Morphological disparity, metabolic rate, and dispersal in mountain populations of Brown trout (Salmo trutta L.)

Abstract

Brown trout (Salmo trutta Linnaeus 1758) is a widely distributed species inhabiting almost all inland water with clear, cold and well-oxygenated waters. Previous works have revealed that interactions with the environment and other individuals can determine relative social status, dispersal and, in long-term, evolutionary processes. Behavioural, physiological, morphological and ecological processes mediate these interactions. The main objective of this thesis lie in describing to what extent these factors act as mediators of these processes. Many authors have reported that Brown trout is aggressive, defends territories, generates dominance hierarchies competing for resources and prompts competitors to disperse. A higher dominance has often been positively associated to body size, which has been linked with preferential access to resources. On the other hand, Brown trout varies highly in morphology by exhibiting large-scale plasticity with the different habitats and to some degree also their ecology. These are the starting keys and pillars from which this doctoral thesis is going to be built. One of the aims of this dissertation is the analysis of morphological differences and disparity in body shape characteristics at a microgeographical scale. To attain this objective, the thesis examines, for the first time, patterns of morphospace occupation, morphological structure of populations and morphological disparity in a river basin (Dobra River, Cantabrian range, northern Iberian Peninsula). A second general objective tries to provide a more detailed description of the relationships between metabolic rate and morphology, because, in spite of its implications for fish species with hierarchical structures and dispersal processes, the relationship between metabolic rate and shape still remains unknown. This relationship has been evaluated, to deal with other of our aims: knowing how and why they disperse and which are their motivations for dispersing by evaluating how they get adapted to a new environment, and how fish morphology and metabolic rate determine their interaction with conspecific individuals. Furthermore, we have analysed the phenotypic plasticity of body shape in Brown trout juveniles by monitoring the shape drift experienced by artificially reared individuals after stocking in a natural stream, and comparing these shape configurations to the shapes of the wild trout from the receptor river. As a result, not only it was detected a relationship between shape, morphological disparity and environment, but also between geographical and morphological distances. Moreover, it has been also found out that a deeper body shape is related with a higher metabolic rate. Some authors sustain that a deeper body shape and a higher metabolic rate are optimal for burst swimming that is advantageous in structurally complex habitats. According to the obtained results, individuals showing a deeper body have a stronger territorial behaviour, forcing other individuals to move. And, we have detected a morphological convergence between trout from different origins (hatchery-reared versus wild) which reveals that trout populations retain a large amount of phenotypic plasticity, which allows for adjusting body shape to a wide range of environmental conditions, microhabitats, and foraging mode Finally, the main goal of this PhD thesis is the description of a morphological pattern (elongated versus dorso-ventral depth) that, moreover, is common and it is repeated not only between 0+ and 1+, but also it could be considered as the main pattern of morphological differentiation at population level. Furthermore, we have characterised dispersal processes as a result of an interaction between metabolic rate, interaction with conspecific individuals and, in minor degree, morphology.