Mechanics and Morphology of Silk Drawn from Anesthetized Spiders

 CO₂ and N₂ anesthetized Nephila spiders produced dragline silk with mechanical properties that differed from control silk as a function of time under anesthesia. Silk from CO₂ spiders had a significantly lower breaking strain and breaking energy, significantly higher initial modulus, and marginally lower breaking stress. At the onset of anesthesia the silk diameter became highly variable. During deep anesthesia silk either became thinner or retained cross-section but fibrillated. Received: 26 August 1999 / Accepted in revised form: 22 December 1999     

Landmark memories are more robust when acquired at the nest site than en route: experiments in desert ants

Foraging desert ants, Cataglyphis fortis, encounter different sequences of visual landmarks while navigating by path integration. This paper explores the question whether the storage of landmark information depends on the context in which the landmarks are learned during an ant's foraging journey. Two experimental set-ups were designed in which the ants experienced an artificial landmark panorama that was placed either around the nest entrance (nest marks) or along the vector route leading straight towards the feeder (route marks). The two training paradigms resulted in pronounced differences in the storage characteristics of the acquired landmark information: memory traces of nest marks were much more robust against extinction and/or suppression than those of route marks. In functional terms, this result is in accord with the observation that desert ants encounter new route marks during every foraging run but always pass the same landmarks when approaching the nest entrance.     

Inter and intra-population variation in shoaling and boldness in the zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>)

Population differences in anti-predator behaviour have been demonstrated in several species, although less is known about the genetic basis of these traits. To determine the extent of genetic differences in boldness (defined as exploration of a novel object) and shoaling within and between zebrafish (Danio rerio) populations, and to examine the genetic basis of shoaling behaviour in general, we carried out a study that involved laboratory-raised fish derived from four wild-caught populations. Controlling for differences in rearing environment, significant inter-population differences were found in boldness but not shoaling. A larger shoaling experiment was also performed using one of the populations as the basis of a North Carolina type II breeding design (174 fish in total) to estimate heritability of shoaling tendency. A narrow-sense heritability estimate of 0.40 was obtained, with no apparent dominance effects.