from sections next to the present shoreline in the Bay of Isvika, from a core in the Bay of Isvika and from a core from Lake Einstaken. OSL and AMS 14C age determinations were performed on samples from the three archives, and the results show deposition of marine sediments during ice-free periods of the Early Weichselian, the Middle Weichselian and the Late Weichselian, as well as during the Holocene in the investigated area. Marine sediments from the Early and Middle Weichselian were sampled from isostatically uplifted sections along the present shoreline.Sediments from the transition from the Late Weichselian to early Holocene time intervals were found in the bottom of the core from Lake Einstaken. Holocene sediments were investigated in the sections and in the core from the Bay of Isvika. The marine sediments from the sections are comprised of five benthic foraminiferal assemblages. The Early Weichselian is represented by two foraminiferal assemblages, the Middle Weichselian, the early and the late Holocene each by one. All five foraminiferal assemblages were deposited in glacier-distal shallow-water environments, which had a connection to the open ocean. Changes in the composition of the assemblages can be ascribed to differences in the bottom-water currents and changes in the salinity. The Middle Weichselian assemblage is of special importance, because it is the first foraminiferal assemblage to be described from this time interval from Svalbard. Four benthic foraminiferal assemblages were deposited shortly before the marine to lacustrine transition at the boundary between the Late Weichselian and Holocene in Lake Einstaken. The foraminiferal assemblages show a change from a high-arctic, normal marine shallow-water environment to an even shallower environment with highly fluctuating salinity. The analyses of the core from 100 m water depth in the Bay of Isvika resulted in the determination of four foraminiferal assemblages. These indicated changes from a glacier-proximal environment during deglaciation, to a more glacier-distal environment during the Early Holocene. This was followed by a period with a marked change to a considerably cooler environment and finally to a closed fjord environment in the middle and late Holocene times. Additional sedimentological analyses of the marine and glacially derived sediments from the uplifted sections, as well as observations of multiple striae on the bedrock, observations of deeply weathered bedrock and findings of tills interlayered with marine sediments complete the investigations in the study area. They indicate weak glacial erosion in the study area. It can be concluded that marine deposition occurred in the investigated area during three time intervals in the Weichselian and during most of the Holocene. The foraminiferal assemblages in the Holocene are characterized by a transition from glacier-proximal to glacier-distal faunas. The palaeogeographical change from an open fjord to a closed fjord environment is a result of the isostatic uplift of the area after the LGM and is clearly reflected in the foraminiferal assemblages. Another influencing factor on the foraminiferal assemblage composition are changes in the inflow of warmer Atlantic waters to the study area.