Melanic Frequency Research Articles

Increase in the frequency of melanism in Abert’s Squirrel in Boulder, Colorado

Abstract In the northern portions of its range, Abert’s Squirrel (Sciurus aberti) has two color morphs: a wild-type gray morph and a melanistic morph. Using camera traps, citizen science data and in-person observations in and near Boulder, Colorado (USA), we compared current color morph frequencies to those reported in a 1969–1971 study. At all study sites, we observed a large and statistically significant increase in the frequency of the melanistic morph compared to historic data. We hypothesize that this increase may be due to selection favoring the melanistic morph in a changing forest environment.

Fifty per cent and all that: what Haldane actually said

Abstract In 1924, J. B. S. Haldane used the observation of increasing melanic frequencies in peppered moths (Biston betularia L.) to illustrate strong selection in a natural population. Since the phenomenon was first observed, there has been criticism and misinterpretation of work on industrial melanism in moths coming from a number of directions, increasingly on the Internet. Haldane’s calculation, its reception and his other interests in peppered moths are reviewed. An example of Internet comments attributing opinions to him, and their origin and background, are discussed.

New data on polymorphism of the meadow spittlebug Philaenus spumarius (L.) (Hemiptera: Aphrophoridae) from the island of São Miguel (Azores).

The meadow spittlebug, Philaenus spumarius (L.) (Hemiptera, Aphrophoridae) is a widespread insect species in the Holarctic region, exhibiting a dorsal colour balanced polymorphism. In the Azores the species is known from high elevations in Terceira and São Miguel islands. A sample of 235 individuals from Pico da Vara and Graminhais protected areas (São Miguel, Azores) (between 645 and 935 m a.s.l.), collected in 2000 and 2017, showed a remarkable high frequency of the melanic morphs flavicollis (FLA) and quadrimaculatus (QUA). In addition, a high frequency of melanics was observed in males. We explore the hypotheses for the origin of Azorean colonization and for the high proportion of melanism in the Azorean populations.

Mapping black panthers: Macroecological modeling of melanism in leopards (Panthera pardus).

The geographic distribution and habitat association of most mammalian polymorphic phenotypes are still poorly known, hampering assessments of their adaptive significance. Even in the case of the black panther, an iconic melanistic variant of the leopard (Panthera pardus), no map exists describing its distribution. We constructed a large database of verified records sampled across the species’ range, and used it to map the geographic occurrence of melanism. We then estimated the potential distribution of melanistic and non-melanistic leopards using niche-modeling algorithms. The overall frequency of melanism was ca. 11%, with a significantly non-random spatial distribution. Distinct habitat types presented significantly different frequencies of melanism, which increased in Asian moist forests and approached zero across most open/dry biomes. Niche modeling indicated that the potential distributions of the two phenotypes were distinct, with significant differences in habitat suitability and rejection of niche equivalency between them. We conclude that melanism in leopards is strongly affected by natural selection, likely driven by efficacy of camouflage and/or thermoregulation in different habitats, along with an effect of moisture that goes beyond its influence on vegetation type. Our results support classical hypotheses of adaptive coloration in animals (e.g. Gloger’s rule), and open up new avenues for in-depth evolutionary analyses of melanism in mammals.

Melanism of Coyotes (Canis latrans) in Florida

Abstract Occurrence of melanism in the coyote (Canis latrans) has been poorly documented. We collected 244 coyote carcasses throughout Florida during 2011–2014 and documented 18 cases of melanism (7.4%). Melanistic individuals were positively correlated with tree canopy cover (βcanopy mean = 0.11, se = 0.03, P < 0.001) and consequently observed only in northern portions of Florida. However, geographic trends (e.g., northing, easting, north-westing) did not explain variation in our data as well as habitat. Melanism varied through space from locally abundant to absent, but the drivers perpetuating variation in frequency of melanism are likely complex as the mechanisms for polymorphic maintenance are unclear.

