Bluefins can generate so much heat in their bodies that their muscle fibres denature. Sometimes this happens while stressed on a fishing line, for example.
Some days ago there was news about some researchers predicting mammals would be doomed by the next supercontinent cycle, due to too high temperatures incompatible with warm blooded creatures. Well, if mammals can just evolve back cold blood, perhaps that makes their thesis moot. See https://news.ycombinator.com/item?id=37654289
Mammals have adapted to adverse conditions before. However, the current rate of change is unprecedented. Evolution does not happen in one or two generations.
This prediction isn't about climate change, it's about the formation of a new super continent. Because it'll be such a large landmass, and the energy from the sun increases by about 1% every 100 million years, the inner parts of this continent are predicted to be too hot to support most life as we currently know it. Of course, who can really say what will happen / evolve / be there by that time anyway?
That argument is only true for humans and other "long" lived species. For example look at at how much canines have evolved in the same time span that homosapiens have stayed relatively "static".
Long and static, in very very relative terms, of course.
Does that mean it can’t? I know at least a few people who are especially sensitive to heat and cold. It seems likely there are folks out there who could continue to survive environmental changes given our population, just not as many as currently exist.
Turning to cold blooded probably doesn’t, but evolution most certainly occurs in a generation. It may mean all but a few who manage to survive die but those are the ancestors of the new species
They have the same problems as mammals with high temperatures, but at higher temperatures, because their normal internal temperatures are higher than those of mammals.
There are bison on Catalina Island, left there by a film company around a hundred years ago. They are smaller than bison on the mainland:
“They’re very challenged healthwise when they’re on this island because they don’t have the adequate nutrition during the right time of year,” King said. “So, our bison are in fact a little smaller than the mainland, and it’s not a genetic difference. It’s due to not having the right nutrients at the right time.”
The article also notes that bison from the island were relocated back to the mainland on three separate occasions to try to reestablish herds here. I can't currently find a citation, but I recall reading that bison that were returned to the mainland put on weight.
It's well established that island populations of animals trend physically smaller. That part isn't at all news.
Endothermic: Generating internal heat to moderate body temperature, e.g., modern birds and mammals.
Ectothermic: Relying on the environment and behavior to regulate body temperature, e.g., typical reptiles.
Homeothermic: Maintaining a constant internal body temperature, e.g., modern mammals, birds, and some others.
Poikilothermic: Having a fluctuating internal body temperature depending on the local environmental conditions, e.g., typical reptiles and actinopterygiian fish.
Looking at only what you presented, it seems like Endothermic/Homeothermic share a lot of overlap (hot blooded) and Ectothermic/Poikilothermic share a lot of overlap (cold blooded)?
I think endo/ecto are mechanisms and homeo/poikilo are results. They mostly match up (why spend all that energy generating body heat if you're not going to use it to maintain a constant maximally-biochemically-effective temperature?) but not 100%. An ectothermic-homeothermic animal would have to put more effort into using the environment to maintain a constant body temperature. Google says there are some lizards in that category.
Huh. Is the evidence mostly bone growth patterns? That certainly seems likely to follow metabolism... but it does make me wonder what the difference is compared to hibernating mammals. (Much) longer periods at each rate? Something else?
Yes, it is a huge jump to assume the were cold blooded, rather than slow growing, or seasonal depending on the plants they ate. There's a lot of mammalian metabolism that stops working at room temperature.
Bears, and some other mammals, hibernate during which their metabolism drops. Any reason to believe this isn't just an exaggeration of that? It just seems really hard to believe actual cold bloodedness could appear like that. Why wouldn't lizards colonize the island instead?
I would suggest that it's best to think of it as the exact opposite, mammals came from ectothermic ancestors, and gradually began to develop what could be considered "extreme hyper-metabolic states" in comparison, which offered various advantages (denatures the proteins in many microorganisms, allows for consistent physical performance and activity at night when when most of the reptile predators were inactive) at the cost of needing a much higher and constant food/energy intake, and began to spend most of their time in such a state until it became "normal". However many mammals still require the ability to enter significantly lower metabolic states to survive every winter.
A good example is Golden Mantle Ground Squirrels for example, which need to consume enough omega-6 PUFAs (I believe linoleic acid is the primary one involved here, not sure about the others) in order to activate a switch in metabolism that ultimately drops energy use and puts them in a feedback loop to keep them there. [0] They'll periodically have rises in metabolism followed by some activity, and then drop back down into torpor throughout the winter. Squirrels that fail to kick off this change strongly enough are at big risk of burning too much energy and failing to survive the winter. Far less extreme and more well known are bears who also undergo significant fatty acid content changes. [1] Of course, metabolism is hideously complicated, and is effected by things like sunlight (touches vitamin D related pathways, among other things), vitamins (B vitamins are particularly notable) and fatty acids, proteins and carbs which all have have their own individual effects which can change in magnitude or even result in the reverse of what they "should" be doing. Look at this fucking shit and despair of ever trying to make a single correct context independent statement.[2] A perfect example I just found while looking up the other study is that while golden mantle ground squirrels appear to require linoleic acid to enter torpor, this study found that removing linoleic acid 19 days prior to hibernation enhanced how deeply they entered torpor. This isn't surprising to me, because I've heard of the possibility of linoleic acid being potentially exothermic in unusual circumstances, like extreme amounts. So laying off it once the cycle has started may allow the various feedback loops in place when monounsaturated fats run the show to more strongly express [3]
I personally consider all mammals as retaining echos of our cold blooded heritage and capable of enter lower metabolic states, both daily and seasonally (to a widely varying degree) depending on the aforementioned very complex set of conditions. This study seems to agree with me. [4]
So I also personally find it quite plausible that if evolution begins selecting against the hypermetabolism that was adopted, then the genetics are still ready and waiting for re-emergence, especially on an island where disease pressure is going to be much more limited. Evolution seems to like adding and repurposing things we already have, adding layers upon layers and rarely ever actually removing things.
