Numerous laboratory studies with at least 12 species of rodents have reported that exposure of females to strange males results in pregnancy disruption or infanticide. The proximate causes and ultimate benefits of these behaviors have been proposed from an evolutionary perspective. To determine if exposure to strange males or females caused pregnancy disruption and (or) infanticide in a resident gray-tailed vole (Microtus canicaudus) population, pregnancy rate and juvenile recruitment were monitored in populations of 12 female and 12 male voles following introduction of unfamiliar adults. These experiments were conducted in 12 0.2 ha enclosures using three treatments and a control. Every 10 days 12 males, six males, or six females were removed and replaced in the three treatments, respectively, or the populations were left unmanipulated in the control (3 replicates/treatment). The time to first parturition, time between parturitions, number of juveniles recruited/parturition, and percent of births followed by lactation did not vary among the controls and three treatments. The only observable effects of treatment were a slight non-significant delay in time to first birth in the 12-male treatment and a slightly significant difference in the number of pregnancies per female. These results do not support previous laboratory studies indicating that exposure to strangers causes pregnancy disruption and (or) infanticide at high rates. Therefore, in field conditions, little evidence was found indicating that female gray-tailed voles' reproductive fitness declines after exposure to strangers. I propose that results from laboratory studies on behavioral aspects of mammals should be validated with field data prior to being extrapolated to natural populations and applied to evolutionary paradigms. / Graduation date: 1997

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Rhabdomys pumilio, in the Eastern Cape of South Africa, does not use short day length as an inhibitory cue for reproductive activity, and, despite previous records indicating that these mice are strictly seasonal in their reproduction, litters have been found during the winters of some years,both in the Eastern Cape and in the Western Cape. This led me to believe that the reproductive activity of Rhabdomys pumilio is more opportunistic and that the cue or cues used to control reproduction are less predictable and, or more variable than the photoperiod cue used by many seasonally reproducing rodents. Two experiments were conducted, investigating the influence of low ambient temperature (15⁰C)and reduced food availability on the reproductive activity of both male and female four striped field mice. Mice were maintained in one of four conditions (food restricted at 15⁰C, food restricted at 26⁰C, ad lib. food at 15⁰C, and ad lib. food at 26⁰C) for 4 (males) and 8 weeks (females)(photoperiod 12L:12D, humidity 40%). Results indicated that the males reduced their reproductive activity slightly when exposed to either low temperature or low food availability and that maximum inhibition of reproduction occurred when mice were exposed to both low temperature and low food availability. However, female reproductive activity was inhibited when exposed to low food availability, irrespective of the temperature. Both sexes of mice showed varying abilities to resist fat loss and, in the males, the size of the fat store had a significant effect on reproduction. This varying ability to resist fat loss could be related to levels of activity and in the females (where activity was quantified), high activity scores were significantly associated with reproductive inhibition. These results support the hypothesis that reproduction in Rhabdomys pumilio is opportunistic and controlled by the availability of energy. I propose that the females will be more sensitive to reproductive inhibition due to their far greater post-fertilization responsibilities, where the reproductive activity of the females is rapidly inhibited by a reduction in food availability, while the males are less readily inhibited by low food availability or low temperature, unless the change in the controlling factors is severe enough, or prolonged, at which stage their reproductive activity will cease. The significance of opportunistic reproduction in the seasonal but unpredictable climate of the study area is discussed.

This study was initiated in an attempt toadd the four-striped field mouse (Rhabdomys pumilio) to the small group of mammals that are used to study and develop assisted reproductive technologies. To accomplish this, a complete knowledge of both the male and female gametes was necessary, as well as a repeatable and successful IVF protocol. The gametes of the field mouse, both the falciformspermand the mature oocytes, were shown to be similar in several respects to those of many other rodent species. The induction of both the capacitated state and the acrosome reaction in the sperm were readily achieved. The success of retrieving mature oocytes was very low, with the rare occurrence of polar bodies within ovulated oocytes. The difficulties with oocytes was either related to the lack of a regular oestrous cycle, or to the hormonal regime used to induce superovulation. Although several protocols were used to accomplish superovulation in this species, it was seldom achieved. In in vitro fertilization trials, sperm were found to attach to both the cumulus oophorus and the zona pellucida of the oocytes. However, fertilization was never accomplished. This failure to achieve fertilization was probably related to the immaturity of the oocytes. Without further studies on Rhabdomys pumilio and further attempts at accomplishing in vitro fertilization, it would seem that this species would not easily be introduced as an animalmodelfor assisted reproduction.