A proposed selective mechanism based on metal chelation in industrial melanic moths

Industrial melanism, a phenomenon observed in some moths and especially in the case of the peppered moth (Biston betularia), has received much attention as an example of Darwinian evolution in action. The rapid rise in the proportion of the darker melanic form of the adult moth coincided with the advent of atmospheric pollution resulting from industrialization, and was ascribed to the improved camouflage of the melanotic insects against a background blackened by soot, which conferred a selective advantage in the avoidance of predation by birds. The topic of the increase in melanization during the initial period of industrial expansion and the reversal of the process after the introduction of the Clean Air Act has received much attention. Although there is sound experimental evidence to support selective avian predation as a major mechanism to account for the changes in the relative frequency of melanics, it is not clear that this is the only selective factor involved in industrial melanism. It is possible that other processes may have made a contribution to the preponderance of melanic variants. In the present study, the hypothesis is advanced that melanization may have conferred a selective advantage by protecting the insects from the toxic effects of metals by virtue of the strong metal chelating action of melanin. Biological Journal of the Linnean Society, 2013, 109, 298–301.

How the Leopard Hides Its Spots: ASIP Mutations and Melanism in Wild Cats

The occurrence of melanism (darkening of the background coloration) is documented in 13 felid species, in some cases reaching high frequencies at the population level. Recent analyses have indicated that it arose multiple times in the Felidae, with three different species exhibiting unique mutations associated with this trait. The causative mutations in the remaining species have so far not been identified, precluding a broader assessment of the evolutionary dynamics of melanism in the Felidae. Among these, the leopard (Panthera pardus) is a particularly important target for research, given the iconic status of the ‘black panther’ and the extremely high frequency of melanism observed in some Asian populations. Another felid species from the same region, the Asian golden cat (Pardofelis temminckii), also exhibits frequent records of melanism in some areas. We have sequenced the coding region of the Agouti Signaling Protein (ASIP) gene in multiple leopard and Asian golden cat individuals, and identified distinct mutations strongly associated with melanism in each of them. The single nucleotide polymorphism (SNP) detected among the P. pardus individuals was caused by a nonsense mutation predicted to completely ablate ASIP function. A different SNP was identified in P. temminckii, causing a predicted amino acid change that should also induce loss of function. Our results reveal two additional cases of species-specific mutations implicated in melanism in the Felidae, and indicate that ASIP mutations may play an important role in naturally-occurring coloration polymorphism.

The peppered moth and industrial melanism: evolution of a natural selection case study

From the outset multiple causes have been suggested for changes in melanic gene frequency in the peppered moth Biston betularia and other industrial melanic moths. These have included higher intrinsic fitness of melanic forms and selective predation for camouflage. The possible existence and origin of heterozygote advantage has been debated. From the 1950s, as a result of experimental evidence, selective predation became the favoured explanation and is undoubtedly the major factor driving the frequency change. However, modelling and monitoring of declining melanic frequencies since the 1970s indicate either that migration rates are much higher than existing direct estimates suggested or else, or in addition, non-visual selection has a role. Recent molecular work on genetics has revealed that the melanic (carbonaria) allele had a single origin in Britain, and that the locus is orthologous to a major wing patterning locus in Heliconius butterflies. New methods of analysis should supply further information on the melanic system and on migration that will complete our understanding of this important example of rapid evolution.

A steep cline in ladybird melanism has decayed over 25 years: a genetic response to climate change?

A cline in the frequency of melanic morphs of the two-spot ladybird, Adalia bipunctata, was first surveyed in 1980 along a transect extending inland from the coast in the Netherlands. At that time, the frequency of melanics increased over some 40 km from 10% near the coast to nearly 60% inland. Additional surveys made in 1991 and 1995 demonstrated some progressive change in cline shape. New samples from 1998 and 2004 confirm these dynamics, and show that over a period of about 50 generations for the beetle, the cline had decayed rapidly to yield rather uniform frequencies of melanic morphs at around 20% along the whole transect by 2004. Climate data and evidence for thermal melanism in this species support our contention that these dynamics reflect a dramatic example of a rapid genetic response within populations to climate change and local selection.

