Relevance of crustacean carapace wettability for fouling

Carapace wettability and density of fouling organisms (bacteria, diatoms, protozoa, fungi, macro-organisms) were investigated for 45 crustacean species (Hoplocarida, Decapoda) from 15 families in the Gulf of Thailand. The results show that crustaceans can create and maintain characteristic carapace wettabilities. About 21 species (47%) possess highly wettable carapaces with contact angles below 20°. Contact angles between 20° and 40° were recorded for four species (2%), angles between 40° and 60° for eight species (4%) and from 60° to 70° for 11 (24%) species. One species, Alpheus euphrosyne (Alpheidae, Decapoda), exhibited an extremely low surface wettability (contact angle: 91°). Densities of colonisers and contact angles did not correlate. Very low wettability by water ( > 90°) may only contribute little to fouling reduction in A. euphrosyne which showed the most hydrophobic carapace surface and was colonised by the lowest numbers of bacteria among all species and no other colonisers at all. We conclude that surface wettability is of little relevance for antifouling defence in crustaceans.     

The role of wingless in the development of multibranched crustacean limbs

 Arthropods are the most diverse and speciose group of organisms on earth. A key feature in their successful radiation is the ease with which various appendages become readily adapted to new functions in novel environments. Arthropod limbs differ radically in form and function, from unbranched walking legs to multibranched swimming paddles. To uncover the developmental and genetic mechanisms underlying this diversification in form, we ask whether a three-signal model of limb growth based on Drosophila experiments is used in the development of arthropod limbs with variant shape. We cloned a Wnt-1 ortholog (Tlwnt-1) from Triops longicaudatus, a basal crustacean with a multibranched limb. We examined the mRNA in situ hybridization pattern during larval development to determine whether changes in wg expression are correlated with innovation in limb form. During larval growth and segmentation Tlwnt-1 is expressed in a segmentally reiterated pattern in the trunk. Unexpectedly, this pattern is restricted to the ventral portion of the epidermis. During early limb formation the single continuous stripe of Tlwnt-1 expression in each segment becomes ventrolaterally restricted into a series of shorter stripes. Some but not all of these shorter stripes correspond to what becomes the ventral side of a developing limb branch. We conclude that the Drosophila model of limb development cannot explain all types of arthropod proximodistal outgrowths, and that the multibranched limb of Triops develops from an early reorganization of the ventral body wall. In Triops, Tlwnt-1 plays a semiconservative role similar to that played by Drosophila wingless in segmentation and limb formation, and morphological innovation in limb form arises in part through an early modulation in the expression of the Tlwnt-1 gene. Received: 22 September 1998 / Accepted: 12 January 1999     

Summer depth selection in crustacean zooplankton in nutrient‐poor boreal lakes is affected by recent residential development

1. Strong vertical gradients in light, water temperature, oxygen, algal concentration and predator encounters during summer in stratified lakes may influence patterns of depth selection in crustacean zooplankton, especially Daphnia species. 2. To test how crustacean depth selection varies among lakes along a gradient of catchment disturbance by recent residential development and land use change, we calculated the weighted mean depth distribution of the biomass of crustaceans by day and night in eight nutrient‐poor boreal lakes. 3. Generally, the greatest biomass of crustaceans was located at the metalimnion or at the lower boundary of the euphotic zone during thermal stratification in July. The crustacean zooplankton avoided warm surface layers and tended to stay in colder deep waters by both day and night. They also remained at greater depths in lakes with a more extensive euphotic zone. 4. There was some evidence of upward nocturnal migrations of large Daphnia and copepods in some lakes, and one case of downward migration in a lake inhabited by chaoborid larvae. 5. Multivariate regression trees (MRT) were used to cluster crustaceans and Daphnia species in homogeneous groups based on lake natural and disturbance factors. For crustaceans, the depth of the euphotic zone, the sampling depth (epilimnion, metalimnion and hypolimnion), time (day or night) of sampling and the biomass of chlorophyll a were the main driving factors. For Daphnia species, the drainage area, the sampling depth, the cleared land surface area within the catchment and the concentration of total dissolved phosphorus were the main factors.     

