General description of the project
Our aim is to understand the evolution of behavioral and physiological mechanisms that allow animals to respond adaptively to their changing natural environment. This will help us to understand how animals can respond to climate change. We use methods from ecology, behavioral ecology, physiology and evolutionary biology to understand how ultimate factors integrate with proximate mechanisms.
Our work has generated four major findings that are of importance to further develop concepts and theory
1. The first good empirical data from long-term studies and from field experiments to show that reproductive competition is one of the main reasons for solitary-living (Schradin et al, 2010; Schoepf & Schradin, 2012).
2. We developed the concept of the single strategy from our results that the fitness consequences of alternative reproductive tactics can differ between generations, depending on the generation specific ecological conditions (Schradin & Lindholm, 2011).
3. The concept of social flexibility was developed, which is a form of reversible phenotypic plasticity where the social system of an entire population can change facultatively as a function of individuals of both sexes changing their social and reproductive tactics depending on ecological conditions (Schradin et al., 2012; Schradin 2013).
4. First eco-physiological studies demonstrating that individuals change their endocrine patterns when changing reproductive tactics (Schradin & Yuen, 2011), and that hormonal differences between tactics are seasonally dependent (Schradin, 2008).
We use several methods in physiology to understand how the physiology of individuals reacts to environmental change (physiological adaptation) and the physiological mechanisms of social behavior. We take blood samples, of which me measure several parameters in the field or using an ABAXIS Vet-scan at the research station, which tells us the health state of individuals. Blood samples are thensent on dry ice to Strasbourg where we measure different hormones and other blood parameters. We also have respirometry laboratory at the research station where we can measure oxygen consumption and carbine-dioxide production. Using the doubly-labelled water technique we can measure daily energy expenditure.
During the last decades, intensive field studies have enormously increased our knowledge about mammalian social systems and behavior. However, whereas most of these studies have been performed with large mammals such as primates, carnivores and ungulates, the majority of mammals are rodents (nearly 50%), and most of them belong to the family Muridae. Unfortunately, our knowledge about the natural biology of murids is still very poor.
The Succulent Karoo of South Africa is a semi-desert with rainfall in winter and a wildflower season in spring. This habitat is characterized by bushes, shrubs, ephemerals and succulents. Several small diurnal mammals inhabit this habitat: The striped mouse (Rhabomys pumilio), the bush Karoo rat (Otomys unisulcatus), two species of whistling rats (Parotomys spec.) and the round-eared elephant shrew (Macroscelides proboscideus). Our project focusses on the striped mouse. We collect field data from trapping, direct observations, radio-tracking and videotaping in the nest, which describe the social system of the four-striped mouse (Rhabdomys pumilio) in the Succulent Karoo. We tests hypothesis regarding paternal care, group living, communal nesting and alternative reproductive tactics.Thus, one focus is on the ecology, evolution and physiological mechanisms of social behavior. The striped mouse is an indeal model for such studies, because it is higly socially flexible. Both males and females can follow one of three tactics: 1. living as adult non-breeding helper in a group, 2. living as a solitary breeder, or 3. living in a group as a breeder. Thus, within the same population we can compare between solitary and group-living individuals. By following individuals over their entire life, we can study which ecological factors cause them to switch from group-living to solitary-living, and later often back to group-living. At the same time, we study the associated physiological consequences.
We conduct experiments directly in the field by changing environmental conditions such as population density or food availability. We can also present topics for exploration to individuals (personality research) and do other experiments.
Behavioral measurements under standardized conditions
Not all tests can be done in the field. Then we take individuals in the morning to the research station where we do standard behavioral measurements such as open field tests, tests for anxiety, encounter tests or tests for different cognitive traits.