Biology subjects

Zachar, I.

Publications and source records attributed to Zachar, I..

7 recordsLinked to original sources

bioRxiv2026

Metabolic inhibition can enable compact physical integration of microbial partners

Microbes often generate by-products that inhibit own or consortial growth. Such imposing constraints can be alleviated by symbiotic partnerships where the partner consumes the limiting factor resulting in mutually beneficial cooperation. Theories of mitochondrial origin envisage such metabolic syntrophy of partners as the initial interaction, often coupled with mechanistic membrane gymnastics to trap the alphaproteobacterial symbiont to ensure vertical inheritance and as a prerequisite or vestibule of endosymbiosis. Yet we do not know how this happened. Here, using a mathematical model, we investigate how such metabolic self-inhibition enables and facilitates the evolution of compact physical integration between syntrophic partners. We show that when one species produces a metabolite that is self-inhibitory, selection favors increasingly tight spatial association of a detoxifying partner to mitigate local accumulation of the self-limiting product. Under a broad parameter range, this process drives the emergence of surface-associated configurations promoting morphological adaptations such as membrane protrusions or invaginations that increase inter-partner contact area. Our results prove that such costly host membrane contortions can evolve as a means to improve benefits of inhibition reduction by protective syntrophic ectosymbionts. Additionally, a unilateral syntrophic interaction between parties is sufficient for the transition; a mutualistic (or bilateral) one is not necessary. Our model establishes a direct evolutionary link between metabolic coupling and physical integration, suggesting that the need to alleviate (self-generated) inhibition can be a primary driver of ectosymbiotic attachment and its transition toward more intimate associations. Our findings provide a general theoretical framework for understanding how microbial consortia evolve structural complexity from initially loose metabolic interactions, with implications for the origins of stable symbioses and the early steps toward cellular integration.

evolutionary biology↗

bioRxiv2024

A Darwinian model of cultural replication over the continuum of Weismannian and Lamarckian inheritance

Universal Darwinism argues that entities capable of multiplication, variation and inheritance evolve by natural selection. Besides genetic reproduction implementing Weismannian inheritance, other adaptive systems were proposed to support Darwinian evolution, most notably culture, assuming autonomous cultural replicators akin to genes. Culture, on one hand, lacks direct template copying and inherits acquired changes, while on the other its overall behaviour is Darwinian as languages attest. The properties of culture setting it apart from biological evolution suggests a Lamarckian, while its overall behaviour a Weismannian interpretation, which is often coined as "the duality of cultural replication". According to canonical Darwinism, Lamarckian and Weismannian inheritance are disjunct mechanisms and only the latter is sufficient to maintain cumulative evolution. We resolve this apparent contradiction via a mathematical model of cultural information replication. We model the inheritance of information, cultural or genetic, as a successive set of template-based transformations of digital information between generations. We demonstrate that Lamarckian and Weismannian inheritance form a continuum and that both can reconstruct information stably for an indefinite time. Our formalism naturally unifies Lamarckian and Weismannian inheritance, proving that cultural replication, in theory, can approximate the fidelity of genetic replication. We claim that (well-defined) Lamarckian inheritance is an adequate low-level model of culture and can support population-level Darwinian evolution. We discuss the implications of our results to bridge the gap between the Lamarckian and Darwinian explanations of cultural evolution. Significance statementMuch of the standstill of cultural evolution theory stems from under-defined concepts that lack rigorous mathematical formalism. We provide a strict application of established concepts of biological evolution to the replication of cultural information. According to our analogy, cultural replication corresponds to Lamarckian inheritance (inheriting acquired changes), genetic replication to Weismannian inheritance, both being part of the same continuum of informational replication. We prove in our model, that despite a lack of template copying in Lamarckian replication, overall copying fidelity can approximate that of Weismannian replication, i.e. culture can approximate genetic copying fidelity. Cultural inheritance may be Lamarckian at the level of inheritance (microevolution) while it can still lead to Darwinian evolution at the population level (macroevolution).

evolutionary biology↗

bioRxiv2023

Cue-driven microbial cooperation and communication: evolving quorum sensing with honest signalling.

BackgroundQuorum sensing (QS) is the ability of microorganisms to assess local clonal density by measuring the extracellular concentration of signal molecules that they produce and excrete. QS is also the only known way of bacterial communication that supports the coordination of within-clone cooperative actions requiring a certain threshold density of cooperating cells. Cooperation aided by QS communication is sensitive to cheating in two different ways: laggards may benefit from not investing in cooperation but enjoying the benefit provided by their cooperating neighbors, whereas Liars explicitly promise cooperation but fail to do so, thereby convincing potential cooperating neighbors to help them, for almost free. Given this double vulnerability to cheats, it is not trivial why QS-supported cooperation is so widespread among prokaryotes. ResultsWe investigated the evolutionary dynamics of QS in populations of cooperators for whom the QS signal is an inevitable side effect of producing the public good itself (cue-based QS). Using spatially explicit agent-based lattice simulations of QS-aided threshold cooperation (whereby cooperation is effective only above a critical cumulative level of contributions) and three different (analytical and numerical) approximations of the lattice model we explored the dynamics of QS-aided threshold cooperation under a feasible range of parameter values. We demonstrate three major advantages of cue-driven cooperation. First, laggards cannot wipe out cooperation under a wide range of reasonable environmental conditions, in spite of an unconstrained possibility to mutate to cheating; in fact, cooperators may even exclude laggards at high cooperation thresholds. Second, lying almost never pays off, if the signal is an inevitable byproduct (i.e., the cue) of cooperation; even very cheap fake signals are selected against. And thirdly, QS is most useful if local cooperator densities are the least predictable, i.e., if their lattice-wise mean is close to the cooperation threshold with a substantial variance. ConclusionsComparing the results of the four different modelling approaches indicates that cue-driven threshold cooperation may be a viable evolutionary strategy for microbes that cannot keep track of past behavior of their potential cooperating partners, in spatially viscous and in well-mixed environments alike.

