Genetic diversity and life-history strategies
May 20, 2018 6:43 AM Subscribe
This previous genetics question led to this answer, with links to some fascinating papers about genetic diversity. These papers have led me to a random smattering of questions, below the cut. I'd be happy for answers to (or informed speculation about) any or all of them. Thanks!
- K-strategists with high parental investment have lower genetic diversity for a given effective population size than r-strategists with low parental investment. As I understand it, measures of genetic diversity are used to estimate past population bottlenecks. Does this mean that previous estimates of human population bottlenecks might have to be revised given the lower rates of genetic diversity in K-strategists that we've recently learned about?
- Linked selection has a significant impact on genetic diversity. Does this mean that one role for "junk" DNA might be simply as spacers between genes, so that alleles can be selected independently rather than driven to fixation by their more strongly-selected neighbours?
- I've recently been obsessed with reframing evolutionary ideas in terms of conservative vs. diversified bet-hedging, broadly conceived. Am I completely off-base to think of r-strategists as diversified bet-hedgers and K-strategists as conservative bet-hedgers?
- Why have I never heard of the recombination that happens in humans between X and Y chromosomes in the pseudoautosomal region?
- What do you think of this hypothesis as a potential explanation for the differences in genetic diversity between K- and r-strategists?
In species with high parental investment, there's an opportunity to pass information to offspring by means other than DNA. Consistently building - i.e. with low genome diversity - parallel information-transfer mechanisms (ways to teach and learn other than DNA) is useful. Information that's useful to offspring about local and short/medium-term conditions can be transferred and stored via neuronal learning or chemical signalling or one of the other means.
In species with low parental investment, DNA is (close to) the only information transfer mechanism. If genomic diversity is eliminated, information about how to deal with different local and short/medium-term conditions is eliminated. Diversified bet-hedging becomes essential if you want at least some of your many offspring to be successful on the constantly-changing evolutionary seascape.
- K-strategists with high parental investment have lower genetic diversity for a given effective population size than r-strategists with low parental investment. As I understand it, measures of genetic diversity are used to estimate past population bottlenecks. Does this mean that previous estimates of human population bottlenecks might have to be revised given the lower rates of genetic diversity in K-strategists that we've recently learned about?
- Linked selection has a significant impact on genetic diversity. Does this mean that one role for "junk" DNA might be simply as spacers between genes, so that alleles can be selected independently rather than driven to fixation by their more strongly-selected neighbours?
- I've recently been obsessed with reframing evolutionary ideas in terms of conservative vs. diversified bet-hedging, broadly conceived. Am I completely off-base to think of r-strategists as diversified bet-hedgers and K-strategists as conservative bet-hedgers?
- Why have I never heard of the recombination that happens in humans between X and Y chromosomes in the pseudoautosomal region?
- What do you think of this hypothesis as a potential explanation for the differences in genetic diversity between K- and r-strategists?
In species with high parental investment, there's an opportunity to pass information to offspring by means other than DNA. Consistently building - i.e. with low genome diversity - parallel information-transfer mechanisms (ways to teach and learn other than DNA) is useful. Information that's useful to offspring about local and short/medium-term conditions can be transferred and stored via neuronal learning or chemical signalling or one of the other means.
In species with low parental investment, DNA is (close to) the only information transfer mechanism. If genomic diversity is eliminated, information about how to deal with different local and short/medium-term conditions is eliminated. Diversified bet-hedging becomes essential if you want at least some of your many offspring to be successful on the constantly-changing evolutionary seascape.
In species with low parental investment, DNA is (close to) the only information transfer mechanism.
Along this line, I invite you to fall down the rabbit hole of epigenetics, where information from environmental cues can activate or suppress certain genes, and those induced characters can be heritable without being actually coded in DNA. I'm working for a lab that has done a lot of research into epigenetic characters in spadefoot toads, and it's so nuts that I'm still trying to wrap my mind around it.
posted by Drosera at 5:00 AM on May 21, 2018 [1 favorite]
Along this line, I invite you to fall down the rabbit hole of epigenetics, where information from environmental cues can activate or suppress certain genes, and those induced characters can be heritable without being actually coded in DNA. I'm working for a lab that has done a lot of research into epigenetic characters in spadefoot toads, and it's so nuts that I'm still trying to wrap my mind around it.
posted by Drosera at 5:00 AM on May 21, 2018 [1 favorite]
Response by poster: SaltySalticid: Got your MeMail, thanks! And you know Wikipedia is user-editable, right? ;-)
Drosera: I've read a little bit about epigenetics. I seem to recall that epigenetic markers are stripped when gametes are formed in at least some species (mammals, mostly?). It would be interesting to know whether there's any connection between number of heritable epigenetics markers and life history strategies as there is with genetic diversity. I'll check out the paper, thanks!
posted by clawsoon at 5:49 AM on May 21, 2018
Drosera: I've read a little bit about epigenetics. I seem to recall that epigenetic markers are stripped when gametes are formed in at least some species (mammals, mostly?). It would be interesting to know whether there's any connection between number of heritable epigenetics markers and life history strategies as there is with genetic diversity. I'll check out the paper, thanks!
posted by clawsoon at 5:49 AM on May 21, 2018
I'm really swamped at work right now. I wish I had the time and energy to contribute more to the discussion!
A few random thoughts...
Noncoding RNAs are really interesting. Have you heard of RNA-directed DNA methylation? It's a mechanism of epigenetic regulation. Maternal siRNAs can have some function in offspring tissues, at least in model plants. So there's a non-DNA mechanism that's transmitted through generations. Here's a paper on RdDM (some of the authors are in my department).
One reason for the accumulation of 'junk' DNA is that selection is too weak to purge it. Check out Mike Lynch's mutation-hazard hypothesis.
Relevant to genome size evolution and noncoding DNA, an interesting case is that of Utricularia gibba, a carnivourous, aquatic plant with a very small genome. Paper
End transmission of random biology thoughts. Gotta get back to writing.
posted by vortex genie 2 at 2:40 PM on May 22, 2018
A few random thoughts...
Noncoding RNAs are really interesting. Have you heard of RNA-directed DNA methylation? It's a mechanism of epigenetic regulation. Maternal siRNAs can have some function in offspring tissues, at least in model plants. So there's a non-DNA mechanism that's transmitted through generations. Here's a paper on RdDM (some of the authors are in my department).
One reason for the accumulation of 'junk' DNA is that selection is too weak to purge it. Check out Mike Lynch's mutation-hazard hypothesis.
Relevant to genome size evolution and noncoding DNA, an interesting case is that of Utricularia gibba, a carnivourous, aquatic plant with a very small genome. Paper
End transmission of random biology thoughts. Gotta get back to writing.
posted by vortex genie 2 at 2:40 PM on May 22, 2018
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No, that's totally reasonable, and a good first-order intuitive explanation of what those strategies are doing.
But I should point out that the WP article has some problems with how it's using "fitness". For example I would not let this sentence stand without heavy qualification if I got it as a reviewer "an annual plant's fitness is maximized for that year if all of its seeds germinate." There are many notions of fitness, but that sentence is problematic if not wrong for most of the ones currently in favor. All this stuff is best understood in terms of environmental variation in space and time, and a lot is lost by only looking at variation withing species' traits. Also, if you look closely enough, virtually all species are really doing some sort of adaptive strategy, modulating reproduction based on current and recent past conditions is by far the norm, not the exception.
This is all very interesting stuff, I'll memail you later to share some of my work involving life-history strategies :)
posted by SaltySalticid at 7:07 AM on May 20, 2018 [1 favorite]