THE EVOLUTIONARY SIGNIFICANCE OF CERTAIN BEHAVIORAL, PHYSIOLOGICAL, AND MORPHOLOGICAL ADAPTATIONS OF THE OLD-FIELD MOUSE, Peromyscus polionotus By MICHAEL HOWARD SMITH A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA June, 1966 ACKNOWLEDGMENTS During the period of this study, many recommendations and constructive criticisms were received from various people; to them, I express my appreciation. I wish to thank Dr. D. Jameson because it was his en- thusiasm that initially kindled my interest in zoology, and his encouragement and support that prompted me to enter graduate school. I would like to thank the members of my supervisory committee, Drs. E. G. F. Sauer, B. K. McNab, H. M. Wallbrunn, and B. N. Bunnell, for their patience, support, and suggestions; Dr. J. Layne served on the committee for a short time and con- tributed much to this work. I am especially indebted to my chairman, Dr. E. G. F. Sauer; without him, the completion of my work in the department would have been impossible. Many other people contributed in various ways to my work; A. Avenoso, D. Burnside, C. Collins, D. Crane, W. Criss, M. Glenn, G. Gourley, R. McFarlane, C. Trost-, J. Wyrick, P. Yingling, and my son, Michael W. Smith, assisted with the field work and/or cared for the laboratory animals from time to time. Paul Laessle, staff artist, supervised and helped in shaping the illustrations. Doctor and Mrs. W. Dawson, Mr. R. Archbold, Mr. and Mrs. R. Wyrick, and Mr. and Mrs. R. Lind kindly extended their hospitality to me and made many aspects of the field work more enjoyable and less expensive than they would have been otherwise. C. Colson, R. McFarlane, and G. Phanuel critically read parts of the manuscript. Doctors F. Nordlie and A. Laessle, W. W. Bow en , and R. McFarlane discussed certain parts of the paper at length with me. Mister Bowen also provided a copy of a manuscript on subspeciation in Peromyscus polionotus that he is preparing for publication. To all of the above, I express my appreciation. This investigation was supported in part by the American Museum of Natural History, Sigma Xi , the Department of Zoology at the University of Florida, a summer fellowship from the National Science Foundation, and a Public Health Service pre- doctoral fellowship from the National Institute of Mental Health (1-F1-MH-22, 122-01A1 ) . I am grateful for this financial aid. Finally my wife, Irma Smith, deserves special acknowledg- ment for the assistance she has given me. She helped with the field work, the writing, typing and illustrating of this report, care of the laboratory animals, and has provided moral and financial support whenever needed. I sincerely appreciate her many efforts. TABLE OF CONTENTS Page ACKNOWLEDGMENTS ii LIST OF TABLES viii LIST OF ILLUSTRATIONS xi INTRODUCTION . 1 Systematic relationships 1 ECOLOGICAL ASPECTS ... 5 Collecting Methods . 5 Range of the old-field mouse 5 Ocala National Forest 9 Habitat relationships 11 Distribution of burrows soil characteristics ... 13 Description of an average burrow ......... 15 Local variation of burrows 17 Geographical variation in the depth of the burrow. 18 Depth of the nest cavity and seasonal temperature fluctuations * 18 Ambient temperature and rainfall .... 22 Other species in burrows 26 SUBSPECIFIC CROSSES AND ASSORTATIVE MATING 32 Laboratory colony 32 Subspecific crosses 33 Inheritance of white cheeks 39 iv TABLE OF CONTENTS (Continued) Page Assortative matings 39 Calculation of inbreeding coefficient 45 REGULATION OF BODY TEMPERATURE 51 Torpidity in the field » « 52 Torpor and availability of food 53 Concentration of respiratory gases and torpor. 54 Significance of torpor 63 FACTORS AFFECTING REPRODUCTION 65 Results of field work. .............. 65 Correlation between production of young, rainfall, and ambient temperature •• 70 Effect of temperature on the male's reproductive system .......... 74 Minimum critical temperature .... 79 Breeding performance of Peromyscus polionotus subgriseus in the laboratory • 80 Onset of sexual activity 80 Post-partum estrus and gestation period 83 Synchronization of reproductive activity ..... 85 Bruce effect ..' • 88 Effect of litter sequence upon litter size .... 89 Sex ratio at birth 90 Seasonal variation in litter size 92 Effect of light intensity and day length 93 Effect of food, temperature, and thyroid injections upon production of young 95 Geographical variation in litter size. ...... 97 v TABLE OF CONTENTS (Continued) Page DISPERSAL AND PREDATION 99 Dispersal of the Ocala population 99 Predation in the Ocala National Forest 104 Geographical variation in selection pressure . 109 Possible predators 110 MORPHOLOGICAL VARIATIONS . Ill General trends in pelage color 114 Interpopulational variability of coat color in north central Florida . 116 Interpopulational variation of external dimensions 121 BEHAVIOR PATTERNS OF THE OLD-FIELD MOUSE IN THE WILD AND IN CAPTIVITY 132 Individual Behavior 132 Burrowing 132 Nest building 134 Hoarding of food 136 Escape behavior 138 Social Behavior. 