Here is how environmental tolerances can interact with growing mass/complexity.
Temperature: As mass/complexity increases, tolerance ranges approach average (13-23 Celsius) relatively fast.
Pressure: As mass/complexity increases, tolerance range approaches lower pressure at an average pace.
Sunlight: As mass/complexity increases, tolerance range reduces tolerance to light relatively fast.
Salinity: As mass/complexity increases, tolerance to freshwater reduces at a fast pace.
Oxygen: No tolerance initially spawning. If needed at first before implementation of atmospheric changes, as mass/complexity increases, tolerance to oxygen decreases.
Editing this because I feel like the write up for salinity is short/simple enough to not have its own post for.
Salinity
Salinity tends to vary from sea to sea, though for the Microbe Stage we would mostly want to focus on the freshwater/saltwater divide. Realistically, there is only one patch that consists of freshwater in Thrive (river patches).
Though certain adaptations to salinity exist as macroscopic morphological structures, such as contractile vacuoles in eukaryotes, the majority of adaptations are focused on the membrane. Given how there is only one patch in the Microbe Stage which is freshwater, and given how the only meaningful differences in salinity are between two options, I honestly think it might be worth it to just have a freshwater/saltwater toggle in the membrane tab. We don’t need a very dynamic system since there is minimal variability, so it might be best to just make the adaptation simple and easy to manage, reducing the workload placed on the player to maintain their tolerance ranges.
We can involve a more detailed simulation of adaptations to salinity in the multicellular stage, where variance between patches won’t be as drastic.
Adding temperature tolerances to this post because of the consecutive reply limit.
Temperature
Probably the environmental condition which varies the most from patch to patch, it is important to nail down a player’s control over their tolerances to temperature.
Heat
Thermosynthase - Thermosynthase will inherently make a player favor high temperature environments, making them reliant on high temperature environments.
Thermosynthase Slider - A slider will be offered to organisms with thermosynthase allowing them to tolerate even the most stubbornly hot environments. This might be unnecessary if we don’t implement strong variances between extreme patches (there aren’t a large number of hydrothermal vents in the average playthrough anyways).
Sulfur Part Slider - A LAWK option for organisms who inhabit warmer environments. It will be harder for larger or more complex organisms to rely on this adaptation to survive in extreme environments, but prokaryotes and the simplest of eukaryotes will find them invaluable to life in warm ponds or hydrothermal vents.
Iron Part Slider - A LAWK option for organisms who inhabit warmer environments, analogous to the sulfur sliders.
More Fluid Membranes - Having a more fluid membrane will provide a slight boost to heat tolerance. This will allow complex organisms to ever so slightly adjust their tolerance ranges incase they inhabit slightly more heated oceans. The effects would be more dramatic in more simple organisms of course.
Cold
The biggest issue with cold adaptations relate to a snowball globe event or the frozen sea patches. Players can generally avoid both of these extremes by going to deeper patches, but even these environments will cool and the surface patches are very important hubs for various strategies (high oxygenation, sunlight, etc.) So it is important that these adaptations are relatively accessible for players.
Metabolosome/Mitochondria Slider - Since oxygenic respiration will likely be very common in the surface patches, this will help enhance accessibility.
Thylakoid/Chloroplast Slider - Similar to the above line of logic, photosynthetic organisms will inherently prefer surface environments which are more vulnerable to snowball earth events, so this helps those organisms.
More Rigid Membranes - More rigid membranes will serve as a slight boost to colder environments, allowing all organisms to finetune themselves. This will coincide with a greater tolerance to depths, which lines up nicely with the nature of deep-sea environments.
Attaching tolerances to the rigidity slider will allow a more universal capacity to adapt to non-extremophile environments, while attaching more dedicated upgrades to parts which relate to common compounds in patches will allow players to adapt to local extremophile conditions. I think it is important to emphasize the greater capacity of prokaryotes and simple organisms to adapt to temperature, so temperatures could be one of the more sensitive tolerance ranges to complexity and size.
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Oxygen
Perhaps the most important compound in the game, oxygen should be an influential resource in the game, dramatically transforming the nature of a player’s niche. The inherent challenge of oxygen in the beginning is between a caution of jumping the gun too quick by adopting oxygen tolerance before the compound becomes widespread, and missing out on the heightened capacities oxygenic metabolism can give you.
Bioluminescence - As Buckly had brought up in prior posts, bioluminescence is theorized to have originated partially as a way for bacteria to neutralize oxygen. Bioluminescence can be a useful adaptation for bacterial players who do not want to transition to oxygenic-metabolism yet or photosynthesis. It can provide a moderate resistance to oxygen which can be rather strong for less complex organisms, but perhaps not worth the energy for larger complex organisms.
Metabolosomes/Mitochondria - Metabolosomes and mitochondria, and really, any other oxygenic process, will provide a strong boost to oxygen tolerance (the first two parts mentioned getting the strongest boost).
Thylakoids/Chloroplasts - Because they produce oxygen, these parts can receive a moderate tolerance boost to their oxygen tolerances.
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Sunlight
Implementing a way to gain tolerance to sunlight can lead to interesting cases later, such as tidally locked planets. Adaptations to sunlight should be rather accessible.
Thylakoids/Chloroplasts - being dependent on sunlight, these parts will receive a strong tolerance boost to sunlight.
Non-Single Membranes - Providing a moderate boost to sunlight tolerance, this will incentivize players to transition away from single-layer membranes, which I think is important to encourage players to eventually move away from as they get more complex.
Melanin - A dedicated part to sunlight accessible to all cells, these can be a very accessible way to gain tolerance to sunlight.