Lennart Olsson | Friedrich-Schiller-Universität Jena (original) (raw)
Papers by Lennart Olsson
Acta Zoologica, Jan 1, 2007
Skip to Main Content. Wiley Online Library will be disrupted 4 Feb from 10-12 GMT for monthly mai... more Skip to Main Content. Wiley Online Library will be disrupted 4 Feb from 10-12 GMT for monthly maintenance. ...
Developmental Biology, 2001
The contribution of cranial neural crest cells to the development and patterning of cranial muscl... more The contribution of cranial neural crest cells to the development and patterning of cranial muscles in amphibians was investigated in the phylogenetically basal and morphologically generalized frog, Bombina orientalis. Experimental methods included fluorescent marking of premigratory cranial neural crest and extirpation of individual migratory streams. Neural crest cells contributed to the connective tissue component, but not the myofibers, of many larval muscles within the first two branchial arches (mandibular and hyoid), and complex changes in muscle patterning followed neural crest extirpation. Connective tissue components of individual muscles of either arch originate from the particular crest migratory stream that is associated with that arch, and this relationship is maintained regardless of the segmental identity—or embryonic derivation—of associated skeletal components. These developmental relations define a pattern of segmentation in the head of larval anurans that is similar to that previously described in the domestic chicken, the only vertebrate that has been thoroughly investigated in this respect. The fundamental role of the neural crest in patterning skeleton and musculature may represent a primitive feature of cranial development in vertebrates. Moreover, the corresponding developmental processes and cell fates appear to be conserved even when major evolutionary innovations—such as the novel cartilages and muscles of anuran larvae—result in major differences in cranial form.
Ivan. I. Schmalhausen was one of the central figures in the Russian development of the "Modern Sy... more Ivan. I. Schmalhausen was one of the central figures in the Russian development of the "Modern Synthesis" in evolutionary biology. He is widely cited internationally even today. Schmalhausen developed the main principles of his theory facing the danger of death in the totalitarian Soviet Union. His great services to evolutionary and theoretical biology are indisputable. However, the received view of Schmalhausen´s contributions to evolutionary biology makes an unbiased reading of his texts difficult. Here we show that taking all of his works into consideration (including those only available in Russian) paints a much more dynamic and exciting picture of what he tried to achieve. Schmalhausen pioneered the integration of a developmental perspective into evolutionary thinking. A main tool for achieving this was his approach to living objects as complex multi-level self-regulating systems. Schmalhausen put enormous effort into bringing this idea into fruition during the final stages of his career by combining evolutionary theory with cybernetics. His results and ideas remain thought-provoking, and his texts are of more than just historical interest.
Today the Mexican axolotl is critically endangered in its natural habitat in lakes around Mexico ... more Today the Mexican axolotl is critically endangered in its natural habitat in lakes around Mexico City, but thrives in research laboratories around the world, where it is used for research on development, regeneration, and evolution. Here, we concentrate on the early history of the axolotl as a laboratory animal to celebrate that the first living axolotls arrived in Paris in 1864, 150 years ago. Maybe surprisingly, at first the axolotl was distributed across Europe without being tied to specific research questions, and amateurs engaged in acclimatization and aquarium movements played an important role for the rapid proliferation of the axolotl across the continent. But the aquarium also became an important part of the newly established laboratory, where more and more biological and medical research now took place. Early scientific interest focused on the anatomical peculiarities of the axolotl, its rare metamorphosis, and whether it was a larva or an adult. Later, axolotl data was used to argue both for (by August Weismann and others) and against (by e.g., Albert von Kölliker) Darwinism, and the axolotl even had a brief history as a laboratory animal used in a failed attempt to prove Lysenkoism in Jena, Germany. Nowadays, technical developments such as transgenic lines, and the very strong interest in stem cell and regeneration research has again catapulted the axolotl into becoming an important laboratory animal.
