Physiology & Behavior, Vol. 23, pp. 75-78. Pergamon Press and Brain Research Publ., 1979. Printed in the U.S.A.
Responses of Spiny Mouse Weanlings to Conspecific Chemical f l i e S 1 RICHARD H. PORTER AND HELEN
M. D O A N E 2
John F. Kennedy Center for Research on Education and Human Development George Peabody College, Nashville TN 37203 R e c e i v e d 8 F e b r u a r y 1979 PORTER, R. H. AND H. M. DOANE. Responses o f spiny mouse weanlings to conspecific chemical cues. PHYSIOL.
BEHAV. 23(1) 75-78, 1979.--Twenty-five-day-old A. cahirinus pups (weanlings) were tested for their responses to chemical cues produced by various classes of conspecific agemates. In Experiment 1, both male and female pups preferred bedding soiled by weardings of either sex over clean bedding material. Subsequent experiments indicate that male but not female weanlings prefer chemical cues emanating from iittermates over comparable stimuli from unfamiliar agemates. Also, chemicals produced by agemates maintained on the same diet as the animals were preferred by weanlings of either sex over cues from unfamiliar-diet weanlings. At weaning, as for other periods of development, the individual's responsiveness to conspecific chemical cues is probably a function of age-specific environmental and social demands and the salience of various classes of conspecifics for ultimate reproductive success. Weanlings
V A R I O U S species of rodents produce chemical cues (pheromones) that are important in intraspecific communication. Although the role of such chemical cues in the mediation of adult social behavior (especially of an agonistic and sexual nature) and mother-infant interactions has been the subject of intensive research, only a few studies have focused upon chemical communication in animals of weaning age. Rat pups show a reduced attraction to maternal chemical cues beginning at 27 days of age (i.e. displaying no preferential responsiveness to such cues produced by nonlactating vs lactating females) . However, when tested for their responses to feeding sites soiled by nulliparous females as contrasted to unsoiled feeding sites, 35-day-old rats ate and explored more at the former . In the wild, Norway rats initiate prolonged movements from the nest area at approximately this same age (i.e. at 34 days) . From 1-20 days of age, spiny mouse pups (Acomys cahirinus), which are unique among the Muridae in their advanced state of sensory and motor development at birth, prefer chemical cues produced by a lactating female over such cues emanating from a non-lactating female [7,8]. By 25 days of life, however, this pattern is reversed so that pups then respond preferentially to chemical cues produced by a non-lactating female . Interestingly, recent observations of mother-infant interactions reveal that this latter age is the approximate time at which suckling shows a precipitous decline and mothers are most likely to adopt a posture that inhibits approaching offspring from suckling . Thus, A. cahirinus pups appear to be weaned at about the same age
that they cease to be selectively responsive to maternal chemical cues. Given the critical nature of the weaning period for subsequent space utilization, social interactions and reproductive potential , detailed investigation of intraspecific communication at this stage of development would seem warranted. Accordingly, in the series of experiments reported herein, sex-differences and the role of dietary factors, in the responsiveness of weanlingA, cahirinus pups to chemical cues produced by conspecific agemates were investigated. GENERAL PROCEDURE
Animals F o r each of the experiments reported below, appropriate animals were randomly selected from the offspring born into the laboratory breeding colony ofAcomys cahirinus. Prior to testing, all pups remained in their respective home cages which housed the mated pair (mother and father) along with their preweanling litter. Each animal was tested only once at 24--26 days of age; with no more than two pups from any one litter included in an experiment.
Testing Procedure Test trials were conducted in a glass terrarium measuring 30 × 58 x 30 cm high. Two galvanized metal inserts partitioned the terrarium into two 30x23 cm "stimulus choice" ends separated by a 30x 12 cm wide clean starting area. An 8 x 8
1The research project reported in this paper was supported by NICHD grant No. 00973.
2Now at the University of Minnesota at Duluth.
C o p y r i g h t © 1979 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/79/070075-04502.00/0
PORTER AND DOANE TABLE 1
OF MALE AND FEMALE WEANLINGS A G E M A T E S VS C L E A N B E D D I N G
Male Weanlings (N = 24)
Female Weanlings (N = 24)
Agemate Soiled Bedding
Agemate Soiled Bedding
Male stimulus animals
171.6 (SD = 39.4)
91.6 (SD = 31.4)
172.8 (SD = 51.0)
131.6 (SD = 37.8)
Female stimulus animals
168.5 (SD = 40.6)
103.9 (SD = 19.9)
177.6 (SD = 30.0)
99.7 (SD = 34.1)
F(1,22) = 89.61, p