Inbreeding and evolution

[Dr Lou Natic]

I was watching a documentary(I say that alot here I watch alot of documentaries) that was called "the island of the vampire birds" and it really was remarkable.
In 1983 the galapogas(sp?) islands suffered a drastic 'el nino'. What was usually a fairly arid climate suddenly was drenched in torrential rain for months on end.

You would think this would be a welcome change, thirsty sea birds took their first drink in weeks but for some of the islands inhabitants it was disastrous. Marine iguana's starved as seagrasses (their staple diet) stopped growing because they couldn't survive in the now fresh water near the coast, they needed saltwater. As did the fish which moved away, forcing mother sealions to abandon their pups and travel out further to sea.

But the tiny number of finches that live their thrived. In 1983 there was one male and 3 females. I can't remember how they got there. Anyway with the new rain and plants the adaptable finch's numbers flourished to enormous proportions, somewhere in the tens of thousands.
But eventually the area went back to its old self, it stopped raining and the plants died, the finches food was in short supply, but the finch is far from specialised and will eat anything it can get. The finches started sucking the blood out of other animals wounds and eating afterbirth and so on. Hence the "island of the vampire birds title".

But in an alarmingly short amount of time the birds started evolving physically to be better suited for blood sucking. Their beaks became narrower and longer and their nasal cavities and smelling ability changed to be more efficient at sniffing out bleeding animals.

Anyway my theory(and this was not mentioned in the documentary) is inbreeding can speed up the process of evolution. Remember their was one male and three females to start with. Those finches evolved REALLY fast. Clearly all those birds were inbred and pretty much everything must be to a certain degree. We all know inbreeding can cause deformities but what if the reason for that is to form a new species when populations are low.

The only reason inbreeding would/should occur is if there were only few members of a species in an area. Perhaps it weakens the genetic history to allow for better adaptations to the species' current environment.

I should try and get a grant to test this theory
Although I suppose you'd have to be a "scientist" to get one of those

 

[river-wind]

two things-

1)I worked on a study of the relationship between marine iguana size/water temp in the Galapagos (the Marine iguana population drop off, IMO, has more to due with the pushing of the warm, mineral barren el nino current into the territories normally covered by the northern, cold (and nutrient rich) Humbolt current; I think this because the el nino rains are caused by the pushing north of the el nino current, and the sea grass as well as the marine iguanas are significantly smaller in the warmer el nino waters), and I've never heard of blood sucking finches. However:
http://www.gct.org/birdfact.html
"...(and one, the sharp-billed ground finch, also known as the vampire finch, feeds on blood from other birds!)..."

so that shows what I know.



2)to take an example from the computer industry- the smaller the code that needs to be changed, the faster it can evolve- the change to a single line of code in 100 lines will produce a more profound effect on the final program that the same change will in the midst of 10 million lines of code.

from a genetics standpoint, inbreeding is not a bad thing- it simply condenses mutations. If those mutation end up helping the survival of the population, then the mutations are called 'evolution', and they are good. If the mutations hinder the survival of an individual, then the idividual will be less likely to reproduce, and therefore pass on the mutation. therefore, the mutationwas bad, and it doesn't survive.
The smaller the population in question, the more profound the effect of one mutation will be. If the one male finch held a mutation in his genes, then 100% of the next generation would have that mutation; if one funch on an island full of finches has a mutation, then something like 1/5000th of the next generation would hold that same mutation.



and if you want a grant, apply for one! you prolly won't get it w/o a BS degree at least, but you never know. Another option would be to become a TA on some college professor's summer feild study- you could get paid to help do this sort of thing.

If you want to do any work on the Galapagos isl., I suggest you get ahold of the head of the Charles Darwin Research Station
I don't know who is heading it up now, but you should be able to conact them via the Universidad de San Fransisco de Quito , located in Ecuador's capital city of Quito.

Washington College (Chestertown, MD); Carnegie Mellon Uni, Cornell, Berkley, and San Jose Uni all do summer Galapagoes biology trips.