Decline of melanism in two British moths: spatial, temporal and inter-specific variation

The decline in industrial melanism over the last quarter century constitutes an exceptional case of an evolutionary change, varying in both time and space, and between species. In Biston betularia and Odontoptera bidentata, the change in melanic frequency is closely replicated at two sites 0.5 km apart. Between seven sites 50-100 km apart, there is heterogeneity in both the speed and timing of change. At sites that were heavily industrialized, the change is faster, from an initially higher frequency, and starts later than at sites which are more rural.We propose a method for estimating systematic change during sigmoid declines in melanic frequencies. This fails to show any significant change over time in selective coefficients. It is concluded that the overall pattern of change has been driven largely by events in the most polluted and industrialized parts of the country. Although migration may contribute to the estimated selective values, natural selection is the only credible explanation for the overall decline.

Melanic Moth Frequencies in Yorkshire, an Old English Industrial Hot Spot

A survey has been carried out in Leeds, England, in the west Yorkshire industrial heartland, and in neighboring York, surrounded by agriculture, of melanic frequency in the moth species Biston betularia, Odontoptera bidentata, and Apamea crenata. All show a decline in melanics in the postindustrial environment, the first over almost the full range from nearly 100% to less that 10%, the others to smaller extents. Changes in several species over as great a magnitude and as wide an area must result from selection. The results are compared with others along a transect through northern England. The onset of response is progressively later from west to east. The rate of decline is lower at the extremes of the transect to west and east than it is in the center. We still do not have a clear picture of the causes of the changes. One major factor is likely to be selective predation, which is shown to be critically dependent on predation rate. As a consequence, differences in settling behavior between the species could account for different responses even if the species are attacked by the same predators.

Melanic frequencies in three species of moths in post industrial Britain

Changing patterns of morph frequency in three moth species (Biston betularia, Odontoptera bidentata and Apocheima pilosaria) have been investigated using data from the Rothamsted Insect Survey. All three exhibited industrial melanism during the period of high atmospheric pollution in Britain. Three historical and habitat types are compared, the old industrial north of England, rural Scotland, Wales and South-West England, and a southern English intermediate region of high human population density but generally low industrialization. Between 1974 and 1999 the carbonaria morph of B. betularia declined in frequency in the industrial region and is nearly absent from rural areas. It is the form which most closely tracks atmospheric change. It is shown that the insularia forms of B. betularia and the melanic morphs in the other two species have decreased in the industrial region, commencing later than carbonaria, but have maintained their presence and possibly reached equilibrium elsewhere. They may be non-industrial polymorphisms. B. betularia is rarer than the other species and all three species are at lower densities in industrial than in non-industrial regions.

Changing views on melanic moths

The rapid rise in frequency of melanic morphs in several moth species, especially the peppered mothBiston betularia , in industrial regions during the 19th century, and the subsequent rapid decline, indicate the action of strong selection. There has recently been a tendency to criticise and question all aspects of research on industrial melanism, including the experiments which suggest that selective predation plays an important part in the changes. These experiments are reexamined, together with evidence for changes in appearance of tree surfaces and for relation of initial melanic frequency to subsequent rate of decline. It is suggested that intense pollution may have been required to drive the carbonaria morph to a high frequency, with frequency patterns over a mosaic environment smoothed by migration. Improvements in these extreme locations then triggered the decline, with little indication of the environmental changes in areas of moderate pollution. Reasons for criticism of past work are discussed. Industrial melanism continues to provide an exceptional opportunity to analyse a pattern of selection and change in gene frequency.

