Gray opossum

Various aspects of chemical communication have recently been studied and reported for one South American didelphid, the gray shorttailed opossum (Monodelphis domestica), hereafter referred to as the gray opossum. Scent-marking behavior was described and conspecific responses to olfactory cues quantified in a recent study (Fadem and Cole, 1985). 

CHARACTERISTICS OF SCENT MARKING BEHAVIOR IN MARSUPIALS AND MONOTREMES Scent Marking in Gray Opossums... 

Sex and age relationships to scent-marking in gray opossums. Male gray opossums marked significantly more frequently than females (P < 0.005). Males marked with head, flank and chest, while diestrous females marked only with head and flank. Gray opossums tended to place... 

Fig. 1. Mean number of scent-marks of all types made over 30 min test period by gray opossums of different ages (Fadem and Cole, 1985) ... 

Functional significance of scent-marking in gray opossums. 

Fig. 2. The suprasternal scent gland in a male gray opossum (a). A section through this gland (b). (Fadem and Schwartz, 1985.)...

Physical examination of 40 adult male and 40 adult female gray opossums aged 30-122 weeks, and 25 juvenile males and 15 juvenile females aged 10-15 weeks revealed that all of the adult males and three juvenile males ages 13, 14 and 15 weeks of age possessed a suprasternal gland. 

Chest-marking in the koala occurred primarily upon introduction to an unfamiliar tree and declined thereafter. Females rarely chest-marked (only one chest mark was seen in over 20 15-min trials), and highest levels of chest-marking behavior were seen in males 5-10 years old males 1-2 years old marked less frequently (Fig. 5). This is probably related to the fact that puberty occurs at between 1 and 3 years of age and the sternal gland first appears at about 1 year of age in this species (Thompson, personal communication). Thus, age, sex, and time-related aspects of scent-marking in the koala were remarkably similar to those seen in the gray opossum (c.f.. Fig. 1). 

Social aspects of scent-marking in gray opossums. As previously noted, little is known about the natural social behavior of gray opossums. In a laboratory study of sexual behavior in this species, males placed into cages recently occupied by females sniffed and then scent-marked areas of the cage using the chest, flank, and head (Trupin and Fadem, 1982). 

Recent studies also indicate that the odor of males alters the estrous cycle of female gray opossums (Fadem and Rayve, 1985 Fadem, 1985). 

THE EFFECTS OF OLFACTORY COMMUNICATION ON FEMALE REPRODUCTIVE PHYSIOLOGY IN GRAY OPOSSUMS... 

Estrous synchrony in the gray opossum. Each symbol represents the first day of a period of estrus (Fadem and Ra3rve, 1985). 

Fig, 7. The temporal pattern of births by female gray opossums following pairing with males on day zero. Each symbol represents one litter (Fadem, 1985). 

Estrus, ovulation and mating were expected to occur in a random pattern over the 32 days ("ideal" estrous cycle length) following the familiarization period. Since the gestation period is approximately 15 days in gray opossums, and there was a two day familiarization period, births were expected to occur uniformly over the 17-49 days following pairing, A chi-square test for uniform occurrence of births between days 17 and 49 was therefore conducted. 

The results of this experiment indicated that a factor associated with males altered the expected occurrence of estrus in female gray opossums. To obtain information on the nature of this factor, the temporal pattern of the appearance of vaginal estrus following sensory exposure to males without actual mating stimulation was then examined. 

The temporal pattern of the appearance of vaginal estrua in female gray opossums prior to and following the introduction of males to the experimental group. Each bar represents one period of estrus (Fadem, 1985). 

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