Biological Journal ofthe Linnean Soczep (1990), 39; 301-322. With 4 figures
Industrial melanism and peppered moths (Bistom betularia (L.)) Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 R. J. BERRY
Department of Biology, University College London, Gower Street, London WClE 6B T
The spread of melanic forms of the peppered moth (Biston betuluriu (L.)) over polluted areas of Britain from the mid-nineteenth century onwards, has become widely known and quoted as a classical example of microevolutionary change. Probably the most important factor in the spread (and subsequent decline, following the Clean Air Act) of the melanics has been bird predation on less cryptic individuals, but a range of other factors may also affect the maintenance of allele frequencies at any one place (site selection, dispersion, heterosis, frequency dependent selection, larval hardiness, etc). The development of the “Peppered Moth Story” is described, and suggestions made about needed research.
KEY WORDS: Peppered moth - microevolution natural selection - bird prrdation - air pollution.
CONTENTS
Introduction ...... 30 1 Observations and interpretations ...... 302 Genetics ...... 304 Geographical distribution ...... 305 Natural selection, etc ...... 308 Behaviour...... 309 Multiple factor analysis and models ...... 312 Acknowledgements ...... 314 References...... 314 Appendix A: Tutt (1896) on peppered moth melanism ...... 317 Appendix B: Suggestions for further work ...... 318 Appendix C: History of peppered moth melanism work ...... 319
IN’I’RODUCTION The spread of black forms (several insularia phenotypes and the more extreme carbonaria) of the peppered moth (Biston betularia (L.)) in the mid-nineteenth century following the widespread increase of air pollution, and their subsequent maintenance by bird predation, has become a standard text-book example of the operation of natural selection. Savage (1977: 84) has described its elucidation as a series of “brilliant investigations (which) provide an exciting insight into the operation of selection under natural conditions”; Wright (1978: 186) called it “the clearest case in which a conspicuous evolutionary process has been actually observed”. MacArthur & Connell (1964: 67) point out, “It used to be argued 30 I 0024-4066/90/040301+ 22 $03.00/0 0 1990 The Linnean Society of London 302 K. J. BEKKY that natural selection was only a conjecture, because it had not been actually witnessed. By now we have become aware of many examples of natural selection in action. One of the best documented cases deals with the peppered moth . . .” The classical peppered moth work is properly associated with the work of H. B. D. Kettlewell who collected “evidence for selective elimination through experiments of release and recapture coupled with direct observations of bird predators capturing selectively one or the other form. The complementary series of experiments in contrasting habitats is especially impressive” (Spiess, 1964: xlviii). It has been a major factor in the recognition that “selection Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 pressures in operation on natural populations are of greater importance than theorists such as Sewall Wright and R. A. Fisher thought them to be. Selective advantages for alleles were calculated at the level of 0.5 to 1.0 per cent. Study of natural selection by investigators such as J. B. S. Haldane, S. Gershenson, E. B. Ford and H. B. D. Kettlewell indicate to the contrary that selective advantages from 20 to 40 per cent are not uncommon” (Hamilton, 1967: 28). Kettlewell was a general medical practitioner and keen lepidopterist. After an extended collecting trip in central Africa, at the age of 45 he took up a fellowship in E. B. Ford’s laboratory in the Department of Zoology at Oxford University, where he remained until his retirement in 1974. He died in 1979 (Lees, 1979). His Biston betularia studies were published in nine primary papers between 1955 and 1977 (Kettleworth, 1955a, 195513, 1955~~1956a, 1958, 1959, 1965a, 196513; Kettlewell & Conn, 1977), and largely summarized in his definitive book The Evolution of Melanism, published in 1973. Kettlewell’s work remains the core of our knowledge of industrial melanism in general, and the peppered moth in particular, but it has been continued and extended by a number of workers (reviewed Bishop & Cook, 1980; Lees, 1981; Brakefield, 1987, 1988; Majerus, 1989). In most cases, these later studies have confirmed Kettlewell’s conclusions, but in some respects, the emphasis has been changed. In particular, the maintenance of melanic frequencies is now perceived to be less directly dependent on bird predation than Kettlewell believed. The purpose of this paper is to summarize work on the peppered moth so that current work and criticisms can be put into context, and, following a workshop organized by L. M. Cook and G. S. Mani in November 1987, to identify gaps in our current understanding (Appendix B).
OBSEKC‘ATIONS AND IN’I’EKPKETATIONS The first published observation of a melanic peppered moth seems to have been that of Edleston (1964) (although Ford, 1975, records that a carbonaria caught from an unknown locality prior to 1811 is in the Entomology Department collection of the University of Oxford). Writing from Manchester, Edleston noted “Some sixteen years ago the ‘negro’ aberration of this common species (B.betularia) was almost unknown; more recently it has been had by several parties . . . Last year I placed some virgin females in my garden in order to attract the males, and was not a little suprised to find that most of the visitors were the ‘negro’ aberration: if this goes on for a few years the original type of B. betularia will be extinct in this locality”. Edleston’s report has led to 1848 becoming the accepted date for the start of the rise of frequency of carbonaria in north-west England. By the 1870s the INDCSTRIAL MELANISM AND PEPPERED MOTHS 303 amateur entomological journals contain many references to black individuals as the melanics spread to other parts of the country (Cook, 1981). A remarkable (for the time) account of the status and industrial dependence of peppered moth melanism was given by Tutt (1896) (see Appendix A). In 1900, the Evolution Committee of the Royal Society attempted to collect evidence of the history and increase in industrial melanism, but was frustrated by the lack of firm information. The data available were summarized by Doncaster (1906). He cited Barrett (1901) that only the typical form was known “until about 1848”, and carbonaria (then known as doubledayaria) “appeared in the Manchester district Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 1850, at Cannock Chase in 1878, in Berkshire in 1885, Cambridge 1892, Norfolk 1893, Suffolk 1896, London 1897”. The best review of the spread of carbonaria is that of Steward (1977a) (Fig. 1). His conclusion is that carbonaria was widely distributed in northern England and the Midlands by 1885, but was still absent from a large area of southern Britain. The report that ‘black’ and typical forms were equally common in Newport, Monmouth in 1870 probably refers to the less intensely melanic form, insularia rather than carbonaria, since the former still occurs at over 40% there. Similarly, a “dark individual” caught by Holland (1884) near Reading in 1885 may also have been an insutaria. After 1890, carbonaria seems to have spread very rapidly through a large area including East Anglia and London. For example, James (1915) found no melanics in 77 B. betularia caught in Highgate (north London) in 1894, but had 74% carbonaria in a large sample taken in the same place in 1915. Despite the fact that the conditions in London were apparently ripe for the spread of industrial melanics, carbonaria did not reach I:/, there until 1895. Many workers have commented on the lack of quantitative information available for carbonaria*. There is even less information for the other peppered moth melanic, insutaria. It was present in Manchester at the same time (or soon after) carbonaria was first caught (Stephenson, 1858)) and Kettlewell (1958) concluded that it was common in Folkestone (on the south coast of England) before carbonaria appeared there. The first record of carbonaria on continental Europe was in 1867 at Breda in Holland, and it was subsequently recorded progressively at places to the east. By the early 1900s it occurred all over north-west Europe, apart from Scandinavia. Carbonaria was not recorded in Denmark and Sweden until the 1940s) and now occurs at low frequencies in Denmark and Sweden; it is absent from Finland (Mikkola, 1975, 1984b; Douwes, Petersen & Vestergren, 1976).
