Lars A. Bach

Looking for a needle in a haystack: Discovery of indigenous Atlantic salmon (Salmo salar L.) in stocked populations

Microsatellite analysis of Atlantic salmon fromfive Danish rivers was performed to determinethe stocked or indigenous status ofindividuals. Genetic variation at six highlypolymorphic microsatellite loci was assayed andused for individual based analyses (assignmenttests). Contemporary samples of adult returningspawners and fry were compared to baseline datafrom: 1) historical DNA samples (from oldscales) representing the indigenouspopulations, 2) samples from another Danishpopulation (Skjern River) used for stocking,and 3) five exogenous populations used forstocking. Assignment power was high. Thepercent of stocked salmon correctly assigned topopulation of origin ranged from 83% to 99%and the percent of indigenous salmon correctlyassigned to population of origin ranged from83% to 90%. For two of the riverssignificantly more individuals were assigned tothe indigenous populations than expected frommisclassification alone, suggesting that someremains of the indigenous populations hadpersisted. Still, many fish were of exogenousorigin. Simulated hybrids among releasedexogenous salmon and between exogenous andreleased Danish salmon (Skjern River) revealedthat natural hybridisation among released fishwas not likely to be the source of the fryclassified as indigenous, however, thepossibility of hybridisation among indigenousand released fish could not be dismissed.Several full sib groups were found amongindigenous natural fry ruling out one or a fewmatings as the source of the indigenous fry.These results show that some native populationsmay persist even after years of introductionand environmental perturbation; geneticinformation can be used to identify thesepopulations and identify individualsrepresenting these populations for use inrestoration programs.

Quantitative Trait Evolution and Environmental Change

Background Given the recent changes in climate, there is an urgent need to understand the evolutionary ability of populations to respond to these changes. Methodology/Principal Findings We performed individual-based simulations with different shapes of the fitness curve, different heritabilities, different levels of density compensation, and different autocorrelation of environmental noise imposed on an environmental trend to study the ability of a population to adapt to changing conditions. The main finding is that when there is a positive autocorrelation of environmental noise, the outcome of the evolutionary process is much more unpredictable compared to when the noise has no autocorrelation. In addition, we found that strong selection resulted in a higher load, and more extinctions, and that this was most pronounced when heritability was low. The level of density-compensation was important in determining the variance in load when there was strong selection, and when genetic variance was lower when the level of density-compensation was low. Conclusions The strong effect of the details of the environmental fluctuations makes predictions concerning the evolutionary future of populations very hard to make. In addition, to be able to make good predictions we need information on heritability, fitness functions and levels of density compensation. The results strongly suggest that patterns of environmental noise must be incorporated in future models of environmental change, such as global warming.

Scaling of the mean and variance of population dynamics under fluctuating regimes

Theoretical ecologists have long sought to understand how the persistence of populations depends on the interactions between exogenous (biotic and abiotic) and endogenous (e.g., demographic and genetic) drivers of population dynamics. Recent work focuses on the autocorrelation structure of environmental perturbations and its effects on the persistence of populations. Accurate estimation of extinction times and especially determination of the mechanisms affecting extinction times is important for biodiversity conservation. Here we examine the interaction between environmental fluctuations and the scaling effect of the mean population size with its variance. We investigate how interactions between environmental and demographic stochasticity can affect the mean time to extinction, change optimal patch size dynamics, and how it can alter the often-assumed linear relationship between the census size and the effective population size. The importance of the correlation between environmental and demographic variation depends on the relative importance of the two types of variation. We found the correlation to be important when the two types of variation were approximately equal; however, the importance of the correlation diminishes as one source of variation dominates. The implications of these findings are discussed from a conservation and eco-evolutionary point of view.