Ernst Haeckel formulated his biogenetic law, famously stating that ontogeny recapitulates phyloge... more Ernst Haeckel formulated his biogenetic law, famously stating that ontogeny recapitulates phylogeny, in 1872. The Russian evolutionist Alexei Sewertzoff, and the Swiss-born zoologist Adolf Naef were among those who revised Haeckel’s law, thus changing the course of evolutionary theory and of developmental biology. Although Sewertzoff and Naef approached the problem in a similar way and formulated similar hypotheses at a purely descriptive level, their theoretical
viewpoints were crucially different. While Sewertzoff laid the foundations for a Darwinian evolutionary morphology and is regarded as a forerunner of the modern synthesis, Naef was one of the most important figures in ‘‘idealistic morphology’’,
which is usually seen as a type of anti-Darwinism. Both Naef and Sewertzoff aimed to revise Haeckel’s biogenetic law and came to comparable conclusions at the empirical level. This paper is an attempt to explain how their fundamentally different theoretical backgrounds influenced their views on the relationship between ontogeny and phylogeny.
Creationism in Russia and in what is commonly called the “Russian-speaking world” exhibits some d... more Creationism in Russia and in what is commonly called the “Russian-speaking world” exhibits some distinctive features. In this chapter, we outline the situation in Russia and two of its neighboring states, Ukraine and Belarus, and specify the role of the Orthodox Church and of Protestant movements in the growth of creationism in this region.
Integrative and Comparative Biology, 1999
Theory in Biosciences, 2007
Evolution & Development, 2007
SUMMARY The fate of single somites has not been analyzed from a comparative perspective with mode... more SUMMARY The fate of single somites has not been analyzed from a comparative perspective with modern cell-marking methods. Most of what we know is based on work using quail-chick chimeras. Consequently, to what degree cell fate has been conserved despite the anatomical differences among vertebrates is unknown. We have analyzed the cell fate of the cranialmost somites, with the focus on somite two, in the Mexican axolotl (Ambystoma mexicanum). Somite cells were marked by injection of dextran–fluorescein and detected using immunofluorescence after 2 months of development in paraffin sections. Our data confirm and extend earlier studies based on classical histology in salamanders. We show that somite two contributes to different muscles, skeletal elements, and connective tissues of the head and cranial trunk region. Cells from somites two and three migrate latero-ventrally and contribute to the hypobranchial muscles mm. geniohyoideus and rectus cervicis. We provide evidence that the specific formation of the hypobranchial musculature from ventral processes of the somites might be variable in different classes of vertebrates. We further demonstrate that mm. cucullaris and dilatator laryngis, which were earlier thought to have a branchial origin, arise from somitic material in a manner very similar to the findings in quail-chick chimeras. Our findings indicate that the pattern of somitic derivatives is highly conserved within tetrapods.
Theory in Biosciences, 2005
The homology concept has had a long and varied history, starting out as a geometrical term in anc... more The homology concept has had a long and varied history, starting out as a geometrical term in ancient Greece. Here we describe briefly how a typological use of homology to designate organs and body parts in the same position anatomically in different organisms was changed by Darwin's theory of evolution into a phylogenetic concept. We try to indicate the diversity of opinions on how to define and test for homology that has prevailed historically, before the important books by Hennig (1950. Grundzüge einer Theorie der Phylogenetischen Systematik. Deutscher Zentralverlag, Berlin) and Remane (1952. Die Grundlagen des Natürlichen Systems, der Vergleichenden Anatomie und der Phylogenetik. Geest & Portig, Leipzig) brought more rigor into both the debate on homology and into the usage of the term homology among systematists. Homology as a theme has recurred repeatedly throughout the history of the “Phylogenetisches Symposium” and we give a very brief overview of the different aspects of homology that have been discussed at specific symposia over the last 48 years. We also honour the fact that the 2004 symposium was held in Jena by pointing to the roles played by biologists active in Jena, such as Ernst Haeckel and Carl Gegenbaur, in starting the development towards a homology concept concordant with an evolutionary world view. As historians of biology, we emphasize the importance of major treatises on homology and its history that may be little read by systematists active today, and have sometimes also received less attention by historians of biology than they deserve. Prominent among these are the works of Dietrich Starck, who also happened to be both a student, and later a benefactor, of systematics at Jena University.
