Herbivory in Crabs: Adaptations and Ecological Considerations

Plant material is the major source of nutrition for many speciesof crabs in both marine and terrestrial habitats. Physical andchemical characteristics of plants can lead to difficultiesin harvesting and ingestion, to low digestability, unpalatabilityand toxicity, and to deficiencies in specific nutrients, especiallynitrogen, vitamins and fatty acids. We describe the range ofherbivory in crabs, as well as the anatomical, physiologicaland behavioral adaptations that enhance nutrient acquisitionfrom plant material. We assess the impact of herbivory by crabson plant communities, and highlight topics for further research.     

SOME ASPECTS OF THE PHYSIOLOGY AND BIOCHEMISTRY OF MARINE FUNGI

1. This review deals with certain aspects of the physiology and biochemistry of marine fungi. Though it is not easy to define what is meant by a marine fungus, the information presented here relates to those species that by consensus can be accepted as being truly marine. The material is in two parts, that relating to the higher fungi (Ascomycotina, Basidiomycotina and Deuteromycotina) and that relating to the lower fungi, particularly those zoosporic fungi that require sodium for growth. 2. Higher marine fungi appear to have a similar carbon, nitrogen and vitamin nutrition to their terrestrial counterparts. 3. Growth of higher marine fungi can be optimal in 100% sea water, but more frequently optimal growth is at a lower percentage. The percentage giving optimal growth may be determined by the rate of ion uptake required to generate the necessary turgor for growth. The tolerance of the vegetative phase of many terrestrial fungi to salinity appears little different from that of marine fungi. In general, members of the Basidiomycotina are particularly sensitive to salinity, while those of the Ascomycotina and Deuteromycotina are much more tolerant. 4. The degree of tolerance to salinity may be dependent upon temperature and whether or not adaptation by the fungus has occurred. 5. Maintenance of a suitable internal potassium concentration by a higher marine fungus is important for growth in a saline medium. Calcium appears to be necessary for the retention of potassium and organic solutes within the hyphae. 6. It appears that higher marine fungi are able to maintain a ratio of potassium: sodium higher than that of sea water by the presence of a plasma membrane ATPase which may have a higher pH optimum than the equivalent enzyme from terrestrial counterparts. 7. Higher fungi produce more glycerol as the salinity of the external medium is increased. Whether or not the compound is involved in osmoregulation has yet to be determined. 8. Turgor is thought to be generated in higher marine fungi growing in sea water by organic solutes (predominantly glycerol and arabitol) and by ions, with the latter playing the major role. Though interpretation of the data depends on several assumptions, the high concentrations of sodium that seem likely to be present in hyphae or cells have implications for the activity of enzymes, if they have similar properties to those of higher plants. There is a need for information on the effects of high concentrations of ions on enzymes located in the cytoplasm of higher fungi. 9. In spite of some experimental uncertainties, it seems that reproduction and spore germination of higher marine fungi are very much less affected by salinity than are the same processes of terrestrial counterparts. 10. The zoosporic marine fungi require sodium for growth. Though the ion is required at high concentration for growth, sodium cannot be replaced by potassium. Evidence indicates that sodium is involved in the transport of solutes across the plasma membrane. 11. The carbon and nitrogen requirements for the growth of the zoosporic marine fungi demand further investigation, particularly at the biochemical level. There is evidence that the respiration of these fungi possesses many interesting features. 12. Vitamin requirements of the zoosporic marine fungi depend on the isolate under investigation. Vitamin B., does not now seem to be an obligatory requirement. The ability of phospholipids and sterols to stimulate growth requires further investigation. 13. Further studies on marine fungi in the laboratory should focus particularly on growth in continuous culture. Physiological and biochemical studies would be helped by more precise guidance from those concerned with the ecology of these fungi.     

