Reproductive Biology of Ototylomys (Cricetidae)

Abstract

Reproductive biology of the Neotropical climbing-rat, Ototy- lomys, is described, based on the examination of 86 offspring of animals live- trapped from Campeche, Mexico. Animals were maintained in the Michigan State University Live Animal Colony. Vaginal smears were collected from Ototylomys kept in 14 hours of light and 10 hours of darkness. The average interval between comified cell periods was 8.8 ? 0.5 days. A postpartum estrous was observed for all littering females, as evidenced by the presence of sperm in vaginal smears taken within 24 hours after the discovery of new litters. Females mated as early as 29 days and males as early as 175 days. Gestation period was 52.8 ? 2.1 days. No statistical difference was found between the mean gestation lengths of lactating and nonlactating females. Both minimum and maximum extremes in gestation lengths were observed in lactating females. Embryos were first detected by palpation on day 14 of gestation. The fetal head was initially distinguishable at 28 days. Average litter size of 2.4 young consisted of 46 males and 40 females. The standard measurements, in millimeters, on day one were as follows: total length, 119.5 - 0.9; tail length, 47.1 - 0.8; hind foot, 16.4 ? 0.2; ear, 9.4 ? 0.2; weight, 10.2 ? 0.3 grams. The least variance over time was observed in the length of head and body. At birth, head and body length was 46.4 percent of adult body length. No statistical differences were found between males and females. For approximately 30 days after birth, the very precocial neonates adhere tenaciously to their mother's inguinal teats. The largest number of individuals initially responded to loud noises by day two and had opened their eyes by day six. Hearing preceded eye opening in all but four cases. Ototylomys reach 50 percent of adult body length by day two and 90 percent by 58 days of age. The reproductive biology of Ototylomys was judged to be primitive in form and best adapted for scansorial living. Early efforts to evaluate the possible evolutionary significance of reproduc- tive biology were made by Mossman (1953) and Keys (1958). They proposed that the internal mechanisms of implantation and subsequent development of placental membranes occurred under uniform internal conditions and with little influence from external environment. These characteristics would be more conservative than the usual morphological criteria in current use and therefore may be more evolutionarily significant. Within the cricetid genus, Peromyscus, Layne (1968) found that body size and environment were the most influential factors governing gestation length and postnatal development. To further elucidate evolutionary and reproductive relationships found in rodents, I have examined the reproductive biology of Ototylomnys. The re- sults are described herein and compared to the reproductive biology of other cricetid rodents as reported in the literature. Ototylomys belongs to an assemblage of Neotropical cricetine rodents of obscure ancestry. Ototylomys has been placed in the subfamily Neotominae