Biological complexity: single-celled decision making (Introduction)

by David Turell , Wednesday, October 17, 2018, 18:35 (2015 days ago) @ David Turell

Diatoms divide to reproduce but under circumstances of poor food supply they turn to sexual reproduction. They can make decisions:

https://www.sciencedaily.com/releases/2018/10/181016154241.htm

"Unicellular diatoms are able to adapt their behavior to different external stimuli based on an evaluation of their own needs. In experiments, Seminavis robusta diatoms directed their orientation either towards nutrient sources or mating partners, depending on the degree of starvation and the need to mate.

"Unicellular diatoms are able to adapt their behavior to different external stimuli based on an evaluation of their own needs. This was discovered by scientists. The algae depend on nutrients in order to reproduce. However, they also need sexual mates which they find when they follow pheromone traces. In experiments, Seminavis robusta diatoms directed their orientation either towards nutrient sources or mating partners, depending on the degree of starvation and the need to mate. The tiny organisms demonstrated in fact a primitive form of behavioral biology.

"Diatoms are unicellular microalgae. They dominate marine phytoplankton, which is ubiquitous in our oceans. On shores and beaches, these algae can be observed as biofilms on rocks and other surfaces. Diatoms are not only the food source for many marine animals, but also responsible for an extremely important ecosystem service: They contribute significantly to global photosynthesis and thus to the production of oxygen on our planet. Moreover, they are discussed as possible produces of biofuels.

"The diatom Seminavis robusta is an ideal model organism for behavioral studies in the lab: The cells respond to different environmental conditions and their sexuality can be controlled. The research group ...wanted to know whether the tiny organisms are able to make decisions about what they needed more urgently: food or sexual mates.

"In order to find out, the scientists cultivated cells under different conditions. In particular, the cells were confronted with different amounts of nutrients and sex pheromones. Since diatoms primarily reproduce asexually by cell division, sexual reproduction may become necessary for their survival if the cells become smaller and smaller after continuous division. After all, the cells die if they become too small and fall below a minimum size. Diatoms also search actively for nutrients they need for the formation of their cell walls.
They can trace silicate minerals in their environment and move actively towards this food source. A recent study showed that they are attracted by the odor of the minerals.

"'It is striking that even unicellular organisms that obviously lack a nervous system can process different stimuli and even evaluate their individual needs. Our study showed that diatoms can adapt their behavior flexibly to environmental changes. They also responded differently depending on their need to sexually mate.

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"The scientist would now like to find out how the single-cell organisms perceive, process and evaluate chemical signals. "Our goal is to identify the corresponding receptors and signal processing pathways, but this will be a very complex endeavor given the fact that we know so little about these important micoralagae," says Georg Pohnert." ( my bold)

Comment: Note my bold. These scientists are looking to receptors and pathways, which in my opinion will be automatic, to explain the decision making.