Changing views on melanic moths

The rapid rise in frequency of melanic morphs in several moth species, especially the peppered moth Biston betularia, in industrial regions during the 19th century, and the subsequent rapid decline, indicate the action of strong selection. There has recently been a tendency to criticise and question all aspects of research on industrial melanism, including the experiments which suggest that selective predation plays an important part in the changes. These experiments are reexamined, together with evidence for changes in appearance of tree surfaces and for relation of initial melanic frequency to subsequent rate of decline. It is suggested that intense pollution may have been required to drive the carbonaria morph to a high frequency, with frequency patterns over a mosaic environment smoothed by migration. Improvements in these extreme locations then triggered the decline, with little indication of the environmental changes in areas of moderate pollution. Reasons for criticism of past work are discussed. Industrial melanism continues to provide an exceptional opportunity to analyse a pattern of selection and change in gene frequency.

Geographic and temporal variation in the incidence of melanism in peppered moth populations in America and Britain

Industrial melanism in the peppered moth (Biston betularia is the classic example of observable evolution by natural selection. The phenomenon has been most thoroughly documented in Britain, where once rare melanic phenotypes increased in frequency in concert with increased levels of atmospheric pollution generated by industrial development. Populations of the American subspecies of the peppered moth (B. betularia cognataria) also experienced increases in melanisms, which are especially well documented in southern Michigan. Following a succession of governmental regulations designed to improve air quality, melanic phenotypes have been on the decline in moth populations in the United Kingdom and the United States. In both countries, the declines in melanism appear to be correlated primarily with reductions in atmospheric sulfur dioxide. Detailed studies of the evolutionary parallels have focused mainly on two locations: Caldy Common (near Liverpool) in England, and the George Reserve (near Detroit) in the United States. We have expanded the geographic range of American samples to include northeastern Pennsylvania and southwestern Virginia, and we have conducted a national survey in Britain to produce a current melanic frequency distribution map. The results clearly show that the decline in melanism is widespread in both countries, and the changes are generally consistent with decreases in levels of atmospheric SO2.

Parallel Rise and Fall of Melanic Peppered Moths in America and Britain

The moth (Biston betularia) is well known for the rapid rise in the frequency of alleles producing melanic phenotypes correlated with a general blackening of the environment following the nineteenth-century industrial revolution. In recent years the frequency of melanics has been dropping steadily in Britain in apparent response to improved air quality. Some regional American populations of this same species also experienced significant increases in melanics, by 1959 exceeding 90% in southeastern Michigan, but Michigan populations were not reexamined for over 30 years. In 1994 and 1995 we trapped moths in southeastern Michigan and here report that a parallel decline in melanism has occurred in American moths. Furthermore, we document that changes in Michigan's air quality as measured by atmospheric sulfur dioxide (SO2) and suspended particulates also parallel the changes recorded in Britain. The traditional interpretation is that pale phenotypes of moths at rest by day on lichen-encrus ted trees are camouflaged from bird predators; industrial fallout kills lichens and darkens resting surfaces, favoring darker colored moths. However, the changes in allele frequencies in the moth populations we sampled have occurred in the absence of perceptible changes in the local lichen floras. We suggest that the role of lichens has been inappropriately emphasized in chronicles about the evolution of melanism in moths. Industrial melanism in the Lepidoptera ranks among the best examples of observable evolution by natural selection. The most thoroughly documented case is that of the geometrid moth Biston betularia, with the fundamental details of its recent evolutionary history described in virtually every biology textbook. Its common name, peppered moth, describes the appearance of the so-called form or phenotype which is covered with white scales peppered with black over the wings and body. Several other pigmentation phenotypes are known. A melanic form, named carbonaria, is nearly solid black. Intermediates between the pale and fully melanic phenotypes are called insularia. The range in variation from lightest to darkest is continuous, but the phenotypic differences result from multiple alleles at a single locus which exhibit an approximate dominance hierarchy: the carbonaria allele shows complete dominance over the insularia and typical alleles, and