Acta Zoologica, 2009
Our research on the evolution of head development focuses on understanding the developmental orig... more Our research on the evolution of head development focuses on understanding the developmental origins of morphological innovations and involves asking questions like: How flexible (or conserved) are cell fates, patterns of cell migration or the timing of developmental events (heterochrony)? How do timing changes, or changes in life history affect head development and growth? Our ‘model system’ is a comparison between lungfishes and representatives from all three extant groups of amphibians. Within anuran amphibians, major changes in life history such as the repeated evolution of larval specializations (e.g. carnivory), or indeed the loss of a free-swimming larva, allows us to test for developmental constraints. Cell migration and cell fate are conserved in cranial neural crest cells in all vertebrates studied so far. Patterning and developmental anatomy of cranial neural crest and head mesoderm cells are conserved within amphibians and even between birds, mammals and amphibians. However, the specific formation of hypobranchial muscles from ventral somitic processes shows variation within tetrapods. The evolution of carnivorous larvae in terminal taxa is correlated with changes in both pattern and timing of head skeletal and muscle development. Sequence-heterochronic changes are correlated with feeding mode in terminal taxa and with phylogenetic relatedness in basal branches of the phylogeny. Eye muscles seem to form a developmental module that can evolve relatively independently from other head muscles, at least in terms of timing of muscle differentiation.
Theory in Biosciences, 2003
In the evolution of land-living vertebrates, the transition from spending the entire life cycle i... more In the evolution of land-living vertebrates, the transition from spending the entire life cycle in the water to first a biphasic (adult on land, eggs and larvae in water) and later a terrestrial life-history mode was achieved by changes in developmental processes and regulatory mechanisms. Lungfishes, salamanders and frogs are studied as examples of species which span this transition. The migration and fate of the embryonic cells that form the head is studied, using experimental embryology (extirpation and transplantation of cells), molecular markers and novel microscopy techniques – such as confocal microscopy. Knowing the migratory routes and fates of the cells that form head structures is important for an elucidation of the changes that took place e.g. when gill arches transformed into head cartilages, and when the specialised larval mouth structures present in today's frogs and toads arose as an evolutionary innovation. Results so far indicate that the early migration and pattern formation of neural crest cells in the head region is surprisingly conserved. Both the amphibians investigated and the Australian lungfish have the same number of migrating neural crest streams, and the identity of the streams is preserved. The major difference lies in the timing of migration, where there has been a heterochronic shift such that cell migration starts much later in the Australian lungfish than in the amphibians. The molecular mechanisms regulating the formation of streams of cranial neural crest cells seem, at least in part, to be differential expression of ephrins and ephrin receptors, which mediate cell sorting. Our understanding of the behaviour of migrating cells (primarily the more well characterised neural crest cells) could be enhanced by a modelling approach. I present preliminary ideas on how this could be achieved, inspired by recent work on Dictyostelium development and our own previous work on pigment cells and their pattern formationduring salamander embryogenesis.
Theory in Biosciences, 2007
Until the 1940s research traditions were often imported from Germany to Sweden, and young scienti... more Until the 1940s research traditions were often imported from Germany to Sweden, and young scientists went to German universities to learn new techniques and get in touch with the latest ideas. In developmental biology, the comparative, phylogenetic embryology advocated most forcefully by Ernst Haeckel co-existed with the "Entwickelungsmechanik" tradition developed by Wilhelm His, Wilheln Roux and others partly as a reaction to Haeckel's ideas. I use the zoology department at Uppsala University as a microcosmos to reflect the tensions between these traditions: Gösta Jägersten (1903-1993) and Sven Hörstadius (1898-1996) are used as exemples. Jägersten was a marine biologist who worked on the morphology and evolution of invertebrates, especiallly their larval forms. He developed a comprehensive theory describing the evolution of the life cycle in early metazoans. Recapitulation was an important ingredient, and Jägersten explicitly based his reasoning on Ernst Haeckel's "biogenetic law". Jägersten developed Haeckel's "Gastraea" theory into another hypothetical animal-Bilaterogastraea-that came into being when the holopelagic Blastaea settled on the ground as an adult and kept a pelagic, planktonic larval form. This was the birth of the pelago-benthic life cycle, which plays such an important role in Jägersten's speculations on the deep phylogeny of metazoans. Sven Hörstadius was a leading experimental embryologist in the mid-twentieth century. His most important work was on the determination and differentiation of the sea urchin embryo. Early work inspired by his teacher John Runnström's double gradient theory showed that gradients of animalness (ectodermal determination) and vegetalness (endodermal determination) existed in the 16- and 32- cell embryos. Hörstadius became famous for his elegant extirpation and transplantation experiments using glass needles, and for his microsugical skills. He also made important contributions to the study of cranial neural crest development in the Mexican axolotl, in collaboration with his student Sven Sellman. Hörstadius was the great experimentalist, but did not develop speculative hypotheses the way Jägersten did. The very different styles of scientific research might have played a role also in the development of the personal difficulties that existed for a long time between the two professors.
