Rapid changes in genetic architecture of behavioural syndromes following colonization of a novel environment.

Behavioural syndromes, that is correlated behaviours, may be a result from adaptive correlational selection, but in a new environmental setting, the trait correlation might act as an evolutionary constraint. However, knowledge about the quantitative genetic basis of behavioural syndromes, and the stability and evolvability of genetic correlations under different ecological conditions, is limited. We investigated the quantitative genetic basis of correlated behaviours in the freshwater isopod Asellus aquaticus. In some Swedish lakes, A. aquaticus has recently colonized a novel habitat and diverged into two ecotypes, presumably due to habitat-specific selection from predation. Using a common garden approach and animal model analyses, we estimated quantitative genetic parameters for behavioural traits and compared the genetic architecture between the ecotypes. We report that the genetic covariance structure of the behavioural traits has been altered in the novel ecotype, demonstrating divergence in behavioural correlations. Thus, our study confirms that genetic correlations behind behaviours can change rapidly in response to novel selective environments.

Changes in behavioural trait integration following rapid ecotype divergence in an aquatic isopod.

Colonization of new habitats can relax selection pressures, and traits or trait combinations no longer selected for might become reduced or lost. We investigated behavioural differentiation and behavioural trait integration in the freshwater isopod Asellus aquaticus. This isopod has recently colonized a novel habitat and diverged into two ecotypes which encounter different predator faunas. We investigated sex-specific behavioural differences and phenotypic integration in three behavioural assays: (i) time to emerge (TE) from a shelter, (ii) activity and (iii) escape behaviour. General activity and escape behaviour differed between ecotypes. Furthermore, general activity and TE differed between sexes. Behavioural traits were more frequently correlated in the ancestral habitat, and phenotypic integration tended to be higher in this habitat as well. Our study suggests that different predator types, but also other ecological factors such as habitat matrices and population densities, might explain the differences in behavioural integration in these ecotypes.

Effects of enrichment on simple aquatic food webs.

Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.

Energetics, cost reduction and functional consequences of fish morphology.

Cost reduction strategies are often invoked as explanations when studies of adaptation fail to find predicted costs. This might seem discouraging, offering little opportunity for further investigation. In this paper, we demonstrate that cost reduction strategies can themselves be investigated by arguments from design. Recent work on inducible morphological defences has shown that hydrodynamical disadvantages (e.g. high drag) in fishes can be compensated for by standard metabolic rate (SMR) adjustments. Here, we theoretically investigate the possibilities and limitations for swimming cost compensation through SMR adjustment. We continue by modelling how intraspecific power curve variation affects the optimal swimming velocity between food patches. Our results show that, even though SMR modifications may compensate for hydrodynamical disadvantages, low-drag fishes will nevertheless have a marked advantage under high food abundance. The relative advantage will decrease with decreasing food levels. We also show that hydrodynamical properties of fishes can be used to predict their propensity to become foraging (or swimming) specialists. Low-drag fishes can use a broad range of swimming velocities without substantial increases in swimming cost, whereas the cost of deviating from the optimal swimming velocity increases markedly in high-drag fishes. The results have important implications for the evolution of morphological diversity in fishes.