The effect of cardiac glycoside storage on growth rate and adult size in the butterflyDanaus chrysippus (L.)

Summary Danaus chrysippus grows faster and attains significantly greater size when fed as a larva on several species of Asclepiadaceae (milkweeds) containing cardiac glycosides than on one which does not.Acknowledgment. I thank Professor D. Schneider and Dr M. Boppré for sending me a sample of butterflies of Kenya stock reared in the Federal Republic of Germany.     

Organotin complexes of pyridine-2-carbothioamide

Summary Complexes of pyridine-2-carbothioamide with diethyltin dichloride, dibenzyltin dichloride and phenyltin trichloride are described. In each case, the chelating agent is bound to the tin(IV) atom by the pyridine nitrogen and the carbothioamide sulphur, giving support to proposals that certain organotin compounds cause enzyme deactivation via the formation of tin-sulphur bonds.Acknowledgment. We thank the Tin Industry (Research and Development) Board, Kuala Lumpur, for financial support.     

Mantle compensation of active metamorphic core complexes at Woodlark rift in Papua New Guinea

In many highly extended rifts on the Earth, tectonic removal of the upper crust exhumes mid-crustal rocks, producing metamorphic core complexes. These structures allow the upper continental crust to accommodate tens of kilometres of extension, but it is not clear how the lower crust and underlying mantle respond. Also, despite removal of the upper crust, such core complexes remain both topographically high and in isostatic equilibrium. Because many core complexes in the western United States are underlain by a flat Moho discontinuity, it has been widely assumed that their elevation is supported by flow in the lower crust or by magmatic underplating. These processes should decouple upper-crust extension from that in the mantle. In contrast, here we present seismic observations of metamorphic core complexes of the western Woodlark rift that show the overall crust to be thinned beneath regions of greatest surface extension. These core complexes are actively being exhumed at a rate of 5-10 km Myr(-1), and the thinning of the underlying crust appears to be compensated by mantle rocks of anomalously low density, as indicated by low seismic velocities. We conclude that, at least in this case, the development of metamorphic core complexes and the accommodation of high extension is not purely a crustal phenomenon, but must involve mantle extension.