Norman C. Negus

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 .

Energy Acquisition and Allocation in Male Collared Lemmings (Dicrostonyx groenlandicus): Effects of Photoperiod, Temperature, and Diet Quality

This study examined the effects of photoperiod (long photoperiod [LD, 20L:4D] and short photoperiod [SD, 8L:16D]), temperature (cold [C, 5° C] and warm [W, 18° C]), and diet quality (high-quality diet [HQ, 18% fiber] and low-quality diet [LQ, 49% fiber]) on growth, energy allocation, food intake, digestive efciency, and gut size in male collared lemmings (Dicrostonyx groenlandicus). Lemmings exposed to SD at weaning showed an increase in adult body mass relative to animals from the LD regimens and allocated twofold more energy to growth. Exposure to C increased adult body mass under LD but not SD. Adult body mass was reduced in lemmings fed the LQ diet relative to lemmings consuming the HQ diet. Lemmings exposed to SD tended to consume less food and showed a reduction in digestive efciency relative to lemmings exposed to LD even though gut size was relatively and absolutely larger under SD conditions. Lemmings acclimated to 5° C showed an increase in food intake and digestive efficiency relative to lemmings acclimated to 18° C The ability to increase digestive efficiency while increasing food intake at 5° C may have been due to the observed increases in the size of the small intestine, cecum, and large intestine. Similarly, the size of the gastrointestinal tract was larger in lemmings fed the LQ diet than in lemmings consuming the HQ diet. Use of fiber accounted for 32% of metabolizable energy (ME) in animals fed the LQ, but only 4% of the ME in those fed the HQ.

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.

Pelage Stages in the Cottontail Rabbit

A number of criteria have been employed to determine the age of cottontail rabbits. These include weight measurements, total length measurements, condition of the hymen in females, size of male genitalia, and ossification of epiphyseal cartilage in the bones of the forefeet. Having undertaken a study of reproduction in the cottontail rabbit, Sylvilagus floridanus mearnsi , in Ohio in 1952, I was faced with the problem of accurately aging rabbits in the field. The above methods had the disadvantage of either being impractical for field use or of not being useful in accurately aging young rabbits late in the breeding season. This study was made possible through financial assistance from the Ohio Cooperative Wildlife Research Unit and a grant from the Wildlife Management Institute. For cooperation and assistance during the study I am greatly indebted to many of the faculty and graduate students in zoology at Ohio State University, and to personnel of the Ohio Division of Wildlife, whose names are too numerous to mention here. In particular I should like to acknowledge the invaluable advice and criticism afforded me throughout the study by Dr. Eugene H. Dustman, Leader of the Research Unit. A portion of these data was presented at the 16th Midwest Wildlife Conference. The pelage stages of cottontails have not been adequately described. Nelson (1909) recognized three distinct pelage stages apparently common to all North American hares and rabbits. These were designated as juvenal, postjuvenal and adult pelage. He described Sylvilagus as a genus having only one annual molt. He did recognize that species in the genus Lepus and subgenus Brachylagus experienced two molts annually. Dalke et al. (1942) concluded that adult cottontails experienced a continual molt over a nine-month period, from March to November. Three constituents of the dorsal pelage of cottontail rabbits have been described …