*In a book which (according to Bennett, 1983) considerably influenced R. A. Fisher, Punnett (1915: 102) pointed out “two things are ofinterest in the case ofthe peppered moth --the rapidity with which the change in the nature of the population has taken place, and the fact that the two forms exhibit Mendelian heredity, doubledgaria (=carbonana) being dominant and belularza (=!@a) recessive . . . This rase of the peppered moth shows how swiftly a change may come over a species. It is not at all improbable that the establishing of a new variety at the expense of an older one in a relatively short space of time is continually going on, especially in tropical lands where the conditions appear to be more favourable to variation and where generations succeed one another in more rapid succrssion. At present, however, we are without data . . . Much could be learned if some common forms were chosen for investigation in which there are both mimetic and non-mimetic forms. Large numbers should be caught at stated intervals, large enough to give trustworthy data as to the proportions of the different forms that occurred in thr population. Such a censiis of a polymorphic species, if done thoroughly and ocer a series of years at regular intervals, might be expected to give us the necessary data for deciding whether the relative proportion of the different forms was changing whether there were definite grounds for supposing natural selection to be at work, and if so what was the rate at which it brought the change about”. Three-quarters of a century later, this exhortation is still not properly assimilated (Taylor, 1989; Berry, 1989). 304 R. J. BERRY Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021
Figure 1. Spread of carbonaria in England and Wales. Solid circles indicate first reports of carbonaria; solid squares show sites where carbonaria was already reported as common at the date indicated; open circles are sites where carbonaria was reported as absent. The dashed lines separate areas where carbonaria was present before 1890, from where it appeared later. Based on Steward (1977a).
The North American equivalent of carbonaria is the swettaria form of Biston cognataria (which is phenotypically indistinguishable from carbonaria). It was first recorded in Philadelphia in 1906. It was then found in New Jersey in 1920, Chicago 1935, and New York City only in 1948. But its spread was rapid: by 1961, it constituted over 90% of the population in parts of Michigan (Owen, 1961, 1962).
Genelics The earliest recorded controlled cross involving peppered moth melanics was in 1868, only three years after Mendel published his results (Orville, 1868; Lemche, 193 l), but arguments about environmental us. genetic determination of melanism persisted until the turn of the century (Tutt, 1891; Doncaster, 1906). Nowadays, it is commonly assumed that melanism is inherited as a simple dominant. (Harrison, 1928, 1956, claimed that melanism was the result of directed mutation produced by the ingestion of pollutants; this assertion was repudiated in detail by Kettlewell, 1956b, see also Thomson & Lemche, 1933; Fisher, 1933.) In fact five alleles are known at the melanism pattern locus in the peppered moth: t, i', i2, i3 and C. carbonaria. The form is produced by C, and is INDUSTKIAL MELANISM AND PEPPERED MOTHS 305 inherited as a condition fully dominant to the other alleles. The typical form is produced by the tt homozygote. All combinations of the i alleles with each other and with t produce insularia phenotypes (Lees & Creed, 1977; Steward, 1977b), although i3i3and i3t may be difficult to distinguish from carbanaria (Clarke, 1979; Bishop & Cook, 1980). Kettlewell argued that peppered moth melanism was a clear example of the evolution ofdominance, as advocated by R. A. Fisher (1928). The context for his belief was the fact that the great majority of industrial melanic forms are inherited as dominants, implying (on Fisher’s theory) that melanism had been Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 selected for at some time in the past. Kettlewell suggested that a melanic peppered moth form may have been adaptive in some previous geographical or climatic situation, and that carbonaria attained dominance under those conditions. Kettlewell’s interest in such non-industrial melanism led to his work on Amathes glareosa in Shetland (Kettlewell, 1961; Kettlewell et al., 1969), Lasiocampa quercus in Caithness, North Scotland (Kettlewell, Cadbury & Lees, 1971) and Boarmia repandata in the primaeval Black Wood of Rannoch in the Central Highlands of Scotland (Kettlewell, 1973: 171--4). Kettlewell’s evidence of dominance evolution in the peppered moth was based on the presence of white markings on the wings of nineteenth century melanics (Kettlewell, 1958) and the fact that the British C allele did not produce distinct melanic and typical phenotypes when British moths were crossed with typical peppered moths from Canada (where melanism was unknown); in other words, there was a breakdown of dominance when the allele was introduced into a genome where dominance might be expected not to have evolved (see also Ford, 1955). Just as Ford showed in his classical test of Fisher’s theory with Abraxas grossulariata (Ford, 1937), Kettlewell found that clear carbonaria-typica expression and segregation was restored when “broken-down” melanics (phenotypically indistinguishable from &pica) were crossed with British &pica (Kettlewell, 1965a). However, this evidence is not as clearcut as it may appear. West (1977) crossed British carbonaria with &pica from the Appalachians where the melanic had a frequency of only about 1%, and observed no breakdown in dominance. Likewise, Mikkola (1984b) found no breakdown in crosses between carbonaria from Liverpool and typica from Finland. Moreover, individuals like Kettlewell’s “ancient” carbonaria are regularly found in modern samples from the Liverpool and Birmingham areas (Lees, 1971; Bishop, Cook & Muggleton, 1978). Notwithstanding, there is plenty of circumstantial evidence suggesting that dominance modifiers may be acting (Haldane, 1956; Steward, 1977a); the subject needs more study.
Geographical distribution Kettlewell (1958, 196513) made the first extensive survey of the distribution of any industrial melanic in Britain, compiling data supplied largely by amateur entomologists. Later data have been collected by Lees & Creed (1975), Steward (1977a), Bishop el al. (1978) and Cook, Mani & Varley (1986). As is well- known, the distribution of both carbonaria and insularia show a correlation with, and a displacement down-wind from, sources of industrial pollution. In other words, they exhibit industrial melanism. The broad outline of the spread and distribution of melanics has been known 306 R. J. BERRY loo. AB = I -50 years B = Primary mutation occurs BC = -t 29 years at 30 per cent 90 - advantage BD = f 38 years at 30 per cent advantage 80 - DE = ? I5 years Period of rapid increase EF = 2 1000 years Period of slow elimination or 70 - balanced polymorphism Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021
T 60- a,0 B 50- 0 K - 3 40-
30 -
20-
10-
I- &-- &-- /. A B CD E F
Figure 2. Rate of increase of a melanic mutant, assuming a constant advantage of the heterozygote over the typical homozygote. Based on Haldanc (1956; after Kettlewell, 1973).
for several decades. Punnett ( 19 15) referred to increases in carbonaria frequencies as evidence that natural selection may produce observable evolutionary change, and concluded that the melanics must have some advantage over the typical form. He cited the experience of breeders who found that melanics were “somewhat hardier, at any rate in captivity”. The next step was Haldane’s (1924) use of the available data to postulate a period of establishment of carbonaria, followed by a rapid increase in frequency, and than an apparent equilibrium (Fig. 2). From this he calculated that in smoke polluted areas typica and homozygous carbonaria had fitnesses relative to the heterozygote of 0.5 and 0.92 respectively (Haldane, 1956). Detailed studies of B. betularia melanics have subsequently been in the North Wales to Liverpool-Manchester conurbation, and in South Wales. Following an initial survey by Clarke & Sheppard (1966),Bishop (1972) carried out a detailed investigation of the factors affecting frequencies over a 120 km transect, and modelled the expected cline using estimates of movement and differential predation he obtained himself (Fig. 3). Like Haldane, he concluded that there was apparently some heterozygous advantage. INDUSTRIAL MELANISM AND PEPPERED MOTHS 307 Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021
3 5 Clegyr Mawr Miles .o '6
% carbonaria in samples
20 -
Distance from Sefton cbrk, Liverpool (miles)
Figure 3. Change in the frequencies of carbonaria between Liverpool and North Wales. Aboue, Percentage carbonaria frequencies. Below, Cline, along the line drawn in the above figure. The heavy line shows the observed frequencies; the lighter line the expected frequencies, based on the best available estimates of predation, differential migration rate and heterozygous advantage. Based on Bishop (1972).
