Observations on the biology of the trochid gastropod Austrocochlea constricta (Lamarck) (Prosobranchia). II. The effects of available food on shell-banding pattern

The trochid gastropod Austrocochlea constricta (Lamarck) shows a variable pattern of shell banding. The concentration of the major shell pigment, uroporphyrin I, has been shown to differ between stripe-classes and, within each stripe-class, between shores. This paper describes the relation between amount of available food and shell pigmentation on six shores.Qualitative and quantitative methods were used to determine the concentrations of chlorophyll pigments in the substratum of each shore. Thin-layer chromatography showed differences in the type of microalgae present. Quantitative, spectrophotometric determinations of the chlorophyll concentrations of acetone extracts of scrapings of the substratum showed significant differences in total chlorophyll between the six shores. A uroporphyrin index gives an estimate of the total amount of uroporphyrin/unit area on each shore, and enables the wet wt/animal, density/area, and proportions of the population in different stripe-classes to be related to the concentrations of uroporphyrin/g shell within the stripe-classes. There was a highly significant linear regression of the uroporphyrin index on total chlorophyll concentration. This provides evidence for the effect of amount of available food on shell pigmentation. The mean concentration of pigment/g shell increased as the chlorophyll content of the substratum increased.A hypothesis is proposed to explain the observed differences in banding-pattern frequencies between shores; this represents the frequency distribution of animals with different concentrations of pigment/g shell as a normal distribution, with increasing mean and standard deviation as the concentration of chlorophyll in the substratum increases. Theoretical distributions are given to show that similar banding pattern frequencies to those observed on the six shores can be produced under this hypothesis. Neither a more complex hypothesis, nor selective nor genetic mechanisms are necessary to explain the observed distributions of banding pattern in Austrocochlea.     

Parameters of brown-headed cowbird Molothrus ater egg discrimination in warbling vireos Vireo gilvus

We examined which egg parameters warbling vireos Vireo gilvus use to discriminate brown-headed cowbird Molothrus ater eggs and, by comparing our results to other studies, tested the prediction that ejecter species with eggs more similar in appearance to cowbird eggs will be less tolerant of foreign eggs. In addition, we tested the hypothesis that egg characteristics influence the cost of ejection and probability of committing ejection errors. Warbling vireos ejected 100% of eggs with a cowbird spot pattern and only spot pattern significantly influenced the probability of ejecting a foreign egg, whereas size and nest stage did not. Foreign eggs that differed in two parameters were not ejected significantly more than those that differed in one parameter. Thus, warbling vireos appear to be less tolerant of foreign eggs than species with eggs more divergent from cowbird eggs. There was no significant difference in the number of vireo eggs that were damaged when foreign eggs of different sizes and spot patterns were ejected, which is counter to the assumptions of the evolutionary equilibrium hypothesis. Similarly, foreign egg characteristics did not significantly influence the probability of ejection errors. Finally, egg discrimination in warbling vireos appears to have evolved directly to counter cowbird parasitism because all conspecific eggs switched into their nests were accepted.     

Supply-side ecology and benthic marine assemblages

Many marine invertebrates have a planktonic stage of their life history during which widespread dispersal and much mortality occur. The numbers surviving to recruit into habitats occupied by adults are therefore very variable in time and space. Models for the structure and dynamics of benthic assemblages tend to focus on processes causing death - often assuming consistent arrivals of recruits. Supply-side ecology is a newly fashionable term to describe recent interest in the long-realized consequences of variations in recruitment. Such variations have important influences on theory and empirical research in these assemblages.     

The localisation of an Mr 74,000 major chromatin antigen on native salivary chromosomes of Drosophila melanogaster

An antigen making a major contribution to the immune response to Drosophila melanogaster chromatin resides primarily on a nonhistone charge-class family of proteins of Mr 74,000. Immunofluorescence detects this antigen at interbands, puffs and diffuse bands of D. melanogaster salivary chromosomes isolated without exposure to acid fixatives, and on nucleoplasmic ribonucleoprotein droplets. In the electron microscope, gold labelling reveals the binding of monoclonal antibodies specific for the antigen at chromosomal loci generally bearing putative ribonucleoprotein (RNP) particles. However, the locus 3C 11–12 is remarkable in that it bears putative RNP particles but is virtually unlabelled, suggesting protein specificity at different active loci.     

