Life history strategies and spatial dynamics of the Barents Sea capelin (Mallotus villosus)

Dr. Scient. Thesis. / Department of Fisheries and Marine Biology. University of Bergen. NorwayThis thesis consists of four papers on the life history strategy and spatial distribution of the Barents Sea capelin (Mallotus villosus). In the first two papers, sex specific aspects of capelin life history are investigated from a combination of field sampling and modelling. Paper III deals with the development of a concept for modelling spatial distribution of fish, and in Paper IV the concept is applied for the Barents Sea capelin. Female capelin were found to invest much more energy into reproductive tissue than males. Capelin fecundity was found to depend upon body weight, and inter annual variation in fecundity is related to variation in body weight. A life history model (Paper II) predicts that males have a higher fitness associated with semelparity than females since males may fertilise many females, whereas female fitness is limited by her number of eggs. Given a high or variable adult mortality risk, it may be more profitable for males to be semelparous than iteroparous. Capelin is therefore predicted to have sex specific life history strategies with semelparous males and iteroparous females. This prediction is supported by literature on capelin ecology. In Paper III a concept for modelling spatial distribution of fish is developed. The background for applying a new approach to studying fish distribution, is the lack of approaches for solving specific problems related to capelin ecology. The model is individual based and behaviour is calculated using an artificial neural network where weights are evolved using a genetic algorithm. Through simulating evolution by natural selection in a seasonal spatial model with life cycle, physiology, mortality, and reproduction, the individuals with the best "genetic weights" become increasingly more common in the population. Eventually the population consists of well-adapted individuals, which migrate back to spawning areas in winter, and grow and avoid being eaten throughout the rest of the year. The importance of separating between reactive and predictive behaviour in controlling local search and long distance migration respectively, is discussed. In Paper IV this model is elaborated to include: explicit representation of each stage in the life cycle of the Barents Sea capelin, larval drift, and evolution of spawning areas and timing of reproduction. Furthermore the model includes life history traits such as size at maturity, allocation of energy, and number of reproductive events. Larval drift was associated with a warm water area, and the evolved spawning ground was situated upstream from this, in the outskirts of the range for capelin spawning. The migration pattern follows the same general pattern as that of the Barents Sea capelin. In a simulation with stochastic mortality rates, sex specific life history strategies with semelparous males and iteroparous females were evolved, which supports the predictions from Paper II. The major achievement of this study is the development of an evolutionary system for fish migration, and the way this is applied to provide predictions about the life history and spatial dynamics of the Barents Sea capelin. Another important finding is the recognition that some aspects of capelin life history strategy are sex specific, with female iteroparity and male semelparity

Evolutionary and proximate mechanisms shaping host-parasite interactions : the case of "Daphnia magna" and its natural bacterial parasite "Pasteuria ramosa"

Host-parasite interactions are composed of a sequence of steps, all necessary for successful infection: parasites need to encounter their hosts, to enter into their bodies, and to proliferate within them. Selection will act on the mechanisms used in each of the steps; the parasite being selected to increase their efficiency, and the host selected to reduce it. I have proposed, and shown, that explicitly analyzing the factors that influence each of the steps and their impact on host and parasite fitness is of crucial importance for a complete understanding of host-parasite interactions. In my Ph.D. research work, I identified markers of different steps of the interaction between the host crustacean Daphnia magna and its natural bacterial parasite Pasteuria ramosa, and investigated factors influencing different steps, as well as the contribution of each of them to shaping the interaction between the two species. I established that the infection of Daphnia magna by Pasteuria ramosa could be decomposed in at least five sequential steps (Chapter 1): 1) the encounter between the host and the parasite, 2) the activation of the parasite transmissible, resting stage, which happens once it contacts the host, 3) the attachment of the parasite to the host cuticula, 4) the penetration of the parasite into the host body cavity, and 5) the proliferation of the parasite within the host. The factors affecting the likelihood of encounter between host and parasite had been investigated before, in a study that revealed that there is a host genetic component, and polymorphism for the ability of the host to avoid encountering the parasite. Resolving the interaction into its different steps and focusing on steps affect the encounter allowed me to see that: i) different steps are under the influence of different factors (Chapter 1), ii) the traits underlying some steps, but not all, do not seem to be polymorphic (Chapter 1), iii) the parasite genotype specificity of the success of the attachment step can explain the genotype specificity of the host susceptibility (Chapter 1), iv) the speed with which the parasite penetrates the host body after attachment is crucial for the parasite success (Chapter 2), v) the molting, usually seen as a cost against parasite, can be beneficial to reduce the likelihood of infection, vi) once in the host body, the parasite will adapt to the environment that is characteristic of the most common host sex, here female characteristic (Chapters 3 and 4), vii) the success of proliferation of P. ramosa inside D. magna hosts is not influenced by previous host exposure to that same parasite (Chapter 5). All in all, I show that considering each of the steps explicitly provides new light into the mechanisms and selective pressures on hosts and their parasites. Each of the two interacting parties will, indeed, be under more or less strong selection to maximize their success at each of the steps. Below I will elaborate on this idea in relation to my specific findings and the research perspectives they open