This work led on to a series of comparisons between the factors affecting melanic frequencies in B. betularia and Gonodontis bidentata (Askew, Cook & Bishop, 1971; Bishop & Cook, 1975; Bishop et al., 1978): whereas carbonaria frequencies declined smoothly westward into rural areas, the G. bidentala melanic, nigra, does not extend into rural North Wales, and ranges in frequency from 10 to 80% with marked peaks and troughs in the area between the River Dee and Manchester (where carbonaria is consistently over 85%). At least part of the 308 R. J. BERRY difference must depend on different dispersal distances in the two species. The present frequencies of carbonaria are imperfectly known, although they have certainly declined substantially since the classical surveys were carried out. In Britain, a Clean Air Act was finally passed in 1956; it was stimulated by post war building, a change from coal to oil heating (Bishop & Cook, 1980), but also a response to a smog in which prize cattle died at the (national) Smithfield Show and opera performances at Sadlers Wells Theatre had to be cancelled because the audience could not see the stage rather than to rational political (or scientific) pressure (Ashby & Anderson, 1981). Cook, Askew & Bishop (1970) Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 published data showing that the frequency of &pica at Didsbury on the outskirts of Manchester had increased from zero in 1952-1964 to 2.6% in 1966-1969 (whereas insularia remained constant at c. 1.3%). Clarke, Mani & Wynne (1985) extended these data, showing that frequencies of carbonaria in Clarke’s garden in the Wirral (c. 15 km west of Liverpool) declined increasingly rapidly from 927” in 1959 to 61% in 1984; by 1989 the population contained only 30% (Clarke, Clarke & Dawkins, 1990). Cook et al. (1986) reported a large scale survey showing a pattern of decline over the country from 1952-1970 to 1983-1984 which resulted in a north-easterly movement of the steep cline which runs obliquely from NW to SE England. Brakefield (1990) has described a similar fall in the Netherlands.
Natural selection, etc. Perhaps taking his cue from Punnett, (1915)*, E. B. Ford (1937) put forward the hypothesis that industrial melanism was the result of natural selection operating “in favour not of the colour but of the physiological advantages possessed by those black forms which have spread” and which were eliminated by predators before pollution made melanic colouration less of a handicap than previously. He maintained these views in print at least as late as 1953. Viability differences do exist between the melanic and typical forms of some species, but for B. betularia, Kettlewell (1973: 78c see also Robinson, 1971: 363) reviewed the available evidence and found it “unconvincing”, (although) “until broods from contrasting areas in Britain are bred on a large scale under stress (for example, fed on leaves contaminated with the various types of pollution, starvation, polyhedrosis, etc.), we shall not know whether f. carbonaria survives better than J opica . . . (But) the rate of spread of the carbonaria form throughout polluted Britain could be accounted for entirely by the cryptic advantage of the imago alone”. However, Creed, Lees & Bulmer (1980) showed significant pre-adult viability deficiencies between genotypes involving both heterozygous insularia-carbonaria (they did not distinguish between insularia allelles) and homozygous carbonaria in laboratory stocks (fitness of heterozygote relative to carbonaria homozygote was 0.52; of carbonaria homozygote to insularia homozygote was 0.72). In contrast, homozygous carbonaria had a much greater viability than &pica (1.48: 1). These estimates were based on all the data from different sources then available, so that effects of local stocks or rearing conditions are minimized. Indirect estimates of viability differences from change in phenotype frequency
*Ford (1980) described Punnett as a most dedicated and vociferous selectionist, but “he did nnt carry as much weight as he might have because he knew absolutely no genetics at all”. INDUSTRIAL MELANISM AND PEPPERED MOTHS 309 TABLE1. Summary of Kettlewell's original mark-release-recapture experiments
ppica carbonaria Jv
Dorsct (carbonarta frequency under 1 'lo) Releawd 496 473 969 Recaptured 62 (12 5",) 30 (6 3",,) 92 Birrninghan (carhonana frequency 87",,) Released 137 447 584 Recaptured 18 (13.2",,) 123 (27.5",,) 141
with time, have indicated a 8- 15y0 disadvantage of carbonaria homozygotes Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 compared to carbonaria-typica heterozygotes (Haldane, 1956; Clarke & Sheppard, 1966). However in neither case is the possible effect of migration on the morph frequencies considered (cf. Bishop el al., 1978). Lees & Creed (1975) suggested on the basis of discrepancies between the results of predation experiments and sample frequencies in East Anglia, that non-carbonaria has a physiological disadvantage of up to 30%, and that this could explain the existence of carbonaria in rural areas of North Wales (Bishop, 1972). As is well known, the key observations and experiments on the importance of visual predation on non-cryptic forms were carried out by Kettlewell (1955a, 1956a). Having shown that great tits (Parus major) in an aviary eat both melanic and typical peppered moths, taking them in the same order of conspicuousness as scored by a human observer, in 1953 and 1955 Kettlewell released marked moths of both morphs in a wood near the industrial centre of Birmingham, repeating the experiment in 1955 in a heavily lichened and pollution-free wood in Dorset, southern England. The experiments are summarized in Table 1. In Birmingham 28% of the marked carbonaria were recaptured, but only 13% of &pica; whereas in Dorset 13% of the typicals were recaptured, but only 6% carbonaria. Historically as important in convincing the scientific community of the effectiveness of bird predation was a film made by Kettlewell in collaboration with Niko Tinbergen. In Dorset, five species of birds were observed selectively to prey on the more conspicuous form. Kettlewell's predation results have been confirmed in at least five different studies: by Clarke & Sheppard ( 1966) (using killed and deep-frozen specimens), Bishop (1972), Lees & Creed (1975), Steward (1977~)and Bishop et al. (1978). They have been criticized on the grounds that the density of prey moths in them was far greater than under normal conditions (Lambert, Millar & Hughes, 1986; Millar & Lambert, 1990), but there can be no doubt that "bird predators exert a significant influence on the B. betularia polymorphism in heavily polluted areas where the melanic frequency is very high and in completely rural areas where it is low. At intermediate frequencies and pollution levels their effect is less clear" (Lees, 1981).
Behauiour A. Dispersal The relationship between selection, giving rise to local adaptation, and dispersal, tending to obscure it, has received much attention (Haldane, 1947- 1948; Kettlewell & Berry, 1969; Endler, 1977). The influence of dispersal on differences in melanic distributions between B. betularia and G. bidentata has already been noted; mean adult flight distances are several times greater in the former species than the latter (Bishop, 1972; Bishop et al., 1978). Individual 310 R. J. BERRY Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021
Figure 4. Flight distances of marked peppered moths released in a park in the centre of the Wirral Peninsula. The black circles are moth traps. Built-up areas are shaded. After Bishop (1972). peppered moths may fly up to 5 km in a single night (Fig. 4);indeed Brakefield (1990) indicated that even longer distances are common. Bishop et d. (1978) concluded that the maintenance of carbonaria frequencies in the North Wales cline (Fig. 3) can be explained entirely as a balance between migration and visual selection, with no need to invoke heterozygous advantage (see also May, Endler & McMurtrie, 1975).