The effects of tidal height,wave-exposure,seasonality and rock-pools on grazing and the distribution of intertidal macroalgae in New South Wales

The effects of grazers (mostly gastropods), height on the shore, wave-exposure, season of the year and the presence of shallow rock-pools on the abundance of intertidal macroalgae were examined on shores at Cape Banks (Botany Bay). At the beginning of each of the four seasons, experimental plots with and without grazers were cleared at four heights on three shores, of increasing exposure to waves, The colonization and growth of algae in these plots were monitored (by measurement of per cent cover and dry wt) for approximately the next 3 months in each season.In grazed plots, foliose algae only grew at the lowest levels on the shores. They were more abundant where wave-action was greater, and during the cooler periods of the year, when growth of the plants was enhanced. Higher on the shore, there was a positive correlation between algal cover in grazed plots and the amount of rainfall during the previous 10 days. In all seasons, there was much greater colonization of foliose algae where grazers were excluded. There was greater algal growth at lower levels on the shore, and where wave-action was stronger. Less algae grew in sheltered areas during warmer times of the year. The major seasonal difference found was the more rapid growth and occupancy of the rock by algae during the cooler seasons of the year.Experimental rock-pools were colonized more rapidly at lower levels on the shore, and during the winter. There was no difference between pools and control (non-pool) areas during winter. During summer, however, there was a greater per cent cover and biomass of algae in pools from which grazers had been excluded than in similar control areas.The results can be interpreted as being due to the greater survival and more rapid growth of algae under conditions of increased moisture, decreased emersion and decreased temperatures and light regimes during low tide (i.e. when physical stresses were reduced). These physical factors were, however, less important to the distribution of the algae than were the effects of grazers. Although few algae were present in any experimental plot, the number of species of algae per plot was considerably reduced in grazed areas.The results confirm that the patterns of vertical distribution and abundance of algae on rock-platforms in New South Wales are primarily the result of the activities of grazers. All algae in the present study were capable of living higher on the shore than they were normally found. Much of the variation along a gradient of wave-exposure, from season to season, and small-scale variation from place to place at any time can be explained by the complex interactions between the activities of grazers, and the effects of variations in the physical environment that influence the recruitment, survival and growth of the algae.     

The Effect of Extracellular Matrix Molecules on the in Vitro Behavior of Bovine Endothelial Cells

Extracellular matrix (ECM) is an important mediator of endothelial functions such as adhesion, spreading, migration, proliferation, and maintenance of differentiated functions. Attachment of cultured cells to tissue culture polystyrene (TCPS) is dependent on vitronectin which adsorbs onto the surface from the serum in the culture medium. Vitronectin (VN) will adsorb efficiently to TCPS even if the latter has been coated with another matrix molecule and blocked with albumin. This means that studies of the interactions of cells with individual coated ECM molecules will be confounded by the presence of adsorbed VN if serum is present in the culture medium. In this study, the adhesion, spreading, growth, and output of endogenous matrix molecules by bovine corneal endothelial (BCE) cells were measured on five different matrix substrates using medium which had been depleted of vitronectin to avoid such confounding effects. The same cell adhesion and spreading maxima were achieved on vitronectin, fibronectin (FN), laminin (LM), and types I and IV collagen (col I, col IV). The coating concentrations required to achieve these maxima, however, differed among the substrates, LM needing considerably higher concentrations than the other substrates for both maximal adhesion and spreading and FN needing higher concentrations for cell spreading. When cells were continuously passaged on each of the five substrates coated at concentrations optimal for cell spreading, no differences in cell proliferation rates or cell morphology were observed. Significant differences, however, were observed in the subcellular output of endogenous matrix molecules (FN, LM, col IV, and thrombospondin) between the different substrates. Col I was a poor substrate for the production of all ECM molecules tested over the 10 passages of the experiment, whereas col IV was a consistently good substrate. LM and FN substrates displayed differential effects on the output of different ECM molecules. VN was unique in that BCE cells at early passage on this substrate produced high levels of endogenous matrix molecules, whereas with continued passage on this substrate, a progressive decline in ECM secretion was observed. These results show that incorporation of individual molecules into the ECM by BCE cells in culture is significantly affected by the nature of the substratum. They further suggest that passage of endothelial cells in media containing serum (which results in coating of VN onto the substrate) may result in a progressive reduction of ECM output.     

Intertidal zonation of prosobranch gastropods: Analysis of densities of four co-existing species

