A New Model and Method for Understanding Wolbachia-Induced Cytoplasmic Incompatibility

Wolbachia are intracellular bacteria transmitted almost exclusively vertically through eggs. In response to this mode of transmission, Wolbachia strategically manipulate their insect hosts' reproduction. In the most common manipulation type, cytoplasmic incompatibility, infected males can only mate with infected females, but infected females can mate with all males. The mechanism of cytoplasmic incompatibility is unknown; theoretical and empirical findings need to converge to broaden our understanding of this phenomenon. For this purpose, two prominent models have been proposed: the mistiming-model and the lock-key-model. The former states that Wolbachia manipulate sperm of infected males to induce a fatal delay of the male pronucleus during the first embryonic division, but that the bacteria can compensate the delay by slowing down mitosis in fertilized eggs. The latter states that Wolbachia deposit damaging “locks” on sperm DNA of infected males, but can also provide matching “keys” in infected eggs to undo the damage. The lock-key-model, however, needs to assume a large number of locks and keys to explain all existing incompatibility patterns. The mistiming-model requires fewer assumptions but has been contradicted by empirical results. We therefore expand the mistiming-model by one quantitative dimension to create the new, so-called goalkeeper-model. Using a method based on formal logic, we show that both lock-key- and goalkeeper-model are consistent with existing data. Compared to the lock-key-model, however, the goalkeeper-model assumes only two factors and provides an idea of the evolutionary emergence of cytoplasmic incompatibility. Available cytological evidence suggests that the hypothesized second factor of the goalkeeper-model may indeed exist. Finally, we suggest empirical tests that would allow to distinguish between the models. Generalizing our results might prove interesting for the study of the mechanism and evolution of other host-parasite interactions

The evolution of social learning

Menschen unterscheiden sich von anderen Tieren insbesondere dadurch, dass ihr Alltag durch vielfältige kulturelle Praktiken bestimmt wird. Diese erlaubten es dem Menschen, fast alle terrestrischen Habitate auf der Erde in hoher Dichte zu besiedeln. Kulturelle Merkmale werden nicht genetisch vererbt, sondern durch soziales Lernen zwischen Menschen übertragen -- niemand könnte ohne den vorhandenen Wissensbeitrag anderer ein funktionstüchtiges Kanu bauen. Daraus zu schließen, kulturelle und genetische Evolution seien komplett getrennt zu behandeln, wäre allerdings falsch. Genetische Evolution hat es überhaupt erst erlaubt, von anderen in adaptiver Weise zu lernen. Kulturelle und genetische Evolution müssen zusammen betrachtet werden, um die Einzigartigkeit des Menschen zu verstehen. Der offensichtlich vorhandene adaptive Nutzen sozialen Lernens konnte in theoretischen Arbeiten allerdings nicht repliziert werden. Das deutet darauf hin, dass das Verständnis über die Funktionsweise sozialen Lernens noch unvollständig ist. Zwar haben einige Wissenschaftler mögliche Lösungen für dieses Paradox vorgeschlagen, aber unser Modell zeigt, dass diese unzureichend sind. Stattdessen hält sich der Widerspruch hartnäckiger als geglaubt. Wir analysieren zwar neue soziale Lernstrategien, die den Widerspruch lösen könnten, doch das erfolgt nur unter sehr beschränkten Bedingungen. Außerdem treten wir für eine neue Sicht auf soziales Lernen ein und damit einhergehend für einen Modellierungsansatz, der Lernformen in realistischerer Weise berücksichtigt. Die Untersuchung des evolutionären Ursprungs sozialen Lernens sollte den gleichen Stellenwert haben wie jene des evolutionären Ursprungs kooperativen Verhaltens. Dass dies sinnvoll wäre, belegen wir, indem wir zeigen, welchen Einfluss soziales Lernen sogar auf moderne Gesellschaften und Volkswirtschaften hat und wie es beispielsweise hilft, Finanzkrisen besser zu verstehen.Humans differ most from other animals in that their lives are shaped by many cultural practices. Having cultural traits allowed human populations to grow considerably in a short time and to conquer almost all terrestrial habitats on Earth. Cultural traits are not inborn but are instead transmitted between humans through social learning -- no individual could build a fully functional kayak without learning from others. Concluding that cultural evolution is thus a separate process from genetic evolution would, however, be rash. The latter has endowed humans with the possibility to learn from others in the first place, and prepared learning to make it especially adaptive. To find out what makes humans unique, cultural and genetic evolution, therefore, have to be studied in concert. Although nobody doubts that evolution gave rise to social learning and that the resulting cultural practices serve an adaptive purpose, theoretical works have shown that simple forms of social learning do not improve human adaptedness. This finding contradicts the observations and thus implies that our understanding of social learning is incomplete. Several authors have proposed solutions to this paradox but, as our model results will show, the solutions are unsatisfying. Instead, we find the paradox to be more resilient than is believed and propose forms of social learning that could solve it, albeit only under very narrow circumstances. Furthermore, we argue for a new perspective on social learning and, consequently, for a different framework that allows for more realistic learning models. We suggest that the study of the evolutionary origin of social learning should be given equal weight as the study of the evolutionary origin of cooperation, and illustrate this by elaborating on the impact of social learning on modern societies and market behaviors in general, and on financial crises specifically

The Evolution of Social Learning and its Economic Consequences

AbstractWe use an evolutionary model to simulate agents who choose between two options with stochastically varying payoffs. Two types of agents are considered: individual learners, who rely on trial-and-error methods, and social learners, who imitate the wealthiest sampled individual. Agents adapt to changing environments within one generation by using their respective learning strategy. The frequency of the agent types adapts between generations according to the agents’ acquired wealth. During the course of evolution, social learning becomes dominant, resulting in three major effects: First, for better or worse, the decisions of social learners are more exaggerated than those of individual learners. Second, social learners react with a delay to changes in the environment. Third, the behavior of social learners becomes more and more detached from reality. We argue that our model gives insights into economic systems and markets

Heterogeneous Photochemistry in the Atmosphere

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