Worker rank, reproductive status and cuticular hydrocarbon signature in the ant, Pachycondyla cf. inversa

Workers in de-queened colonies of the neotropical ant, Pachycondyla cf. inversa, form linear or near-linear dominance hierarchies by violent antennation and biting. In these rank orders, social status and ovarian activity are on average highly correlated. Whereas the presence of a fertile queen appears to be sufficient to prevent workers from laying eggs, fertile workers do not completely control reproduction by their nestmates, suggesting that workers are able to differentiate between an egg-laying queen and an egg-laying worker. Here we show that the composition of cuticular hydrocarbons of egg-laying workers is quantitatively and qualitatively different from that of non-laying workers and resembles the hydrocarbon blend of the queen but does not completely match it. Furthermore, using discriminant analysis, it was possible to distinguish workers with four different classes of ovarian development based only on their cuticular hydrocarbon profiles. Fertility-associated changes in cuticular hydrocarbons may play an important role in the behavioural regulation of reproduction in this ant.     

OBSERVATIONS ON PHYTOPLANKTON PRODUCTIVITY IN RELATION TO HYDROGRAPHY IN THE NORTHERN ADRIATIC

This work, carried out within the framework of the PRISMA II project, aims at evaluating the effects of the Po River flow on primary productivity, measured by C with in situ sample incubations. A total of four cruises was carried out in late winter and early summer (1996-1998) along transects from the coast offshore. In both seasons, the highest primary productivity was found in the most oligohaline stations. The effects of the Po River inputs were therefore clearly evident in the westernmost area, both in high productivity values and in the shape of productivity profiles. In late winter, extensive blooms of Skeletonema costatum and Pseudo-nitzschia delicatissima resulted in productivity values that were sometimes higher than in early summer. In early summer 1996, greatly reduced river flow clearly influenced productivity which was much lower than in 1997.