A single-cell census of mouse limb development identifies complex spatiotemporal dynamics of skeleton formation

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An antennal-specific role for bowl in repressing supernumerary appendage development in Drosophila

In Drosophila, antennae and legs are serially homologous appendages, and yet they develop into organs of very different structure and function. This implies that different genetic mechanisms operate onto a common developmental ground state to produce antennae and legs. Still few such mechanisms have been uncovered. During leg development, bowl, a member of the odd-skipped gene family, has been shown to participate in the formation of the leg segmental joints. Here we report that, in the antennal disc, bowl has a dramatically different role: bowl is expressed in the ventral antennal disc to prevent inappropriate expression of wg early during development. The removal of bowl function leads to the activation of wg in the dpp-expressing domain. This ectopic expression of wg, together with dpp, results in a new proximo-distal axis that promotes non-autonomous antennal duplications. The role of bowl in suppressing a supernumerary PD axis is maintained even when the antennal disc is homeotically transformed into a leg-like appendage. Therefore, bowl is part of a genetic program that suppresses the formation of supernumerary appendages specifically in the fly's head.     

Appendage development in embryos of the oribatid mite Archegozetes longisetosus (Acari, Oribatei, Trhypochthoniidae)

The development of reliable techniques to provide large numbers of fixed mite embryos free of their tough membranes has allowed us to produce scanning electron micrographs of oribatid embryos for the first time. Antibody staining for expression of the gene Distal-less demonstrates the formation of the labrum from a pair of regions in the ocular lobes, indicating a possible appendicular origin for the labrum. The chelicerae are followed from their initial postoral position through their anterior rotation to become preoral. The pedipalpal lobe, involved in the formation of the gnathosoma, is shown to be almost the size of the pedipalp at some stages, as well as expressing Distal-less . The fourth pair of walking limbs are not present in oribatid prelarvae and larvae, however, their anlage are visible in later embryonic stages but these do not express the gene Distal-less , suggesting that formation of distal structures is suppressed at this stage. Claparède's organs, present between coxae of legs I and II of larvae, are shown for the first time unequivocally to derive from the base of legs II. These are proposed to be homologous to the lateral organs of other arachnid groups.     

Early steps of paired fin development in zebrafish compared with tetrapod limb development

The development of zebrafish paired fins and tetrapod forelimbs and hindlimbs show striking similarities at the molecular level. In recent years, the zebrafish, Danio rerio has become a valuable model for the study of the development of vertebrate paired appendages and several large-scale mutagenesis screens have identified novel fin mutants. This review summarizes recent advances in research into zebrafish paired fin development and highlights features that are shared with and distinct from limb development in other main animal models.     

Methyl farnesoate and its role in crustacean reproduction and development

Studies with Libinia emarginata suggest that methyl farnesoate (MF), a product of the mandibular organs (MOs), may be a crustacean juvenile hormone. In order to better understand the significance of this compound in crustacean physiology, we first investigated the presence of MF in other decapods. MF was synthesized and secreted by MOs from all species tested. However, large differences in the level of MF secretion were observed between species and also between individuals of a species. For example, the level of secretion by MOs from L. emarginata was 100-fold greater than that observed in MOs from Homarus americanus. Analysis of hemolymph from these two species by GC-MS indicated comparable differences in the amount of MF present. Differences in the level of MF secretion by MOs from individuals of a species appear to reflect the physiological roles of this compound. For example, a close relationship was seen between MF secretion and gametogenesis in females of L. emarginata. Finally, treatment of lobster larvae with seawater containing MF caused a small but significant delay in their metamorphosis when compared with untreated larvae. These data suggest that MF affects reproduction in a manner similar to the effects of JH on insects, and may also have effects on the development of crustacean larvae. Taken together, these data support the classification of MF as a crustacean JH.     

N-acetyl-D-glucosamine in crustacean hemocytes; possible functions and usefulness in hemocyte classification

Abstract. The lectin wheat-germ agglutinin (WGA) selectively binds N-acetyl-D-glucosamine. Fluorescence and electron microscopy were used to show that WGA stains the cytoplasmic granules in the granulocytes, but not the hyaline cells, of two decapods, the ridgeback prawn Sicyonia ingentis and the American lobster Homarus americanus. Using fluorescence microscopy, two intermediate stages in granulocyte maturation were observed. Cells smaller than typical small-granule hemocytes were observed with 5 or fewer granules, which in previous studies using brightfield and phase optics were probably counted as hyaline cells. Also, some granulocytes were observed containing both small and large granules, supporting the suggestion that small and large granule hemocytes represent stages in the maturation of one cell line. Granules in the single type of hemocyte in the branchiopod Artemia franciscana did not stain with WGA. The possible roles of N-acetyl-D-glucosamine in wound healing, pathogen encapsulation, and maintenance of normal crustacean connective tissues are discussed.     