This study was undertaken primarily to examine the skeletal and muscular anatomy of a small species of field mouse, Microtus oregoni serpens Merriam, which inhabits the Puget Sound area of British Columbia and Washington. This species is largely subterranean in its habits and in an attempt to discern the degree of specialization for its habitat comparison was made between serpens and Microtus townsendi townsendi, (Backman) and Microtus longicauda vellerosa (Allen) species which burrow to a limited degree only. A detailed comparison of the external features, skeletal and muscular anatomy of the three species was made and a juvenile specimen of Microtus richardsoni richardsoni, (De Kay) was used for some comparisons. Certain parts of Microtus oregoni serpens were found to be strongly modified in a direction which seems to better adapt the animal to its subterranean mode of life. The external features which are of adaptive significance are the soft plush-like pelage, the short tail and the arrangement of the vibrissae the longest ones being furthest from the snout rather than scattered. The eyes are only about one-half the size of those of the larger species and associated with them is an interesting modification of the orbicularis oculi muscle whereby it is strongly developed doubtless as an aid in preventing dirt from entering the eyes. Microtus oregoni serpens does not have conspicuously enlarged or elongated fore-feet but among the modifications for digging which do occur are the shortening of the limbs and the inclusion of a larger part of them within the body skin. Almost the entire musculature of the anterior segment of the body is more strongly developed in serpens including the muscles of the shoulder, chest, and fore-limbs and to some extent the masticatory musculature and the musculature of the spinal column. The muscles attached to the pectoral girdle show the most marked modifications they are almost universally better-developed in serpens than in townsendi or longicauda. Correlated with a greater development of the pectoralis muscles is the development of a heel on the manubrium sterni and the sternebras in serpens, providing a larger area for muscle attachments. Microtus oregoni serpens seems to represent one of the earliest stages of adaptive specialization of a mammal for subterranean life externally approaching the condition found in specialized burrowers such as the mole but having no radical skeletal modifications. / Science, Faculty of / Zoology, Department of / Graduate

A number of studies on small mammals have shewn that changes in the frequency of alleles at polymorphic loci are correlated with population fluctuations. To determine whether this association between demography and genetics is causal, I altered gene frequencies in two field populations of M. townsendi Using starch gel electrophoresis, I detected a leucine aminopeptidase (LAP) polymorphism in M. townsendi. The fast allele, LAP-F, was present in a control population at a frequency of about .35 from July 1971 to July 1973. By removing homozygous SS voles from one experimental population I maintained an LAP-F frequency of about .75. Removal of FF homozygotes from a second population resulted in an LAP-F frequency of about .25. I monitored demographic variables of the populations while the selection was being applied. The populations went through increasing and peak phases and then declined sharply during the spring of 1973. There were indications that different genotypes had an advantage in survival and reproduction during different phases of population density. The selection that maintained the polymorphism on the control area could be correlated with population density. However, the overall fitness of each experimental population was not affected by its genotypic composition at this locus. / Science, Faculty of / Zoology, Department of / Graduate

The population dynamics of Microtus townsendii in a linear habitat were monitored weekly for one year (June, 1971-August, 1972). Demographic characteristics such as location on study area, sex, weight (age), reproductive condition, and survival were recorded weekly. An Intensive study of early Juvenile survival was also undertaken. The population was observed to decline in the spring of 1972 from peak densities the previous summer and early spring. The decline did not appear to result from decreased reproductive effort or dispersal, but could be explained solely on the basis of mortality. Several observations were made which did not follow the usual demographic trends in microtine population biology. Extremely high densities with small home ranges for individuals were found on the linear study area as compared with areas of continuous habitat. This population became sexually mature at much lower body weights than other populations of Microtus townsendii in the area and average body weights were lower, although growth rates were comparable. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Seasonal differences in odor preference and social behavior existed among adult meadow voles. During the breeding season, a female preferred its own odor and the odor of males to the odor of another females. Males preferred the odor of females to the odor of other males. Paired encounters between breeding females were more agonistic than encounters between males or encounters between males and females. During the nonbreeding season, a female preferred the the odor of another female to the odor of males. Males did not display an odor preference for any conspecifics. Paired encounters between males were more agonistic than encounters between males and females or encounters between females. Encounters between nonbreeding females contained few agonistic acts. Seasonal differences also existed in the interactions between adults and juveniles. During the early breeding season, adult males were more agonistic than adult females toward juvenile males. During the late breeding season, adult females were more agonistic than adult males toward juvenile males. Encounters between an adult female and a juvenile female in the late breeding season contained few agonistic acts, indicating that overwintering groups are female-biased, and contain juvenile females. Juveniles did not display a shift in odor preferences. They preferred the odor of opposite-sex adults to the odor of same-sex adults, regardless of season. Familiarity, through association during rearing, reduced agonistic behavior between parents and young, and between siblings. Paired encounters between close-kin that were not familiar were agonistic, and similar to encounters between unfamiliar, and unrelated conspecifics. Conspecifics were more agonistic toward closely related males than females. Voles also preferred the odor of a familiar nestmate, independently of genetic relatedness. Familiarity decreased the number of agonistic behaviors between adult females, but increased the number of agonistic behaviors between adult males. Familiarity had no effect on the number of agonistic behaviors between a male and a female. / 2031-01-01

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