The densities of populations of Nerita atramentosa Reeve, Austrocochlea constricta Lamarck, Bembiciuin nanum (Lamarck), and Cellana tramoserica (Sowerby) were recorded in 0.25 m² quadrats on landward and seaward halves of a sheltered and a moderately exposed rock platform from June 1972 to June 1973. The data have been subjected to variance and multiple regression analysis. Differences between densities of each species on the two shores and in the two areas of each shore are discussed with respect to the regressions on littoral height. Densities of Nerita on the sheltered shore, Austrocochlea and Bembicium on both shores, and Cellana, on the exposed shore, increased with height. The density of Cellana on the sheltered shore decreased as height increased. The density differences in the landward and seaward areas on the two shores were attributable to the effect of height for Nerita and Austrocochlea. Height was the major variable affecting the density of these two species on the sheltered shore. Bembicium and Cellana densities on both shores, and Austrocochlea density on the exposed shore, are not primarily determined by height.On the sheltered shore, Nerita and Cellana increased in density with increasing cover of water in rock pools. On the exposed shore, Bembicium and Cellana became sparser with increasing water cover. Bembicium on both shores increased in density with increasing cover of the alga Peyssonelia, as did Cellana on the exposed shore. Cellana and Austrocochlea tended to increase in density with Nerita on the sheltered shore. Cellana tended to be sparse where Bembicium was dense on the exposed shore. The biological effects of substrata and other species on the densities of each species remain unexplained.Significant time effects were found for variations in the densities of Nerita and Cellana on the sheltered shore and of Austrocochlea and Cellana on the exposed shore. The seasonal change in density of Nerita was parabolic with a minimum in summer, and is consistent with the known period of recruitment of this species. The lack of significant time effects on density of Austrocochlea on the sheltered shore is consistent with the known continuous recruitment of this species. The declining density of Austrocochlea on the moderately exposed shore was found, by size-frequency analysis, to be due to reduced recruitment compared with surrounding shores. The density of Cellana on both shores showed seasonal changes, with a maximum in summer, which is consistent with the known period of recruitment in Cellana. The lack of seasonal changes in density of Bembicium is briefly discussed.This type of multifactor analysis identifies biological interactions affecting variation in density of these species. It also corroborates the results of other ecological investigations and determines the relative importance of a variety of physical and biological factors in the distribution of density of intertidal gastropods.     

Steric effects in antibody reactions with polyvalent antigen

Antigen valency has been defined (Singer, 1965) as the maximum number of epitopes per antigen which can be simultaneously occupied by antibody. If the epitopes are closely spaced, steric hindrance prevents the simultaneous occupancy of all epitopes. Current methods of estimating both the antigen valency and the association constant (Ka) from equilibrium binding data do not allow for the effects of steric hindrance. We have developed a theory which accounts rigorously for steric hindrance when monovalent ligands of quite general shape (antibodies) react reversibly with multivalent acceptor molecules (antigens). The surfaces of the acceptors are modelled by completely general two-dimensional lattices. Using this theory we demonstrate that curvature of Scatchard plots can arise from steric effects alone in the absence of other known causes such as cross-linking, cooperativity and heterogeneous epitope affinities. Our results generalize the conclusions of McGhee & von Hippel (1974) who dealt with one-dimension acceptor molecules such as DNA. We discuss inaccuracies in the estimation of both Ka and antigen valency using the traditional approach of fitting straight lines to Scatchard plots.     

Copper induced oxidation of serotonin: analysis of products and toxicity

Serotonin is a major neurotransmitter that controls many functions, ranging from mood and behaviour through to sleep and motor functions. The non-enzymatic oxidation of serotonin is of significant importance as some oxidation products are considered to be neurotoxic. An interaction between copper and serotonin has been suggested by symptoms observed in a number of neurodegenerative diseases such as Wilson's and Prion diseases. Using PC12 cells as a model of neuronal cells, we show that the interaction between copper and serotonin is toxic to undifferentiated cells. The toxicity is largely due to reactive oxygen species as cell death is significantly reduced in the presence of the antioxidant mannitol. Differentiation of the PC12 cells also confers resistance to the oxidative process. In vitro oxidation of serotonin by copper results in the eventual formation of a coloured pigment, thought to be a melanin-like polymeric species. Using spectroscopic methods we provide evidence for the formation of a single intermediate product. This dimeric intermediate was identified and characterized as 5,5'-dihydroxy-4,4'-bitryptamine. These results indicate that copper structurally alters serotonin and this process may play a role in copper related neurodegenerative diseases.     

Movements of intertidal gastropods

Movements of marked individuals of Nerita atramentosa Reeve, Austrocochlea constricta (Lamarck), Bembicium nanum (Lamarck), and Cellana tramoserica (Sowerby) were recorded at various sites in New South Wales in 1974 and 1975. A model of random movements during feeding at high tide was proposed, i.e., that animals wandered in random directions and the distances moved were exponentially distributed. Appropriate statistical tests for departures from such a model are given. The types of departure tested were non-random directions, non-exponentially distributed dis- tances, different distances in different directions, and correlated distances or directions of movement between days. With two exceptions, the movements of the animals over short periods were adequa- tely described by the assumption of random movements. One exception was A. constricta in one locality where movements of the sample were limited by it being in a large rock-pool and the other was the limpet C. tramoserica which displayed homing behaviour, so that the population could be divided into homers and non-homers. Movements of non-homing limpets were random.The mean distance moved by N. atramentosa was not significantly different from that of A. con- stricta. The mean distances moved by these two species were greater than those of B. nanum and the non-homing C. tramoserica, which were not different from each other. Adult and one-year old N. atramentosa did not differ significantly in mean distance moved, but both moved more than juveni- les. These patterns of movement are discussed with respect to hypotheses about feeding in these species.The model of movement was used to predict the effect of different percentage cover in small pools on the movement of A. constricta, which shows a preference for this micro-habitat. Increased availability of small pools reduced the mean distance moved by this species.