of Females by Male Guinea Pigs Olfactory Recognition of Reproductive State and Gender of Females by Male Guinea Pigs ABSTRACT Mammals have two major ways of communication: vocal and olfactory. Olfactory cues convey information for an individual’s gender, reproductive state, and dominance status. In guinea pigs, it was demonstrated that mothers recognize their offspring, and vice versa, through urine smell. More over, male guinea pigs also displayed recognition of dominance by perineal gland secretion. We studied male recognition of sex (male versus female) and breeding state of females (estrous from non-estrous) in captive guinea pigs. We used secretions from the perineal gland to test male recognition of sex and breeding state. Male guinea pigs were randomly selected to trials and were offered two glass balls covered with perineal secretions; the two glass balls had either 1) male and female secretions, or 2) estrous and non-estrous female secretions. Behaviors were recorded, along with time spent investigating the various scents. Our results showed that males can discriminate sex, and that they also recognize breeding state. Male guinea pigs showed more excited behavior and spent more time on the female (versus male) and estrous (versus non-estrous) samples (P < 0.05). RESULTS Experiment I—Gender Males spent significantly more time on female perineal secretion samples (40.9 + 21.7sd) than male samples (16.4 + 11.4sd) (t = 5.06, df = 15, P = 0.0001). Males tended to investigate the female odor more, act with more excited, and several males exhibited specific behavior. Experiment II—Reproductive State Male guinea pigs spent more time and displayed excited behavior on samples obtained from estrous females (35.1 + 18.8sd) compared to time spent on non-estrous female samples (21.3 + 11.9sd) (t = 3.69, df = 14, P = 0.0024). Only a few males had specific behaviors toward the estrous samples. MATERIALS AND METHODS Setting: Experiments took place indoors, at the Department of Animal Behavior, University of Bielefeld. Trials were carried out in 1 x 1.5 m plastic box, equipped with video camera inside. Design: Perineal gland secretions were deposited on two glass balls. Every tested male had a choice to approach and investigate either glass ball. Tested animals were observed for 10 minutes. Time spent (seconds) investigating each sample (within 1 cm) was recorded and compared using paired t-tests. Experiment 1: Males (n = 16) were given the choice of male and female perineal secretions. Experiment 2: Males (n = 15) were given the choice of estrous non-estrous female perineal secretions. Estrous females were determined by daily checking the vaginal membrane opening, which is fully opened only during estrous. GENDER Female Male Mean 40.9 16.4 Median 45.5 15.5 Standard Deviation 21.7 11.4 Minimum--Maximum 8--70 0--44 N 16 INTRODUCTION Domestic guinea pigs (Cavia porcellus) form long-lasting relationships between individual males and females within a group that has a polygynous mating system. For animals living in groups, olfactory cues are important for discrimination and recognition of conspecifics. Communication by scent marking is also an important component of territorial behavior in small mammals. Scent markers can function as a danger or warning signal, and communicates age, sex, or dominance of an individual. In guinea-pigs, multiple sources of odors exist: urine, feces, and excretions from various glands such as the supracaudal, perineal, or nipple. Olfactory identification is mostly used in male-female and mother-pup recognition or establishing male-male dominance. Research has shown that lactating females can discriminate related from unrelated pups, and pups can recognize their mother by olfactory cues using urine scent. When it comes to reproductive state recognition, reproductive status has been demonstrated to influence olfactory preferences. Male rats (Rattus norvegicus) preferred odors of receptive females to those of non-receptive females, and sexually experienced males prefer urine samples of female conspecifics, regardless of whether the donors are in estrous or not, to urine obtained from male conspecifics. ESTROUS STATE Estrous Non-Estrous Mean 35.1 21.3 Median 34.0 17.0 Standard Deviation 18.8 11.9 Minimum—Maximum 0--67 7--45 N 15 CONCLUSIONS Male guinea pigs can recognize gender of conspecifics through scent of perineal gland secretions. Male guinea pigs can recognize estrous state of females through scent of perineal gland secretions.