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F. H. BRONSON and D. CAROOM

Preputial glands of male rodents have long been suspected as sites of pheromone secretion on the basis of little or no experimental evidence (e.g. Noble & Collip, 1941; Spener, Mangold, Sansone & Hamilton, 1969). The present report documents a signalling function for the preputial gland of the male house mouse, i.e. the male's gland apparently secretes a substance which acts as an attractant for females.

Two sets of experiments were conducted, both using sexually experienced C57BL/6J females in random stages of their oestrous cycles. In the first set, a group of thirty-two females (6 to 8 months old) were tested for various odour preferences seven times in 5-min trials over an 8-week period. All females were individually housed and maintained between and during testing in the same room which contained no male mice. Test chambers utilized

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F. H. BRONSON and T. H. HAMILTON

Comparatively little is known about cyclic activity in the oviducts of mammals having relatively short oestrous cycles. For example, the literature is even in conflict on the basic question of what histological changes in the oviducal epithelium can be correlated with various stages of the oestrous cycle (see Brenner, 1969). As far as we know, neither the rat nor the mouse oviduct has been the subject of any detailed investigations using the traditional techniques of ovariectomy and steroid replacement. Furthermore, oviducal nucleic acids have not been extensively examined in any mammalian species. The results now reported document alterations in the concentrations of RNA and protein in the mouse oviduct during the oestrous cycle and, in addition, show the partial dependence of oviducal RNA metabolism on the circulating levels of ovarian hormones, particularly oestrogen. The concentration

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P. D. Heideman and F. H. Bronson

Summary. A population of cloud forest mice (Peromyscus nudipes) at latitude 10° N near Monteverde, Costa Rica, was sampled four times by live-trapping twice during the 7–8 month wet season and twice during the 4–5 month dry season in 1989 and 1990. Body weights were lower during the early part of the dry season in males and throughout the dry season in females than at other times. Testes and seminal vesicles were somewhat lighter early in the dry season, but epididymal spermatozoa were abundant in most males throughout the year. Adult females ovulated, mated and became pregnant in the wet and dry seasons, but young were produced only during the wet season. Most embryos failed to implant during the dry season, and the few that did complete implantation were reabsorbed before midpregnancy. Apparently, every year, the females in this population spend several months actively engaged in a behavioural and metabolically costly process that is doomed to be unsuccessful. This reproductive strategy is termed pseudoseasonal, because reproductive success is highly seasonal, but attempts to reproduce are nonseasonal. Implantation failures similar to those seen in the wild were induced in the laboratory using mild restriction of food or water. Field evidence points to food restriction as the more important cause of pregnancy losses in the wild. Exposure to the gradually changing daylengths typical of Costa Rica had no effect on the production of young by adults, and maintenance on light cycles of 8 h light:16 h dark, 11 h light:13 h dark, 13 h light:11 h dark and 16 h light:8 h dark had no effect on the reproductive development of young animals of either sex.

Keywords: seasonal breeding; reproduction; nutrition; photoperiod; Peromyscus; tropical

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F. H. BRONSON and W. K. WHITTEN

Summary.

Two methods for the assay of a pheromone produced by male mice were compared. Using these methods it was shown that the pheromone was present in urine from males of two inbred strains and from androgenized, spayed females, but not in urine from castrate males. It was present in urine collected directly from the bladder free from any accessory gland secretion.

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F. S. vom Saal, Susan Pryor and F. H. Bronson

Summary. Female mice that had developed in utero between 2 male (2M females) or 2 female (0M females) fetuses were housed individually at 32 days of age in the presence of a male. The 0M females had a significantly shorter cycle. When the females were housed in groups of 5 in the presence of a male, cycle length in OM females was significantly longer than that of 2M females for the first cycle recorded, but this relationship reversed completely by the third and fourth cycles. These results are compatible with a hypothesis that former intrauterine proximity to male fetuses affects the intrinsic timing of the oestrous cycle and the capacity to emit oestrus-suppressing cues and/or the sensitivity to such cues.

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J. A. MARUNIAK, CLAUDE DESJARDINS and F. H. BRONSON

Summary.

Urine marking was examined in house mice, deermice, gerbils and hamsters. The frequency of urine deposition varied with the species, and a correlation is suggested between the propensity of males to mark in this fashion and prepuce length and morphology. We postulate an adaptational advantage for a long penis sheath and for a particular configuration of the prepuce; i.e. to act as a wick for the deposition of urinary pheromones.

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F. H. BRONSON, B. E. ELEFTHERIOU and E. I. GARICK

Summary.

Inseminated deermice (Peromyscus maniculatus bairdii) were exposed for 24 hr to strange male or female (1) P. m. bairdii; (2) P. m. gracilis (an inter-fertile subspecies); or (3) C57BL/10J house mice (members of a different family of rodents). Implantation was significantly affected except in the case of exposure to bairdii or C57BL/10J females. Exposure to male bairdii and male gracilis caused the highest incidence of blocked pregnancies. Differences between the sexes in producing implantation failures in inseminated bairdii were marked in bairdii and negligible in gracilis and C57BL/10J mice.

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P. D. Heideman, P. Deoraj and F. H. Bronson

Summary. Anoura geoffroyi (Chiroptera, Phyllostomidae, Glossophaginae), Geoffroy's hairy-legged long-tongued bat, were collected from September 1984 to August 1985, and these bats were found to breed seasonally in the wild on Trinidad, West Indies, at 10°N latitude. Histological examination of these samples indicated that females became pregnant in July or August, and young were born in late November or early December. The testes and epididymides were small from September to mid-April, increased threefold in weight between mid-April and late May, reached a peak weight in July, and decreased in weight in August. Spermatogenesis occurred throughout the testes of males captured from May to August. In 1990, the timing of parturition in females that gave birth in the laboratory to young conceived in the wild was similar to the timing in the field in 1984–1985. Groups of 10–13 males were subjected in the laboratory to (i) a gradually changing, civil twilight photoperiod that mimicked the natural cycle of annual change at 10°N latitude, (ii) the same gradually changing cycle of photoperiod accelerated to a six-month period, or (iii) a constant photoperiod (light 12:54 h: dark 11:06 h). These treatments began in mid-December, four months before the initiation of testicular recrudescence in the wild. In all three groups, testicular volume remained low until April, and then increased two- to threefold between late April and late June, rising to a peak in July, as occurred in the wild. Thus photoperiodic cues are not required for testicular recrudescence during the six months before peak testis size, nor is the timing of recrudescence sensitive to the accelerated pattern of photoperiodic change provided here. It is possible that other photoperiod treatments might affect reproductive timing in this species, or that other portions of the reproductive cycle are sensitive to photoperiod.

Keywords: photoperiod; tropical, seasonal breeding; bat; Phyllostomidae

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Emilie F. Rissman, R. J. Nelson, J. L. Blank and F. H. Bronson

Summary. Musk shrews (Suncus murinus) were maintained for 8 weeks in long (16 h light:8 h darkness) or short (8 h light:16 h darkness) daylengths. Males housed in short daylengths had significantly lighter androgen-dependent sex accessory organs than did males kept in long daylengths. This same trend was noted in male sexual behaviour. However, the weights of the testes and epididymides and sperm numbers did not differ. Females housed in short daylengths had significantly lighter cervices and were less likely to demonstrate sex behaviour than animals kept in under long daylengths. Ovarian and uterine weights did not differ. These results suggest that the ability to respond to photoperiod can exist in tropical mammals, even if it is not used as a cue to time seasonal breeding.