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s_r_constantin's profile
Sarah Constantin
Sarah Constantin
Sarah Constantin
@s_r_constantin

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Sarah Constantin

@s_r_constantin

Math/ML/data-science person now working on solving aging...and helping with COVID19?! Founder, LRI and Daphnia Labs. Married to @oscredwin

Be
srconstantin.posthaven.com
Joined February 2019

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    1. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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      There's a cool literature about the evolution of Daphnia aging. Since they're short-lived, and are found in ponds and lakes all over the world, you can see how in some environments they evolved to live longer, while in others, they evolved to live shorter.

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    2. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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      The big determinant seems to be extrinsic mortality: the risk of dying of something *other* than old age. For instance, Daphnia that live in temporary ponds (which die when the pond dries up) have shorter lifespans in the lab than Daphnia that live in permanent lakes.

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    3. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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      https://academic.oup.com/plankt/article/35/2/253/1443660 … The evolutionary logic is: if you're going to die young anyway, it's better to put your energy resources towards producing offspring early and often, rather than making yourself durable. ("r-selection.")

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    4. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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      The opposite of r-selection is K-selection, in which you have fewer offspring, more of which survive. K-selected species tend to have larger bodies and longer lifespans. Humans, whales, elephants, and several bird species are among the most strongly K-selected animals.

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    5. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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      Going back to Daphnia: there is a lineage of Daphnia pulicaria in cold, fishless Lake Czarny (in the Tatra Mountains of Poland) that lives *two years.* Same species that in most lakes lives 3 months at most. https://sci-hub.tw/10.1007/s10750-012-1420-6 …

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    6. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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      That is, under conditions of low extrinsic mortality (no predators, no seasonal drying-up), Daphnia were able to evolve the capacity to octuple their lifespan.

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      Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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      In fact, there are *two* lineages in Lake Czarny: a short-lived, exclusively asexual strain (asexual reproduction accumulates more deleterious mutations than sexual reproduction; it seems to be another r-selected adaptation) and the long-lived sexually-reproducing strain.

      7:47 AM - 1 Sep 2019
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        2. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          The long-lived Daphnia are larger, and have more fat reserves to help them survive the winter. They are orange, possibly due to beta-carotene. And they stay in deeper, colder water, lowering their metabolic rates, which makes them live longer.

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        3. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          Small aquatic animals are governed by the Arrhenius equation: if you cool them down, *all* their chemical reactions go slower, including the ones that make their bodies break down with age. This obviously doesn't apply directly to warm-blooded mammals like us.

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        4. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          The connection between metabolic rate and lifespan does extend to mammals though. Smaller, short-lived, more r-selected mammals (like mice) have higher metabolic rates than long-lived K-selected mammals.

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        5. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          Vertebrates with exceptional longevity (tortoises and sharks can live centuries) are all cold-blooded; the naked mole rat (a mammal that appears not to senesce with age) is a rare example of a cold-blooded mammal; and mammals that hibernate age slower than mammals that don't.

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        6. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          Also, inducing hypothyroidism in rats (which lowers their metabolic rate) makes them live 30% longer. http://sci-hub.tw/https://doi.org/10.1016/0047-6374(86)90052-7 …

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        7. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          Genetic differences between short- and long-lived strains of similar species could point the way towards mechanisms to delay aging in humans. I don't expect simply lowering metabolism to be a good trade-off, but there may be other resilience mechanisms that we could "borrow."

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        8. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          The "bad" news is that humans are already pretty K-selected; we may already have most of the long-life adaptations we see in other animals. (Though it's worth doing a lot more comparative genomics to find out!)

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        9. Sarah Constantin‏ @s_r_constantin 1 Sep 2019
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          The "good" news is that evidence is accumulating all over the place that aging rates respond to evolutionary incentives. Any knob that Evolution can turn, Man can in principle learn to turn.

          0 replies 2 retweets 24 likes
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        10. End of conversation

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