2 industrial melanism this used to be the prime

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2. Industrial melanism . This used to be the prime example. a. Many species including Biston betularia in Britain. Monomorphic (Def. one form only) and light-colored at first (typical = peppered). Melanic begin to be seen in 1848, and it increased all over the industrial world. Up to 98% of total in some places at peak. Melanic match dark background. Slides b. Heritable. Multiple alleles at single locus. c. Kettlewell did famous experiment . Film loop . Showed that blackened trees camouflaged melanic and vice versa. Looked like clear case of natural selection caused by change in tree-trunk color. Tree trunks blackened by soot. d. Book by Majerus Melanism in 1998 gave much criticism. Review by Grant in your discussion section. One of the main objections was that Kettlewell used wrong part of tree, the trunk: only 2 seen on trunk in 40 years. Moths are very hard to find in nature, and they seem to be on branches in canopy, but not sure where most are . Slide The experiment definitely showed differences, but if predation artificially enhanced…? TWS reads paragraph by Paul Raeburn of review of book by Judith Hooper
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e. What do we know? i. Works on average over the two types of environments. Capture-recapture Slide ii. There was a rapid evolution. Def of evolution: change in gene frequency. Something did it. Roughly the same pattern occurred in different species and places including North America. Timing appropriate: when anti-pollution took hold, reversed. f. Melanism itself has alternative explanations for other organisms. It is rather common. In the silver-washed fritillary (a butterfly), only the female is melanic and only some of them (this is called polymorphic. Def. Having several forms, in contrast to monomorphic). Slide . It gets thermal advantage by warming up sooner (see physiological ecology topic shortly) and so can fly longer and find better places to lay eggs – but less likely to mate, doesn’t look like the right species perhaps.
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