Aelita J. Pinter

Reproductive responses of Microtus montanus to plants and plant extracts in the diet.

Breeding experiments with Microtus montanus indicate that small dietary supplements of either sprouted wheat or acetone-ether extracts of sprouted wheat elicited improved reproductive performance. The improvement resulted primarily in more frequent postpartum matings and lower rates of litter loss. Spinach extract, fed to 4-week-old female Microtus , stimulated an increase in uterine weight and in number of developing follicles in the ovaries. Sprouted wheat, fed to immature females, stimulated immediate onset of estrus, as well as an increase in uterine and adrenal weights. It is suggested that hormone-like substances in plants may influence reproduction in natural populations of Microtus montanus .

Litter Sizes of Microtus Montanus in the Laboratory

Consecutive litter sizes of Microtus montanus are reported on the basis of 314 litters produced by 43 females in the laboratory. Irrespective of the age (subadult or adult) of females at mating, mean litter sizes increase from the first through the fifth litter. Then a decreasing trend ensues. Mean litter size of first litters in females that start breeding as subadults is 3.6, for those that start as adults—4.2. Mean litter size of fifth litters for subadults is 4.9, for adults 5.8. These differences between mean litter sizes of subadults and adults are statistically significant, indicating that in Microtus montanus litter size is affected by the age of the female at the onset of her reproductive activity. This observation on litter sizes is further supported by embryo counts collected from subadult and adult females in natural populations. The laboratory and field data are discussed in terms of their implications at the population level.

Reproduction and Growth for Two Species of Grasshopper Mice (Onychomys) in the Laboratory

Growth and reproduction were studied in laboratory colonies of the southern grasshopper mouse, Onychomys torridus torridus, and of the northern grasshopper mouse, Onychomys leucogaster articeps. Litters were born in all months of the year. Reproductive quiescence occurred from late summer to early winter in O. torridus, and from late fall to early winter in O. leucogaster. Reproduction in females of O. leucogaster articeps extended from 4 to 19 months of age; in males, from 4 to 24 months. One male continued breeding until he was 4½ years old. Litter size (based on 153 litters) ranged from one to six. the gestation period was 26 to 37 days. O . torridus torridus males and females started breeding at approximately 9 weeks. Females generally ceased breeding at 24 and males at 29 months of age. Litter sizes (based on 213 litters) ranged from one to five. the gestation period was 26 to 35 days. Growth rates in 220 southern and northern grasshopper mice of both sexes were studied from 2 to 18 weeks of age. All animals grew most rapidly during their first 7 to 8 weeks of life. Significant sexual dimorphism in body weight (but not in total length or tail length) was observed in the postpuberal period in both species. Body weight and tail length (but not total length) differed significantly between the two species starting at 2 weeks of age. a correlation was suggested between the onset of sexual maturity and the beginning of a plateau in growth rate.

The Flea, Megabothris abantis: An Invertebrate Host of Hepatozoon sp. and a Likely Definitive Host in Hepatozoon Infections of the Montane Vole, Microtus montanus

In searching for an invertebrate host for Hepatozoon sp. infecting the montane vole (Microtus montanus), we collected fleas, ticks, and mites from live-trapped voles and searched squash preparations for Hepatozoon oocysts. From 1989 through 1996, we identified six species of fleas in Grand Teton National Park: Megabothris abantis, Megabothris asio megacolpus, Aetheca wagneri, Peromyscopsylla selenis, Peromyscopsylla. hesperomys, and Hystrichopsylla dippiei dippiei. We found Hepatozoon oocysts only in M. abantis; we found no oocysts in mites or ticks. We conclude that M. abantis is an invertebrate host of Hepatozoon sp. and is likely to be the definitive host for the Hepatozoon spp. of M. montanus.

Intestinal Parasites of Small Mammals from Grand Teton National Park

A study of the prevalence and identity of Giardia spp. in small mammals of Grand Teton National Park was undertaken. All 90 montane voles examined were positive for Giardia, as were 4 pocket gophers, 1 water shrew, 4 water voles, and 2 meadow voles. How and why these findings contrast with the findings of others are discussed.

Hybridization between Two Species of Grasshopper Mice (Onychomys) in the Laboratory

Interspecific reciprocal hybridization was achieved in the laboratory between the northern grasshopper mouse, Onychomys leucogaster articeps , and the southern grasshopper mouse, Onychomys torridus torridus . The hybrids were mated to O. torridus and the backcross (B1) offspring were then mated to each other. The body weight, total and tail lengths were measured for all hybrids and backcross offspring between 2 and 18 weeks of age and compared to O. leucogaster and O. torridus of the same ages. Hybrids were significantly lighter than O. leucogaster and heavier than O. torridus . With the exception of two individuals they also had significantly longer tails than O. leucogaster , but were indistinguishable from O. torridus on the basis of this character. The B1 and B2 progenies were indistinguishable from each other as well as from O. torridus . However, they differed significantly from O. leucogaster in body weight and tail length. At intervals between 2 and 18 weeks of age, B2 individuals also had significandy lower body weight and total length, but greater tail length, than did hybrids. Offspring from the B2 × B2 cross differed significandy from O. leucogaster in body weight, but were indistinguishable from the B1 progenies. Between 2 and 18 weeks of age the B2 × B2 progenies differed only periodically from O. torridus , from the hybrids, and from the B2 offspring. One B1 male contrasted markedly with his littermates in that he closely resembled O. leucogaster in body weight and exceeded in total length any other grasshopper mouse in this laboratory. The apparent lack of interspecific hybridization between sympatric populations of Onychomys is discussed here on the basis of possible geographical, anatomical, physiological, and behavioral barriers. Hybrids from natural populations may have escaped recognition. As the present data show, such hybrids or backcross offspring might be indistinguishable from the two species of grasshopper mice.