B. Resting site selection Consistent camouflage while resting depends, of course, on the ability of individuals to choose backgrounds on which they are cryptic. Kettlewell (1955b) released typical and melanic peppered moths into a large cider barrel (1 m high,
TABLE2. Rrsults of offering Qpzca and carbonaria forms of the peppered moth equal arras of black and whitr surfaces, in barrels, to rest upon (from Kettlewell, 1955b)
carbonaria gpzia Total
-- ~- ~ ~ ~~ ~ Rlnrk hnc kground 38 20 58 \Vhire bat kground 21 39 60 fotal 59 59 118 INDUSTRIAL MELANISM AND PEPPERED MOTHS 311 0.7 m diameter) lined with alternate black and white vertical stripes, and found that a significant proportion were on a matching background when scored the following morning (Table 2). He confirmed this result in further experiments (Kettlewell, 1973: 69, 88; Kettlewell & Conn, 1977). In contrast, Sargent (1966, 1974) failed to find such clear background choice. Kettlewell (1973: 70) argued that Sargent’s experimental chambers were too small and crowded. Mikkola ( 1979, 1984a) criticized the conclusions from predation experiments, particularly those involving the placing of dead specimens on trees, on the grounds that they were all based on the assumption that the moths rest naturally Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 on tree trunks. His observations on partly paint-sprayed trunks and branches in an outdoor cage led him to believe that the normal resting place of the peppered moth is actually on the underside of branches in the canopy. Howlett & Majerus (1987) have confirmed this experimental conclusion on the basis of the sites where peppered moths have been found in the wild, with most individuals found close to a trunk/branch joint. They showed that the chance of a dead moth disappearing was significantly greater if it was placed on a trunk rather than on a branch. Liebert & Brakefield (1988) have extended knowledge about the natural behaviour of peppered moths by watching virgin females released after confining them in a cage until initial dispersal flights was over. Pairing usually occurred quickly, and once females paired they walked short distances and did not fly. If their initial alighting site is close to the niche identified by Mikkola, Howlett and Majerus, this would bring them near to epiphytic growth except in the most polluted environments. Mated pairs remain in copulation for 20-24 hours; &pica pairs in particular resemble foliose lichens, whilst typica and carbonaria are likely to be at a disadvantage in most situations when compared with other combinations. Howlett & Majerus (1987) analysed the light reflected from the wings of peppered moths. They showed that the wings of typica are partially translucent, and hence are more similar to a plain black surface than a plain white one. They inferred from this that both forms should prefer a darker surface when offered a choice, and found this to be so experimentally (Table 3). Finally, texture has been shown to be important in the choice of resting position for many species which have melanic polymorphisms (Sargent, 1969; Kettlewell, 1973; Lees, 1975). Kettlewell ( 195813) put forward a “contrast/conflict” hypothesis of site selection. He suggested that light stimuli from the resting substrate are compared by alighting moths to the colour and pattern of the circumocular scales. If the two are dissimilar, the moth moves until this contrastlconflict is reduced. Sargent
TABLE3. The resting sites of the typica, iiisularia and carbonaria forms of the peppered moth when presented with a choice of black and white rurfaces of equal area in cylinders (after Howlett & Majcrus, 1987)
QJpzta znmlnrza rarbonnrin 7 otal ~____~______Black \ide 58 30 70 158 Whit? sidc 20 7 14 41 Floor 21 5 36 62
Otdl 99 4“ 120 26 I 312 R. J. BERRY (1968) attempted to test this idea by painting the tufts of scales around the eyes of two North American moths, Catocala actinympha and Campaea perlata, but found no difference in their behaviour. But, as Kettlewell (1973: 72) pointed out, both these species are monomorphic, and have had no cause to evolve differential site choice. Grant & Howlett (1988) showed that some individual peppered moths appear to have preferences for backgrounds of particular colours, but that these preferences are not correlated with the moth’s phenotype.
C. Evolution of resling site choice Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 Sargent (1968) and Steward (1985) have argued that differential rest site selection is inherited. This raises the problem that the selection must be either a pleiotropic effect of the melanism locus, or the behavioural gene must be tightly linked to the melanic-controlling one (these two alternatives are very similar in effect). Howlett (1989) has modelled the evolution of resting site preferences in the absence of linkage to the colour pattern locus. His results suggest that the selection of appropriate resting sites will only evolve if there is linkage between the colour pattern locus and the behavioural locus. The likelihood of such a system evolving could thus be, at least in part, a function of the length of time that the various alleles for the different forms and the different resting preferences have existed in the population. Majerus (1989) has pointed out that the occurrence of different frequencies of carbonaria in populations of the peppered moth throughout Britain over the last 140 years will mean that if alleles which cause moths to rest preferentially on dark surfaces arise by mutation, but are not linked to the carbonaria locus, some of these will spread to fixation (in areas of high carbonaria frequency), others being lost from populations (where typica predominates). Consequently three types of population may be envisaged: (a) Those in which a dark preference allele has never arisen or has failed to spread, so the peppered moths in the population all tend to rest on pale heterogeneous backgrounds. (b) Those in which a dark preference allele has recently arisen and is in a state of transient polymorphism as it spreads towards fixation. In these populations some peppered moths will have a preference to rest on pale heterogeneous backgrounds, others will prefer dark homogeneous ones. (c) Those in which a dark preference allele has become fixed in the population so that all the moths show a tendency to rest on dark homogeneous surfaces. If this is so, it is important to know from where Kettlewell obtained the moths he used in his choice experiments. It is possible that he only used moths trapped in Oxford which he collected nightly at that time but he also had extensive stocks of bred material and was working at that time both in Dorset and Birmingham, and may have used moths from any of these sources. lhe problem of the variation in results is unresolved, but it should not be difficult to design tests to resolve this controversy, in the light of the suggestion that the phenomenon of rest site selection is a dynamic one.
MULIIPLE FACTOR ANALYSIS AND MODE1.S It is clear that melanic peppered moth frequencies are determined by much more than differential visual predation by birds. Jones (1982) encapsulated this in a review called “more to melanism than meets the eye”. Lees, Creed & INDUSTRIAL MELANISM AND PEPPERED MOTHS 313
TABLE4. Multiple regression analyses of carbonaria and insularza gene frequencies (after Steward, 1977b)
Dependent variable (gene frequency)
Independent variable Carbonaria Insularia
Smoke (J[Pgm-31) ~ Sulphur dioxide (J[pg m-'1) 6.497*** - Distance north (min) 0.107*** -0.036** Distance west (min) -0.105*** - Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 Altitude (ft) 0.079* Rainfall (mm) March -0.459** -0.128 June 0.883*** -. October -0.223* 0.160*** Temperature ("C) Winter minimum -0.530*** Spring minimum 0.607*** Summer maximum 0.159 Autumn minimum -
R2 0.722 0.313 First variable entered Sulphur Distance dioxide north R2 at first step 0.467 0.107
The partial regression coefficients of the independent variables included in the multiple regression equation are shown at the step where the next variable to be entered would increase the coefficient of multiple determination (R') by less than l(yo. The values of R2 at the first and final steps are given. The significance of the deviation of the partial regression coefficient from 0, as indicated by the value of Student's 1 statistic, is shown: *P < 0.05; **P < 0.01; ***P < 0.001.
Duckett ( 1973) used multiple regression techniques to investigate variation in frequency in B. betularia and P.pilosaria in southern Britain in terms of the more obvious environmental variables (eight physical, e.g. temperature, rainfall etc; and six biotic characteristics of the surface of trees). For P.pilosaria, tree trunk reflectance was the most important variable; for the peppered moth, the three most important variables were bryophyte height, January temperature, and sulphur dioxide concentration, indicating that crypsis was less important, although lichen cover would clearly be affected by sulphur dioxide concentration. In contrast, Bishop et al. (1975) found tree trunk surface and epiphyte cover to be the most important factors in north-west England and North Wales. A more extensive analysis of peppered moth data from 165 sites in Britain by Steward (1977b) identified sulphur dioxide as the most important of 13 variables included in the analysis of carbonaria frequency. In contrast insularia frequency showed no clear associations with any of the variables (Table 4). In an analysis of carbonaria frequency from 92 of the sites, distance west was more important than pollution level in predicting frequency; correlation showed that this relationship could not be accounted for by any geographical trend in pollution concentration. Bishop et al. (1975) properly emphasized the weakness of multiple regression analysis for identifying causal factors or distinguishing the relative importance of visual and non-visual selection. Mani (Cook & Mani, 1980; Mani, 1980, 1982) has extended Bishop's 314 R. J. BERRY computer simulations to national carbonaria frequencies. He has shown that a balance between selection and migration is enough to explain why the areas of rapid decrease in melanic frequencies do not coincide with urban boundaries. However, his fit to observed values and to spread of the carbonaria allele since 1850 was improved by including constant non-visual fitness differences, albeit different ones to those obtained by Creed, Lees & Duckett (1973) from their laboratory breeding experiments. The development and problems of the model are reviewed by Mani (1990). Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 ACKNOLVLEDGEMEN'IS 'The stimulus for this paper came from a workshop organized by L. M. Cook and G. S. Mani to which all the European peppered moth workers were invited. It was supported by the Linnean Society. I am grateful to all who have provided information for this background paper, particularly for Appendix C.