Journal of Morphology, 2007
The African Clawed Toad, Xenopus laevis, has been a major vertebrate model organism for developme... more The African Clawed Toad, Xenopus laevis, has been a major vertebrate model organism for developmental studies for half a century. Because most studies have focused on the early stages of development, this has had the effect that many aspects of organogenesis and later development remain relatively poorly known in this species. In particular, little is known about cranial muscle development even at the level of morphology and histological differentiation of muscle anlagen and muscle fibers. In this study, we document the morphogenesis and histological differentiation of cranial muscles in X. laevis. We provide a detailed account of the timing of development for each of the cranial muscles, and also describe a new muscle, the m. transversus anterior. The cranial musculature of X. laevis larvae generally develops in a rostrocaudal sequence. The first muscles to differentiate are the extrinsic eye muscles. Muscles of the mandibular and hyoid arches develop almost simultaneously, and are followed by the muscles of the branchial arches and the larynx, and by the mm. geniohyoideus and rectus cervicis. Despite the fact that differentiation starts at different stages in the different muscles, most are fully developed at Stage 14. These baseline data on the timing of muscle differentiation in the X. laevis can serve as a foundation for comparative studies of heterochronic changes in cranial muscle development in frogs and other lissamphibians. J. Morphol., 2007. © 2007 Wiley-Liss, Inc.
Theory in Biosciences, 2006
... Frank Zachos and Uwe Hossfeld write about the morphologist and systematist Adolf Remane. ... ... more ... Frank Zachos and Uwe Hossfeld write about the morphologist and systematist Adolf Remane. ... We have thus come full circle, back to the time when Ernst Haeckel and Fritz Mfiller were active. Unlike them, however, Reinke believed that life was created, not evolved. ...
Theory in Biosciences, 2003
Acta Zoologica, Jan 1, 2007
Skip to Main Content. Wiley Online Library will be disrupted 4 Feb from 10-12 GMT for monthly mai... more Skip to Main Content. Wiley Online Library will be disrupted 4 Feb from 10-12 GMT for monthly maintenance. ...
Developmental Biology, 2001
The contribution of cranial neural crest cells to the development and patterning of cranial muscl... more The contribution of cranial neural crest cells to the development and patterning of cranial muscles in amphibians was investigated in the phylogenetically basal and morphologically generalized frog, Bombina orientalis. Experimental methods included fluorescent marking of premigratory cranial neural crest and extirpation of individual migratory streams. Neural crest cells contributed to the connective tissue component, but not the myofibers, of many larval muscles within the first two branchial arches (mandibular and hyoid), and complex changes in muscle patterning followed neural crest extirpation. Connective tissue components of individual muscles of either arch originate from the particular crest migratory stream that is associated with that arch, and this relationship is maintained regardless of the segmental identity—or embryonic derivation—of associated skeletal components. These developmental relations define a pattern of segmentation in the head of larval anurans that is similar to that previously described in the domestic chicken, the only vertebrate that has been thoroughly investigated in this respect. The fundamental role of the neural crest in patterning skeleton and musculature may represent a primitive feature of cranial development in vertebrates. Moreover, the corresponding developmental processes and cell fates appear to be conserved even when major evolutionary innovations—such as the novel cartilages and muscles of anuran larvae—result in major differences in cranial form.
Ivan. I. Schmalhausen was one of the central figures in the Russian development of the "Modern Sy... more Ivan. I. Schmalhausen was one of the central figures in the Russian development of the "Modern Synthesis" in evolutionary biology. He is widely cited internationally even today. Schmalhausen developed the main principles of his theory facing the danger of death in the totalitarian Soviet Union. His great services to evolutionary and theoretical biology are indisputable. However, the received view of Schmalhausen´s contributions to evolutionary biology makes an unbiased reading of his texts difficult. Here we show that taking all of his works into consideration (including those only available in Russian) paints a much more dynamic and exciting picture of what he tried to achieve. Schmalhausen pioneered the integration of a developmental perspective into evolutionary thinking. A main tool for achieving this was his approach to living objects as complex multi-level self-regulating systems. Schmalhausen put enormous effort into bringing this idea into fruition during the final stages of his career by combining evolutionary theory with cybernetics. His results and ideas remain thought-provoking, and his texts are of more than just historical interest.