The Effects Of Perceived Predation Risk On The Avian Brain

Predators do not affect prey solely through direct killing. The fear (i.e. the prospect of imminent, violent death) of predators shapes prey ecology– the mere presence of a predator leaves lasting effects. Current models of fear are based on post-traumatic stress disorder (PTSD) in humans. The scientific community has identified brain regions involved in mammalian fear processing. The neurobiological effects of predator fear on wild animals are unknown. I exposed wild black-capped chickadees (Poecile atricapillus) to auditory playbacks simulating acute and chronic predation risk and quantified the expression of short- and long-term immediate-early genes in brain regions implicated in the avian fear network: the nucleus taeniae of the amygdala (TnA), hippocampus (Hp), and caudal nidopallium (NC). The TnA and Hp showed short- and long-term changes in response to predation risk. NC results were ambiguous. I provide new information to be incorporated into the biomedical model of fear and the field of predator-prey ecology

Some aspects of animal behavior and community dynamics

We simulate the dynamical behavior of a few two - dimensional predator - prey systems in two - dimensional parameter spaces to gain insight into how functional responses affect community dynamics. The insight gained helps us design three dimensional systems. We construct models for a few ecosystems with three species and study them using computer simulations. The models have been developed by linking food chains which have both kinds of predators: specialist as well as generalist. The linking functions are weakly non-linear. The three dimensional model ecosystems have sexually reproducing top - predators. We perform extensive simulations to figure out dynamics of dynamical possibilities caused by changes in animal behavior. The animals change the foraging strategies and behave differently in different environments. At the end of the paper, we examine how diseases can govern transitions in meandering of dynamical models in bounded volume of their phase spaces

The role of visual adaptation in cichlid fish speciation

D. Shane Wright (1) , Ole Seehausen (2), Ton G.G. Groothuis (1), Martine E. Maan (1) (1) University of Groningen; GELIFES; EGDB(2) Department of Fish Ecology & Evolution, EAWAG Centre for Ecology, Evolution and Biogeochemistry, Kastanienbaum AND Institute of Ecology and Evolution, Aquatic Ecology, University of Bern.In less than 15,000 years, Lake Victoria cichlid fishes have radiated into as many as 500 different species. Ecological and sexual sel ection are thought to contribute to this ongoing speciation process, but genetic differentiation remains low. However, recent work in visual pigment genes, opsins, has shown more diversity. Unlike neighboring Lakes Malawi and Tanganyika, Lake Victoria is highly turbid, resulting in a long wavelength shift in the light spectrum with increasing depth, providing an environmental gradient for exploring divergent coevolution in sensory systems and colour signals via sensory drive. Pundamilia pundamila and Pundamilia nyererei are two sympatric species found at rocky islands across southern portions of Lake Victoria, differing in male colouration and the depth they reside. Previous work has shown species differentiation in colour discrimination, corresponding to divergent female preferences for conspecific male colouration. A mechanistic link between colour vision and preference would provide a rapid route to reproductive isolation between divergently adapting populations. This link is tested by experimental manip ulation of colour vision - raising both species and their hybrids under light conditions mimicking shallow and deep habitats. We quantify the expression of retinal opsins and test behaviours important for speciation: mate choice, habitat preference, and fo raging performance

The Adaptive Evolution of Herbivory in Freshwater Systems

Herbivory is thought to be nutritionally inefficient relative to carnivory and omnivory. But, herbivory evolved from carnivory in many lineages, suggesting that there are advantages to eating plants. To understand the adaptive significance of the transition from carnivory to herbivory, I proposed five hypotheses for the adaptive evolution of herbivory and reviewed the current freshwater literature to identify conditions where eating plants might be adaptive over eating animals. I tested three of these ideas (Suboptimal Habitat, Heterotroph Facilitation, and Lipid Allocation) using the herbivorous Sailfin Molly (Poecilia latipinna)and identified each as a potential mechanism for the evolution of herbivory. To understand the origins of herbivory in Sailfin Mollies, I reconstructed ancestral habitats and dietsacross a phylogeny of the genus Poeciliaand then used phylogenetically independent contrasts to identify patterns of diet evolution. I found that the degree of herbivory increases with increasing salinity affiliation, suggesting that in this genus, herbivory evolved as an adaptation for invading less productive saline habitats from freshwaters. This result is consistent with the Suboptimal Habitat hypothesis, which states that herbivory allows organisms to invade and persist in ‘suboptimal’ habitats. To understand how herbivory is maintained in extant populations, I raised juvenile Sailfin Mollies in mesocosms and enclosure cages placed in the Everglades to document that dietary autotrophic lipids play a role in early life history by supporting rapid growth (Lipid Allocation). However, dietary bacterial fatty acids promoted fish survival, consistent with the Heterotroph Facilitation hypothesis, which states that indirect detritivory supplements the herbivorous diet. Finally, I quantified periphyton quality/availability and consumer density across the Everglades landscape to examine the correlates of trophic dynamics in nature. Results revealed that herbivores can persist in diverse habitats and survive on varying resources when habitats are unfavorable, supporting the Suboptimal Habitat hypothesis