John J. Christian

Fighting, Maturity, and Population Density in Microtus pennsylvanicus

A study of a population of Microtus pennsylvanicus was conducted in Wayne County, Pennsylvania, using snap-traps. Densities probably were between 100 and 200 per acre in 1968 and half that in 1969. Inhibition of growth and maturation were seen in both years but was greater in 1968. Fighting between males, as indicated by the prevalence and severity of wounds, was severe in 1968 but reduced the following year. Male voles, with rare exception, were not attacked or did not fight until testicular weight was more than 900 milligrams and seminal vesicular weight greater than 100 milligrams. Thus voles in which maturation was inhibited showed essentially no evidence of having been attacked or having fought. Changes in rate of maturation with density may explain many of the observed differences in the tolerance of young males by old male voles.

Reproductive Activity of Individual Females in Three Experimental Freely Growing Populations of House Mice (Mus Musculus)

Three populations of house mice (Mus musculus) were established by placing two sibling females with one sibling male into each of three cages. the proportion of the total number of females that successfully reproduced was limited and decreased as the density of the populations increased. Although only 35.9 per cent of the surviving females produced litters, 74.7 per cent of the surviving females showed evidence of having been pregnant prior to sacrifice. As density increased the intervals between litters born to individual females increased. Factors implicated in affecting reproduction of individuals in this experiment were rank of the females in the social hierarchy, fetal resorption, inhibition of estrus, and sudden increases in infant mortality.

Relationship of Activity and Aggression to Density in Two Confined Populations of House Mice (Mus Musculus)

Two separate populations of house mice ( Mus musculus ) were established by placing two sibling females with one sibling male into each of two cages. Food and water were provided ad libidum and nest cans and materials were made available. Daily checks were made for births and deaths. Observations of behavior were made during 10-min intervals between 8:00 am and 8:00 pm at various times of the day. The number of mice active and number of attacks and aggressive chases were recorded. From the data gathered, an activity rate and an aggression rate were calculated. In both populations activity rates showed fluctuations with a decreasing trend with increasing density in one population. Aggression rates in both populations fluctuated cyclically with a decreasing trend as density increased in one of the populations. The relationship of aggression to infant mortality is discussed. In view of the data gathered from the populations it was concluded that aggression did not directly affect infant mortality in either of the populations.

Annual Cycle of Spermatogenesis and Testis Morphology in Woodchucks

Testes of woodchucks in central Pennsylvania were examined histologically to determine effects of season and age on morphology and spermatogenic activity. Spermatogenic activity and size of the seminiferous tubules were greatest in adults at the time of emergence from hibernation in February and least during autumn. Maturation depletion and a decline in mean testes weight were evident prior to the period of reproductive activity in March. Mean testes weight declined less rapidly than did tubule size and spermatogenic activity, apparently due to an increase in interstitial tissue as tubule size dimished. Mature spermatozoa were present in testes of some yearlings at the time of emergence from hibernation. However, most males probably mature sexually at 2 years of age. During each month through May, some yearlings tended to mature sexually more than others, as evidenced by active progression and degeneration of spermatogenesis in known-age animals.

Effect of Preputialectomy on Fighting Behavior in Mice

Summary Indices of aggressive behavior were measured in paired male house mice which previously had been preputialectomized or sham-operated. Total fights and attacking time were increased in pairs comprised of a preputialectomized and a sham-operated animal as compared to that observed in sham-operated pairs. Preputialectomized males also showed a tendency to initiate first attacks of a paired encounter, but social rank was independent of presence or absence of preputial glands in an individual. Results indicate that the preputial glands influence fighting behavior, possibly through olfactory pathways.

The effect of ACTH, group caging, and adrenalectomy in Peromyscus leucopus with emphasis on suppression of reproductive function.

