Skibiel-Final Dissertation.Pdf
Total Page:16
File Type:pdf, Size:1020Kb
The evolution of milk composition and lactation strategy of the Columbian ground squirrel, Urocitellus columbianus by Amy L. Skibiel A dissertation submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Auburn, Alabama August 4, 2012 Keywords: lactation, life history, hibernation, cost of reproduction, reproductive performance, survival Copyright 2012 by Amy L. Skibiel Approved by Wendy Hood, Chair, Assistant Professor of Biological Sciences F. Stephen Dobson, Professor of Biological Sciences Mary Mendonça, Alumni Professor of Biological Sciences Mary Beth Voltura, Assistant Professor of Biological Sciences Abstract The evolution of parental care improved the efficiency of the reproductive process, allowing for the production of fewer offspring with a higher probability of survival. This adaptation is exemplified in the taxon named for their unique and efficient mechanism of nourishing young following parturition. Lactation and milk production is a key feature of the mammalian reproductive strategy contributing to maternal and offspring fitness. Because the quantity and quality of care provided is a balance between maternal cost and benefit, identifying factors contributing to inter and intra-specific variation in lactation effort as well as the costs and benefits involved can provide keen insight into the evolution of mammalian life history strategies. Herein, I determined factors influential in the evolution of milk composition and examine the causes, benefits and costs associated with lactation effort in the Columbian ground squirrel, Urocitellus columbianus. First, I examined factors contributing to the evolution of the diverse nutritional composition of milks observed across mammals using a phylogenetic comparative approach. The biome inhabited, length of the lactation period, and maternal diet were correlated with milk composition. Second, I described the composition of milk produced by Columbian ground squirrels. The concentration of most milk constituents changed over the course of lactation with most exhibiting a distinct peak around 19 days postpartum. Columbian ground squirrel milk was relatively low in lipid concentration but ii high in protein and calcium concentration and the proportion of energy from protein. Third, I assessed relationships between maternal characteristics and milk composition and impacts on offspring. Variation among females in milk fat, sugar, and protein concentration and energy density was not associated with differences among females in size or condition. Females giving birth around the median parturition date produced milk that was higher in fat concentration and energy than females giving birth at other times. Milk fat, energy, and sugar concentration had a positive effect on offspring survival over- winter. Finally, I examined the proximate and ultimate costs of lactation. Females raising augmented litters had greater rates of energy expenditure, indicating an energetic cost to lactation. Energy expenditure was not related to female survival over-winter or her fecundity the next breeding season, although pups of augmented litters were lighter at weaning, had slower growth rates, and a lower probability of survival over-winter. These results do not support the predictions associated with the cost of reproduction tradeoff. iii Acknowledgments I owe my advisor, Dr. Wendy Hood, a great deal of gratitude for her enduring patience and continual belief in me especially during the moments when I doubted myself. You are one of the most diligent and hard-working individuals I know and your perserverance, innovation, enthusiasm, and dedication to research is truly inspirational. You have far exceeded my expectations as a mentor, guiding me through the grant writing process, assisting with my field work, sharing insightful ideas and interpretation of results, troubleshooting in the lab (!!!), and helping me prepare for job interviews. I am immensily appreciative for everything you have taught me, for spending countless hours discussing thoughts and ideas, and for your constant encouragement. Although I'm leaving Auburn to embark on new adventures, I look forward to continuing to work with you in the future! Thank you to my committee members, Dr. Steve Dobson, Dr. Mary Mendonca, and Dr. Mary Beth Voltura, for your constructive input on this project from its inception to the final product. A special thanks to Dr. Steve Dobson for your additional contribution to all field aspects of my work. To my family, I sincerely appreciate your faith in me. Thank you for listening when I needed to vent, reminding me to breath during the stressful times, and celebrating with me on my accomplishments, no matter how trivial. I would especially like to thank my partner, Chris Hamilton, for your continual support, praise and encouragement and iv reminding me that I can achieve anything. I am so elated that you were able to share this experience with me, particularly because you can empathize with my passion for and dedication to the sciences! Thank you to all of my friends in Auburn who have made my experience here an enjoyable one and who have helped me maintain my sanity the past several years. To my friends back home, thank you so much for encouraging me to pursue my interests and career aspirations. I feel incredibly lucky to have such amazing and supportive people in my life. Thank you to my field assistants, Sarah Stude, Stephanie George, Matthew Ramirez, Midori Mitsutani, and Amanda Clayton, who contributed to the collection of field data for this project, and the many undergraduate laboratory assistants who helped with preparation of the laboratory assays, particularly Lauren Downing. CHN analyses for protein composition of milk were conducted by Dr. Michael Power and Caitlin Power at the Nutrition Laboratory of the Smithsonian Institution National Zoological Park. Dr. Paul Cobine provided access to and invaluable assistance with the ICP spectrometer and Dr. Mark Liles allowed use of his ultraviolet spectrometer. Thanks to Dr. Ted Garland, Jr. for access to and assistance with the regressionv2.m program and Kevin Middleton for his help with Mesquite. I am extremely grateful to have met and collaborated with several individuals on this project, including Dr. John Speakman, Teri Orr, and Lauren Downing. My labmates in the Hill and Hood laboratories provided invaluable feedback on all chapters of the dissertation. The University of Calgary Biogeoscience (BGS) Institute provided housing in the field at the R. B. Miller Field Station. I would like to especially thank Ed Johnson, the BGS Institute director, Kathreen Ruckstuhl, the BGS Institute associate director, and v Judy Buchanin-Mappin, the BGS Institute research services coordinator. Funding for my research was provided by the Auburn University College of Science and Mathematics (W. R. Hood), Sigma Xi Grants-in-Aid of Research (G2009151040 and G200810150150) awarded to A. L. Skibiel, an Auburn University Graduate Research Award (A. L. Skibiel), an American Society of Mammalogists Grant-in-Aid of Research (A. L. Skibiel), and by a U.S.A. National Science Foundation research grant awarded to F.S. Dobson (DEB-0089473). vi Table of Contents Abstract.........................................................................................................................................ii Acknowledgments........................................................................................................................iv List of Tables ...............................................................................................................................ix List of Figures............................................................................................................................... x Introduction................................................................................................................................... 1 Literature Cited................................................................................................................. 7 Chapter 1. The evolution of the nutrient composition of mammalian milks.............................. 12 Abstract........................................................................................................................... 12 Introduction..................................................................................................................... 14 Methods........................................................................................................................... 21 Results............................................................................................................................. 26 Discussion....................................................................................................................... 29 Appendix 1. Milk composition of mammals at midlactation ........................................ 49 Appendix 2. Natural history, life history, and ecology of mammals whose milk composition has been described...................................................................................... 60 Literature Cited............................................................................................................... 68 Chapter 2. Milk composition in a hibernating rodent; the Columbian ground squirrel, Urocitellus columbianus ................................................................................................. 87 Abstract..........................................................................................................................