Günter Vogt

Midgut gland as monitor organ for the nutritional value of diets in Penaeus monodon (Decapoda)

Midgut gland cells of Penaeus monodon postlarvae were investigated by electron microscopy after starvation and refeeding with different diets. Well nourished postlarvae could be starved for 5 days without irreversible detriment. They recovered easily on a good diet. Only R cells were affected by a short starvation period. After 13 days of food deprivation the structures of all cell types were disintegrated. The postlarvae were able to starve for a maximum of 15 days. The most diversified ultrastructure was obtained by refeeding with cod liver oil and 2s (mixed diet). Casein was not well utilized. Sucrose was the poorest diet. The midgut gland of Penaeus monodon seems to be lipid oriented. Only fat was used as storage material; glycogen was lacking. Different ultrastructures were induced in R cells by a given diet after longer starvation periods. The reestablishment of their ultrastructure by means of a definite diet seems to be impossible after a certain period of starvation (point of no return). R cells are very sensitive to different diets. B cells show slight reactions, while F and E cells remain relatively unchanged. This indicates that R cells could be used to monitor the nutritional value of prawn diets in aquaculture.

Biosynthesis of Astacus protease, a digestive enzyme from crayfish

SummaryFor the first time, the site of biosynthesis of a well characterized invertebrate digestive enzyme is localized. The enzyme chosen, Astacus protease, is a zinc-metalfoenzyme occuring in high concentration in the gastric fluid of the freshwater crayfish Astacus astacus. Enzyme production was stimulated in adult crayfish either by feeding or by removal of the gastric fluid. Immunohistochemistry, cytology and investigation with radioactive tracers demonstrate that in the hours following stimulation, new enzyme was produced in the F-cells of the midgut gland and subsequently discharged into the midgut gland lumen. The enzyme was then accumulated and stored extracellularly in the cardiac stomach in active form. The mechanism of enzyme production observed in Astacus differs considerably from vertebrates suggesting an alternative model for synthesis and storage of digestive enzymes.

Monitoring of environmental pollutants such as pesticides in prawn aquaculture by histological diagnosis

Abstract The influence of water-borne insecticide and herbicide on the midgut glands of Penaeus monodon postlarvae was evaluated by light and electron microscopy. While the herbicide “Pyramin” (active substance: chloridazon) at a concentration of 10 ppm did not cause any detrimental effect, the midgut gland structure was heavily damaged in prawns contaminated with 1 ppm of the insecticide “Perfekthion” (active ingredient: dimethoate). The damage became apparent even before obvious changes in the behaviour of the animals occurred. The use of histology is therefore suggested as an additional tool to monitor the impact of water pollutants to prawns in aquaculture, since alterations in the midgut gland represent a highly sensitive overall response of these animals to the synergistic effect of their nutritional and physiological condition and the quality of the water.

Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda

The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life‐history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean‐type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico‐chemical factors and phytoplankton availability in freshwater habitats. These life‐history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r‐ to K‐strategy in freshwater decapods are traded‐off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio‐temporal alteration of their socio‐ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.

Leucaena leucocephala leaves in formulated feed for Penaeus monodon: a concrete example of the application of histology in nutrition research☆