REFERENCES ASHBY, E. & ANDERSON, M. 1981. The Politics oJClean Air. Oxford: Clarendon Press. ..\SKEW, R. R., COOK, L. M. & BISHOP, J. A,, 1971. Atmosplicric pollution and melanic moths in Manchester and its environs. journal of Applied Ecology, 8: 247-256. BARRETT, C. G., 1901. The Lepidoptera ofthe British Ih,Vol. VII. London: Reevc & Co. BENNETT, J. H., 1983. .Natural Selection, Heredity, and Eugenics: Including selected correspondence of R. A. Fisher with Leonard Darwin and others. Oxford: Clarendon Press. BERRY, R. J., 1988. Natural history in the twenty-first century. Archives ofdVatural his tog^, 15: 1-14. BERRY, R. J., 1989. Ecology: where genes and grography meet. Journal of Animal Ecology, 58: 733-759. BISHOP, J. A,, 1972. An experimental study of the cline of industrial melanism in Biston betularia (L,) (Lepidoptera) between urban Livcrpool and rural North Wales. Journal of Animal Ecology, 41; 209-243. BISHOP, J. A. & COOK, L. M., 1975. Moths, melanism and clean air. Scientijc American, 232: 90-99. BISHOP, J. A. & COOK, L. M., 1980. Industrial melanism and the urban rnvironment. Aduanres in Ecological Research, 11: 373-404. BISHOP, J. A,, COOK, L. M. & MUGGLETON, J., 1978a. The response of two species of moth to industrialization in northwest England. I. Polymorphisms for mrlanisms. Philosophical IranAactions of the Ryal Society of I,ondon, Series B, 281: 489-515. BISHOP, J. A,, COOK, L. M. & MUGGLETON, J., 1978b. lhe response of two species of moth to industrialization in northwest England. 11. Relative fitness of morphs and population size. Philosophical Transactions of the Royal Sociely of London, Series B, 281: 5 17-540. BISHOP, J. A,, COOK, L. M. & SEAWARD, M. K. D., 1975. Moths, lirhens and air pollution along B transect from Manchester to North Wales. Journal of Applied Ecology, 28: 83-98. BOARDMAN, M., ASKEW, R. R. & COOK, L. M., 1974. Experiments on resting sitr selection by nocturnal moths. Journal aJ'~o?oology,London, 172: 343-355. BRAKEFIELD, P. M., 1987. Industrial melanism: do we have the answers? Trends in Ecology and Euolution, 2: I17-1 22. BRAKEFIELD, P. M., 1988. What is the progress towards understanding the selection webs influencing melanir polymorphisms in insects? In G. De Jong (Ed.),Population, Genetics and E'uolution: 148-162. Berlin & Heidelberg: Springer-Verlag. BRAKEFIELD, P. M., 1990. A decline of melanism in the pepprred moth Biston hetularia in 'I'he Netherlands. Biological Journal of the Linnean Society, 39: 327-334. CLARKE, C. A,, 1979. Biston betularia obligate f. insularia indistinguishable from f. carbonaria (Gcometridae). Journal of the Lepidopterists' Society, 33: 60-64. CLARKE, C. A., CLARKE, F. M. M. & DAU'KINS, H. C., 1990. Biston betularia (thc peppered moth) in West Kirby, Wirral, 1959-1989: updating the decline in f. car6onaria. Biological Journal of the Linnean Society, 39: 323-326 CLARKE, C. A,, MANI, G. S. & WYNNE, G., 1985. Evolution in reverse: dean air and the peppered moth. Biological journal of the Liunean Society, 26: 189-199. CLARKE, C. A. & SHEPPARD, P. M., 1964. Genetic control of the melanic form insularia of the moth Biston betularia L. Nature, London, 202: 2 15-2 16. CLARKE, C. A. & SHEPPARD, P. M., 1966. A local survey of the distribution of thr industrial melanic forms of the moth Biston betularia and estimates of the selective values of these in an industrial environment. Proceedings ofthe Royal SocieQ of London (B), 165: 424-439. INDUSTRIAL MELANISM AND PEPPERED MOTHS 315 COOK, L. M., 1981. Manchester and its moths. Biologis,, 28: 49-51. COOK, L. M., ASKEW, R. R. & BISHOP, J. A., 1970. Increasing frequency of the typical form of the peppered moth in Manchester. Nature, London, 227: 1155. COOK, L. M. & MANI, G. S., 1980. A migration-selection model for the morph frequency variation in peppered moth over England and Walcs. Biological Journal ofthe Linnean Society, 13: 179-198. COOK, L. M., MANI, G. S. & VARLEY, M. E., 1986. Post-industrial melanism in the Peppered moth. Science, New York, 231: 61 1-613. CREED, E. R., LEES, D. R. & BULMER, M. G., 1980. Pre-adult viability difference of melanic Biston betularia (L.) (Lepidoptera). Biological Journal of the Linnean Society, 13: 251-262. CREED, E. R., LEES, D. R. & DUCKETT, J. G., 1973. Biological method of estimating smoke and sulphur dioxide pollution. Nature, [.ondon, 244: 278-280. DOBZHANSKY, TH., 1970. Genetics of the Ei&tiotra,y Process. New York & London: Columbia University Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 Press. DONCASTER, L., 1906. Collective inquiry as to progressive melanism in Lepidoptera. Entornologist’s Record and Journal of Variation, I8: 165-168; 206-208; 222-226; 248-254. DOUWES, P., PETERSON, B. & VESTERGREN, A,, 1976. Melanism in Biston betularia from north-west Europe (Lepidoptera: Geometridae). Entomologia Scandinauica, 7: 261-266. EDELSTON, R. S., 1864. Amptydasis betularia. The Entomologist, 2: 150. ENDLER, J. A,, 1977. Geographic Chriation, Speciation, and ClineJ. Princcton: University Press. ENDLER, J. A,, 1984. Progressive background matching in moths, and a quantitative measure of rrypsis. Biological Journal of the Linnean Sociecv, 22: 187-23!. ENDLER, J. A., 1990. On the measurement and classification of colour in studies of animal dour patterns. Biological Journal of the Linnean Society, in press. FISHER, R. S., 1928. The possible modification of the response of the wild type to recurrent mutations. American Naturalist, 62: 1 15-126. FISHER, R. A,, 1933. On the evidence against the chemical induction of melanism in Lepidoptera. Proceedings of the Royal Society of London (B), 112: 4074.16. FORD, E. B., 1937. Problems of heredity in the Lepidoptera. Biological Reuiews, 12: 461-503. FORD, E. B., 1953. Mendelism and Euolution, 5th edition, reprint. London: Methuen. FORD, E. B., 1955. Polymorphism and taxonomy. Heredity, 9: 255-264. FORD, E. B., 1975. Ecolozical Genetics, 4th edition. London: Chapman and Hall. FORD, E. B., 1980. Some recollections pertaining to the evolutionary synthesis. In E. Mayr & 1%’.B. Provine (Eds), The Evolutionary Synthesis: 334-342. Cambridge, Mass. & London: Harvard University Press. GRANT, B. & HOWLETI‘, R. J., 1988. Background selection by the peppered moth (Biston betularia Linn): individual differences. Biological Journal of the Linnean Society, 33: 2 17-232. HALDANE, J. B. S., 1924. A mathematical theory of natural and artifical selection. Transactions of the Cambridge Philosophical Society, 23: 26. HALDANE, J. B. S., 1947-8. The theory of a cline. Journal of Genetics, 48: 277-284. HALDANE, J. B. S., 1956. The theory ofselection far melanism in Lepidoptera. Proceedings of the Royal SocieQ of London (B), 145: 303. HAMILTON, T. H., 1967. Process and Pattern in Evolution. New York: Macmillan. HARRISON,J. W. H., 1928. A further induction of melanism in the lepidopterous insect Selenia bilunaria Esp. and its inheritance. Proceedings ofthe Royal Society of London (R), 102: 338-347. HARRISON, J. W. H., 1956. Melanism in the Lepidoptera. Entomologi.rt’s Record, 68: 172-181. HOLLAND, W., 1884. Observations on Lepidoptera near Reading. Entomologist’s Monthb Magazine, 21: 158. HOWLETT, R. J., 1989. Thegenetics and evolution ojrest siteprefirence in the Lepidoptera. Unpublished Ph.D thesis, Cambridge University. HOWLETT, R. J. & M..ZJERUS, M. E. N., 1987. ‘The understanding of industrial melaniam in the peppered moth (Biston betularia) (Lepidoptera: Geometridae). Riologzcal ,jJoiirnal of the Linnean Sorzety, 30: 3 1-44. JAMES, R., 1915. Lepidopteralogical notes for 1914. Errtonologirt’s Record and Journal of C’ariation, 27: 3. JONES, J. S., 1982. More to melanism than meets the eye. .Vature, London, 300: 109-1 10. KETTLEWELL, H. B. D., 1955a. Selection experiments on industrial melanism in the Lepidoptcra. Heredily, 9: 323-342. KETTLEWELL, H. B. D., 1955b. Recognition of the appropriate backgrounds by pale and black phases of the Lepidoptera. Nature, London, 175: 943. KETTLEWELL, H. B. D., 1955~.Brood size and disprrsal in Biston hetularia L. Entomologist, 88: 50. KETTLEWELL, H. B. D., 1955d. How industrialization can alter species. Discovery, 16: 507-51 1. KETTLEWELL, H. B. D., 1956a. Further selection experiments on industrial melanism in the Lepidoptera. Heredity, 10: 287-301. KETTLEWELL, H. B. D., 1956b. Melanism and an answer to J. W. H. Harrison. Entomologist’s Record and Journal of Variation, 68: 286-292. KETTLEWELL, H. B. D., 1956~.A resume of investigations on the evolution of melanism in the Lepidoptera. Proceedings of the Royal Society of London (B), 1’45: 297-303. KETTLEWELL, H. B. D., 1958. A survey of the frequencies of Biston 6etularia (L.) (Lepidoptera) and its melanic forms in Great Britain. Heredity, 12: 51-72. 