Today the Mexican axolotl is critically endangered in its natural habitat in lakes around Mexico ... more Today the Mexican axolotl is critically endangered in its natural habitat in lakes around Mexico City, but thrives in research laboratories around the world, where it is used for research on development, regeneration, and evolution. Here, we concentrate on the early history of the axolotl as a laboratory animal to celebrate that the first living axolotls arrived in Paris in 1864, 150 years ago. Maybe surprisingly, at first the axolotl was distributed across Europe without being tied to specific research questions, and amateurs engaged in acclimatization and aquarium movements played an important role for the rapid proliferation of the axolotl across the continent. But the aquarium also became an important part of the newly established laboratory, where more and more biological and medical research now took place. Early scientific interest focused on the anatomical peculiarities of the axolotl, its rare metamorphosis, and whether it was a larva or an adult. Later, axolotl data was used to argue both for (by August Weismann and others) and against (by e.g., Albert von Kölliker) Darwinism, and the axolotl even had a brief history as a laboratory animal used in a failed attempt to prove Lysenkoism in Jena, Germany. Nowadays, technical developments such as transgenic lines, and the very strong interest in stem cell and regeneration research has again catapulted the axolotl into becoming an important laboratory animal.
Ernst Haeckel formulated his biogenetic law, famously stating that ontogeny recapitulates phyloge... more Ernst Haeckel formulated his biogenetic law, famously stating that ontogeny recapitulates phylogeny, in 1872. The Russian evolutionist Alexei Sewertzoff, and the Swiss-born zoologist Adolf Naef were among those who revised Haeckel’s law, thus changing the course of evolutionary theory and of developmental biology. Although Sewertzoff and Naef approached the problem in a similar way and formulated similar hypotheses at a purely descriptive level, their theoretical
viewpoints were crucially different. While Sewertzoff laid the foundations for a Darwinian evolutionary morphology and is regarded as a forerunner of the modern synthesis, Naef was one of the most important figures in ‘‘idealistic morphology’’,
which is usually seen as a type of anti-Darwinism. Both Naef and Sewertzoff aimed to revise Haeckel’s biogenetic law and came to comparable conclusions at the empirical level. This paper is an attempt to explain how their fundamentally different theoretical backgrounds influenced their views on the relationship between ontogeny and phylogeny.
Creationism in Russia and in what is commonly called the “Russian-speaking world” exhibits some d... more Creationism in Russia and in what is commonly called the “Russian-speaking world” exhibits some distinctive features. In this chapter, we outline the situation in Russia and two of its neighboring states, Ukraine and Belarus, and specify the role of the Orthodox Church and of Protestant movements in the growth of creationism in this region.
Integrative and Comparative Biology, 1999
Theory in Biosciences, 2007
Evolution & Development, 2007
SUMMARY The fate of single somites has not been analyzed from a comparative perspective with mode... more SUMMARY The fate of single somites has not been analyzed from a comparative perspective with modern cell-marking methods. Most of what we know is based on work using quail-chick chimeras. Consequently, to what degree cell fate has been conserved despite the anatomical differences among vertebrates is unknown. We have analyzed the cell fate of the cranialmost somites, with the focus on somite two, in the Mexican axolotl (Ambystoma mexicanum). Somite cells were marked by injection of dextran–fluorescein and detected using immunofluorescence after 2 months of development in paraffin sections. Our data confirm and extend earlier studies based on classical histology in salamanders. We show that somite two contributes to different muscles, skeletal elements, and connective tissues of the head and cranial trunk region. Cells from somites two and three migrate latero-ventrally and contribute to the hypobranchial muscles mm. geniohyoideus and rectus cervicis. We provide evidence that the specific formation of the hypobranchial musculature from ventral processes of the somites might be variable in different classes of vertebrates. We further demonstrate that mm. cucullaris and dilatator laryngis, which were earlier thought to have a branchial origin, arise from somitic material in a manner very similar to the findings in quail-chick chimeras. Our findings indicate that the pattern of somitic derivatives is highly conserved within tetrapods.
