Cholinesterase activity in white-winged doves exposed to methyl parathion.

Captive white-winged doves (Zenaida asiatica) were exposed to various levels of methyl parathion (MP) in drinking water to determine effects on brain and blood cholinesterase (ChE) activity. We conducted two experiments to test the influence of MP dose (the amount of MP actually ingested), MP concentration (the amount of MP per unit water), and exposure duration (number of days exposed to a constant MP concentration) on ChE activity. Plasma ChE activity was not useful in predicting brain ChE activity. Methyl parathion concentration had a greater influence on plasma and brain ChE activity levels than dose or time of exposure. These results contribute to the evaluation of irrigation water as a route of exposure of wildlife to pesticides.

Genetic mediation of infanticide and parental behavior in male and female domestic and wild stock house mice.

Infanticide is a reproductive strategy found in many mammals, especially rodents. The proportion of male and female house mice (Mus domesticus) that are either infanticidal or noninfanticidal is strain specific and varies widely from stock to stock. Male house mice also show strain-specific variation in the behavioral mechanisms that inhibit infanticidal individuals from killing their own offspring. The adult offspring generated from reciprocally crossed CF-1 and Wild stock house mice were tested for their behavior toward newborn pups. In male CF-1 x Wild hybrids, the proportion of infanticidal and noninfanticidal males matched with their maternal phenotype, whereas female CF-1 x Wild hybrids exhibited a proportion of behaviors typical of the CF-1 phenotype, regardless of their mother's genotype. Our results suggest three conclusions: first, that infanticide is a highly labile and heritable behavior in both sexes; second, that there is a sex difference in the genetic substrate that regulates the inheritance of infanticidal behavior; and third, that selection pressures in male mice may operate independently on the mechanisms that promote spontaneous infanticidal behavior versus the mechanisms that inhibit infanticide.

Time and sex in the male mouse: temporal regulation of infanticide and parental behavior.

Infanticide is a violent but successful reproductive strategy found in many mammals, particularly rodents. In male house mice (Mus domesticus and M. musculus), the act of ejaculation provides a reliable neural signal for timing the birth of their offspring. However, a unique chronobiological aspect of this phenomenon is the extraordinary temporal latency that can occur between the stimulus (coital ejaculation) and its adaptive neural response (male mice cease killing pups and behave parentally toward them instead). Specifically, the inhibition of infanticide is often time delayed for many days after a male ejaculates, but virtually always occurs before or around the time his own sired offspring would be born 18-20 days later. Furthermore, infanticide spontaneously reemerges 50-60 days after mating. In CF-1 stock male mice this entire behavioral sequence is synchronized with the female's reproductive cycle, and occurs even in the total absence of social cues or changes in pituitary or gonadal hormones after mating. When entrained and mated at 22 h (light:dark 11:11) or 27 h (light:dark 13.5:13.5) T-cycles, photoperiodic cues appeared to synchronize this dramatic shift in behavior, because a sudden transition from pup killing to parenting was matched with the number of light/dark cycles experienced after ejaculation rather than the amount of real time experienced, suggesting a circadian timing link. Housing in constant light accelerated the postmating transition to parenting, whereas constant dark significantly delayed the transition to parenting, but still occurred by 3 weeks after mating. Most males tend to oscillate between infanticide and parental behavior for several days before locking in to constant parenting, regardless of lighting conditions. Variation in the time delay between ejaculation and the inhibition of infanticide was consistent within young individuals (< 10 months of age), but in older males (> 18 months of age) the time interval between ejaculation and parenting was significantly prolonged and attenuated. Another unique aspect of this phenomenon is that variation among individuals in their timing and response to light cues is correlated with phenotypic variation in sex steroid exposure during late fetal development. So far, no simple physiological explanation can account for the neural mechanism triggered by ejaculation that coordinates these time-delayed behavioral changes toward pups.

Individual variation in the neural timing of infanticide and parental behavior in male house mice.

In male house mice (Mus domesticus and M. musculus), the act of coital ejaculation provides a fail-safe neural signal for timing the birth of their offspring. A unique aspect of this phenomenon is the extraordinary latency that can occur between the stimulus (ejaculation) and its adaptive neural response (male mice cease killing pups and behave parentally toward them). Thus the inhibition of infanticide is routinely time-delayed for many days after mating. In the absence of mating, cohabitation with a female will not inhibit infanticide in CF-1 stock males (M. domesticus), whereas the birth of pups in the male's home cage will inhibit infanticide. But with regard to the ejaculatory phenomenon, which also includes the spontaneous reemergence of infanticide 50-60 days after mating, this entire behavioral cycle toward pups can occur in the total absence of regular time cues from a light/dark cycle following ejaculation. However, exposure to photoperiodic (L:D 12:12) or constant light (LL) accelerated the transition time from infanticide to parenting after ejaculation, while in constant dark (DD), the transition time to parenting was significantly prolonged. The time interval between ejaculation and the inhibition of infanticide, which varied among individuals first mated at 6 months of age, was repeatable when the same males were remated at 9 months of age; however, when males were again mated at 18 months of age, the time interval between ejaculation and parenting was dramatically prolonged. In general, coital ejaculation triggers a neural timing system that cannot be explained by any presently known physiological mechanism. Our results do suggest, however, that the neural timing variation observed among individuals is influenced by sex steroid exposure during late fetal development.

