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Author Topic:   Wells' Icons of Evolution - Peppered Moths
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 76 of 88 (114788)
06-13-2004 5:43 AM


rock pocket mice the new peppered moth?
Although this may seem off-topic at first, I feel this recent study in wild desert mouse populations serves as a genetic proof of the kind of melanic selection the peppered-moth studies suggest. I'm interested to see if others agree...
The genetic basis of adaptive melanism in pocket mice.Nachman MW, Hoekstra HE, D'Agostino SL. Proc Natl Acad Sci U S A. 2003 Apr 29;100(9):5268-73. PMID: 12704245
Briefly: Populations of "rock pocket" mice live in (mostly light-colored) rock outcroppings in the desert, and since mice avoid open areas, they are effectively geographically isolated to the rock outcroppings. Geologically recent outcroppings have formed through volcanic activity, these outcroppings are dark colored. Mice living on the light-colored rocks have light coats, those on the dark rocks have dark coats - the selection here being predation by birds.
The authors were able to determine the specific gene mutation (a melanocortin receptor) responsible for the melanism in one population of dark mice. Importantly, they were able to show that the dark coat allele was relatively young compared to the (presumably ancestral) light coat allele, since the light coat allele had ten times as many variant neutral polymorphisms. Also, the dark allele is dominant, so its initial recipient would have immediately received the benefits of camoflauge.
I guess part of the lure of the peppered moth is the idea that their selection has been witnessed (depending on who you ask) on a recent human timescale - though I appreciate that the dark mice with the younger allele in the above study are found on the geologically younger outcroppings - new niches were filled by those that adapted.
Unfortunately, the study includes photos of mice of different coat colors on different colored rocks - I'm sure the experiments will be discredited someday because the pictures were likely staged...
To some extent I don't understand the obsession surrounding the peppered moth observation (or its discreditation), given the many other examples of selection.
Thanks.

Replies to this message:
 Message 77 by JonF, posted 06-13-2004 9:07 AM pink sasquatch has not replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 78 of 88 (114870)
06-13-2004 5:55 PM
Reply to: Message 6 by cromwell
04-27-2004 5:44 AM


Re: The pepped -up myth
JonF, I don't know that I agree with you that Cromwell's attacks on selection in peppered moths is sophisticated - I feel he discredited his own argument in his first message in this thread:
Cromwell wrote : "All that has happened is a fluctuation of two variants of pre-existing moths,one becoming more dominant over the other in a given period of time and then reverting back to the original dominant variation through yet unknown means. Not natural selection."
To me, in this quote he has essentially stated, 'we witnessed selection occur, but it wasnt selection.
Which is very strange to me since, while trying to discredit predation-by-selection, he specifically proposes two other possible selection forces:
Cromwell: "Birds generally find ladybirds distasteful The bold colouring is a warning to most predators.Camouflage and predation played no part in the melanism of these insects.He also mentions the presence of other melanics in non polluted areas.Wells go’s on to say that several other factors could be involved, including possible differences in the tolerances of larvae to pollutants e.t.c."
(In fact, I would be interested to see a study on larval toxicity susceptibility to death or sterility it seems to be the best alternative selective force Ive heard of for this case)
I dont feel that Cromwell is actually arguing against selection, hes arguing against predation-by-bird as the specific selective force. Selection is selection regardless of the force even divine intervention if you want to take it that far
I would be interested to hear how Cromwell specifically defines selection, since from a genetic point of view he appears to have contradicted himself.
Thanks.

This message is a reply to:
 Message 6 by cromwell, posted 04-27-2004 5:44 AM cromwell has not replied

Replies to this message:
 Message 79 by JonF, posted 06-14-2004 9:30 AM pink sasquatch has not replied

  
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