316 R. J. BERRY KETTLEWELL, H. B. D., 1959. New aspects of the genetic control of industrial melanism in the Lepidoptera. Nature, London, 183: 9 18-92 I. KETTLEWELL, H. B. D., 1961. The phenomenon of industrial melanism in Lepidoptera. Annual Review of Entomology, 6: 245-262. KETTLEWELL, H. B. D., 1965a. Insect survival and selection for pattern. Science, New York, 148: 1290-1295. KETTLEWELL, H. B. D., 1965b. A 12-year survey of the frequencies of Biston betularia L. and its melanic forms in Great Britain. Entomologist’s Record, 77: 195-2 18. KETTLEWELL, H. B. D., 1973. The Euolution of’ Melanicm. Oxford: Clarendon Press. KETTLEWELL, H. B. D. & BERRY, R. J., 1961. The study of a cline. Heredity, 16: 403-414. KETTLEWELL, H. B. D. & BERRY, R. J., CADBURY, C. J. & PHILLIPS, G. C., 1969. Differences in behaviour, dominance and survival within a cline. Heredity, 24: 15-25. KETTLEWELL, H. B. D., CADBURY, C. J. & LEES, D. R., 1971. Recessive melanism in the moth Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 Lasiocampa guercus L. In E. R. Creed (Ed.), Ecological Genetics and Evolution: 175-201. Oxford: Blackwell. KETTLEWELL, H. B. 1). & CONN, 1). L. l,,1977. Further background choice experiments on cryptic Lepidoptera. Journal of zoology, London, 181: 371-376. LAMBERT, D. M., MILLER, C.D. & HUGHES, ‘1.J., 1986. On the classic case of natural selection. Biology Forum, 79: 11-49. LEES, D. R., 1968. Genetic control of the melanic insularia of the peppered moth Bislon betularia. Heredib, 39: 67-73. LEES, D. R., 1971. A stug ofsome factors affecting geographic distribution of melanism in moths. Unpublished D.Phil thesis, Oxford University. LEES, D. R., 1975. Resting site selection in the geometrid moth Phigalia pilosaria (Lepidoptera: Geometridar). Journal of zoology, London, 176: 341-352. LEES, D. R., 1979. Obituary of Bernard Kettlewell. Entomologist’s Monthly Magazine, 114: 251-255. LEES, D. R., 1981. Industrial melanism: genetic adaptations of animals to air pollution. In J. A. Bishop & L. M. Cook (Eds), Genetic Consequences of Man-Made Change: 129-1 76. London: Academic Press. LEES, D. R. & CREED, E. R., 1975. Industrial melanism in Biston betularia: the role of selective predation. Journal of Animal Ecology, 44: 67-83. LEES, D. R. & CREED, E. R., 1977. The genetics of the insularia forms of the peppered moth Biston betularia. Heredib, 39: 67-73. LEES, D. R., CREED, E. R. & DUCKETT, J. G., 1973. Atmospheric pollution and industrial melanism. Heredity, 30: 227-232. LEMCHE, H., 1931. Amphidasis betularia (L.) and its melanic varieties. Journal of Genetics, 24: 235-341. LIEBERT, T. G. & BRAKEFIELD, P. M., 1987. Behavioural studies on the peppered moth Biston betularia and a discussion of the role of pollution and epiphytes in industrial melanism. Biological Journal ofthe Linnean Society, 31: 129-150. MAcARTHUR, R. H. & CONNELL, J. H., 1966. The Biology ofPopuluttons. New York & London: Wiley. MAJERUS, M. E. N., 1989. Melanic polymorphism in the peppered moth Biston hetularia and other Lepidoptera. journal of Biological Education, 23: 267-284. MANI, G. S., 1982. A theoretical analysis of the morph frequency variation in the peppered moth over England and Wales. Biological Journal of the Liunean Society, I: 259-267. MANI, G.S., 1990. Theoretical models of melanism in Biston hetuluria-a review. BiologicalJournal of the Linnean Society, 39: 355-371. MAY, R. M., ENDLER, J. A. & McMURTIE, R. E., 1975. Gene frequency clines in the presence ofselection opposed by gene flow. American Naturalist, 109: 659475. MIKKOLA, K., 1975. Frequencies of melanic forms of Oligia moths (Lepidoptera Noctuidae) as a measure of atmospheric pollution in Finland. Annales SARGENT, T. D., 1974. The evolution of melanism, by Bernard Kettlewell. Journal of the Lepidopterists’ Socieb, 28: 176-178. SAVAGE, J. M., 1977. Enolution, 3rd edition. New York: Halt, Rinehart and Winston. SLATKIN, M.,1973. Gene flow and selection in a cline. Genetics, 75: 733-756. SPIESS, E. B. (Ed.), 1964. Papers on Animal Population Genetics. London: Methuen. STEPHENSON, H., 1858. Varieties of A. betularia. Entomologist’s Weekly Intelligencer, 4: 75. STEWARD, R. C., 1977a. Industrial and non-industrial melanism in the peppered moth Biston betularia (L). Ecological Entomology, 2: 231-243. STEWARD, R. C., 1977b. Multivariate analysis of variation within the insularia “complex” of the melanic moth Bisfon betularia. Heredity, 39: 97-109. STEWARD, R. C., 1977~.Melanism and selcctive predation in three species of moths. Journal of Animal Ecology, 46: 483-496. STEWARD, R. C., 1985. Evolution of resting behaviour in polymorphic industrial melanic moth species. Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 Biological Journal of the Linnean Sociely, 24: 285-293. TAYLOR, L. R., 1988. Objective and experiment in long-term rescarrh. In G. E. Likens (Ed.), Long-term Studies in Ecology: 20-70. New York: Springer-Verlag. THOMSON, M. & LEMCHE, H., 1933. Experimentr zur Erzirlung eincs erblichen hlelanismus bei dem Spanner Selenia bilunaria Esp. Biologisches APPENDIX A Tutt (1896) on peppered moth melanism “The speckled peppered moth as it rests on trunks in our southern woods is not at all conspicuous and looks like a . . . piece of lichen and this is its usual appearance and manner of protecting itself. But near our large towns where there are factories and where vast quantities of soot are day by day poured out from countless chimneys, fouling and polluting the atmosphere with noxious vapours and gases, this peppered moth has during the last fifty years undergone a remarkable change. The white has entirely disappeared, and the wings have become totally black. As the manufacturing centres have spread more and more, so the ‘negro’ form of the peppered moth has spread at the same time and in the same districts. Let us see whether we can understand how this has been brought about! Do you live near a large town? Have you a greenhouse which you have tried to keep clean and beautiful with white paint? If so what is the result?, the paint is put on, all is beautifully white, but a little shower comes and the beauty is marred for ever. But in country places . . . it is not spoilt . . . No! near large towns, when the rain falls it brings down with it the impurities, the smoke and dirt, hanging in the air . . . and so we find fences, trees, walls and so on getting black with the continual deposit on them. Now let us go back to the peppered moth. In our woods in the south the trunks are pale and the moth has a fair chance of escape, but put the peppered moth with its white ground colour on a black tree trunk and what would happen? It would . . . be very conspicuous and would fall a prey to the first bird that spied it out. But some of these peppered moths have more black about them than others, and you can easily understand that the blacker they are the nearer 318 K.J. BEKKY they will be to the colour of the tree trunk, and the greater will become the difficulty of detecting them. So it really is; the paler ones the birds eat, the darker ones escape. But then if the parents are the darkest of their race, the children will tend to be like them, but inasmuch as the search by birds becomes keener, only the very blackest will be likely to escape. Year after year this has gone on, and the selection has been carried to such an extent by nature that no real black and white peppered moths are found in these districts but only the black kind. This blackening we call melanism”. Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 APPENDIX B Suggestions forfuture work The Manchester workshop reviewed past work and present understanding. It agreed that the latter was well presented by Brakefield (1987), who has clearly showed the complexity of factors that operate on the B. betularia polymorphism; conversely, there is no justification for the assertion of some that selection is trivial (or even non-existent). Legitimate criticisms of published work are: (1) Artefacts arising from experiment: (a) excessive densities, (b) site selection assumptions naivety, (c) resting position (and use of dead specimens). (2) Heterogeneity of sampling sites. (3) Over-concentration on crypsis at expense of non-visual effects. Gaps in knowledge (1) Effects on moths of the physical nature of their resting surface, and their perception thereof (including possible asymmetry). (2) Initial dispersal phase of females. (3) Intensity and range of predation, including possibility of non-avian predators and importance/persistence of search images. (4)Factors affecting fitness at different stages during the life history, noting the extended period of copulation and consequences for cry psis of disassortative mating. (5) Effects of ‘genetic background’ especially: (a) possibility of repeated melanic mutations, (b) differences between betularia and cognataria. (6) Comprehension of niche of betularia, including (a) other moths, (b) nature of biological background (e.g. crypsis is strongly influenced by the epiphytic flora including crustose and foliose lichens where they are present; eggs are laid in foliose lichens), (c) significance of SO,. (7) Znsularia maintenance and selection. (8) Effects of non-visually determined difference in fitness between morphs. Ways forward (1) Analysis of the effect of differences within the life cycle on net fitness (cf. INDUSTRIAL MELANISM AND PEPPERED MOTHS 319 the poor disguise of melanic Boarmia repandata when resting, but excellent crypsis when on flight-which is often necessary because of disturbance by ants). (2) Studies of physiology and biochemistry, particularly energetics. (3) Evaluation of niche perception by moth and predators, building on Endler’s techniques (Endler, 1984, 1990). Collaboration between disciplines will be particularly necessary here. (4) Need to consider and interpret betularia as part ofwidespread occurrence of melanism, including (a) other lepidopteran industrial melanics, Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 (b) industrial melanism in other groups, (c) non-industrial melanics in Lepidoptera, e.g. Western Scotland and islands (q.v. Thornson’s (1980) studies of Scottish butterflies) and in ‘high latitudes’ (North Atlantic islands, Scandinavia). APPENDIX C History of peppered moth melanism work Peppered moth work went through a bottle-neck and flowering with the work of H. B. D. Kettlewell in early 1950s. It does not seem to be known how much E. B. Ford suggested the details of the mark-release studies to Kettlewell, and how much Kettlewell contributed himself. Miriam Rothschild recalls long discussions with Ford, and her pointing out to him that melanics were not new events in history, but that they must have repeatedly recurred in prehistoric times (as R. A. Fisher had argued in deriving his theory of the evolution of dominance). Kettlewell had three successive research assistants: James Cadbury, David Lees and David Conn, and all three were involved in some extent in the peppered moth work (although the earlier classical work was over by the time Cadbury began working with Kettlewell). Kettlewell had an enormous respect for Philip Sheppard, who was working in Oxford when he (Kettlewell) joined Ford. Sheppard was not initially interested in B. betularia; Sheppard’s studies on the species began after his move to Liverpool, when he teamed up with Cyril Clarke, then Reader in Medicine at Liverpool University and a Cambridge contempory of Kettlewell. Kettlewell visited Liverpool in 1956, and suggested to Clarke and Sheppard that sampling peppered moths in the Liverpool conurbation would be highly rewarding. Clarke’s sampling began in 1957. Jim Bishop came to Liverpool for a post-doctoral year with Sheppard, having worked on the ecology of crustacea in his native Sydney. In Liverpool, he began by studying the isopod Sphaeroma, but soon got involved in the B. betularia work of Clarke and Sheppard, particularly in estimating selective predation in the cline of declining carbonaria. In 1966 he moved to Manchester and joined Laurence Cook, who writes, “At that time Manchester was still distinctly satanic in appearance but was being cleaned and rebuilt. Since it was the type locality for the melanic moth it seemed obvious that we should survey the morph frequencies in the area. Our first paper (Nature, 227: 1155, 1970) compared the results with earlier data of H. N. Michaelis and showed that an increase in frequency of typicals had occurred. 320 R. J. BERRY Subsequently, Jim returned to Liverpool; his 1972 paper in the Journal ofhima1 Ecology on work carried out when he was first in Liverpool, was published after his return there. We developed a research programme together and I managed to get a grant to support John Muggleton to work on the survey and fitness estimations. As part of this programme, we decided to use the Lees & Creed method of scoring epiphytes and reflectance on trees, and we approached Mark Seaward as a lichen specialist to provide taxonomic expertise. My first letter from him, agreeing to join in, dates from March 1973”. Cook’s own initiation into industrial melanism occurred “inadvertantly as an Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 undergraduate at University College London, when I bumped into J. B. S. Haldane on the stairs saying that he had just come back from a very boring afternoon at the Royal Society. It was a discussion meeting arranged by E. B. Ford (Proc. Roy. SOC.Lond. B, 145: 1956), where Haldane pointed out that the change in melanic frequency in peppered moths in Manchester could be accounted for by assuming a degree of heterozygote advantage*. Subsequently, I put a fair amount of effort into arguing that the mobility of the insects makes heterozygote advantage unnecessary to explain the frequencies and that it probably does not exist. I went to Oxford in 1957 to do research on scarlet tiger moths (Punaxia dominula), and therefore soon got to know the three people who had been most involved with them; Kettlewell, Sheppard and Ford. I always assumed that Ford’s concern with the industrial melanism story arose from his preoccupation with systems exhibiting strong selection and his awareness of the survey published by Barrett (1901) and related work. In his 1924 paper Haldane has also stressed the significance of the high selection pressure operating, and the rapid change it should produce. Kettlewell’s work on industrial melanism was supported by the Nuffield Foundation at the instigation of Ford. On my first meeting with Kettlewell he took me