Lehrbuch der vergleichenden Entwicklungsgeschichte der Tiere
01 May 1970-Anzeiger Fur Schadlingskunde-journal of Pest Science (Springer-Verlag)-Vol. 43, Iss: 5, pp 76-77
About: This article is published in Anzeiger Fur Schadlingskunde-journal of Pest Science.The article was published on 1970-05-01. It has received 73 citations till now. The article focuses on the topics: Ecology (disciplines).
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364 citations
TL;DR: Current hypotheses about head segmentation and the nature of head structures from various perspectives are reviewed, and the concept of “primary” and “secondary antennae” in Recent and fossil arthropods are developed, it is proposed that Trilobita are stem lineage representatives of the Mandibulata.
Abstract: Understanding the head is one of the great challenges in the fields of comparative anatomy, developmental biology, and palaeontology of arthropods. Numerous conflicting views and interpretations are based on an enormous variety of descriptive and experimental approaches. The interpretation of the head influences views on phylogenetic relationships within the Arthropoda as well as outgroup relationships. Here, we review current hypotheses about head segmentation and the nature of head structures from various perspectives, which we try to combine to gain a deeper understanding of the arthropod head. Though discussion about arthropod heads shows some progress, unquestioned concepts (e.g., a presegmental acron) are still a source of bias. Several interpretations are no longer tenable based on recent results from comparative molecular developmental studies, improved morphological investigations, and new fossils. Current data indicate that the anterior arthropod head comprises three elements: the protocerebral/ocular region, the deutocerebral/antennal/cheliceral segment, and the tritocerebral/pedipalpal/second antennal/intercalary segment. The labrum and the mouth are part of the protocerebral/ocular region. Whether the labrum derives from a former pair of limbs remains an open question, but a majority of data support its broad homology across the Euarthropoda. From the alignment of head segments between onychophorans and euarthropods, we develop the concept of "primary" and "secondary antennae" in Recent and fossil arthropods, posit that "primary antennae" are retained in some fossil euarthropods below the crown group level, and propose that Trilobita are stem lineage representatives of the Mandibulata.
246 citations
Cites background or methods from "Lehrbuch der vergleichenden Entwick..."
...Interestingly, Urbach and Technau (2003a) adopt the classical subdivision of the protocerebrum into the archicerebrum (comprising the optical lobes and the mushroom bodies) and the prosocerebrum (comprising the central complex) (see Siewing 1969)....
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...One is the more traditional Articulata hypothesis, which favors a close relationship between Annelida and Arthropoda (Wägele and Misof 2001; Scholtz 2002; Jenner and Scholtz 2005)....
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...Accordingly, we find typical French (Chaudonneret 1987; Casanova 1996), German (Heymons 1901; Siewing 1969, Paulus and Weygoldt 1996) or Swedish (Holmgren 1916; Hanström 1928; Dahl 1956) heads (see Rempel 1975) with different segmental compositions which were, and sometimes still are, discussed in…...
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...For example, it has a bilobed origin and is equipped with mesoderm which resembles the formation of appendages in the trunk (e.g. Siewing 1969; Lauterbach 1973; Rempel 1975)....
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...…of the preantennal segment The labrum as the appendage of a preantennal segment situated between the ocular region and the antennal segment (see Siewing 1969; Lauterbach 1973; Rempel 1975; Cohen and Jürgens 1991) is also unlikely, as based on segmental gene expression data, there is no…...
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TL;DR: The results illustrate both the limitations of the 18S rRNA molecule alone for high-level phylogeny inference and the importance of considering both molecular and morphological data in phylogeny reconstruction.
Abstract: Complete coding regions of the 18S rRNA gene of an enteropneust hemichordate and an echinoid and ophiuroid echinoderm were obtained and aligned with 18S rRNA gene sequences of all major chordate clades and four outgroups. Gene sequences were analyzed to test morphological character phylogenies and to assess the strength of the signal. Maximum-parsimony analysis of the sequences fails to support a monophyletic Chordata; the urochordates form the sister taxon to the hemichordates, and together this clade plus the echinoderms forms the sister taxon to the cephalochordates plus craniates. Decay, bootstrap, and tree-length distribution analyses suggest that the signal for inference of dueterostome phylogeny is weak in this molecule. Parsimony analysis of morphological plus molecular characters supports both monophyly of echinoderms plus enteropneust hemichordates and a sister group relationship of this clade to chordates. Evolutionary parsimony does not support chordate monophyly. Neighbor-joining, Fitch-Margoliash, and maximum-likelihood analyses support a chordate lineage that is the sister group to an echinoderm-plus-hemichordate lineage. The results illustrate both the limitations of the 18S rRNA molecule alone for high-level phylogeny inference and the importance of considering both molecular and morphological data in phylogeny reconstruction.
235 citations
TL;DR: A comparison of the function of the Brachyury homologues suggests an evolutionary conservation of a molecular mechanism that has been co-opted for a number of developmental processes throughout evolution.
Abstract: A homologue of the T-box gene, Brachyury, has been isolated from hydra. The gene, termed HyBra1, is expressed in the endoderm and is associated with the formation of the hypostome, the apical part of the head in four different developmental situations. In adults, which are continuously undergoing patterning, HyBra1 is continuously expressed in the hypostome. During budding, hydra's asexual form of reproduction, the gene is expressed in a small area that will eventually form the hypostome of the developing bud before any morphological sign of budding is apparent. The gene is also expressed very early during head regeneration and is confined to the region that will form the hypostome. During embryogenesis, HyBra1 is expressed shortly before hatching in the region that will form the apical end of the animal, the hypostome. The absence of expression at the apical end of decapitated animals of reg-16, a head formation-deficient mutant, provides additional evidence for a role of HyBra1 during head formation. Further, treatments that alter the head activation gradient have no effect on HyBra1 expression indicating the role of the gene is confined to head formation. Transplantation experiments indicate that the expression occurs before head determination has occurred, but expression does not irreversibly commit tissue to forming a head. A comparison of the function of the Brachyury homologues suggests an evolutionary conservation of a molecular mechanism that has been co-opted for a number of developmental processes throughout evolution.
212 citations
TL;DR: A Drosophila gene, the T-related gene (Trg), with high similarity to T within a stretch of approximately 200 amino acids, the DNA-binding domain of T is identified, raising the question of a common evolutionary origin of the hindgut of insects and the notochord of chordates.
Abstract: The Brachyury (T) gene is required for notochord differentiation in vertebrates. We have identified a Drosophila gene, the T-related gene (Trg), with high similarity to T within a stretch of approximately 200 amino acids, the DNA-binding domain of T. Trg is expressed throughout embryogenesis, first at the blastoderm stage in the hindgut primordium under the control of the terminal gap genes tll and hkb, and then until the end of embryogenesis in the differentiating hindgut. Drosophila embryos deficient for Trg do not form the hindgut, a phenotype that can be rescued by a Trg transgene. Thus, a common feature of T and Trg is their requirement in specifying the development of a single embryonic structure. Homologs of Trg are also expressed in the developing hindgut of Tribolium and Locusta embryos suggesting a highly conserved function of Trg in insects. This conservation and the high similarity of T and Trg raise the question of a common evolutionary origin of the hindgut of insects and the notochord of chordates.
208 citations