Laura Smale - US grants

Dr. Holekamp and her colleagues are continuing their field study of behavioral development in the spotted hyena. Spotted hyenas live in complex, primate-like societies, called "clans," with 5 to 100 members. Whereas female hyenas remain in their natal clans for life, all young males eventually emigrate. Each hyena clan is structured by a rigid, linear dominance hierarchy, or "pecking order." Spotted hyenas differ from most other mammals in that females are socially dominant to males among adults. Coalitions in which one animal joins an aggressor against a third individual occur frequently and may function importantly in the development and maintenance of rank relations in hyena societies. This phase of the research has three goals: (1) to document the development, causes, and consequences of coalitionary behavior; (2) to determine why males emigrate from their natal clans, how they become integrated into their new social groups, and how dispersal influences their social rank; (3) to elucidate the mating system in the study population. The 80 hyenas being studied comprise one large clan in the Masai Mara National Reserve, Kenya. The age, social history, and kin relations of each clan member are known from previous study. The researchers are using radio tracking, behavioral observation, and molecular-genetic analysis of paternity. The research will help elucidate (1) the causes and consequences of mammalian dispersal behavior, (2) the development and maintenance of social dominance, and (3) the social biology of large carnivores.

DESCRIPTION (adapted from applicant's abstract): The proposed research is aimed at determining how the neural mechanisms controlling daily rhythms differ in nocturnal and diurnal mammals. A small group of neurons in the mammalian brain called the suprachiasmatic nucleus (SCN) is responsible for the generation of 24 hour rhythms. To date, most research into the SCN and how it controls circadian rhythms has been done with nocturnal rodents. Until recently there has been no suitable diurnal rodent model with which to investigate these issues. These investigators have been working with a diurnal rodent, Arvicanthis niloticus, that they recently imported to the United States from East Africa. In the research proposed here they intend to use these rodents to determine how the neural structures controlling circadian rhythms differ in nocturnal and diurnal animals. The first objective is to compare nocturnal and diurnal animals with respect to rhythms in the concentration of a molecule that regulates gene expression, within the SCN and several brain regions to which it projects. Second, the investigators will compare rhythms in metabolic activity of the SCN in nocturnal and diurnal animals. Third, they will use SCN transplants to determine whether activity rhythms of diurnal and nocturnal animals differ because of differences within the SCN or differences in responsiveness to signals emanating from the SCN. Finally, they will evaluate rhythms within one brain region that receives signals from the SCN and controls rhythms in hormone secretion. It is important to understand these issues because the circadian system influences virtually every physiological and behavioral variable, and this influence is profoundly different in nocturnal and diurnal species.

The occurrence of sibling rivalry has now been documented in many species of animals, including humans. Mammalian sibling rivalry is widely believed to be less deadly than that among avian brood mates. The broad goal of the current research is to evaluate the generality of existing sibling rivalry theory by exploring sibling conflict in mammals. The work will focus specifically on one species of gregarious mammal, the spotted hyena, in which sibling rivalry is more intense than is that described in other mammals. A combination of techniques, including behavioral observation, monitoring of excreted hormone levels, and fetal ultrasonography, will be used to determine whether siblicide occurs facultatively or obligately in free-living hyenas in Kenya. The influence of hormones on dispersal will also be addressed.

Siblings are often each other's closest associates and closest competitors, so they often bear the heaviest costs of selfish behavior. Because the best interests of rival siblings need not necessarily coincide with those of their parents, conflict between parents and
offspring often affects the form and outcome of sibling competition. The study of sibling rivalry is thus of great significance for understanding the occurrence of both selfish and altruistic behaviors among close kin in our own species and in other animals.

Animals have internal biological clocks that enable them to coordinate physiological and behavioral rhythms relative to the time of day, termed circadian rhythms. In mammals, a key part of clock in the brain is the supra-chiasmatic nucleus (SCN) of the hypothalamus. In nocturnal rodents, which are widely used in the laboratory, the SCN is known to be important for the timing of female reproductive behavior and a surge in the luteinizing hormone (LH) that triggers ovulation. However very little is known about diurnal rodents, which have evolved from nocturnal species. This project asks how the neural mechanisms responsible for circadian control of the female reproductive cycle have changed in diurnal compared to nocturnal rodents. The model animal is the unstriped Nile grass rat, which is related to common laboratory rats, but has a virtually complete reversal in the timing of a variety of events associated with female reproduction, including morning instead of evening timing for both mating behavior and for the surge in LH. Cytochemical, anatomical and behavioral approaches will be used to distinguish whether the SCN itself changes signal timing, whether there is instead a change in the timing of receptiveness of target sites to SCN signals, or whether there is a change in the neuroanatomy connecting SCN to different targets in nocturnal and diurnal species.
The results will have an impact beyond neuroendocrinology to chronobiology, hypothalamic physiology, and evolutionary physiology. In addition, training of students and researchers at several levels is an important part of the project.