Threshold Games and Cooperation on Multiplayer Graphs

Objective The study investigates the effect on cooperation in multiplayer games, when the population from which all individuals are drawn is structured—i.e. when a given individual is only competing with a small subset of the entire population. Method To optimize the focus on multiplayer effects, a class of games were chosen for which the payoff depends nonlinearly on the number of cooperators—this ensures that the game cannot be represented as a sum of pair-wise interactions, and increases the likelihood of observing behaviour different from that seen in two-player games. The chosen class of games are named “threshold games”, and are defined by a threshold, M > 0, which describes the minimal number of cooperators in a given match required for all the participants to receive a benefit. The model was studied primarily through numerical simulations of large populations of individuals, each with interaction neighbourhoods described by various classes of networks. Results When comparing the level of cooperation in a structured population to the mean-field model, we find that most types of structure lead to a decrease in cooperation. This is both interesting and novel, simply due to the generality and breadth of relevance of the model—it is likely that any model with similar payoff structure exhibits related behaviour. More importantly, we find that the details of the behaviour depends to a large extent on the size of the immediate neighbourhoods of the individuals, as dictated by the network structure. In effect, the players behave as if they are part of a much smaller, fully mixed, population, which we suggest an expression for.

Environmental Fluctuations and Level of Density-Compensation Strongly Affects the Probability of Fixation and Fixation Times

The probability of, and time to, fixation of a mutation in a population has traditionally been studied by the classic Wright–Fisher model where population size is constant. Recent theoretical expansions have covered fluctuating populations in various ways but have not incorporated models of how the environment fluctuates in combination with different levels of density-compensation affecting fecundity. We tested the hypothesis that the probability of, and time to, fixation of neutral, advantageous and deleterious mutations is dependent on how the environment fluctuates over time, and on the level of density-compensation. We found that fixation probabilities and times were dependent on the pattern of autocorrelation of carrying capacity over time and interacted with density-compensation. The pattern found was most pronounced at small population sizes. The patterns differed greatly depending on whether the mutation was neutral, advantageous, or disadvantageous. The results indicate that the degree of mismatch between carrying capacity and population size is a key factor, rather than population size per se, and that effective population sizes can be very low also when the census population size is far above the carrying capacity. This study highlights the need for explicit population dynamic models and models for environmental fluctuations for the understanding of the dynamics of genes in populations.

Correction: Threshold Games and Cooperation on Multiplayer Graphs.

The affiliation for the second author is incorrect. Lars A. Bach is affiliated with: 1 Interacting Minds Center, Aarhus University, DK-8000 Aarhus C, Denmark, 3 Interdisciplinary Center for Organizational Architecture(ICOA), Aarhus University, DK-8210 Aarhus V, Denmark The Data Availability statement for this paper is incorrect. The correct statement is: All relevant data are within the paper and Supporting Information files.

Behavioural Instability; What Is Next. A Holistic Approach to Behavioural Studies

Phenotypic variability and fluctuating asymmetry are the most often used indices for the estimation of developmental instability of an individual. [...]

Possible Evolutionary Response to Global Change – Evolutionary Rescue?

1.1 Climate-induced environmental changes With a pace that is higher than observed in the past 10,000 years global warming is currently changing the global and local environments. On average, the global temperature has increased by 0.7 degree over the past century and future projections show an acceleration of global temperature rise (Walther et al., 2002) which produces climate-induced environmental changes (CIEC). Increasing the mean temperature furthermore corresponds to an increasing range between the minimum and the maximum temperatures due to a pure scaling effect of the variance with the mean (Pertoldi et al., 2007a). Additional factors may then add even more to the increased range of temperatures combined with increased variability in precipitation patterns. An increased temperature range is translated into a fluctuating selective regime for natural populations and amplified environmental variability (2e) which have several consequences at different levels of organization. In order to understand what limits the ability of species to adapt to CIEC, we need to integrate (local) short-term and (local) long-term changes and to increase our knowledge on the importance of genetic and environmental components on phenotypic variability (2p) (Pertoldi et al., 2005). A notorious debate between ecologists and geneticists concerns the relative importance of genetic and ecological factors for the persistence of populations. There is a need for a deeper understanding of how genetic measures can be used to indicate causal processes, including the genetic signature of population declines or expansions due to CIEC. Evolutionary biologists and ecologists have increasingly turned to molecular genetics to study the demographic and genetic consequences of CIEC on populations. However, this approach has some serious limitations: 1) many different population processes lead to similar patterns of genetic structure and 2) population genetic models most commonly applied to these systems are based on the assumption of equilibrium conditions typically not found in nature and surely not in disturbed ecosystems.