ADAPTATION AND PLASTICITY IN NEST CONSTRUCTION: BEHAVIOURAL AND MOLECULAR FACTORS AFFECTING DESIGN IN AN EXTENDED PHENOTYPIC TRAIT

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Nest building is an essential component of reproductive behaviour in many animals, from invertebrates to birds. Parents construct nests as receptacles for eggs and developing offspring, and their design has important implications for their efficacy. Nests and other animal constructions have been described as extended phenotypic traits / extra-body characteristics that nonetheless reflect the genotype of the builder. Hence, we might expect populations of a species living in different environments to have evolved different nest construction, a process called 'adaptive divergence'. However, just as conventional traits result from the interaction of genes and environment, so the design of animal built structures is shaped by external factors. The ability of individuals to adjust patterns of behaviour beneficially when faced with environmental change is described as 'phenotypic plasticity'. In this project, we will investigate adaptive divergence and phenotypic plasticity in the nest building behaviour of a fish, the 3-spined stickleback. Male sticklebacks build nests, which provide a focus for courtship and a place for females to lay eggs. We chose sticklebacks because (1) they naturally occupy, and build nests in, a wide range of aquatic habitats, from static ponds to fast flowing streams; (2) they are extremely well suited to laboratory studies, so we already know a great deal about their reproductive behavioural ecology; and (3) their genome has recently been sequenced, allowing us to ask questions about how individuals adjust nest building at molecular, as well as behavioural, levels. We will undertake a series of experiments to ask 4 related and important questions, using sticklebacks from different populations; some that have evolved in rivers, and some from lakes. First, we will examine how the flow regime experienced during nest building, and the type of materials available, interact to determine the design of nests. We will then allow males to build nests under one regime ('still' or 'flow') before testing aspects of its performance (including resistance to high flow rates, susceptibility to low oxygen levels, and attractiveness to females) under the regime in which it was built, and under the opposite regime. This will quantify the costs of building a nest that is unsuited to prevailing flow conditions. We will then examine to what extent males are able to adjust nest building behaviour when environments change, by examining building behaviour and nest design of individual males under first one, and then the alternate, flow regime. Male sticklebacks secrete a 'glue', Spiggin, which used to stick nesting materials together and anchor them to the substratum. Recent research has identified the genes responsible for Spiggin synthesis in the kidney. We want to know if male sticklebacks can regulate the production of Spiggin in response to changing flow conditions by altering the expression of Spiggin genes. This might allow males to adjust nest strength in direct response to changing flow rates. We will therefore collect males from the different populations, and also from experiments in which males are held under controlled flow regimes, and undertake an analysis that allows the amount of gene product (rather than just it presence/absence) in the kidney to be quantified. Our study will be among the first to examine the relative roles of adaptive divergence and phenotypic plasticity in animal construction behaviour, and is unique in incorporating both a behavioural and molecular approach. Our results will show to what extent the nest building behaviour of fish is adapted to their local environment, and to what extent they can adjust patterns of construction when conditions change. Understanding the extent and limitations of behavioural plasticity is important because, for example, it will help us predict how species introductions and global climate change are likely to affect success of individuals and of populations.