139 Communication 139 Social units 141 Mating behavior 141 Parental care 151 Discriminatory behavior ...... 153 TABLE OF CONTENTS (Continued) Page GENERAL DISCUSSION 161 SUMMARY 168 LITERATURE CITED 171 BIOGRAPHICAL SKETCH 186 LIST OF TABLES Table Pa9 e l a Collecting locality and habitat 6 2. Relative abundance of mice as it relates to the physical and moisture retention data for some of the common soil types found in Florida. Soil data were taken from Stewart, et al. (1963) and Bryan (I960) ..... 12 3. Animals found in burrows occupied (0) or un- occupied (U) by old-field mice. The invertebrates in unoccupied burrows were not identified 27 4. List of food items commonly found in nest cavities . 30 5. List and number of live animals placed into cages with hungry old-field mice 31 6. Analysis of crosses within and between different subspecies of Peromyscus polionotus . The matings included sexually active adults born and reared in the laboratory unless otherwise noted. Wild animals were paired in the laboratory in the same combinations in which they were captured in the field. Only data from pairs that remained to- gether for at least three months during the fall, winter or spring are listed below 34 7. Detailed statistical comparisons of the results from the crosses presented in Table 6. Some of the comparisons are interdependent but "the associated increases in the P values were not enough to alter the significance of the Chi * square values at the level indicated ( .05 - and .01 = **) 36 8. The number of times females were observed in or out of their nest on the second, third, and fourth nights following the birth of a litter. All ob- servations were made with the aid of a red light within two hours after the overhead lights went off in the colony room. Chi square = 19.7 and P was less than .01 • 38 LIST OF TABLES (Continued) Table Page 9. Inheritance of white cheeks in Peromyscus polionotus . The expected values for the statistical analysis were calculated by assuming that the inheritance of the trait was due to a single gene with two alleles, 42 10. The frequence of mice with white or brown cheeks and the observed and expected number of paired mice with these phenotypes in the Ocala National Forest and at Archbold's Biological Station in Highlands County, Florida. Expected values were calculated from the observed phenotypic frequencies and Yate's correction for continuity was used in the Chi square analysis of the data for the popula- tion from Highlands County to compensate for the small sample size of some cells. 44 11. The number of times brown-cheeked females mated with brown-cheeked siblings, white-cheeked non- siblings, white-cheeked siblings and brown- cheeked non-siblings. The choice always involved either the first two possibilities or the later two and no combinations thereof. Expected values were calculated for the Chi square analysis by assuming the null hypothesis. They had to be adjusted for the choice involving the heterozygous white-cheeked sibling because a certain percentage of the litters sired by this animal would contain all brown-cheeked offspring, and thus, would be counted for the brown-cheeked non-sibling 46 12. Variations in the femals' reproductive character- istics. Pregnant or perforate females were con- sidered to be reproductively active 66 13. Monthly variation in reproductive characteristics of adult males 68 14. Breeding histories of five typical laboratory- reared females. The size of each litter is indicated in parentheses after the date of birth . 84 15. Effects of four different treatments upon the reproductive performance of laboratory-reared mice. The group injected with thyroxine had its own control group because this experiment was started after the others had been completed. 96 LIST OF TABLES (Continued) Table Page 16. Social units found in excavated burrows of Peromyscus polionotus subgriseus . 142 17. Mating data for laboratory-reared Peromyscus polionotus subgriseus 146 18. The nightly distribution of mice of Peromyscus polionotus and P_. gossypinus in a cage with four compartments 156 19. The nightly distribution of mice of the two sub- species, Peromyscus polionotus subgriseus and P. p_. phasma , in a cage with four compartments 157 20. The nightly distribution of mice in a cage with four compartments. The tests involved two species, Peromyscus polionotus and P_. gossypinus , or two subspecies, P_. p_. subgriseus and P_. p_. phasma 158 LIST OF ILLUSTRATIONS Page Figure mouse, 1. The approximate range of the old-field Peromyscus polionotus parts 2. Relative abundance of burrows on different of old sand dunes in the Ocala National Forest - . 14 mouse, 3. Lateral view of the burrow of the old-field Peromyscus polionotus 4. The depth of the bottom of the nest cavity at various localities. Mean values are given plus or minus the standard error.