The Coolidge Effect in Northern Grasshopper Mice (Onychomys leucogaster)

Abstract

-The is a resumption of copulatory behavior in satiated males that occurs on replacement of the original mating partner with a novel female. Eighteen male northern grasshopper mice were studied in tests in which at the attainment of the satiety criterion either (a.) the original female was removed and reintroduced, (b.) the original female was replaced with a novel unmated female, or (c.) the original female was replaced with a novel mated female. Males were significantly more likely to resume copulation with the novel unmated females than with the original females. Results with the novel mated female were intermediate. has been proposed that species that are monogamous in the field should fail to display a effect. The present findings are incompatible with either this proposal or with the proposal that grasshopper mice are monogamous. Better field data are needed on Onychomys social organization. Although the males of many species are capable of achieving several ejaculations in a single episode of copulation, eventually all reach a point where copulations become so infrequent that the males can be said to be sexually satiated. If at this point the original female partner is replaced by a novel female, males of many species resume copulation. This has been referred to as the Coolidge effect (Wilson, Kuehn, and Beach, 1963) and evidence suggestive of such an has been found in species as diverse as cattle, sheep, and domestic cats (Almquist and Hale, 1960; Pepelko and Clegg, 1965; Whalen, 1963). Such a pattern would function to spread a male's genes among several females (Adler, 1979; Barash, 1979). Wilson et al. (1963) noted that some mammalian species are monogamous and proposed that It would be worthwhile to investigate whether in such species the male fails to exhibit a revival of sexual interest when offered a new mate (p. 643). Dewsbury (1971) studied old-field mice, Peromyscus polionotus, and found no evidence of a in that monogamous species. Gray and Dewsbury (1973) found no in prairie voles, Microtus ochrogaster, a species some authors have proposed to be monogamous (Getz, 1978; Thomas and Birney, 1979). Thomas and Birney (1979) wrote We suggest that the absence of a reliable may prove to be indicative of (p. 182). is generally believed that grasshopper mice of the genus Onychomys are monogamous in nature (Egoscue, 1960; Dewsbury and Jansen, 1972; Kleiman, 1977; Horner and Taylor, 1968; Ruffer, 1965). However, there have been no tests of the in these species. Monogamous mating patterns can be established definitively only in field studies. However, laboratory data on the can provide evidence suggestive of mating systems in the field and can help establish an empirical foundation so that the proposal linking monogamy to the absence of a can be evaluated properly. Northern grasshopper mice, Onychomys leucogaster, display a copulatory pattern characterized by a lock (mechanical tie between penis and vagina), THE SOUTHWESTERN NATURALIST 26(2):193-197 MAY 21, 1981 This content downloaded from 157.55.39.224 on Wed, 14 Dec 2016 05:03:07 UTC All use subject to http://about.jstor.org/terms 194 The Southwestern Naturalist vol. 26, no. 2 no intravaginal thrusting, prior intromissions not prerequisite to ejaculation, and multiple ejaculations (Ruffer, 1965; Lanier and Dewsbury, 1977). METHODS.-Eighteen male and 18 female Onychomys leucogaster, from the colony maintained at the University of Florida (see Lanier and Dewsbury, 1977), were used in this experiment. This colony was established in 1972 with the purchase of 15 males and 15 females from Ecodynamics Inc., Salt Lake City, Utah. The original stock for this population was trapped in Toole County, Utah (see Egoscue, 1960). The breeding program at the University of Florida has been conducted so as to minimize the inbreeding of close relatives. Males were housed in clear plastic cages measuring 48 by 27 by 13 cm, whereas females were housed in cages that were 29 by 19 by 13 cm. Cage floors were covered with wood shavings and Purina laboratory rodent chow and water were provided ad lib. A reversed 16L:8D photoperiod of fluorescent light (General Electric Lite White Model F40LW/RS/WM) was used with light going