Influence of prostaglandins and of cyclic nucleotides on the metabolism of 25-hydroxyvitamin D3 in primary chick kidney cell culture

Prostaglandins (PG) are likely to be involved in a number of regulatory mechanisms in the kidney, which may be mediated by cyclic nucleotides. The present study describes the effects of prostaglandins and cyclic nucleotides on the hydroxylases of 25-hydroxycholecalciferol (25(OH)D₃) in a primary chick kidney cell culture. 3–30 nM PG E₂ produced significant increases in the 25(OH)D₃-1-hydroxylase associated with decreases in the 25(OH)D₃-24-hydroxylase at 6 hours but not at 1 hour. PG F_2α, in concentrations between 0.3 nM and 3 μM affected the hydroxylases in a similar manner. A significant increase of 1-hydroxylase activity was observed with 0.1 mM cyclic AMP (cAMP) or dibutyryl cyclic AMP (dbcAMP) in 6 hours, but again no effect on either hydroxylase was observed when the incubation time was reduced to 1 hour. These results suggest that PG E₂ and PG F_2α might be involved in the regulation of renal 25(OH)D₃ metabolism, and that the effects on the 25(OH)D₃-hydroxylases might be mediated by cAMP.     

Socially cued anticipatory adjustment of female signalling effort in a moth

Juvenile population density has profound effects on subsequent adult development, morphology and reproductive investment. Yet, little is known about how the juvenile social environment affects adult investment into chemical sexual signalling. Male gumleaf skeletonizer moths, Uraba lugens, facultatively increase investment into antennae (pheromone receiving structures) when reared at low juvenile population densities, but whether there is comparable adjustment by females into pheromone investment is not known. We investigate how juvenile population density influences the ‘calling'' (pheromone-releasing) behaviour of females and the attractiveness of their pheromones. Female U. lugens adjust their calling behaviour in response to socio-sexual cues: adult females reared in high juvenile population densities called earlier and for longer than those from low juvenile densities. Juvenile density also affected female pheromonal attractiveness: Y-maze olfactometer assays revealed that males prefer pheromones produced by females reared at high juvenile densities. This strategic investment in calling behaviour by females, based on juvenile cues that anticipate the future socio-sexual environment, likely reflects a response to avoid mating failure through competition with neighbouring signallers.     

Flocking and predator surveillance in house sparrows: Test of an hypothesis

The argument that individuals benefit from foraging in flocks through spending less time in predator surveillance and hence more time foraging and feeding, has been formalized in terms of a mathermatical relationship (Pulliam 1973). We have tested the model using house sparrows (Passer domesticus), and our results support its prediction of an inverse relationship between the time spent in predator surveillance and the flock size. The data did not fit the model exactly, and we attribute this to an unrealistic assumption.