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Dryad

Understanding ecological adaptation in the microorganism Tetrahymena pyriformis through the lens of energy allocation

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Mar 15, 2024 version files 186.33 MB
Mar 15, 2024 version files 186.33 MB

Abstract

To survive and reproduce, living organisms need to maintain an efficient balance between energy intake and energy expenditure. When the environment changes, a previously efficient energy allocation strategy may become inefficient in the new environment, and organisms are required to adapt to the new environment by changing their morphology, physiology, and behaviour. However, how multiple phenotypic traits interact with each other and with the characteristics of the environment to determine energy allocation is poorly understood. To address this knowledge gap, we adapted axenic populations of the ciliate Tetrahymena pyriformis to different environmental conditions of temperature and resource levels, and measured population growth, metabolic rate, cell size, and movement speed. On a very short time scale, movement speed and metabolic rate increased with environmental temperature in a way that could be predicted from simple physical scaling relations such as the Boltzmann-Arrhenius equation and the `viscous drag' impacting movement. However, soon after the introduction of Tetrahymena into a novel environment, all measured quantities were further modulated in a direction that likely provided higher biomass production in the new environment. Changes in cell size played a central role in mediating these adaptations, by simultaneously affecting multiple phenotypic traits, such as metabolic rate and the energetic costs of movement, and -- in a small organism like Tetrahymena -- size changes can happen over rapid timescales, relative to the timescales of ecological changes and seasonal environmental fluctuations.