Combined effects of allelochemical-fed and scarce prey on the generalist insect predator Podisusmaculiventris

1. The simultaneous effects of allelochemicals ingested by herbivorous insect prey and prey scarcity on the performance of a generalist insect predator were examined.
2. Fifth-instar predatory stinkbugs ( Podisus maculiventris : Pentatomidae) were fed caterpillars ( Manduca sexta : Sphingidae) in three prey scarcity treatments: every day (unlimited amount), one caterpillar every third day, one caterpillar every fifth day. The caterpillars were fed either a plain diet or a diet containing rutin, chlorogenic acid and tomatine, which are three of the major allelochemicals in tomato leaves ( Lycopersicon esculentum : Solanaceae), the preferred food of these caterpillars.
3. Food consumed, efficiency of conversion of ingested food to biomass (ECI), biomass gained, stadium duration and relative growth rate (RGR) of predators were negatively affected by prey scarcity. The allelochemicals negatively affected food consumed and ECI.
4. There were prey scarcity by allelochemical interactions for ECI, biomass gained and RGR. For ECI, the allelochemicals had a greater negative impact on the predatory stinkbugs when prey were scarce. When prey diet contained allelochemicals, biomass gained and RGR declined more steeply with increased prey scarcity. There was an allelochemical by predator gender interaction for biomass gained. Allelochemicals had no effect on biomass gained by female stinkbugs, whereas biomass gained declined more steeply with increased prey scarcity for male stinkbugs fed caterpillars containing allelochemicals than for males fed control caterpillars.     

Biological Communities of the South Texas Continental Shelf

A multi-disciplinary study of the south Texas continental shelfin 1975–1977 investigated physical, chemical, geological,and biological characteristics over spatial and temporal scales,and the results are briefly summarized here. Chlorophyll a concentrationsand zooplankton density and biomass showed reductions relatedto distance from shore. These factors also displayed north-southgradients and correlations with surface salinities. Bottom sedimentsgraded seaward from fine sands nearshore to silts and clayson the outer shelf. Coarser sediments were associated with geologicand physical features such as ancestral deltas and wave action.Benthic populations were distributed in relation to sedimenttype, but other features such as depth, bottom water variability/stability,and primary production in the overlying waters were also importantin determining benthic community structure. The study providesa baseline for future process-oriented investigations and environmentalassessments.     

Rapid flow through the sediments of a headwater stream in the southern Appalachians

SUMMARY. 1. The flow of water through the sediment layer (underflow) of streams can influence nutrient uptake dynamics and the supply of materials to microbes, meiofauna and macroinvertebrates living within stream sediments. We examined the extent of underflow in Hugh White Creek, a headwater stream in the southern Appalachian Mountains and compared underflow at different depths and at different sites within the stream.
2. Initially rhodamine dye was used to trace the flow of water through the sediments; however, the dye was strongly absorbed by the sediments in Hugh White Creek. Thus rhodamine was not suitable as a tracer of water flow. Chloride reacted conservatively in laboratory experiments and was used as a tracer.
3. The tracer infiltrated the sediments within 5 min to depths of 10 cm at all six sites. Chloride infiltration tended to decrease with depth of sediments at all sites although there was no consistent statistical pattern in chloride concentration with depth for the different sites. Equilibrium between the water column and sediments was reached rapidly, within minutes for the sites with coarse sediments and within a few hours for sites with finer sediments. Minimum rates of chloride infiltration into the sediments ranged between 1.0 cm min⁻¹ for the sites with cobble substrate to 0.2 cm min⁻¹ for sites with fine sand sediments associated with debris dams. These data suggest that underflow may be a major component in the functioning of Appalachian mountain streams.     

Evolution of Calcium Regulation in Lower Vertebrates

Calcium regulation in lower vertebrates appears to be a continuum.The predominant hypercalcemic hormone in reptiles, birds andmammals is parathyroid hormone, while the major hypercalcemiccontrol in fishes is a pituitary factor, probably prolactin.In the amphibians dual controlling mechanisms are at work, sothat both the pituitary and parathyroids exert their influence.Prolactin may still retain some hypercalcemic potency in thehigher vertebrate groups, either directly or indirectly by influencingthe secretion of other hypercalcemic hormones. On the otherhand, parathyroid hormone does not occur in, nor does it elevateblood calcium in fishes. It thus seems to be a new inventionof tetrapods, or possibly to have evolved from a pituitary factorof fishes. The ability to lower blood calcium seems to be veryimportant in seawater fishes, in which the corpuscles of Stanniusexert major control. In terrestrial forms, the corpuscles ofStannius are not present, and hypocalcemic factors assume aminor role in overall calcium regulation