Biology subjects

Akcay, E.

Publications and source records attributed to Akcay, E..

6 recordsLinked to original sources

bioRxiv2018

The blind choreographer: evolution of social norms and correlated equilibria

Social norms regulate and coordinate most aspects of human social life, yet they emerge and change as a result of individual behaviours, beliefs, and expectations. A satisfactory account for the evolutionary dynamics of social norms therefore has to link individual beliefs and expectations to population-level dynamics, where individual norms change according to their consequences for individuals. Here we present a new model of evolutionary dynamics of social norms that encompasses this objective and addresses the emergence of social norms. In this model, a norm is a set of behavioural prescriptions and a set of environmental descriptions that describe the expected behaviours of those with whom the norm holder will interact. These pre-scriptions and descriptions are functions of exogenous environmental events. These events have no intrinsic meaning or effect on the payoffs to individuals, yet beliefs/- superstitions regarding them can effectuate coordination. Though a norm's prescriptions and descriptions are dependent upon one another, we show how they emerge from random accumulations of beliefs. We categorize the space of social norms into several natural classes and study the evolutionary competition between these classes of norms. We apply our model to the Game of Chicken and the Nash Bargaining Game. Further, we show how the space of norms and evolutionary stability is dependent upon the correlation structure of the environment, and under which such correlation structures social dilemmas can be ameliorated or exacerbated.

evolutionary biology↗

bioRxiv2018

Evolution of transmission mode in conditional mutualisms with spatial variation in symbiont quality

While some symbioses are always mutualistic or parasitic, others have costs and benefits that depend on environmental factors. The environmental context may itself vary in space, in some cases causing a symbiont to be a mutualist in one location and a parasite in another. Such spatially conditional mutualisms pose a dilemma for hosts, who might evolve (higher or lower) horizontal or vertical transmission to increase their chances of being infected only where the symbiont is beneficial. To determine how transmission in hosts might evolve, we modeled transmission evolution where the symbiont had a spatially conditional effect on either host lifespan or fecundity. We found that over ecological time, symbionts that affected lifespan but not fecundity led to high frequencies of infected hosts in areas where the symbiont was beneficial and low frequencies elsewhere. In response, hosts evolved increased horizontal transmission only when the symbiont affected lifespan. We also modeled transmission evolution in symbionts, which evolved high horizontal and vertical transmission, indicating a possible host-symbiont conflict over transmission mode. Our results suggest an eco-evolutionary feedback where the component of host fitness that a conditionally mutualistic symbiont influences affects its distribution in the population, and, through this, the transmission mode that evolves.

evolutionary biology↗

bioRxiv2017

Competition and niche construction in a model of cancer metastasis

Niche construction theory states that not only does the environment act on populations to generate Darwinian selection, but organisms reciprocally modify the environment and the sources of natural selection. Cancer cells participate in niche construction as they alter their microenvironments and create pre-metastatic niches; in fact, metastasis is a product of niche construction. Here, we present a mathematical model of niche construction and metastasis. Our model contains producers, which pay a cost to contribute to niche construction that benefits all tumor cells, and cheaters, which reap the benefits without paying the cost. We derive expressions for the conditions necessary for metastasis, showing that the establishment of a mutant lineage that promotes metastasis depends on niche construction specificity and strength of interclonal competition. We identify a tension between the arrival and invasion of metastasis-promoting mutants, where tumors composed only of cheaters remain small but are susceptible to invasion whereas larger tumors containing producers may be unable to facilitate metastasis depending on the level of niche construction specificity. Our results indicate that even if metastatic subclones arise through mutation, metastasis may be hindered by interclonal competition, providing a potential explanation for recent surprising findings that most metastases are derived from early mutants in primary tumors.

cancer biology↗

bioRxiv2017

Collapse and rescue of cooperation in evolving dynamic networks

The evolutionary dynamics of social traits depend crucially on the social structure of a population, i.e., who interacts with whom. A large body of work studies the effect of social structure on behaviors such as cooperation, but relatively little is known about how social structure itself coevolves with social traits. Here, I use a simple yet realistic model of within-group social structure to study such coevolution. In this model, social connections are either inherited from a parent or made with random individuals. My model shows cooperation can evolve when individuals make few random connections, but the presence of cooperation selects for increased rates of random connections, which leads to the collapse of cooperation. Inherent costs of social connections can prevent this negative feedback, but the more beneficial cooperation is, the higher linking costs have to be maintain it, and linking costs can negate some or all of the aggregate benefits of cooperation. Exogenously maintained social inheritance can mitigate the latter problem and allow cooperation to persist and increase the average fitness of a population. These results illustrate how coevolutionary dynamics can constrain the long-term persistence of cooperation.

evolutionary biology↗

bioRxiv2017

Deriving C4 photosynthesis parameters by fitting intensive A/Ci curves

Measurements of photosynthetic assimilation rate as a function of intercellular CO2 (A/Ci curves) are widely used to estimate photosynthetic parameters for C3 species, yet few parameters have been reported for C4 plants, because of a lack of estimation methods. Here, we extend the framework of widely-used estimation methods for C3 plants to build estimation tools by exclusively fitting intensive A/Ci curves (6-8 more sampling points) for C4 using three versions of photosynthesis models with different assumptions about carbonic anhydrase processes and ATP distribution. We use simulation-analysis, out-of-sample tests, existing in vitro measurements and chlorophyll-fluorescence-measurements to validate the new estimation methods. Of the five/six photosynthetic parameters obtained, sensitivity analyses show that maximal-Rubisco-carboxylation-rate, electron-transport-rate, maximal-PEP-carboxylation-rate and carbonic-anhydrase were robust to variation in the input parameters, while day-respiration and mesophyll-conductance varied. Our method provides a way to estimate carbonic anhydrase activity, a new parameter, from A/Ci curves, yet also shows that models that do not explicitly consider carbonic anhydrase yield approximate results. The two photosynthesis models, differing in whether ATP could freely transport between RuBP and PEP regeneration processes yielded consistent results under high light, but they may diverge under low light intensities. Modeling results show selection for Rubisco of low specificity and high catalytic rate, low leakage of bundle sheath and high PEPC affinity, which may further increase C4 efficiency.

plant biology↗

bioRxiv2016

Phylogenetic analysis suggests joint control of transmission mode in a grass-endophyte symbiosis

How symbionts are transmitted between hosts is key to determining whether symbioses evolve to be harmful or beneficial. Vertical transmission favors mutualistic symbionts, and horizontal transmission more virulent ones. Transmission mode evolution itself depends on whether the host or symbiont can respond to selection on transmission mode. When hosts control the transmission mode, vertical transmission should evolve under more restrictive circumstances than when symbionts are in control. We take a phylogenetic approach to determine whether the host, symbiont, or both control transmission mode using the pooid grass-epichloid endophyte symbiosis as a model system. This study is the first to investigate control of transmission mode evolution in a phylogenetic context. We find a signal of host phylogeny but only in conjunction with symbiont identity. This pattern suggests joint control of transmission mode by the host and symbiont. It also suggests that non-genetic or non-conserved symbiont traits may determine whether host traits lead to vertical or horizontal transmission.

evolutionary biology↗