Cook to Lodge: Insularia morphs of B. betularia

Cook to Lodge: Insularia morphs of B. betularia

Excerpts below are taken from

Cook, LM, Dennis, RLH & Dockery, M (2004) Fitness of insularia morphs of the peppered moth Biston betularia. Biol.J.Linn.Soc. 82, 359-366.

Thousands of peppered moths have been bred, both to investigate their genetics and to provide material for assembling and experiments. Inheritance appears to be Mendelian. In spite of that the idea of induction by environmental factors, which was raised in the 1920s (see Kettlewell, 1973), has been kept alive in one quarter (Lambert, Millar & Hughes, 1986; Sargent, Millar & Lambert, 1998). The argument appears to be as follows. An environmental factor, usually assumed to be metal salts in larval food, triggers production of melanism through some cytoplasmic agency. Newly formed melanics become incorporated into the nuclear genome, so that operationally the process increases the mutation rate. The rise in melanic frequency is then due either to selection or to the high conversion rate itself. If it results from selection, then heightened mutation rate is irrelevant except insofar as it may help to establish the condition in the first place.

If, as Sargent et al.(1998) suggest, induction occurred in many individuals all over industrialised regions, then it is surprising that the pattern appears to have a single source and that it did not develop at an earlier date in London. Lambert et al. (1986) do not believe that melanic mutations arise spontaneously, rather that the origin of form must always involve a unique series of multiple and reciprocal interactions through levels in a developing organism. It is noteworthy, however, that in rural western Siberia, the one region where the peppered moth occasionally reaches defoliating densities in forests, Gninenko (2002) observed two or three carbonaria over a study period of three decades. It can evidently be found even in unpolluted areas if sample numbers are sufficiently large.

If change were due to induction alone, then several types of evidence have to be accommodated. Haldane (1924) pointed out that if induction caused the observed increase it would be impossible to obtain crosses between typicals that bred true, whereas data on large families of true-breeding progenies had been published. Kroupa, Spitzer & Novak (1990), found different metal concentrations in peppered moths from localities with different levels of pollution, but concluded that they were not important selective agents. It is impossible to prove the absence of an effect, but experimental evidence for it is lacking. The induction hypothesis has to explain recent reductions in melanic frequency; does a newly arisen agent cause reverse induction? It must account, too, for the behaviour of insularia, as outlined here and in Cook & Grant (2000). The insularia morphs remained rare when carbonaria was increasing, and have sometimes increased while it is declining. These changes are explicable on a selective model, but mystifying on the basis of induction alone. We conclude that there is no evidence for induction in B. betularia.

Dr L. M. Cook sent me the attached material on August 1, 2004, with a statement that it gave a better representation of his views than other material that I have quoted on my web site.	Arthur S. Lodge \| home Cook to Lodge: Insularia morphs of B. betularia \| Sargent's 1st Reply to Cook \| Cook (2); Sargent(2) \| Industrial Melanism \| Natural selection: the only mechanism?
	Cook to Lodge: Insularia morphs of B. betularia Excerpts below are taken from Cook, LM, Dennis, RLH & Dockery, M (2004) Fitness of insularia morphs of the peppered moth Biston betularia. Biol.J.Linn.Soc. 82, 359-366. Thousands of peppered moths have been bred, both to investigate their genetics and to provide material for assembling and experiments. Inheritance appears to be Mendelian. In spite of that the idea of induction by environmental factors, which was raised in the 1920s (see Kettlewell, 1973), has been kept alive in one quarter (Lambert, Millar & Hughes, 1986; Sargent, Millar & Lambert, 1998). The argument appears to be as follows. An environmental factor, usually assumed to be metal salts in larval food, triggers production of melanism through some cytoplasmic agency. Newly formed melanics become incorporated into the nuclear genome, so that operationally the process increases the mutation rate. The rise in melanic frequency is then due either to selection or to the high conversion rate itself. If it results from selection, then heightened mutation rate is irrelevant except insofar as it may help to establish the condition in the first place. If, as Sargent et al.(1998) suggest, induction occurred in many individuals all over industrialised regions, then it is surprising that the pattern appears to have a single source and that it did not develop at an earlier date in London. Lambert et al. (1986) do not believe that melanic mutations arise spontaneously, rather that the origin of form must always involve a unique series of multiple and reciprocal interactions through levels in a developing organism. It is noteworthy, however, that in rural western Siberia, the one region where the peppered moth occasionally reaches defoliating densities in forests, Gninenko (2002) observed two or three carbonaria over a study period of three decades. It can evidently be found even in unpolluted areas if sample numbers are sufficiently large. If change were due to induction alone, then several types of evidence have to be accommodated. Haldane (1924) pointed out that if induction caused the observed increase it would be impossible to obtain crosses between typicals that bred true, whereas data on large families of true-breeding progenies had been published. Kroupa, Spitzer & Novak (1990), found different metal concentrations in peppered moths from localities with different levels of pollution, but concluded that they were not important selective agents. It is impossible to prove the absence of an effect, but experimental evidence for it is lacking. The induction hypothesis has to explain recent reductions in melanic frequency; does a newly arisen agent cause reverse induction? It must account, too, for the behaviour of insularia, as outlined here and in Cook & Grant (2000). The insularia morphs remained rare when carbonaria was increasing, and have sometimes increased while it is declining. These changes are explicable on a selective model, but mystifying on the basis of induction alone. We conclude that there is no evidence for induction in B. betularia.