N G van Kampen 1981 Amsterdam: North-Holland xiv + 419 pp price Dfl 180 This is a book which, at a lower price, could be expected to become an essential part of the library of every physical scientist concerned with problems involving fluctuations and stochastic processes, as well as those who just enjoy a beautifully written book. It provides an extensive graduate-level introduction which is clear, cautious, interesting and readable.

https://iopscience.iop.org/article/10.1088/0031-9112/34/4/040/pdf

Stochastic Processes in Physics and Chemistry

I. the origin of species by means of natural selection

In the Hamadryas baboon, males are substantially larger than females. A troop of baboons is subdivided into a number of ‘one-male groups’, consisting of one adult male and one or more females with their young. The male prevents any of ‘his’ females from moving too far from him. Kummer (1971) performed the following experiment. Two males, A and B, previously unknown to each other, were placed in a large enclosure. Male A was free to move about the enclosure, but male B was shut in a small cage, from which he could observe A but not interfere. A female, unknown to both males, was then placed in the enclosure. Within 20 minutes male A had persuaded the female to accept his ownership. Male B was then released into the open enclosure. Instead of challenging male A , B avoided any contact, accepting A’s ownership.

Evolution and the Theory of Games

where A represents the magnetic vector potential, is an integral of the hydromagnetic equations. This -integral made it possible to formulate a variational principle for the force-free magnetic fields. The integral expresses the fact that motions cannot transform a given field in an entirely arbitrary different field, if the conductivity of the medium isconsidered infinite. In this paper we shall show that the full set of hydromagnetic equations admit five more integrals, besides the energy integral, if dissipative processes are absent. These integrals, as we shall presently verify, are I2 =fbHvdV, (2)

Proceedings of the National Academy of Sciences

Governing the Commons

The immense diversity observed in natural microbial communities is surprising in light of the numerous weapons microbes have evolved to inhibit each other’s growth. It is thus imperative to understand which interaction patterns can sustain a biodiverse community when individual species antagonistically affect one another. In this study, we leverage potent methods from theoretical ecology to show how antibiotic-mediated interactions between microbes drive biological diversity. Building on previous experimental and theoretical results, we analyse the dynamics induced by various interaction graphs involving antibiotic production, resistance, and degradation. Previous work has recognised the importance of a particular producer-sensitive-degrader (PSD) motif in the interaction graph. We study this motif in detail and elucidate the mechanistic reason for this importance. Concretely, we give exact rules for coexistence in some simple cases where exhaustive enumeration of the interaction graphs is feasible. More generally, our results suggest that the PSD motif, in combination with a cyclic interaction structure, is sufficient for stable coexistence in well-mixed populations. Using individual-based simulations, we then study the importance of the PSD motif in spatially structured populations. We show that community coexistence is robust for an extensive range of antibiotic and degrader diffusivities. Together, these findings illuminate the interaction patterns that give rise to diversity in complex microbial communities, stressing that antagonism does not imply a lack of diversity and suggesting clear approaches for culturing synthetic microbial consortia.

/pdf/antibiotic-mediated-interactions-underlying-microbial-r3ai1ncp.pdf

Antibiotic-mediated interactions underlying microbial diversity

Crop rotation, a sustainable agricultural technique, has been at humanity’s disposal since time immemorial and is practised globally. Switching between cover crops and cash crops helps avoid the adverse effects of intensive farming. Determining the optimum cash-cover rotation schedule for maximizing yield has been tackled on multiple fronts by agricultural scientists, economists, biologists and computer scientists, to name a few. However, considering the uncertainty due to diseases, pests, droughts, floods and impending effects of climate change is essential when designing rotation strategies. Analysing this time-tested technique of crop rotations with a new lens of Parrondo’s paradox allows us to optimally use the rotation technique in synchrony with uncertainty. While previous approaches are reactive to the diversity of crop types and environmental uncertainties, we make use of the said uncertainties to enhance crop rotation schedules. We calculate optimum switching probabilities in a randomized cropping sequence and suggest optimum deterministic sequences and judicious use of fertilizers. Our methods demonstrate strategies to enhance crop yield and the eventual profit margins for farmers. Conforming to translational biology, we extend Parrondo’s paradox, where two losing situations can be combined eventually into a winning scenario, to agriculture.

Optimizing crop rotations via Parrondo’s paradox for sustainable agriculture

How did biological organisms become so complex? Endosymbiosis is the prototypical example of an egalitarian evolutionary transition and is central to the origins of many complex biological systems. Why do only some symbioses undergo evolutionary transitions, and how does the host-symbiont relationship change during this process? Here, we characterise endosymbiosis by two emergent collective-level properties: the relationship between the host and symbiont (mutual dependence) and reproduction (reproductive cohesion). Using methods from adaptive dynamics, we study the co-evolution of the traits underlying these properties. Our central result is a robust demonstration that even when investments in dependence and cohesion are uncorrelated, host-symbiont mutual dependence arises faster than reproductive cohesion. Further, we show that the collective’s formation and shared fate, coupled with different generation times of the host and symbiont, leads to an emergent asymmetry in how much they invest in the collective. Lastly, we account for biological realism that previous models have ignored and show that this can preclude a successful evolutionary transition towards stable endosymbiosis. Together, this work uncovers a fundamental property of endosymbioses, highlighting the immense effects of simple ecological factors and providing a clear way forward for theoretical and empirical investigations.

On the structure of an evolutionary transition: dependence and cohesion in incipient endosymbioses

Acoustic signals used by organisms to attract mates are known to attract parasitoid flies. The parasitoid flies lay their eggs inside the host signaler, eventually killing the host. We build a host-parasitoid acoustic model to investigate the effect of parasitoid flies on the signalling host’s eco-evolutionary dynamics. We used field crickets as a system to build the framework of the model. We explore how the sex ratio and the female parasitoid fecundity impact the evolution of the acoustic signal and population density of the signalling hosts. We also explore the stability of the host populations with an increase in parasitoid load. We find that up to a threshold value, an increase in parasitoid load leads to a thriving yet silent host population. Consistent with field observations, we show how this emergence of silence as an evolutionary strategy is immediate. Our results show that a drastic increase in the parasitoid load can rapidly push the signalling host population towards instability and extinction.

Chaitanya S. Gokhale

Papers

Antibiotic-mediated interactions underlying microbial diversity

Optimizing crop rotations via Parrondo’s paradox for sustainable agriculture

On the structure of an evolutionary transition: dependence and cohesion in incipient endosymbioses

Parasitoid pressures and silence evolution