 

[Dr Lou Natic]

Oh so it is known that inbreeding is what causes the mutations that cause the evolution of a new species? Is that what you are saying?
And here I was thinking I was onto something.... oh well.
It makes sense though, a successful species won't change because their gene pool is so large and varied, they obviously won't need to change either considering the fact that they are successful.
But if a small number of a species move to an area inbreeding will cause mutations that will possibly assist them in surviving in their new environment. The finches were more open to change because of their tiny gene pool and this helped them greatly by mutating their beaks to be better suited for their new habitat.
Nature is so logical it would make spock blush

The kind of test I would do would be something along the lines of this:
Build 2 habitats. Get 2 groups of mice with about 4 mice in one group and many in the other.
Make the habitats have a large pool and put all the mice food in the water so they need to swim to get it.
If this theory was correct the inbred mice might start evolving webbed feet or something.
Do you think this would work?
How long do you think it would take for them to start evolving?
I'm thinking at least 20 years or something
Also this would cost heaps of money as the habitats would need to be fairly large

And I just got a thought, mice probably wouldn't be the best as they are naturally adapted to everything. They already can swim well. They are already very well rounded creatures.
Anyone else have any other ideas?

 

[spuriousmonkey]

use a species with a short lifespan, such as drosophila or c. elegans.

C. elegans is nice of course because they are so easy to keep. To check for inbreeding would be real easy, because they are hermaphrodite. Just pick up one worm and make a colony out of that. Or for your experiment, pick one worm, divide the progeny in two colonies. One colony is kept either in the freezer (and hence nothing will change!!!), the other one is kept in non-standard conditions. After a while (year? months?) you thaw your original and compare them with your experimental worms.

 

[river-wind]

Oh so it is known that inbreeding is what causes the mutations that cause the evolution of a new species? Is that what you are saying?

No, sorry if I wasn't more clear. The mutations in the genetic code happen at a regular rate, indipendant of the type of reproduction going on. However, if the genetic population is smaller, then it is more likely for the mutations (which happen all the time), to be passed to the next gereation.


for example, you have 2 individuals, who have a gene X. Each individual have 2 copies of the gene (chromosome pair, each cell has two copies of each chromosome). One of the individuals has a mutation in one copy of the gene.
So, we now have 3 X genes, and 1 x gene.
these two individuals mate, and you get the following:
_|_X|_x
X|XX|Xx
X|XX|Xx

If you haven't seen one of these graphs before, it is showing the probability for each offspring to end up with a certain combination of the genes. as each parent (the p1 generation) gives the child (f1 generation) 1 copy of the gene, the father(XX) has a 100% chance to pass on an X copy, because that's all he has to offer. The mother(Xx) has a 50% chance to give the offspring an X, and a 50% chance to give the offspring an x.
Therefore, there is a 50% (2/4) chance that an individual in the f1 generation will have XX, and a 50% (2/4) chance that it will have Xx.

because we have no other input of genes into this system, lets say that the original two indivuals have two offpsring. let's also say that it ends up that one of the individuals is a male XX, and one is a male Xx. We still ahve 50% of the population 50% likely to pass on the x copy of the gene in question, so no eveolution will occur.
But let's say that having the x copy of the gene causes you to be slightly stronger than your neighbor.
Because we have four individuals now, three of which are males, the graph looks like this:

__|___Xx__|___XX__|___XX
__|_|X_|_x|_|X_|_X|_|X_|_X|
__|X|XX|Xx|X|XX|XX|X|XX|XX|
Xx|x|Xx|xx|x|Xx|Xx|x|Xx|Xx|


Where the first row and left most colums represent the individuals, the second row and the second column from the top and the left are the possible genes to be passed on.
In a normal case, we now have 5/12 (41.67%) chances to get XX, 6/12 (50%) chances to get Xx, and 1/12 (8.33%) chances to get xx.

Now we get to the point where the effect of this mutation come into play. The above graph is assuming that all the genes have the same rate of survival, and all the individuals have the same chance to reproduce.
most of the time, that is the case (most mutations do not result in any sort of change in the individual, as more than one gene triplet will code for the same amino acid- switcha G with a C in the DNA, and you still may code for the same amino acid, so you will never see a change).