Abstract Penaeus monodon postlarvae were fed with formulated diets containing either soaked or unsoaked Leucaena leaves. A similarly prepared feed with soybean in place of Leucaena was used for comparison. Results were analysed by statistical and histological methods. Results of the 4-week feeding experiment showed that mean weight gains and percentage survival of the prawns fed with the two Leucaena -containing diets were higher, but not significantly different from soybean-containing diet. The content of the poisonous amino acid mimosine in the Leucaena leaves could be reduced about 70% by soaking the leaves in freshwater for 24 h. Highest weight gain was obtained with the feed containing these soaked leaves. In addition to growth and survival, the R-cells of the midgut glands of the postlarvae were investigated by light and electron microscopy. Although the statistical growth values and the proximate analyses of the test diets were similar, a food-specific ultrastructure was established after only 4 days of feeding. All diets resulted in subcellular characteristics typical for well fed prawns and, at that time, the Leucaena diets were already slightly superior to the soybean control. This indicates that different sources of macronutrients lead to different ultrastructures even if the proximate analyses of protein, carbohydrate and lipid are similar. Only slight changes in the R-cells were observed after 11, 20 and 28 days in the prawns fed with the soybean diet compared to 4 days of feeding. In the diet containing unsoaked Leucaena leaves, however, many R-cells became heavily damaged after 20 and 28 days, whereas the prawns fed with the diet containing soaked leaves exhibited less pronounced distortion. Statistical analyses of growth and survival rate did not show these adverse effects at that time. Although it is highly probable that the mimosine is responsible for those pathological symptoms, complementary experiments could not clearly prove that. The effects of feed components are visible on the cellular or organ level after only a few days, whereas the individuals (organism level) reflect them about 10 days later. Another 10 days later the changes are manifested in the population. Therefore it is suggested to use histology in nutrition studies as a supplementary source of information to statistical and biochemical parameters. The midgut glands can further be used to monitor the nutritional condition of prawns in aquaculture, sea ranching, and in ecological investigations. The study confirms that Leucaena leaves are a promising protein source for prawn diets if mimosine could be reduced to a very low level. A mimosine level of 0.25% in the feed is still too high, if the diet is used uninterruptedly for several weeks.

Stochastic developmental variation, an epigenetic source of phenotypic diversity with far-reaching biological consequences

This article reviews the production of different phenotypes from the same genotype in the same environment by stochastic cellular events, nonlinear mechanisms during patterning and morphogenesis, and probabilistic self-reinforcing circuitries in the adult life. These aspects of phenotypic variation are summarized under the term ‘stochastic developmental variation’ (SDV) in the following. In the past, SDV has been viewed primarily as a nuisance, impairing laboratory experiments, pharmaceutical testing, and true-to-type breeding. This article also emphasizes the positive biological effects of SDV and discusses implications for genotype-to-phenotype mapping, biological individuation, ecology, evolution, and applied biology. There is strong evidence from experiments with genetically identical organisms performed in narrowly standardized laboratory set-ups that SDV is a source of phenotypic variation in its own right aside from genetic variation and environmental variation. It is obviously mediated by molecular and higher-order epigenetic mechanisms. Comparison of SDV in animals, plants, fungi, protists, bacteria, archaeans, and viruses suggests that it is a ubiquitous and phylogenetically old phenomenon. In animals, it is usually smallest for morphometric traits and highest for life history traits and behaviour. SDV is thought to contribute to phenotypic diversity in all populations but is particularly relevant for asexually reproducing and genetically impoverished populations, where it generates individuality despite genetic uniformity. In each generation, SDV produces a range of phenotypes around a well-adapted target phenotype, which is interpreted as a bet-hedging strategy to cope with the unpredictability of dynamic environments. At least some manifestations of SDV are heritable, adaptable, selectable, and evolvable, and therefore, SDV may be seen as a hitherto overlooked evolution factor. SDV is also relevant for husbandry, agriculture, and medicine because most pathogens are asexuals that exploit this third source of phenotypic variation to modify infectivity and resistance to antibiotics. Since SDV affects all types of organisms and almost all aspects of life, it urgently requires more intense research and a better integration into biological thinking.

How to minimize formation and growth of tumours: Potential benefits of decapod crustaceans for cancer research

Tumours have only rarely been observed in the decapod crustaceans, a large animal group of more than 10,000 species that includes the commercially important and well investigated shrimp, lobsters, crayfish and crabs. Analysis of the literature and information from cancer and diseases data bases revealed a total of 15 incidences, some of them being questionable. Even in the long‐lived species, which can reach life spans of almost 100 years, neoplasias are virtually unknown. The data published so far suggest that the strikingly different frequencies of carcinogenesis between decapods and other well investigated animal groups like mammals, fish, insects and molluscs is based on differences of the metabolic pathways for carcinogens, the immune systems, and the regulation of stem cells. Therefore, representatives of the Decapoda may serve as useful models to study how organisms can successfully prevent or control spontaneously and environmentally induced cell proliferation. A particularly promising candidate for in‐depth investigation of these topics is the marbled crayfish, a rather new clonal lineage that is presently being introduced as a laboratory model in development and epigenetics.

