The role of oxygen availability in the embryonation of Heterakis gallinarum eggs.

The importance of oxygen availability in the embryonation of the infective egg stages of the gastrointestinal nematode parasite Heterakis gallinarum was studied in the laboratory. Unembryonated H. gallinarum eggs were kept under either aerobic conditions by gassing with oxygen, or anaerobic conditions by gassing with the inert gas nitrogen, under a range of constant temperatures. Oxygenated eggs embryonated at a rate influenced by temperature. Conversely, eggs treated with nitrogen showed no embryonation although when these eggs were transferred from nitrogen to oxygen gas after 60 days of treatment, embryonation occurred. This demonstrated that oxygen is an essential requirement for H. gallinarum egg development, although undeveloped eggs remain viable, even after 60 days in low oxygen conditions. The effects of climate on the biology of free-living stages studied under constant laboratory conditions cannot be applied directly to the field where climatic factors exhibit daily cycles. The effect of fluctuating temperature on development was investigated by including an additional temperature group in which H. gallinarum eggs were kept under daily temperature cycles between 12 and 22°C. Cycles caused eggs to develop significantly earlier than those in the constant mean cycle temperature, 17°C, but significantly slower than those in constant 22°C suggesting that daily temperature cycles had an accelerating effect on H. gallinarum egg embryonation but did not accelerate to the higher temperature. These results suggest that daily fluctuations in temperature influence development of the free-living stages and so development cannot be accurately predicted on the basis of constant temperature culture.     

Restoring avian wing digits

The precise identification of the digits of the avian wing is of importance in evolutionary studies. If the digits are numbered two, three and four, this has been taken to suggest that birds are not descended directly from dinosaurs. If the digits are numbered one, two and three, dinosaur origins become more plausible. Studies of the development of the avian wing have failed to resolve this dilemma. However, in some instances, it is possible to deduce information about evolutionary morphologies by manipulating development experimentally. We grafted beads loaded with fibroblast growth factor 4 into the distal tip of chick wing buds at times when the apical ectodermal ridge is regressing. The consequence was that the cartilage structure conventionally labelled ''element 5'' increased dramatically in size and acquired a digit-like morphology in some instances. Corresponding changes in soft tissue morphology were also observed. We conclude that it may be possible to resolve the issue of avian digit homology by the induction of experimental atavisms of this kind.     

A protocol for micropropagation of Alpinia galanga

Emerging buds of rhizome of Alpinia galanga Willd produced shoots and roots simultaneously when cultured in MS medium supplemented with kinetin 3.0 mg l^-1. Each explanted shoot bud produced 8 shoots in average and roots simultaneously within 8 weeks. Shoot proliferation could be continued even after a year by transferring each divided shoot explant to the same medium. Regenerated plantlets could be sucessfully transferred to soil where they grew well within 10–12 weeks with 80% survivality. This revised version was published online in June 2006 with corrections to the Cover Date.