DESCRIPTION (provided by applicant): The proposed research is aimed at determining how the brain mechanisms controlling daily rhythms differ in animals that are active during the day compared to animals that are active at night. This proposal focuses on comparisons between the nocturnal lab rat and a diurnal rodent, the unstriped Nile grass rat. The research will focus primarily on a region of the brain that includes the suprachiasmatic nucleus (SCN), which is the site of the primary circadian "clock," and on neural tissue that surrounds this nucleus. The latter is referred to as the "peri-SCN" region, and it exhibits dramatically different rhythms in the diurnal grass rat compared to the nocturnal lab rat. The peri-SCN region will serve as a powerful model with which to characterize mechanisms that can lead to a reversal in rhythms exhibited by diurnal compared to nocturnal animals. The first Specific Aim is to evaluate the interaction between internal and external mechanisms that influence the peri-SCN rhythm in nocturnal and diurnal rodents. The second Specific Aim is to evaluate inputs to this region that could cause it to function differently in nocturnal and diurnal animals. The third Specific Aim is to elucidate the pathways through which the peri-SCN region could influence rhythms in sleep and body temperature. The fourth Specific Aim is to characterize, in the diurnal species, the molecular mechanisms underlying the "clock," and molecular pathways through which temporal information is transmitted from the clock to the behavioral and physiological systems it controls. The project has important implications for human health. One reason is simply that humans are predominantly diurnal, and the vast majority of medical research is conducted in nocturnal rodents. Somehow, somewhere in the brain, the temporal signals are reversed in day and night-active mammals, which makes it difficult to know whether lessons learned from nocturnal rodents truly apply to humans. A second medically important feature of the proposed work is that many humans have serious problems adapting their internal rhythms to the environment around them, which can lead to serious problems in life in general and on the job in particular.

Mammalian behavioral development under contrasting regimes of interspecific competition.

Proposal # IBN0343381

PIs: Kay E. Holekamp, Michigan State University
Laura Smale, Michigan State University
Jeffrey A. French, University of Nebraska at Omaha


NON-TECHNICAL ABSTRACT

Little is currently known about how the tendency to engage in risky behavior varies across the life-span in mammals, or how the behavior of young mammals varies with ecological circumstances. In most parts of Africa, lions (Panthera leo) and spotted hyenas (Crocuta crocuta) are the most common large carnivores, and these two species compete regularly for food. Here hypotheses will be tested suggesting that risk-sensitive behavior exhibited by free-living hyenas is affected by age and by competitive interactions with lions. Naturally-occurring variation will be documented in ranging behavior, vigilance, and risky behaviors shown by hyenas during interactions with lions over food. In addition, two playback experiments will inquire how age and local lion density influence hyenas' decisions regarding whether to approach or avoid recorded lion roars when these are broadcast from a hidden speaker. Concentrations of excreted stress hormones will be measured in hyena feces to determine whether stress physiology in these animals is affected by age or by local competition with lions. Measures of naturally-occurring behavior, experimental results, and hormone concentrations will be compared among hyenas at three different developmental stages in two Kenyan national parks in which ratios of resident hyenas to lions differ greatly. Finally, in collaboration with the Kenya Wildlife Service, methods will be developed for effective monitoring of large carnivores, and these methods will later be applied in several other national parks in Kenya. This research will thus combine strong basic science focused on behavioral development with direct applications to management and conservation of large African carnivores, including those that are rare and endangered.

The rhythmic daily patterning of activity and rest is a fundamental feature of virtually all forms of vertebrate life, including our own, and is heavily influenced by light. Light has very different effects on day-active and night-active species, with the former responding to darkness by increasing sleep and the latter responding with a decrease. Very little is known about the brain mechanisms mediating these effects of light on rest/sleep, and essentially nothing is known about how these mechanisms differ among day-and night-active species. The research to be undertaken in this project will begin to fill this gap in our fundamental understanding of these issues suing multiple approaches. First the behavioral responses to light will be directly compared in nocturnal and diurnal rodents, then the neural mechanisms mediating those responses will be characterized. The work will determine how specific populations of cells in the brain are affected by the changes in lighting conditions that affect rest and activity, and the role that these structures play in the process will then evaluated experimentally. The project outcomes could yield fundamental new insights into processes that have a profound impact on the lives of day-active animals including humans. A better basic understanding of these issues will lead to improved strategies to help the millions of Americans with sleep problems cope with them more effectively. Strategies that could be informed by the outcomes of this project include appropriately patterned administration of light, as well as, ultimately, new, safer and more effective pharmacological treatments. The project will also engage many undergraduate and graduate students in the research enterprise in ways that will provide them an inside view of how science is done.