The marbled crayfish as a paradigm for saltational speciation by autopolyploidy and parthenogenesis in animals.

ABSTRACT The parthenogenetic all-female marbled crayfish is a novel research model and potent invader of freshwater ecosystems. It is a triploid descendant of the sexually reproducing slough crayfish, Procambarus fallax, but its taxonomic status has remained unsettled. By cross-breeding experiments and parentage analysis we show here that marbled crayfish and P. fallax are reproductively separated. Both crayfish copulate readily, suggesting that the reproductive barrier is set at the cytogenetic rather than the behavioural level. Analysis of complete mitochondrial genomes of marbled crayfish from laboratory lineages and wild populations demonstrates genetic identity and indicates a single origin. Flow cytometric comparison of DNA contents of haemocytes and analysis of nuclear microsatellite loci confirm triploidy and suggest autopolyploidisation as its cause. Global DNA methylation is significantly reduced in marbled crayfish implying the involvement of molecular epigenetic mechanisms in its origination. Morphologically, both crayfish are very similar but growth and fecundity are considerably larger in marbled crayfish, making it a different animal with superior fitness. These data and the high probability of a divergent future evolution of the marbled crayfish and P. fallax clusters suggest that marbled crayfish should be considered as an independent asexual species. Our findings also establish the P. fallax–marbled crayfish pair as a novel paradigm for rare chromosomal speciation by autopolyploidy and parthenogenesis in animals and for saltational evolution in general. Summary: The triploid marbled crayfish is a rare animal example of speciation by autopolyploidisation and parthenogenesis. It seems to be a particularly suitable model to study how much genetic and epigenetic change is necessary to create a new species.

Life stages and tentative life cycle of Psorospermium haeckeli, a species of the novel DRIPs clade from the animal‐fungal dichotomy

Psorospermium haeckeli, an enigmatic parasite of freshwater crayfish, recently was assigned to the newly established DRIPs clade, which is considered to constitute the most basal branch of the Animalia close to the animal-fungal dichotomy (Ragan et al. [1996] Proc. Natl. Acad. Sci. USA, 93:11907–11912). So far, the only lifestages known were immobile sporocysts located within the connective tissue of various organs of crayfish, and smaller developmental stages of these sporocysts. After prolonged incubation of connective tissue from infected crayfish in freshwater we have obtained free-living amoeboid organisms that hatched from the sporocysts in the decaying tissue. The results of further experiments on transmission of the parasite as well as a futile search for additional hosts suggest a diphasic life cycle of Psorospermium haeckeli comprising a histozoic and a free-living phase. The histozoic and free-living stages were investigated by light and electron microscopy and compared to the life stages of other DRIPs species, protists, and lower animal and fungal groups. The morphological characters elaborated fit well into the proposed taxonomic position of the parasite close to the animal-fungal dichotomy. Therefore, together with the other DRIPs species, Psorospermium haeckeli may give an idea of the types of organisms from which animals and fungi may have evolved. J. Exp. Zool. 283:31–42, 1999.

Symmetry variation in the heart-descending artery system of the parthenogenetic marbled crayfish.

The internal anatomy of freshwater crayfish is strictly bilaterally symmetric, with the conspicuous exception of the vertically oriented descending artery (sternal artery), which originates from the heart and terminates in the subneural artery. Serial sectioning of 133 juveniles of the parthenogenetic marbled crayfish revealed that the descending artery was bilaterally symmetric in 4.5% of the specimens, right asymmetric in 45.1%, and left asymmetric in 50.4%. In the bilaterally symmetric variant two branches arise from the left and right chambers of the bulbus of the heart, run laterally around the hindgut, and fuse underneath it. The asymmetric variants have only one dorsal branch, which loops around the hindgut on either the left or the right side. Other structures of the heart, such as the paired antennary and hepatopancreatic arteries and the ostia or the unpaired anterior and posterior aortae, showed no symmetry variation. Because of the genetic identity of the experimental animals and their culture under identical environmental conditions, the variation in symmetry of the descending artery observed is interpreted as the result of developmental variation. We recommend that the marbled crayfish be considered for investigation of the epigenetic mechanisms responsible for the maintenance and breaking of bilateral symmetry in metazoans. J. Morphol., 2009.