However, sometimes, this change does eefect the individual, and selective evolution come into play. Let's say that having a copy of x makes you 10% stronger. There is now a 10% better chance that you wil succeed in sUrviving and reproducing, there is a 20% better chance if you have xx (I am not assuming dominant/recessive genes, like humand have for left/right handedness, but gradual genes, like for haircolor).
So let's say the female one mates one more time before she dies, so she gets with the Xx guy.

you get:
_|_X|_x
X|Xx|Xx
x|Xx|xx

This is the classic 25/50/25 chart you'll see constantly when looking at Gregor Mendel's pea plant experiments. 25% chance XX, 50% chance Xx, 25% chance of xx.
Lets say that these two have 4 off spring, and they fit the graph one for one. so our current population is p1-XX, Xx f1-Xx, XX f2- XX, Xx, Xx, xx. The p1 female is no longer going to have kids, so we remove her from the *reproductive population". For the ease of numbers, lets also say that the p1 male gets eaten by a cat, as does a random other individual, one of the p2 Xx'ers- so we remove them as well
so our reproductive group is now f1- XX, Xx f2- XX, Xx, xx. We have 2/5 individuals with XX, 2/5 with Xx, and 1/5 with xx. that's 40%,40% and 20%. The appearance of the x copy of the gene has gone from 25% in generation 1 to 4/10 copies, or 40% of the genepool in just two generations.
Because the x gene helped with survival, it reproduced more often, and their for the population, overall, evolved to be stronger.


to attach this whole thing to inscest-
Let start with the f1 generation table from above, and produce a mutation in one of the XX males:
__|___Xx__|___XX__|___Xq
__|_|X_|_x|_|X_|_X|_|X_|_q|
__|X|XX|Xx|X|XX|XX|X|XX|qX|
Xx|x|Xx|xx|x|Xx|Xx|x|Xx|qx|

in comparison with with the first chart,:
_|_X|_x
X|XX|Xx
X|XX|Xx

where the x mutation had a 50% chance to be passed onto the next generation, the q mutation above only has a 2/12 chance to be passed on - a mere 16.67%. The smaller the population (ie, the more likely the chance of inscest), the greater the chance that a particular gene can get passed on. To take it further, by having inscetuous sex, you are reducing the reproductive population to your own family gene pool, so any mutation that you have is more likely to exsist i your sister than in a complete stranger. So inscest would make the chances of the offspring having that same mutation higher. If that mutation turns out to help the individuals, then inscest will drive evolution. if it hurts the individual, you end up with the royal family


The mutations happen due to chemistry, the population size has a say only on whether or not that gene gets passed on to the next generation. Other factors, such as male/female ratio, and whent qhysical effect the gene has also plays a large part, but population size is the biggest thing.


The question to test would be is the rate of helpful mutations to harmful mutations- in order for evolution to occur, the mutations have to help reproduction occur. if bad mutations and good mutation occur at the same rate, then the active factor which drives evolution is the failure of those individuals with harmful mutations to reproduce, not the mutations themselves.
What would be interesting to test is if the useful mutation rate actually changed in a small reproductive population. That would be a pretty huge find- that evolution was not only driving changes in a population, but that it was driving changes in itself to; evolution driving changes in rates and methods of evolution. Possibly even top the extent where it could be shown that the rate of usefull mutationtion are not explainable by chance alone. Then you may have proven that God exsists



On a total side note- because we know that DNA mutation happens at a fairly regular rate in humans (the rate of mutation varries slightly from species to species- it's almost not noticeable), we can look at to related individuals, and estimate how long ago their common ansestor lived. Because we can assume that all humans came from a single individual at some point with pretty good certaintly, we can track how far removed everyone is from each other, and about how far back that originall ansestor lived. But we ran into a problem when we tried. It is appearent that there was a huge die off of the global human population a few tens of thousands of years ago (I forget the exact estimate) to the point where there were only fe wthousand individual humans left. The individuals were all on different mutational family lines, so the remaining population was made up of a rag tag group of genetically non-related people. I just find that interesting bit, it doesn't really apply here.


back to work now I'll check back later in case I made any mistakes above, or if there are any questions.

 

[ElectricFetus]

Inbreeding helps evolution in 2 ways:
1. Inbreeding limits a population to very small sizes and a new gene or allele can spread through this population very quickly. The larger the population the slower a new trait travels though it no matter how good it is.
2. Hybriding or normal breed usually allows for new mutated alleles to be covered by their normal working versions, but in inbreeding this does not happens and new freakish mutations run a high chances of being completely phenosized.