As for why lizards wouldn't dominate the island, there were and still are lizards present, unlike the goats who didn't manage to evolve back into lizards fast enough to escape notice by humans and thus extinction (though a quick search seems to show that many lizards on the island are also considered endangered). That said lizards are generally predators/omnivores, whereas the goats are herbivores, so they weren't likely to be strongly competing for the same niche.
Readit News
[1] https://en.wikipedia.org/wiki/Naked_mole-rat
[2] https://en.wikipedia.org/wiki/Swordfish
[3] https://en.wikipedia.org/wiki/Thunnus
Long and static, in very very relative terms, of course.
Dead Comment
“They’re very challenged healthwise when they’re on this island because they don’t have the adequate nutrition during the right time of year,” King said. “So, our bison are in fact a little smaller than the mainland, and it’s not a genetic difference. It’s due to not having the right nutrients at the right time.”
https://www.voanews.com/a/history-catalina-bison-hollywood-t...
The article also notes that bison from the island were relocated back to the mainland on three separate occasions to try to reestablish herds here. I can't currently find a citation, but I recall reading that bison that were returned to the mainland put on weight.
It's well established that island populations of animals trend physically smaller. That part isn't at all news.
Big animals trend smaller (https://en.wikipedia.org/wiki/Insular_dwarfism), and small animals trend bigger (https://en.wikipedia.org/wiki/Island_gigantism). Hence the giant rabbits on Menorca that these goats outcompeted when the islands were connected (https://en.wikipedia.org/wiki/Nuralagus).
You have:
A good example is Golden Mantle Ground Squirrels for example, which need to consume enough omega-6 PUFAs (I believe linoleic acid is the primary one involved here, not sure about the others) in order to activate a switch in metabolism that ultimately drops energy use and puts them in a feedback loop to keep them there. [0] They'll periodically have rises in metabolism followed by some activity, and then drop back down into torpor throughout the winter. Squirrels that fail to kick off this change strongly enough are at big risk of burning too much energy and failing to survive the winter. Far less extreme and more well known are bears who also undergo significant fatty acid content changes. [1] Of course, metabolism is hideously complicated, and is effected by things like sunlight (touches vitamin D related pathways, among other things), vitamins (B vitamins are particularly notable) and fatty acids, proteins and carbs which all have have their own individual effects which can change in magnitude or even result in the reverse of what they "should" be doing. Look at this fucking shit and despair of ever trying to make a single correct context independent statement.[2] A perfect example I just found while looking up the other study is that while golden mantle ground squirrels appear to require linoleic acid to enter torpor, this study found that removing linoleic acid 19 days prior to hibernation enhanced how deeply they entered torpor. This isn't surprising to me, because I've heard of the possibility of linoleic acid being potentially exothermic in unusual circumstances, like extreme amounts. So laying off it once the cycle has started may allow the various feedback loops in place when monounsaturated fats run the show to more strongly express [3]
I personally consider all mammals as retaining echos of our cold blooded heritage and capable of enter lower metabolic states, both daily and seasonally (to a widely varying degree) depending on the aforementioned very complex set of conditions. This study seems to agree with me. [4] So I also personally find it quite plausible that if evolution begins selecting against the hypermetabolism that was adopted, then the genetics are still ready and waiting for re-emergence, especially on an island where disease pressure is going to be much more limited. Evolution seems to like adding and repurposing things we already have, adding layers upon layers and rarely ever actually removing things.
As for why lizards wouldn't dominate the island, there were and still are lizards present, unlike the goats who didn't manage to evolve back into lizards fast enough to escape notice by humans and thus extinction (though a quick search seems to show that many lizards on the island are also considered endangered). That said lizards are generally predators/omnivores, whereas the goats are herbivores, so they weren't likely to be strongly competing for the same niche.
[0] "The Influence of Dietary Fatty Acids on Hibernation by Golden-Mantled Ground Squirrels (Spermophilus lateralis)": https://www.journals.uchicago.edu/doi/10.1086/physzool.65.5....
[1] "Lipidomics Reveals Seasonal Shifts in a Large-Bodied Hibernator, the Brown Bear": https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6474398/
[2] Metabolic pathway charts:
- The famous Roche chart: http://biochemical-pathways.com/#/map/1
- Hand assembled map of the above https://faculty.cc.gatech.edu/~turk/bio_sim/articles/metabol...
[3] Short-Term Variations in Diet Fatty Acid Composition and Torpor by Ground Squirrels: https://www.jstor.org/stable/1383506
[4] "Daily torpor and hibernation in birds and mammals": https://onlinelibrary.wiley.com/doi/10.1111/brv.12137
Dead Comment