Fetal, hormonal and experiential factors influencing the mating-induced regulation of infanticide in male house mice.

When a male house mouse encounters a neonate he either attempts to kill it or he does not harm it. An unusual aspect of his response is that adaptive, time-dependent changes in behavior toward pups result from a unique stimulus-response system triggered specifically by ejaculation. In virgin male CF-1 mice, about 50% of all males are spontaneously infanticidal when they encounter a pup while the other 50% are typically "parental." The stimulus of ejaculation causes virtually all males to kill pups; however, by the time offspring are born three weeks after mating, infanticide is inhibited and almost all males now behave parentally toward pups. Our experiments examine fetal, experiential, and hormonal factors influencing the changes in infanticidal and parental behavior that occur in male mice as a result of mating. Males who developed in utero between two female fetuses, and were thus exposed to relatively low testosterone concentrations during fetal development, were significantly more likely to exhibit infanticide--both before and after mating--than were males who developed between two male fetuses. Concurrent exposure to testosterone appears required in order for naive males to exhibit infanticide and for spontaneously parental males to become infanticidal after ejaculation. In contrast, neither testosterone nor pituitary hormones appeared responsible for the timed inhibition of infanticide occurring by three weeks after mating, since castrated and hypophysectomized males showed a response pattern similar to intact males. The mating-induced inhibition phenomenon appears to be a neurally timed and mediated response that operates independently from pituitary hormone secretions or changes in gonadal hormones resulting from mating.

Effects of water deprivation on urine marking and aggression in male house mice.

This study assessed the effects of water deprivation on male mouse urine marking and aggressive behaviors and endurance. In Experiment 1, the size of marks and frequency of marking were examined in 3 groups given 3 different weights of potato/day as their source of water. Males receiving the least water, 1.5 g potato/day, marked at significantly lower rates than males receiving 3 g potato/day or 6 g potato/day (p less than 0.01). The size of urine marks of males was judged by a panel to be unaffected by water deprivation. In Experiment 2, water-deprived males were not as aggressive as normal males and when paired with them were almost always subordinated. Experiment 3 tested the hypothesis that water-deprived males lost fights simply because they were weaker than normal males. When water-deprived and normal males were tested to determine the maximum length of time they could swim, no differences were found (p greater than 0.05). We conclude that water deprivation can directly affect the urine marking and aggressive behaviors of male mice. Such changes may be of adaptive importance during times of drought.

Behavioral and physiological responses of female house mice to foraging variation.

Peripubertal female house mice were required to work for their food at either 23 degrees C or 9 degrees C. We used a special caging system in which animals had to emerge from a thermally-buffered burrow and run a programmable number of running wheel revolutions to obtain a pellet of food. Of concern here were the behavioral and physiological adjustments necessary to accommodate growth and reproductive development when faced with the need to forage for different lengths of time at different temperatures. When female house mice are confronted with poor foraging at cool temperatures they allot their highest priorities to maintaining energy balance; body growth is next, and reproductive development and nonforaging activity have the lowest priorities. Our results also demonstrate that the time spent foraging while exposed to low ambient temperature is critical for this species. This relationship probably determines whether or not house mice will breed continuously or seasonally in a particular habitat.

Foraging effort, food intake, fat deposition and puberty in female mice.

A novel caging system was used to study the interrelationships between foraging effort, food intake, growth and sexual maturation of peripubertal female mice. Females housed in these cages were forced to work (forage) at various intensities in order to obtain food pellets. It is argued that this is a biologically more meaningful approach to understanding the energetics of sexual development than the traditional approach of simple underfeeding. Female mice exhibited a cascade of developmental adjustments and deficits when challenged to forage harder for less food. The functions most sensitive to increased foraging effort were sexual development and growth in body length; growth in body weight was intermediate and fat deposition was least sensitive of all. The relative insensitivity of fat deposition to higher foraging costs suggests a strategy for survival during the postweaning dispersal movements of the wild ancestors of the laboratory mouse. Finally, regression analyses suggested that heavier females who had less than average body fat and higher than average food intake achieved their pubertal ovulation most rapidly.