Retinoic acid in development and regeneration

Retinoids are low molecular weight, lipophilic derivatives of vitamin A which have profound effects upon the development of various embryonic systems. Here I review the effects on developing and regenerating limbs, regenerating amphibian tails and the developing central nervous system (CNS). In the regenerating amphibian limb, retinoids can proximalize, posteriorize and ventralize the axes of the blastema. In the chick limb bud retinoids can only posteriorize the tissue. In the regenerating amphibian tail retinoids can homeotically transform tail tissue into hindlimb tissue. In the developing and regenerating limb retinoic acid has been detected endogenously, confirming that this molecule plays a role in the generation of pattern and we have shown that limbs cannot develop in the absence of retinoic acid. In the developing CNS retinoic acid specifically affects the hindbrain where it causes a transformation of anterior rhombomeres into more posterior ones. Again, endogenous retinoic acid has been detected in the CNS and in the absence of retinoids the posterior hindbrain has been found to be affected. The effects of retinoids on the CNS are most likely to be mediated via theHox genes acting in the mesoderm after gastrulation. It has also been proposed that the establishment of the head-to-tail axis in the mesoderm is established by retinoic acid. These data show that retinoids play an important role in both the development and regeneration of various systems in the embryo and post-embryonically     

A role for glycosaminoglycans in the development of collagen fibrils

Extensive data on the glycosaminoglycan (GAG) composition and the collagen fibril diameter distribution have been collected for a diverse range of connective tissues. It is shown that tissues with the smallest diameter collagen fibrils (mass-average diameter less than 60 nm) have high concentrations of hyaluronic acid and that tissues with the largest diameter collagen fibrils (mass-average diameter approximately 200 nm) have high concentrations of dermatan sulphate. It is suggested that the lateral growth of fibrils beyond a diameter of about 60 nm is inhibited by the presence of an excess of hyaluronic acid but that this inhibitory effect may be removed by an increasing concentration of chondroitin sulphate and/or dermatan sulphate. It is also postulated that high concentrations of chondroitin sulphate will inhibit fibril growth beyond a mass-average diameter of approximately 150 nm. Such an inhibition may in turn be removed by an increasing concentration of dermatan sulphate such that it becomes the dominant GAG present in the tissue.     

(Non)Parallel developmental mechanisms in vertebrate appendage reduction and loss

Appendages have been reduced or lost hundreds of times during vertebrate evolution. This phenotypic convergence may be underlain by shared or different molecular mechanisms in distantly related vertebrate clades. To investigate, we reviewed the developmental and evolutionary literature of appendage reduction and loss in more than a dozen vertebrate genera from fish to mammals. We found that appendage reduction and loss was nearly always driven by modified gene expression as opposed to changes in coding sequences. Moreover, expression of the same genes was repeatedly modified across vertebrate taxa. However, the specific mechanisms by which expression was modified were rarely shared. The multiple routes to appendage reduction and loss suggest that adaptive loss of function phenotypes might arise routinely through changes in expression of key developmental genes.     

Long-term changes in the rotifer fauna after biomanipulation in Haussee (Feldberg,Germany, Mecklenburg-Vorpommern) and its relationship to the crustacean and phytoplankton communities

In Feldberg Haussee, an anthropogenic eutrophicated lake, biomanipulation was executed for restoration. To increase the biomass of crustaceans, fish grazing on zooplankton was reduced by catching small fishes and introducing pike-perch. After biomanipulation rotifer biomass from a wide range of species decreased to a small spring maximum with three dominant species. The development of food in spring and food competition between crustaceans probably controlled the rotifer development.     

Ancestral patterns in bird limb development: A new look at Hampé's experiment

The “Archaeopteryx limb” of experimentally treated bird embryos has become a standard quotation in the growing literature on developmental factors in evolution. It has not only been claimed that an early manipulation of the chick limb produces a series of atavistic skeletal features, but the experiment is also frequently interpreted within a genome-centered concept of atavism. The present study provides a morphological, quantitative, and comparative analysis of the skeletal and muscular reactions to the classic barrier insertion experiment of Hampé. The main result of this operation, traditionally seen as a “full length fibula”, is shown to be a relative effect due to tibia shortening, while all the other ancestral skeletal features, which are usually pointed out as being provoked by the elongated fibula, do not appear. The experimentally generated fibula/tibia length ratio and distance, however, mimic the pattern in developing reptilian limbs and are seen to induce secondary effects in the muscular system that are reminiscent of archosaur reptiles. Similar muscle patterns are found as interspecific variations in several bird species. The revised view of the skeletal changes and the additional data on muscular effects allow for a renewed interpretation of the experiment, shifting the emphasis from atavisms to the role of heterochrony, developmental integration, and epigenetic constraint in the evolutionary modification of organismic structures.