The novel Drosophila tim(blind) mutation affects behavioral rhythms but not periodic eclosion

Circadian clock function depends on the tightly regulated exclusion or presence of clock proteins within the nucleus. A newly induced long-period timeless mutant, tim(blind), encodes a constitutively hypophosphorylated TIM protein. The mutant protein is not properly degraded by light, and tim(blind) flies show abnormal behavioral responses to light pulses. This is probably caused by impaired nuclear accumulation of TIM(BLIND) protein, which we observed in brain pacemaker neurons and photoreceptor cells of the compound eye. tim(blind) encodes two closely spaced amino acid changes compared to the wild-type TIM protein; one of them is within a putative nuclear export signal of TIM. Under constant conditions, tim(blind) flies exhibit 26-hr free-running locomotor rhythms, which are not correlated with a period lengthening of eclosion rhythms and period-luciferase reporter-gene oscillations. Therefore it seems possible that TIM--in addition to its well-established role as core clock factor--functions as a clock output factor, involved in determining the period length of adult locomotor rhythms.     

The tri-segmented limbs of therian mammals: kinematics, dynamics, and self-stabilization--a review

The evolution of therian mammals is to a large degree marked by changes in their motion systems. One of the decisive transitions has been from the sprawled, bi-segmented to the parasagittal, tri-segmented limb. Here, we review aspects of the tri-segmented limb in locomotion which have been elucidated in our research groups in the last 10 years. First, we report the kinematics of the tri-segmented therian limb from mouse to elephant in order to explore general principles of the therian limb configuration and locomotion. Torques will be reported from a previous paper (Witte et al., 2002. J Exp Biol 205:1339-1353) for a better understanding of the anti-gravity work of all limb joints. The stability of a limb in z-configuration will be explained and its advantage with respect to other potential solutions from modeling will be discussed. Finally, we describe how the emerging concept of self-stability can be explained for a tri-segmented leg template and how it affects the design of the musculoskeletal system and the operation of legs during locomotion. While locomotion has been considered as mainly a control problem in various disciplines, we stress the necessity to reduce control as much as possible. Central control can be cheap if the limbs are "intelligent" by means of their design. Gravity-induced movements and self-stability seem to be energy-saving mechanisms.     

Stages and other aspects of the embryology of the parthenogenetic Marmorkrebs (Decapoda, Reptantia, Astacida)

The early development of the parthenogenetic Marmorkrebs (marbled crayfish) is described with respect to external morphology, cell lineage, and segment formation. Due to its parthenogenetic reproduction mode, the question arises whether or not the marbled crayfish is a suitable model organism for developmental approaches. To address this question, we describe several aspects of the embryonic development until hatching. We establish ten stages based on characteristic external changes in the living eggs such as blastoderm formation, gastrulation process, formation and differentiation of the naupliar and post-naupliar segments, limb bud differentiation, and eye differentiation. The study of the post-naupliar cell division patterns, segment formation, and engrailed expression reveals distinct similarities to that of other freshwater crayfish. On this basis, we evaluate the possibility of a generalization of ontogenetic processes in the Marmorkrebs for either freshwater crayfish or other crustacean developmental systems.     

Q-factor analysis as a tool for phylogenetic studies of morphometric data

The statistical procedure of Q-factor analysis was applied with the aim to detect complex morphological characters, which clearly separate taxonomic groups. Since Q-factor analysis, unlike cluster analysis, does not prescribe a hierarchical grouping, the results can be interpreted phylogenetically using an outgroup comparison. The essential steps of the approach are demonstrated by an empirical study on the phylogeny of Callitrichinae. Except for some complications concerning the determination of the number of relevant factors and factor rotation, the procedure proved to be a suitable instrument for phylogenetic research.     

F-actin is a component of the karyosome in neuropteran oocyte nuclei

The principles underlying the assembly of intranuclear compartments are only beginning to be understood. The karyosome is an organelle typical of oocyte nuclei. It represents the tightly packed oocyte chromosomes, arrested at the diplotene of meiotic prophase. It has been known from several insect orders that a prominent capsule of unknown materials is built around the karyosome in the course of previtellogenesis and vitellogenesis. Here we show that F-actin, detected by dye-coupled phalloidin, is a major molecular component of the karyosome capsule in Neuroptera. We investigated capsule formation in six species belonging to the family Chrysopidae. Though F-actin was present in the capsules of all six species there were striking interspecific differences in the morphological array of actin filaments and the developmental dynamics of actin deposition in the capsule. The potential biological significance of the karyosome capsule is discussed with respect to the presence of extrachromosomal rDNA in neuropteran oocytes and the molecular functions known from F-actin. Our results corroborate the still controversial hypothesis of a role for actin as a nuclear protein.     