to visit some tiger moth colonies in the south of England and then to pick up a specimen of “unpolluted” tree trunk from Dean End Wood, Dorset, which was to be an exhibit at another Royal Society meeting organized by Ford featuring industrial melanism. It is somewhat ironic that as we swung around a sharp corner on the return journey I was nearly crushed to death in the back of Kettlewell’s Plymouth by the log which probably gave rise to the impression that this was the best location for betulariu to be found. He knew better than that; I can remember him telling me of a bearded gamekeeper in his youth who used to point out resting moths to him. When I moved to Leicester I continued to keep in touch with Philip Sheppard, who was studying the betularia cline from Liverpool to North Wales with Sir Cyril Clarke; some of the sites are good pubs and/or fly fishing rivers chosen by Philip. My first samples of melanic moth data were scalloped hazel moths collected in Leicester. My first contact with Jim Bishop was also at *Cook comments that “Ford ncvcr got on with Haldane, although Haldane did not seem to notice”. One of Robert Creed’s stories about this concerned a day when Haldane was looking for Ford while on a visit to Oxford. Very agitated, Ford sought out Robert saying “take mc homr, I do not want to talk to that man”. At that time Robert had a Brooklands Rilry competition rar which was a wry small open two-seater in which one sat about four inches from the ground. When Ford had inserted himself, with hat and briefcase and Robrrt was at the front cranking the engine, Haldane turned up, bent down and said “Ah Henry, I wanted to talk to you” To this Ford replied from his position near the road, “I am so glad to see you, Jack. I would br delighted to talk to you- -but we are very busy. In fact, as you see, we are so busy that we have to use a motor racing car in order to gct about”. INDUSTRIAL MELANISM AND PEPPERED MOTHS 32 1 Leicester, where he wrote to me through a mutual acquaintance about the possibility of a post-doctoral year there. In the event, he went to Liverpool and worked with Sheppard”. G. S. Mani was a colleague of Cook’s in the Physics Department at Manchester, who came to peppered moth studies through his interest in modelling biological populations. Meanwhile David Lees and Robert Creed moved from Oxford to Cardiff, and studied melanism in a number of invertebrates, notably ladybirds and Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 leafhoppers. Steward was a postgraduate student of Lees at Cardiff. Paul Brakefield was inspired by the possibilities of field studies in genetics by reading E. B. Ford’s Ecological Genetics before going up to Oxford as an undergraduate. He spent some time with Lees at Cardiff, but his interest in melanism began when he was a postgraduate student of Sheppard’s in Liverpool, working on Maniolajurtina. He then studied melanism in Adalia ladybirds in The Netherlands, and only began to take an active interest in melanic moths and crypsis when he began collaborating in 1983/4 with Tony Liebert. Liebert was another Clarke-Bishop protegi., and a dedicated amateur in the Kettlewell mould. The other group in Britain who have contributed significantly to the peppered moth story, work in the Cambridge University Genetics Department; their leader (M. Majerus) was inspired by E. B. Ford’s New Naturalist books. Majerus writes: “In 1964, for my tenth birthday, I was given a copy of Ford’s Butterjies. I used my pocket money to buy the companion volume Moths in May 1964, and these two books undoubtedly influenced the rest of my life. From that summer I began to do more than make a child’s haphazard collection of butterflies and moths. I began to run a moth trap, and to record religiously, all species taken, forms, when I could identify them, notes on behaviour, and finally I began trying to rear broods from pairings between different forms, following the advice given in Ford’s books. My own experience is testament to the truth of Ford’s contention that the basic elements of Mendelian genetics can be understood by a child of eleven in an afternoon and thereafter applied (although I was only ten). I think the likely course of my career was laid down with the gift of that book. My interest in polymorphic Lepidoptera was certainly conceived in 1964, and has persisted now for 25 years. I read Ford’s Ecological Genetics in 1972, and the idea of working on green versus brown lepidoptera larvae for a PhD came from that reading and subsequent delvings into the bibliography. Although I never met Ford or Kettlewell (I did hear both of them speak on several occasions, but in those days I was a shy retiring youth), I think it is true to say that Ford influenced my interest very considerably”. Majerus’s student, Rory Howlett was an undergraduate at Oxford in the early 80s where, during his studies he carried out an undergraduate project on the marbled white, under Ford’s supervision. The main non-British contributor to the peppered moth story has been Kauri Mikkola of Helsinki. He stayed with Kettlewell in 1978 at the latter’s home north of Oxford, at a time when he (Mikkola) was developing his own ideas about the resting position of B. betutaria. He writes (personal communication) 322 R. J. BERRY that he decided during the weekend “not to tell Bernard my views about the resting background of the moth . . . when I heard the sad news about Bernard Kettlewell’s death in the next spring, I was most happy that I did not argue with him about the resting background”. To end on a personal note: I took my degree from the Genetics Department at Cambridge University. One of the courses I attended was on ecological genetics, taught by George Owen, with R. A. Fisher (who was Head of the Department) sitting in the front row and taking notes. Whilst the course was in progress, an article by Bernard Kettlewell on “How industrialization can alter species” was Downloaded from https://academic.oup.com/biolinnean/article/39/4/301/2654253 by guest on 29 September 2021 published in the December 1955 issue of the popular science magazine Discovery; it was probably the first account of Kettlewell’s peppered moth work (Kettlewell, 1955d), appearing in the same month as his original Heredity paper. I wrote to Kettlewell, and the following summer helped him on field-work in Aysgarth, Yorkshire (where a medical survey has found “too much” bronchitis for a rural area, and Kettlewell had been asked to assess pollution levels as indicated by melanic moth frequencies), the central valley of Scotland, and the Black Wood of Rannoch in Perthshire, a classical site for “relict” melanics. Kettlewell used to claim that I was the first field assistant he ever had. Subsequently I worked with Kettlewell and other associates (including James Cadbury, David Lees, Christopher Perrins, now Director of the Edward Grey Institute for Ornithology, and Peter Harper, Professor of Medical Genetics in the University of Wales) on geographic melanism in Amathes glareosa in Shetland and Lasiocampa quercus in Caithness (Kettlewell & Berry, 1961; Kettlewell et al., 1969; Kettlewell, Cadbury & Lees, 1971; Slatkin, 1973). Some years later I wrote: “Kettlewell was an exciting person to be with, full of lore and anecdotes. He was the best naturalist and almost the worst professional scientist I have ever known. Writing research papers with him was traumatic; as an experienced clinician he made rapid diagnoses, and refused to be diverted by what he regarded as irrelevant evidence. I learned an enormous amount from Bernard Kettlewell, and was enthused by him at a crucial time in my life when I was in danger of becoming a closet biologist” (Berry, 1988). I have no reason to change my judgement.