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

Evolution of novel material properties and the emergence of group-level heritability in the transition to multicellularity

Evolutionary Transitions in Individuality (ETIs) describe the history of increasing complexity of life and emergence of hierarchical organization in an elegant framework. Each transition is characterized by a group of independent individuals coming together and forming a group that eventually can undergo Darwinian evolution and turns into a new individual level. One of the prominent examples of ETIs is the emergence of multicellularity. In this thesis I address two key questions about the transition to multicellularity: The emergence of heritability of higher level traits and its relationship to cell-level traits. First, I discuss how the heritability of newly-formed group traits emerges as groups emerge. We introduce a simple theoretical model for calculating group-level trait heritability, where the trait is the linear function of a cell-level trait. For cases in which the relationship is more complex than a linear function, we developed a statistical simulation to model and explore different kinds of analytical functions based on biological examples of relationship between cell-level traits and collective-level traits. Finally, using the snowflake yeast model system we did an experiment that shows an ecologically relevant, emergent trait in a nascent multicellular organism can have a higher heritability across a range of conditions than the unicellular-level trait on which it is based. The evolution of complex multicellularity presents an apparent paradox: nascent multicellular organisms are thought to require (relatively) large size to evolve complex traits, but at the same time maintaining large size requires complex organization at the cell and group levels. This poses a chicken and egg problem between large size and cellular development. Here, we show that over the course of a year snowflake yeast can increase its size multiple orders of magnitude with minimal change at the cell level by taking advantage of the physical properties of granular entangled materials.Ph.D

Stochasticity and randomness in eco-evolutionary modelling

Evolution is an inherently stochastic process comprised of many randomly occurring events. The evolutionary fate of a population depends largely on its underlying ecological interactions, while ecological interactions can also be influenced by evolutionary change in turn. This phenomenon is known as an eco-evolutionary feedback loop. Ecological models tend to have a strong focus on how complex ecological features such as interaction structures influence the behaviour of ecosystems, rather than their consequences on long-term evolutionary fates. Evolutionary models on the other hand tend to overlook the complexities associated with their underlying ecological features. This is of particular importance since many evolutionary problems in nature, particularly those associated to the evolution of sexual reproduction, are underpinned by myriad ecological factors. The aim of this thesis is to develop mathematical models for ecological and evolutionary problems in biology, with particular focus on problems surrounding the evolution of sexual reproduction. We begin in chapter 2 by developing an analytical prediction for the stability of generalised Lotka-Volterra systems with biologically motivated interaction structures. In chapter 3, we develop an eco-evolutionary model for the evolution of gamete size and motility to study the evolution of male and female sexes. Chapter 4 repurposes the model of chapter 3 to look at how binary cell fusion can evolve in response to environmental stress. Chapter 5 investigates how genetic recombination evolves in response to environmental stress using an integrative mathematical model that incorporates aspects of population dynamics, population genetics and eco-evolutionary feedback. This allows us to explain analytically how recombination and hibernation evolved to occur together, as well as why they both occur shortly before the onset of environmental stress