SHELL COLOUR IN CALLIOSTOMA ZIZYPHINUM (L.) FROM STRANGFORD LOUGH, N. IRELAND

Shells of Calliostoma zizyphinum taken from Strangford Lough, N. Ireland are divisible into three distinct colour forms: white (=var lyonsi) intermediate (a pale variegated form) and purple (a dark variegated form). The predominance of white and pale shelled individuals within and the absence of white Calliostoma outside the lough was confirmed. The proportions of animals with white and variegated shells at selected sites were almost identical with those previously documented, suggesting a temporal stability of colour form ratios. No differences in shell thickness and pedal adhesion were demonstrated between these forms. Snails with white shells reflect radiant heat better, have lighter coloured feet, move more rapidly, show a greater incidence of shell repair and are more frequently exposed on weed at low tide, than those with either intermediate or purple shells. Increased proportions of white individuals may be associated with high population densities. Under such circumstances, it is suggested that increased mobility may, by increasing dispersion, reduce intraspecific competition. In the event of exposure at low tide a white shell would help minimize thermal stress.

Increased Promiscuity of Human Galactokinase Following Alteration of a Single Amino Acid Residue Distant from the Active Site

Galactokinase catalyses the site-and stereospecific phosphorylation of galactose at the expense of ATP. The specificity of bacterial galactokinase enzymes can be broadened by alteration of a tyrosine residue to a histidine. The effects of altering the equivalent residue in human galactokinase (Tyr379) were investigated by testing all 19 possible variants. All of these alterations, except Y379P, resulted in soluble protein on expression in Escherichia coli and all the soluble variants could catalyse the phosphorylation of galactose, except Y379A and Y379E. The variants Y379C, Y379K, Y379R, Y379S and Y379W were all able to catalyse the phosphorylation of a variety of monosaccharides, including ones that are not acted on by the wild-type enzyme. Novel substrates for these variant galactokinases included D-mannose and D-fructose. The latter monosaccharide is presumed to react in the pyranose configuration. Molecular modelling suggested that the alterations do not cause changes to the overall structure of the enzyme. However, alteration of Tyr379 increases the flexibility of the peptide backbone in regions surrounding the active site. Therefore, it is proposed that alteration of Tyr379 affects the substrate specificity by the propagation of changes in flexibility to the active site, permitting a broader range of compounds to be accommodated.

Additivity Pretraining and cue competition effects: Developmental evidence for a reasoning account of causal learning

The effect of additivity pretraining on blocking has been taken as evidence for a reasoning account of human and animal causal learning. If inferential reasoning underpins this effect, then developmental differences in the magnitude of this effect in children would be expected. Experiment 1 examined cue competition effects in children's (4- to 5-year-olds and 6- to 7-year-olds) causal learning using a new paradigm analogous to the food allergy task used in studies of human adult causal learning. Blocking was stronger in the older than the younger children, and additivity pretraining only affected blocking in the older group. Unovershadowing was not affected by age or by pretraining. In experiment 2, levels of blocking were found to be correlated with the ability to answer questions that required children to reason about additivity. Our results support an inferential reasoning explanation of cue competition effects. (c) 2012 APA, all rights reserved.