Summary Sham-adrenalectomized and adrenalectomized maturing white-footed mice (Peromyscus leucopus noveboracensis) of both sexes were injected subcutaneously with 4 units of ACTH daily for 10 days. Mice were adrenalectomized when 26–28 days old and each mouse was maintained thereafter on subcutaneous injections of 50 μg of cortisol acetate/day. In a second experiment, the effects of 5 units of ACTH daily for 10 days and of group caging (6–8 mice/cage) for 10 days were determined in intact mature P. leucopus 80–100 days old at the start of treatment. ACTH inhibited reproductive function in intact mature and maturing P. leucopus of both sexes, and in adrenalectomized maturing mice of both sexes maintained on cortisol. Group caging inhibited reproductive function in both sexes. In contrast to its effects on house mice, grouping reduced adrenal weight in both sexes. Grouping and ACTH inhibit reproductive function in male P. leucopus to a much greater extent than in house mice. ACTH produced no renal lesions in P. leucopus.

Effects of ACTH on Voles (Microtus pennsylvanicus) Related to Reproductive Function and Renal Disease

Summary Reproductive function in Microtus pennsylvanicus appears to be quite sensitive to inhibition by ACTH while renal glomeruli of voles are remarkably resistant to ACTH. The effects of ACTH on Microtus reproductive function are similar to what has been found in female house mice and both sexes of Peromyscus (4). ACTH had no apparent effect on the renal glomeruli of Microtus.

Adrenal Weight in Prairie Deer Mice (Peromyscus Maniculatus Bairdii) and White-Footed Mice (Peromyscus Leucopus Noveboracensis)

Adrenal weights were obtained for 662 Peromyscus leucopus noveboracensis and 281 wild Peromyscus maniculatus bairdii . The relationship of adrenal weight to body weight was explored using a number of parameters for size of the animals. The best linear fit for adrenal weight for both species was on body weight ,73, although this was only slightly better than for body weight 67. From these relationships it appears that adrenal weight is directly related to surface area and by inference to total metabolism and oxygen consumption. However, adrenal weights of P. m. bairdii are absolutely and relatively much less than those of P. leucopus and the rate of increase in adrenal weight with increasing body weight is much greater in leucopus . It is inferred that these differences reflect basic physiological and probably behavioral differences between these two species. There was no evidence of an increase in adrenal weight in females at maturity, thus raising questions concerning corticoid binding in these animals. Similarly, there was no suggestion of a rise (or fall) in the adrenal weight at maturity in males. Finally, it was suggested that in many instances adrenal weight provides a rapid and certain means for differentiating between P. leucopus and P. m. bairdii .

ACTH-Induced Renal Glomerular Disease in Intact, Adrenalectomized and Castrate Male Mice.

Summary In 3 experiments of balanced design the ability of ACTH to produce renal glomerular disease in intact and adrenalectomized male mice was determined. The effects of castration on ACTH-induced glomerulnephritis were studied and the disease in males and females compared. Adrenalectomized mice were given 35 or 50 μg of hydrocortisone-acetate daily. Four units of ACTH daily for 10 days was used. ACTH-induced glomerular lesions exhibit marked increases in intercapillary mesangial material and deposition of intensely PAS+ material in the mesangial matrix and axial capillaries, and peripheralization and ballooning of capillaries. Four I.U. of ACTH daily induced the severest glomerular disease in non-adrenalectomized males, less in adrenalectomized mice and was unaffected by the presence or absence of the testes. ACTH affected the glomeruli of intact and adrenalectomized male and female mice similarly with respect to control values. Two preparations of ACTH, one assaying 60-80 and the other 110 I.U. per mg, produced similar renal disease. It was concluded that ACTH affected both sexes equally; that its effect was greatest in intact and significantly less in adrenalectomized mice.

Incidence and Effects of Botfly Parasitism in the Eastern Chipmunk 1

Comparison of bot-infested and bot-free chipmunks collected during 1966–1969 revealed no significant differences in rate of infestation among sex-age classes. Splenomegaly and thymic involution were associated with bot infestation, and adrenal weights were greater in bot-infested adult females. Parasitized animals of all sex-age classes tended to be larger than non-parasitized individuals, and reproductive organs were heavier in infested adults of both sexes. Evidence of bot-induced mortality was not found, but results indicate the possibility of differential loss of bot-infested animals from the population.