4,11-Epoxy-cis-eudesmane,soldier cephalic secretion of the Nearctic desert termite,Amitermes minimus Light (Termitidae: Termitinae)

Summary The soldier cephalic secretion of the Nearctic desert termite,Amitermes minimus, consists almost entirely of 4,11-epoxy-cis-eudesmane which was previously identified from soldiers of 2 AfricanAmitermes species. Soldiers ofA. minimus each store circa 61 g of the secretion. Bioassays with the ant,Crematogaster californica, indicate a repellent role for the eudesmane compound in termite defense.Classification as proposed by Sands, W.A., Bull. Br. Mus. nat. Hist., Ent., suppl.18 (1972).Supported by Sigma Xi Grant-in-Aid of Research and California Statewide Critical Applied Research grant.     

Complexity of human T-cell antigen receptor beta-chain constant- and variable-region genes

Immune systems of vertebrates function via two types of effector cells, B and T cells, which are capable of antigen-specific recognition. The immunoglobulins, which serve as antigen receptors on B cells, have been well characterized with respect to gene structure, unlike the T-cell receptors. Recently, cDNA clones thought to correspond to the beta-chain locus of the human and mouse T-cell receptor have been described. The presumptive beta-chain clones detect gene rearrangement specifically in T-cell DNA and show homology with immunoglobulin light chains. The similarity of the T-cell beta-chain gene system to the immunoglobulin genes has been further demonstrated by the recent observation of variable- and constant-region gene segments as well as joining segments and putative diversity segments. We report here the characterization of cDNA and genomic clones encoding human T-cell receptor beta-chain genes. There are two constant-region genes (C beta 1 and C beta 2), each capable of rearrangement and expression as RNA. The gene arrangement, analogous to that of mouse beta-chain genes, shows strong evolutionary conservation of the dual C beta gene system in these two species.     

Scaling laws of marine predator search behaviour

Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology. Lévy walks are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators-sharks, bony fishes, sea turtles and penguins-exhibit Lévy-walk-like behaviour close to a theoretical optimum. Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms, from microbes to humans, as a 'rule' that evolved in response to patchy resource distributions.