J. Mary Taylor

Growth and Reproductive Behavior in the Southern Grasshopper Mouse

Various aspects of reproductive behavior and of both maternal and paternal behavior are described for Onychomys torridus longicaudus. Data are presented on early development of young and are utilized as a background for indicating the age at which mice can enter the population as reproductive contributors. Although laboratory-raised females tend to be slow in attaining sexual maturity, O. t. longicaudus gains reproductive status in the field at an age comparable to that of some of its more prolific peromyscan relatives.

Gonadal Activity in the Marsupial Mouse, Antechinus Bellus, with Notes on Other Species of the Genus (Marsupialia: Dasyuridae)

The fragments of information gathered to date on the genus Ante-chinus in Australia all give supporting evidence that from the tropics to southernmost Australia these small dasyurids are winter breeders. Males as well as females are sexually quiescent except during the breeding season. Within the genus females are equipped with from six (A. bellus, A. swainsonii swainsonii) to 12 (A. flavipes ) teats. A. bellus appears to shed more ova than it can later accommodate as young in the pouch area and this is probably the case in other species of Antechinus, for in A. stuartii, at least, wild-caught females, which presumably experience some prenatal loss, usually bear a full complement of young.

Reproductive Mechanisms of the Female Southern Grasshopper Mouse, Onychomys Torridus Longicaudus

The reproductive pattern of the female southern grasshopper mouse (Onychomys torridas longicaudus Merriam) is presented in terms of gestation period, litter size, ovarian histology, and time of sexual maturation, and is discussed with reference to mechanisms that support the maintenance of a relatively low population density in this species. The major potential contributors of offspring are young mature females a year old or less; their opportunity to contribute to the population appears to be modulated by the time within the span of the breeding season in which they are born.

Nature of Estrus and Ovulation in Microtus townsendii (Bachman)

Townsends vole, Microtus townsendii , begins successive estrous periods at intervals of 2 to 8 days in about 70% of the vaginal smear sequences. Although, with minor exception, the vaginal smears are of estrus or diestrus, and proestrus and metestrus are uncommon, a regular sequence of stages takes place in the vaginal epithelium. Among females that are undergoing estrous periods, regeneration of this lining occurs in a minimum of 2 days and, among anestrous females, following administration of Pregnant Mares Serum, the lining regenerates to the stage of estrus in 53 h. We present evidence that M. townsendii should be added to the list of induced ovulators and speculate on advantages of this type of mechanism to the social system of this vole.

Native Rattus, Land Bridges, and the Australian Region

A phylogenetic link between the Rattus fauna of Australia and New Guinea is indicated in two different lineages of this genus. Rattus sordidus is an Australian species and primarily is a grassland and swamp inhabitant that gained access to New Guinea and now is established there as two endemic subspecies. Rattus leucopus is a New Guinean species of the lowland tropical rain forests that also occupies comparable habitat in the Cape York Peninsula of northern Australia, where it occurs as two subspecies. Previous suggestions, that there is an evolutionary connection between R. leucopus and progenitor stock of R. fuscipes coractus of Australia, and with that of certain New Guinean species, including R. praetor , now are corroborated with craniometric evidence of phenetic similarity. The remaining species in Australia appear to have shared no immediate common ancestry with those of New Guinea and, among all Australian species, only R. leucopus appears to have colonized Australia from New Guinea. Our phylogenetic interpretation is supported by both phenetic analyses and by patterns of geographic distribution.

Reproductive strategies of Pseudomys nanus and Pseudomys delicatulus (Rodentia : Muridae) from the monsoonal tropics of the Northern Territory

In the highly punctuated monsoonal climate of the Alligator Rivers area of Australia, Pseudomys nanus and Pseudomys delicatulus breed in the latter part of the monsoon season and can extend their breeding activity into spring. P. nanus may reproduce virtually year-round, presumably when environmental conditions are favourable. In both species, the predominance of young non-breeding adults and juveniles in the spring signals a new infusion of animals into the population and a large population turnover at the expense of older members. The young survivors of the seasonal transition from extremely dry to intensely wet conditions then become the primary contributors to the next major breeding episode. This study is based on histological evidence from the reproductive systems of both sexes.

Seasonal reproductive dynamics in a tropical Australian rodent, Rattus tunneyi tunneyi (Rodentia : Muridae)

Histological and gross assessments and measurements of gonads and related organs are used to analyse the pattern of reproduction in the native murid rodent, Rattus tunneyi tunneyi. This is the first study to confirm by histological analysis the breeding dynamics of this rat in all seasons of the year. It was found to breed between the latter part of the wet season and the middle of the dry period, at which time seasonal suppression of breeding occurred in both adults and maturing individuals.

Breeding in wild populations of the Australian rock rats, Zyzomys argurus and Z. woodwardi

The murid rodents Zyzomys argurus and Z. woodwardi , found in rocky habitats in monsoonal tropical Australia, breed year round. Females are polyestrous, have small litters, and experience postpartum estrus. The histology of the ovary and testis is typical of that of most other murid rodents. External testicular dimensions provide an index to the developmental state of the testis and to the age category of the individual. The breeding pattern contrasts with that of other murids in the region, which have more clearly defined breeding efforts, mainly in the first half of the dry season. These two species are the only congeners of Z. pedunculatus , currently regarded an endangered species and for which no reproductive information exists.