Theory in Biosciences, 2005
The homology concept has had a long and varied history, starting out as a geometrical term in anc... more The homology concept has had a long and varied history, starting out as a geometrical term in ancient Greece. Here we describe briefly how a typological use of homology to designate organs and body parts in the same position anatomically in different organisms was changed by Darwin's theory of evolution into a phylogenetic concept. We try to indicate the diversity of opinions on how to define and test for homology that has prevailed historically, before the important books by Hennig (1950. Grundzüge einer Theorie der Phylogenetischen Systematik. Deutscher Zentralverlag, Berlin) and Remane (1952. Die Grundlagen des Natürlichen Systems, der Vergleichenden Anatomie und der Phylogenetik. Geest & Portig, Leipzig) brought more rigor into both the debate on homology and into the usage of the term homology among systematists. Homology as a theme has recurred repeatedly throughout the history of the “Phylogenetisches Symposium” and we give a very brief overview of the different aspects of homology that have been discussed at specific symposia over the last 48 years. We also honour the fact that the 2004 symposium was held in Jena by pointing to the roles played by biologists active in Jena, such as Ernst Haeckel and Carl Gegenbaur, in starting the development towards a homology concept concordant with an evolutionary world view. As historians of biology, we emphasize the importance of major treatises on homology and its history that may be little read by systematists active today, and have sometimes also received less attention by historians of biology than they deserve. Prominent among these are the works of Dietrich Starck, who also happened to be both a student, and later a benefactor, of systematics at Jena University.
Acta Zoologica, 2009
Our research on the evolution of head development focuses on understanding the developmental orig... more Our research on the evolution of head development focuses on understanding the developmental origins of morphological innovations and involves asking questions like: How flexible (or conserved) are cell fates, patterns of cell migration or the timing of developmental events (heterochrony)? How do timing changes, or changes in life history affect head development and growth? Our ‘model system’ is a comparison between lungfishes and representatives from all three extant groups of amphibians. Within anuran amphibians, major changes in life history such as the repeated evolution of larval specializations (e.g. carnivory), or indeed the loss of a free-swimming larva, allows us to test for developmental constraints. Cell migration and cell fate are conserved in cranial neural crest cells in all vertebrates studied so far. Patterning and developmental anatomy of cranial neural crest and head mesoderm cells are conserved within amphibians and even between birds, mammals and amphibians. However, the specific formation of hypobranchial muscles from ventral somitic processes shows variation within tetrapods. The evolution of carnivorous larvae in terminal taxa is correlated with changes in both pattern and timing of head skeletal and muscle development. Sequence-heterochronic changes are correlated with feeding mode in terminal taxa and with phylogenetic relatedness in basal branches of the phylogeny. Eye muscles seem to form a developmental module that can evolve relatively independently from other head muscles, at least in terms of timing of muscle differentiation.
Theory in Biosciences, 2003
In the evolution of land-living vertebrates, the transition from spending the entire life cycle i... more In the evolution of land-living vertebrates, the transition from spending the entire life cycle in the water to first a biphasic (adult on land, eggs and larvae in water) and later a terrestrial life-history mode was achieved by changes in developmental processes and regulatory mechanisms. Lungfishes, salamanders and frogs are studied as examples of species which span this transition. The migration and fate of the embryonic cells that form the head is studied, using experimental embryology (extirpation and transplantation of cells), molecular markers and novel microscopy techniques – such as confocal microscopy. Knowing the migratory routes and fates of the cells that form head structures is important for an elucidation of the changes that took place e.g. when gill arches transformed into head cartilages, and when the specialised larval mouth structures present in today's frogs and toads arose as an evolutionary innovation. Results so far indicate that the early migration and pattern formation of neural crest cells in the head region is surprisingly conserved. Both the amphibians investigated and the Australian lungfish have the same number of migrating neural crest streams, and the identity of the streams is preserved. The major difference lies in the timing of migration, where there has been a heterochronic shift such that cell migration starts much later in the Australian lungfish than in the amphibians. The molecular mechanisms regulating the formation of streams of cranial neural crest cells seem, at least in part, to be differential expression of ephrins and ephrin receptors, which mediate cell sorting. Our understanding of the behaviour of migrating cells (primarily the more well characterised neural crest cells) could be enhanced by a modelling approach. I present preliminary ideas on how this could be achieved, inspired by recent work on Dictyostelium development and our own previous work on pigment cells and their pattern formationduring salamander embryogenesis.