Morphology of a thermosensitive multipolar neuron in the infrared organ of Merimna atrata (Coleoptera, Buprestidae)

Two pairs of infrared (IR) organs are situated ventrolaterally on the second and third abdominal sternites of the Australian fire beetle Merimna atrata (Buprestidae). In ventral view, each IR organ has a round IR absorbing area under which a sensory complex is attached to the epidermis. The main component of the complex is a single large multipolar neuron and its mass of highly branched dendrites. All parts of this neuron are enveloped in glial cells. The proximal primary dendrites, which arise from the soma, finally branch into several hundred tightly packed terminal dendrites, which contain many mitochondria. We term this unusual morphology of the dendritic region a terminal dendritic mass (TDM). Additionally, two chordotonal organs were found in each sensory complex. Their somata are integrated in the complex and the dendrites extend to the periphery of the absorbing area. The bauplan of the dendritic region is reminiscent of the thermosensitive trigeminal nerve fibers innervating the absorbing structures in the IR receptors in boid and crotalid snakes. Because this multipolar neuron also functions as a thermoreceptor, another example of a functional analogy between insect and vertebrate sensory systems could be demonstrated.     

Visual discrimination of objects differing in spatial depth by goldfish

Training experiments were performed to investigate the ability of goldfish to discriminate objects differing in spatial depth. Tests on size constancy should give insight into the mechanisms of distance estimation. Goldfish were successfully trained to discriminate between two black disk stimuli of equal size but different distance from the tank wall. Each stimulus was presented in a white tube so that the fish could see only one stimulus at a time. For each of eight training stimulus distances, the just noticeable difference in distance was determined at a threshold criterion of 70% choice frequency. The ratio of the retinal image sizes between training stimulus and comparison stimulus at threshold was about constant. However, in contrast to Douglas et al. (Behav Brain Res 30:37–42, 1988), goldfish did not show size constancy in tests with stimuli of the same visual angle. This indicates that they did not estimate distance, but simply compared the retinal images under our experimental conditions. We did not find any indication for the use of accommodation as a depth cue. A patterned background at the rear end of the tubes did not have any effect, which, however, does not exclude the possibility that motion parallax is used as a depth cue under natural conditions.     

Development,morphology and ultrastructure of the branchial crown of Fabricia stellaris (Müller, 1774) (Polychaeta: Sabellida: Fabriciinae)

Randel, N. and Bick, A. 2011. Development, morphology and ultrastructure of the branchial crown of Fabricia stellaris (Müller, 1774) (Polychaeta: Sabellida: Fabriciinae). —Acta Zoologica (Stockholm) 93 : 409–421. Sabellidae and Serpulidae are well‐known tube‐building polychaetes with a distinctive and often spectacularly colourful branchial crown. Morphological investigations suggest that these taxa form the monophyletic clade Sabellida, with the adelphotaxa Sabellidae and Serpulidae, but the relationship between these taxa remains ambiguous. Molecular investigations have indicated that the Fabriciinae, major taxon of Sabellidae, belongs to Serpulidae, thereby making Sabellidae paraphyletic; however, morphological characters are absent to support this result. We investigate the development, anatomy and ultrastructure of the branchial crown of Fabricia stellaris (Müller, 1774), describing morphological characteristics useful not only for constructing morphological phylogenies but also for understanding the evolution of the branchial crown. The morphology of the radioles and pinnules does not differ from each other. The supporting tissue of the branchial crown consists of myoepithelial cells and a solid extracellular matrix (ECM). Both ciliated and non‐ciliated cells form the epidermal layer; ciliated cells shape the food groove. Most important is the result that radioles and pinnules within Sabellida may not be homologous, because the morphology and the branching of radioles and pinnules are completely different between Sabellinae, Fabriciinae and Serpulidae. The terms ‘primary branch’ for radioles and ‘secondary branch’ for pinnules are proposed for Fabriciinae. The phylogeny of the Sabellida is discussed.