Reassessing the role of the honeybee (Apis mellifera) Dufour's gland in egg marking

Dufour's gland secretion may allow worker honeybees to discriminate between queen-laid and worker-laid eggs. To investigate this, we combined the chemical analysis of individually treated eggs with an egg removal bioassay. We partitioned queen Dufour's gland into hydrocarbon and ester fractions. The bioassay showed that worker-laid eggs treated with either whole gland extract, ester fraction or synthetic gland esters were removed more slowly than untreated worker-laid eggs. However, the effect only lasted up to 20 h. Worker-laid eggs treated with the hydrocarbon fraction were removed at the same rate as untreated eggs. The amount of ester which reduced the egg removal rate was far higher than that naturally found on queen-laid or worker-laid eggs, and at natural ester levels no effect was found. Our results indicate that esters or hydrocarbons probably do not function as the signal by which eggs can be discriminated.     

Adenylic-derived indices and reburying time as indicators of the effects of dredging-induced stress on the clam<Emphasis Type="Italic"> Spisula solida</Emphasis>

Little attention has been given to the behavioural and physiological effects of dredging on clams. The response of the clam Spisula solida under stress imposed by dredging activity is analysed in terms of reburial time and two acute indices: AEC (adenylic energetic charge) and ATP per milligram dry weight. Stress on undersized (<25 mm) S. solida, due to habitat disturbance by dredging itself and subsequent aerial exposure was measured with in situ studies during September 1999 at Vilamoura, a bivalve sandy ground, off the southern coast of Portugal. The study showed significant increases in reburial time and a decrease in adenylic-derived indices of stressed bivalves compared with in situ control bivalves monitored by SCUBA divers. It was concluded that the stress caused by dredging affects the behavioural and physiological responses of S. solida. Moreover, the reburial time is an easy and valuable indicator of stress levels in the studied clam.     

Aspects of the ecology and growth of an intertidal juvenile population of Concholepas concholepas (Mollusca: Gastropoda: Muricidae) at Las Cruces,Chile

The habitat, density and growth rate for an intertidal population of Concholepas concholepas (Bruguière, 1789) were studied at Las Cruces, Chile (Lat. 33°30′S; Long. 71°38′W) during 1977–1978. The growth rate (3.67 mm month^-1) was determined in a newly settled group, whose average length was 11.3 mm, and whose age was estimated at 3 months. The densities found ranged between 1.1 and 107.3 “locos” m^-2. Based on these results, the time of settlement of C. concholepas was calculated; capsule deposition, maximum maturity and recruitment reported by other authors for different localities are discussed.