Eco-evolutionary dynamics across scales of organisation

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Meike Wittmann, Chaitanya S. Gokhale


Evolution proceeding at ecological time-scales is a reality. From numerous experiments and empirical studies across the tree of life, rapid evolution has been attested. However, the separation of time-scales between ecology and evolution has been a handy tool in the inventory of theoretical biology, and the loss of this assumption challenges us to develop new modelling and analysis approaches. Here we would like to highlight new theories and models which successfully address these challenges to understand eco- evolutionary dynamics across scales of organisation: from cells to societies, and across space and time. Our speakers offer four exciting perspectives on the theory of eco-evolutionary dynamics. First, Paula Vasconcelas discusses the joint eco-evolutionary dynamics of multiple traits. This is important because trait evolution and diversification do not happen in isolation when multiple traits are linked. Scaling up to multiple species, Lynn Govaert discusses the consequences of combining approaches from evolutionary biology and community ecology to study eco-evolutionary dynamics playing out in ecological communi- ties at various spatial and temporal scales. Furthermore, trait evolution can alter how individuals affect their environment, and this can then feedback to affect the fitness of other individuals in the population. This feedback loop is explored by Charles Mullon, focusing in particular on non-random interactions between individuals and spatial structure, with impacts ranging from microbiomes to social evolution. Fi- nally, unifying processes across scales of organisation, Josep Sardany ́es discusses the classic hypercycle model and how it can capture eco-evolutionary dynamics from the origins of life to complex eco-systems.

Paula Vasconcelos

"How does joint evolution of consumer traits affect resource specialization?"
The origin and maintenance of diversity in nature are central themes in evolutionary biology and ecology. Recently, the framework of adaptive dynamics has been applied to try and shed light onto these questions, with interesting results. The phenomenon of disruptive selection when extreme phenotypes have a fitness advantage over more intermediate phenotypes is particularly interesting because, under this regime, selection favors the evolution of adaptive phenotypic diversity. More specifically, it can drive speciation as well as the evolution and maintenance of polymorphism within a species. The conditions that result in this specific selective regime are well understood at the theoretical level, but with one fun- damental restriction: the majority of research is based on the assumption of a single evolving quantitative trait. However, biological organisms are complex and initial results from the few models that incorporate multidimensional trait evolution indicate that increasing the number of co-evolving traits facilitates the emergence of disruptive selection. To systematically extend the existing theory, we study the conditions for the emergence of disruptive selection based on models with several co-evolving traits. These models are (i) characterized by a set of evolving traits that determines the fitness of individuals in a population due to interactions with a complex environment (prey, predators, pathogens), and (ii) mechanistic in the sense that each trait has an interpretation at the level of the organism. This approach thus allows us to better understand when and under what circumstances multiple coevolving traits facilitate or hinder the emergence of biological diversity. In this work, we analyze the evolutionary dynamics of consumer traits in a consumer-resource model. Consumer growth depends on search efficiency, handling time and conversion efficiency for two resources. Feeding on these alternative resources is subject to trade-offs such that, for instance, increasing search efficiency for one resource can only be achieved by decreasing search efficiency for the other. We investigate the evolution of these traits in isolation and various combinations. Our results show how moving from one to two, and then three coevolving traits affects the conditions un- der which resource polymorphism arises through evolutionary branching. We also show that the critical trade-off curvatures that lead to the different evolutionary outcomes that is, whether evolution leads to one generalist, one specialist or two specialists depend decisively on the specific combination of coevolv- ing traits. Finally, we show that, with multidimensional trait spaces, the parameter range can be split into one region in which evolutionary branching is independent of the mutational variance-covariance matrix, and another in which branching depends on it.

Lynn Govaert

"Towards an integrated theory of eco-evolutionary communities"
The increasing amount of studies showing evidence of rapid evolution occurring on similar timescales as ecological processes, have demonstrated the importance of including eco-evolutionary dynamics to further our understanding on population, community and ecosystem processes. Most empirical studies still focus on the ecological consequences of evolutionary change within a single species. However, in natural systems species co-occur together, comprising a community. Hence, all member species may display an evolutionary response. Thus focusing on evolution of a single species may lead to an over- or underestimation of evolution on ecological processes. To understand the role of eco-evolutionary dynamics within communities of multiple coexisting species, there is a need for a formal theory of eco-evolutionary communities integrating processes of evolutionary biology and community ecology operating at different temporal and spatial scales. Based on previous frameworks of evolutionary biology and community ecology, I here present an integrated framework for eco-evolutionary communities, bringing together theoretical, conceptual and technical approaches of these two fields. Integrating fundamental processes of evolutionary biology and community ecology improves our understanding of eco-evolutionary dynamics within multi-species communities and allows the design of new experimental approaches and testing for new hypotheses.

Charles Mullon

"Eco-evolutionary dynamics under non-random interactions"
Organisms continuously modify their living conditions, transforming their environment, microbiome, and sometimes culture. Where these modifications influence the fitness of conspecifics, a feedback emerges between the evolution of traits and the environment in which they are expressed. To investigate such feedback, it is typically assumed that individuals interact at random. In this case, one can study the invasion of a rare mutant trait in an environment set by a common resident ignoring mutant-mutant interactions. However, non-random interactions are common in nature. In this talk, I will report some of my results on the effect of non-random interactions on eco-evolutionary dynamics, focusing on two mechanisms that lead to such non-random interactions: spatial structure and biased behaviours between parents and their offspring. In both cases, selection depends on complex feedbacks between individuals of the same mutant lineage. By disentangling and quantifying these feedbacks, this research can help understand the nature of adaptation via non-genetic modifications, with implications for how organisms evolve to transform their environments, microbiome, or culture.

Josep Sardanyés

CRM Barcelona
"Dynamics of cooperation: from origins of life to ecosystems"
In this talk we will introduce the hypercycle model, originally conceived by Manfred Eigen and Peter Schuster to study the dynamics of prebiotic replicators. Hypercycles are dynamical systems formed by replicators with catalytic activity, thus they have been also employed to investigate cooperation in complex ecosystems at different levels. Following this mathematical model, we will show the dynamics and bifurcations tied to cooperation, from origins of life to models of facilitation in metapopulations and dynamics of semiarid ecosystems. We will emphasise on the evidences we have of such dynamics in real biological systems (both at the experimental or field levels), thus showing that dynamical systems theory offers us a unique framework to understand the basic mechanims behind the dynamics and the transitions in systems with strong nonlinearities.

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