Variations in assimilation number of coastal marine phyto-phytoplankton: Effects of environmental co-variates

Seasonal variations in maximum specific production rate (assimilationnumber) of natural phytoplankton from a shallow marine basinwere studied in relation to environmental changes over a 22-monthperiod. Assimilation number variations were considerable (>6fold) and were correlated with both environmental and biologicalco-variates. Temperature was the most significant co-variate,accounting for 40% of the observed variation in assimilationnumber. No significant relationship was apparent between changesin assimilation number and nutrient concentrations.     

THE RELATIONSHIP BETWEEN PHOTOSYNTHESIS AND LIGHT FOR NATURAL ASSEMBLAGES OF COASTAL MARINE PHYTOPLANKTON1

In a series of 188 experiments on the, light-saturation curve for natural assemblages of phytoplankton at 3 stations in Nova Scotia coastal waters, it was found that both the initial slope (α) of the curve and the assimilation number (P_m^B) varied about 5-fold throughout the year. No differences could be detected between stations, but both α and P_m^B decreased with depth. The mean value of α for all the experiments was 0.21 mg C[mg Chl a]^?1· h^?1· W^?1· m² with a range from 0.03 to 0.63. An explanation is offered for the nonconstancy of a in terms of the effect of cell-size and shape on self-shading. An estimate is made from first principles of the physiological maximum-attainable value of α. This estimate corresponds, within the limits of experimental error, to the highest values of α observed in the study. It is deduced that on the average the phytoplankton were photosynthesizing at only 44% maximum capacity. The mean value of P_m^B for all experiments was 4.9 mg C[mg Chl a]^?1· h^?1, with a range from 0.73 to 24.8. In the matrix of partial correlation coefficients, α and P_m^B were positively correlated with each other; α was correlated with mean solar radiation averaged over the 3 days prior to the experiment, but uncorrelated with temperature; P_m^B was correlated strongly with temperature but uncorrelated with recent solar radiation. The results show that P_m^B could be estimated from α and temperature using an empirical multiple regression equation, independent of depth. It is suggested that α and P_m^B are both correlated with some other factor not measured in the study, perhaps the mean cell-size of the populations, or the nutrient status of the cells. The predictability of primary production is discussed in the light of this evidence.     

The social organization and territoriality of short-tailed shrew (Blarina brevicauda) populations in old-field habitats

The social organization of short-tailed shrew (Blarina brevicauda) populations was studied using field and laboratory experiments and observation of a shrew population inside a large enclosure. Short-tailed shrew populations contain resident and nomadic components. Residents occupy small stationary areas at high prey densities and larger areas that are shifted frequently at low prey densities. Areas occupied by residents overlap minimally in winter, non-breeding populations. In summer breeding populations areas occupied by residents of the same sex do not overlap while those of residents of opposite sexes may overlap. Residents defend the area occupied against conspecifics. Scent markings along boundaries appear to maintain the spatial distribution of residents and deter intrusions by nomadic shrews. During encounters vocalizations function as offensive threats, and attacks and chases follow if the intruding shrew does not retreat. Visual communication appears to be less important than chemical and vocal communication in the defence of the area occupied. These data suggest that Blarina is a solitary territorial species.     

Aggression and worker control of caste fate in a multiple-queen wasp, Parachartergus colobopterus

Although famously cooperative, social insect colonies harbour considerable potential for genetic conflict among colonymates. This conflict may be expressed behaviourally as aggression by workers. We investigated aggression in 34 colonies of the wasp Parachartergus colobopterus, by evaluating the characteristics of both instigators and victims of aggressive interactions. We estimated genetic relatedness and queen number using DNA microsatellites and found that workers and emerging females should be most in conflict over the caste of the latter when there are many queens on the nest. We found that aggressive interactions are more likely to involve older workers attacking either males or younger workers, and that victim and aggressor females have more ovarian development than randomly sampled colonymates. Moreover, mated females with low levels of ovarian development relative to active queens were also more likely to be aggressors and victims than were randomly sampled females. Aggression among females supports the hypothesis that older workers use aggression towards younger females as a means of policing the development of emerging females into queens. Workers also may use aggression to suppress the reproduction of some mated females. Our findings thus support the hypothesis that genetic conflicts of interest motivate worker aggression in swarm-founding wasp colonies.     

Gene structure in the tryptophan operon of Escherichia coli: Nucleotide sequence of trpC and the flanking intercistronic regions

We have determined the DNA sequence for the portion of the Escherichia coli tryptophan (trp) operon spanning trpC, which codes for the bifunctional enzyme N-(5′-phosphoribosyl)-anthranilic acid isomerase/indole-3-glycerol phosphate synthetase. The coding region consists of 1356 nucleotides, directing the synthesis of a polypeptide 452 amino acids in length. The predicted protein sequence is consistent with the amino acid composition of the pure enzyme, and with all known partial peptide sequences derived from this molecule. The enzyme is of particular functional interest, because it contains the catalytic activities for two sequential reactions in tryptophan biosynthesis in a single polypeptide chain.The nucleotide sequences of the junctions between trpC and its flanking genes, trpD and trpB, have also been determined. The trpD-trpC junction consists of six untranslated nucleotides and translation of trpC initiates at the second of two adjacent AUG codons. The trpC termination codon is separated from trpB by 11 nucleotides. The short non-translated regions flanking trpC distinguish it from trpA and trpD, whose initiation codons overlap the termination codons of the preceding genes (trpB and trpE), respectively. These differences in the intercistronic regions may reflect functional relationships between the products of adjacent genes in the operon.