Memory and chemical communication in the orientation of two mass-recruiting ant species

Summary The relative contribution of visual and chemical components in the orientation ofLasius niger andIridomyrmex humilis (Argentine ant) workers during mass recruitment to newly discovered food sources is analyzed over short time intervals. While both species orient in response to the trail pheromone, a large number ofL. niger foragers rapidly switch to a more individual orientation, based on their memory of environmental cues.I. humilis workers, on the other hand, predominantly use collective chemical cues. The effect of the number of reinforcements on visual learning and its interference with chemical communication show that olfactory cues always prevail in the Argentine ant. InL. niger, the proportion of ants orienting to visual cues is independent of the trail concentration. Detailed observations of the trail-laying behavior of individually marked foragers show that nearly all theI. humilis workers initially lay a trail, whereas only half theL. niger foragers do so. This proportion decreases considerably with the number of trips performed byL. niger workers, while remaining constant for the Argentine ants. These results are interpreted with respect to the species' behavioral ecology.     

Note on the formulation of a stochastic model of superinfection

We incorporate a process of removal (e.g., death) directly into the basic stochastic model for superinfection and recovery in order to describe explicitly the dynamics of infection within an individual. Formulae are derived for the mean duration of infection and the probability of removal during a bout of infection. A common method of approximating this joint process with a differential equation results in overestimation of these two quantities.     

Effect of atropine sulfate on the phenomena of follicular growth induced by a total anterior pituitary gonadotropic preparation during the estrus cycle in the rat

The question whether atropine inhibits follicular growth in rats induced by Gonadormone Byla was tested. 52 rats of strain WI, and 48 WII rats about 20 gm heavier, were injected at 1700 in diestrous I with 2.5 mouse units of gonadotropin per 100 gm body weight and 28 of each group also with 70 mg atropine sulfate sc, then serial ovarian sections were prepared at 1700 of proestrus. Atropine reduced the mean number of follicles 400 mcm in diameter or above (p less than .02), but did not affect their size distribution. A 2nd series of 48 rats were injected at 1700 of diestrous II with 1.5 units of gonadotropin per 100 gm body weight and half the rats with atropine. Again, atropine reduced the number of developing follicles (p less than .05) without affecting their mean diameter or size distribution.     

Changes in estrogen receptors in the mediobasal hypothalamus mediate the facilitory effects exerted by the male's olfactory cues and progesterone on feminine behavior in the male rat

The purpose of this study was to determine whether facilitory effects exerted by olfactory cues on lordosis behavior in the male rat involved changes in estradiol receptors at the hypothalamic level. Male rats were orchidectomized as adults. They were given either 25 micrograms estradiol benzoate (EB) alone or 25 micrograms EB and 100 micrograms progesterone (P) sequentially and exposed or not to the odor of male urine. Some of them were tested for lordosis behavior at 8 h after P. The other ones were killed 4 h after P and used for estradiol (E2) and P receptor assay in mediobasal hypothalamus (MBH). Olfactory cues were shown to increase the number of E2 receptors in both the animals given EB or EB + P. Progesterone as such appeared to be capable of increasing the number and the rate of occupancy of E2 receptors. A population of constitutive and estrogen-inducible P receptors was detected in the MBH. Since only the animals given EB + P were shown to be sensible to the facilitory effects of male urine on lordosis behavior, it may be assumed that E2 and P on one hand and olfactory cues on the other exert cumulative effects at the level of the MBH and that both a high level and a high rate of occupancy of E2 receptors are necessary for the olfactory cues to facilitate the display of lordosis behavior in the male rat.