The Estrous Cycle of Two Species of Kangaroo Rats (Dipodomys microps and D. merriami)

Abstract

The estrous cycle of the kangaroo rats Dipodomys merriami and D. microps entails spontaneous ovulation and a spontaneous luteal phase. Corpora lutea are present throughout the cycle. The modal cycle length is 12 days in D. microps and 13 days in D. merriami, a significant difference. The duration of the cycle is unaffected by mating with a sterile male. Vulvar swelling and vaginal opening are conspicuous external indicants of estrus. The examination of vaginal cytology provides little information beyond that available from these overt signs. In both laboratory and field, the spontaneous activity of females in estrus is elevated severalfold compared to the anestrous state. Kangaroo rats (Dipodomys) are a genus of some 20 species endemic to arid and semiarid habitats of North America. Although kangaroo rats have been much studied by ecologists, their reproductive biology is not well known. Individual females may produce three successive litters in one season (e.g., D. spectabilis, Holdenried, 1957; D. merriami, Behrends, 1984) and probably sometimes more. In D. microps and D. merriami, gestation periods are 31 and 33 days, respectively, and most litters are of two or three pups (Daly et al., 1984). Several investigators have noted changes in vulvar swelling, vaginal opening, and vaginal cytology of unmated females

Mating strategies of a nocturnal, desert rodent (Dipodomys spectabilis)

“…Because vaginal estrus is a poor predictor of behavioral estrus (Wilson et al 1985), females with swelling vaginal areas were observed for several nights (as described later) until mating behavior was seen or a copulatory plug found. Information on 12 matings was obtained from trapping records alone.…”

An Age‐Structured Demographic Model for the Endangered Stephens’ Kangaroo Rat

“…Captured D. stephensi were marked with numbered eartags, weighed upon first capture during a monthly census, examined for reproductive condition, and released at the point of capture. Males and females were scored as reproductive if testes were fully scrotal or if there were indications of estrus (swollen or perforate vagina; Wilson et al 1985), lactation (elongated nipples from which milk could be expressed), or pregnancy (swollen nipples, high body mass, and/or palpable embryos).…”

“…The n u m b e r of possible litters is directly related to length of the breeding season. Assuming a m i n i m u m interval b e t w e e n successive litters of 45 days (30-day gestation and resumption of estrus t w o weeks postpartum;Wilson et al 1985;Randall 1991), adult females could rear at most three litters b e t w e e n January and July 1990, and first-year females could rear a litter only if Pr/ce & ~ Demo~aph¥ 0fD. stephensi 815…”

Female mobility and the mating system of the banner-tailed kangaroo rat (Dipodomys spectabilis)

“…Every 3^ days, we trapped at all mounds occupied by adults, allowing us both to apply thread spools to target animals and to monitor changes in female reproductive state. Swelling of the vulva indicates proestrus (Wilson et al 1985). Because swelling lasts several days with considerable individual variation (Randall 2007), our categorization of females as "proestrous" indicates they are within 1-5 days of mating.…”

“…Direct observations of mating patterns are limited because D. spectabilis spends all day and most of each night underground, and often mates there (Schroder 1979;Randall 1991). As in other Dipodomys species, the night of behavioral estrus is difficult to predict from visual indicators (swollen vulva), although males can discriminate between urine from estrous and anestrous females (Wilson et al 1985;Randall 1986Randall , 2007. Females may have several litters per breeding season but behavioral estrus is brief, lasting a night or less (Randall 1991).…”