ecology↗

bioRxiv2022

General solution to biological signalling games: costly signalling and beyond

Explaining signal reliability poses a central problem in animal communication. According to Zahavis Handicap Principle (HP), signals are honest only when they are costly at the evolutionary equilibrium - hence the term handicap; otherwise, deception evolves, and communication breaks down. The HP has no theoretical or empirical support, despite claims to the contrary, and yet this idea remains immensely popular. Theoretical evaluations of the HP are difficult, however, because finding the equilibrium cost function in signalling games is notoriously complicated. Here we show how cost functions can be calculated for any arbitrary pairwise asymmetric signalling game at the evolutionary equilibrium. We clarify the relationship between signalling costs at equilibrium and the conditions for reliable signalling. We show that these two terms are independent and the costs of signalling at honest equilibrium have no effect on the stability of communication. We show that honest signals can take any cost value, even negative, being beneficial for the signaller independently of the receivers response at equilibrium, without requiring further constraints. Our results are general, and apply to seminal signalling models, including Grafens model of sexual selection and Godfrays model of parent-offspring communication. Our results refute the claim that signals must be costly at the evolutionary equilibrium to be reliable, as predicted by the HP and so-called "costly signalling" theory. The handicap paradigm can thus be fully rejected. We provide testable predictions to help advance the field and establish a better explanation for honest signals.

evolutionary biology↗

bioRxiv2019

Evolutionary implementation of Bayesian computations

The Bayesian framework offers a flexible language for the consistent modular assembly of statistical models used by both minds and machines. Another algorithmic domain capable of adaptation in potentially high-dimensional and uncertain environments is Darwinian evolution. The equivalence of their fundamental dynamical equations, replicator dynamics and Bayesian update, hints at a deeper algorithmic analogy. Here we show, based on a unified mathematical discussion of evolutionary dynamics and statistical learning in terms of Bayesian graphical models, that this is indeed the case. Building blocks of Bayesian computations, such as inference in hierarchical models, filtering in hidden Markov models, gradient likelihood optimization, and expectation-maximization dynamics of mixture models, map naturally to fundamental concepts of evolution: multilevel selection, quasispecies dynamics, phenotypic adaptation and ecological competition, respectively. We believe that these correspondences point towards a more comprehensive understanding of flavors of adaptive computation observed in Nature, as well as suggesting new ways to combine insights from the two domains in engineering applications.

evolutionary biology↗

bioRxiv2018

Major evolutionary transitions as Bayesian structure learning

Complexity of life forms on Earth has increased tremendously, primarily driven by subsequent evolutionary transitions in individuality, a mechanism in which units formerly being capable of independent replication combine to form higher-level evolutionary units. Although this process has been likened to the recursive combination of pre-adapted subsolutions in the framework of learning theory, no general mathematical formalization of this analogy has been provided yet. Here we show, building on former results connecting replicator dynamics and Bayesian update, that (i) evolution of a hierarchical population under multilevel selection is equivalent to Bayesian inference in hierarchical Bayesian models, and (ii) evolutionary transitions in individuality, driven by synergistic fitness interactions, is equivalent to learning the structure of hierarchical models via Bayesian model comparison. These correspondences support a learning theory oriented narrative of evolutionary complexification: the complexity and depth of the hierarchical structure of individuality mirrors the amount and complexity of data that has been integrated about the environment through the course of evolutionary history.

evolutionary biology↗

bioRxiv2017

One problem, too many solutions: How costly is honest signalling of need?

The \"cost of begging\" is a prominent prediction of costly signalling theory, suggesting that offspring begging has to be costly in order to be honest. More specifically, it predicts that there is a single cost function for the offspring (depending on e.g. offspring quality) that maintains honesty and it must be proportional to parents fitness loss. Here we show another interpretation of the cost. We demonstrate that cost, proportional to the fitness gain of the offspring, also results in honest signalling. Since the loss of the parent does not necessarily coincide with the gain of the offspring, it is provable that any linear combination of the two cost functions (one proportional to parents loss, one to offsprings gain) also leads to honest signalling. Our results, applied for a specific model, support the previous general conclusion that signalling games have different cost functions for different equilibria. Consequently, costly signalling theory cannot predict a unique equilibrium cost in signalling games especially in case of parent-offspring conflicts. As an important consequence, any measured equilibrium cost in real cases has to be compared both to the parents fitness loss and to the offsprings fitness gain in order to provide meaningfully interpretation.

evolutionary biology↗