Theory in Biosciences, 2007
Until the 1940s research traditions were often imported from Germany to Sweden, and young scienti... more Until the 1940s research traditions were often imported from Germany to Sweden, and young scientists went to German universities to learn new techniques and get in touch with the latest ideas. In developmental biology, the comparative, phylogenetic embryology advocated most forcefully by Ernst Haeckel co-existed with the "Entwickelungsmechanik" tradition developed by Wilhelm His, Wilheln Roux and others partly as a reaction to Haeckel's ideas. I use the zoology department at Uppsala University as a microcosmos to reflect the tensions between these traditions: Gösta Jägersten (1903-1993) and Sven Hörstadius (1898-1996) are used as exemples. Jägersten was a marine biologist who worked on the morphology and evolution of invertebrates, especiallly their larval forms. He developed a comprehensive theory describing the evolution of the life cycle in early metazoans. Recapitulation was an important ingredient, and Jägersten explicitly based his reasoning on Ernst Haeckel's "biogenetic law". Jägersten developed Haeckel's "Gastraea" theory into another hypothetical animal-Bilaterogastraea-that came into being when the holopelagic Blastaea settled on the ground as an adult and kept a pelagic, planktonic larval form. This was the birth of the pelago-benthic life cycle, which plays such an important role in Jägersten's speculations on the deep phylogeny of metazoans. Sven Hörstadius was a leading experimental embryologist in the mid-twentieth century. His most important work was on the determination and differentiation of the sea urchin embryo. Early work inspired by his teacher John Runnström's double gradient theory showed that gradients of animalness (ectodermal determination) and vegetalness (endodermal determination) existed in the 16- and 32- cell embryos. Hörstadius became famous for his elegant extirpation and transplantation experiments using glass needles, and for his microsugical skills. He also made important contributions to the study of cranial neural crest development in the Mexican axolotl, in collaboration with his student Sven Sellman. Hörstadius was the great experimentalist, but did not develop speculative hypotheses the way Jägersten did. The very different styles of scientific research might have played a role also in the development of the personal difficulties that existed for a long time between the two professors.
Journal of Morphology, 2007
The African Clawed Toad, Xenopus laevis, has been a major vertebrate model organism for developme... more The African Clawed Toad, Xenopus laevis, has been a major vertebrate model organism for developmental studies for half a century. Because most studies have focused on the early stages of development, this has had the effect that many aspects of organogenesis and later development remain relatively poorly known in this species. In particular, little is known about cranial muscle development even at the level of morphology and histological differentiation of muscle anlagen and muscle fibers. In this study, we document the morphogenesis and histological differentiation of cranial muscles in X. laevis. We provide a detailed account of the timing of development for each of the cranial muscles, and also describe a new muscle, the m. transversus anterior. The cranial musculature of X. laevis larvae generally develops in a rostrocaudal sequence. The first muscles to differentiate are the extrinsic eye muscles. Muscles of the mandibular and hyoid arches develop almost simultaneously, and are followed by the muscles of the branchial arches and the larynx, and by the mm. geniohyoideus and rectus cervicis. Despite the fact that differentiation starts at different stages in the different muscles, most are fully developed at Stage 14. These baseline data on the timing of muscle differentiation in the X. laevis can serve as a foundation for comparative studies of heterochronic changes in cranial muscle development in frogs and other lissamphibians. J. Morphol., 2007. © 2007 Wiley-Liss, Inc.
Theory in Biosciences, 2006
... Frank Zachos and Uwe Hossfeld write about the morphologist and systematist Adolf Remane. ... ... more ... Frank Zachos and Uwe Hossfeld write about the morphologist and systematist Adolf Remane. ... We have thus come full circle, back to the time when Ernst Haeckel and Fritz Mfiller were active. Unlike them, however, Reinke believed that life was created, not evolved. ...
Theory in Biosciences, 2003