A study of nonrandom mating in a British population of the two-spot ladybird with a high frequency of the melanic morph

In some studies of the two-spot ladybird (Adalia bipunctata), melanic males have been found in excess over the typical morph in matings. Data suggest that a genetic female mating preference is responsible. The mating advantage of melanic males may be important in maintaining a polymorphism between melanic and typical ladybirds in many populations in the United Kingdom (U.K.). It has been reported that preference frequency varies linearly with melanic frequency throughout most of the U.K. One particular population ofAdalia bipunctata near Aberdare, South Wales, is noted for its high frequency of melanic individuals. It has been suggested that local environmental factors account for the high melanic frequency in this population. It is also possible, however, that a female mating preference may be at least partly responsible for the high frequency of melanics (as has been proposed for the rest of the U.K.). In this study, experiments have been performed to determine the level of female mating preference in the Aberdare population. No evidence was found for any mating advantage to melanic males. There was inconsistent and unexpected evidence that melanic females were overrepresented in matings, but the cause for this was unclear. Female mating preference does not appear, therefore, to be responsible for the high melanic frequency in the population ofAdalia bipunctata near Aberdare. There is not a simple association between mating preference and melanic frequency in U. K. populations of the two-spot ladybird.

The colour/pattern polymorphism of Philaenus spumarius (L.) (Homoptera: Cercopidae) in England and Wales

The spittlebug Philaenus spumarius is a common and widespread Palaearctic insect exhibiting a striking dorsal colour/pattern polymorphism, which is conveniently divisible into eight ‘melanic’ and five ‘non-melanic’ phenotypes. The polymorphism is controlled by seven alleles at a single autosomal locus with complete or partial female-limitation and variable penetrance in males of certain melanic phenotypes. It is a universal polymorphism but, despite much investigation, little is known of the factors which maintain it or influence morph frequency. Patterns of geographic variation are useful in both these contexts. This study presents an extensive survey of morph frequency variation in 548 populations of P. spumarius across England and Wales. Frequencies of individual phenotypes within the melanic category vary heterogeneously; frequency variation for a ‘core’ group of five phenotypes is broadly in parallel, whereas the other three vary independently. Furthermore, the degree of penetrance in males varies between the melanic phenotypes, which in turn varies between populations; one consequence is that higher melanic frequencies are associated with enhanced expression of certain melanic phenotypes in males. Comparisons are made with previously reported populations around a point source of serious gaseous and particulate pollution in the Cynon Valley, South Wales and with intensively studied populations in southern Finland. The data indicate a pronounced ‘urban effect’ on morph frequencies, with populations in major conurbations exhibiting higher mean melanic frequencies ( x̄ = 19.1%) than rural ones ( x̄ = 7.3%). Populations around three (of the eight investigated) point sources of atmospheric pollution show elevated melanic frequencies, although all are substantially below those recorded from the Cynon Valley Although Finnish populations exhibit substantially higher melanic frequencies than analogous rural populations in Britain the strict female-limitation of certain melanic phenotypes in Finland is relaxed in British populations, where male melanics are approximately 20-fold more frequent. The universality and stability of this polymorphism strongly suggest the overriding influence of natural selection in its maintenance. The predominance of the phenotypes GIB and LCE (mostly black, but with pale heads) over the completely black form (LOP) in populations with the highest overall melanic frequencies demonstrates that the selective agent(s) favouring melanics in intensely polluted areas cannot be operating simply for melanism per se . The near-equality of melanic frequencies between the sexes in the majority of populations reported here suggests that the model of genetic control established for populations in the Cynon Valley also applies to most British populations and remains distinct from the model applying to Finnish populations.

Correlates of melanism in a population of adders (Vipera berus) from the Swiss Alps and comparisons with other alpine populations

Abstract A free-ranging population of adders (Vipera berus) was studied from 1987 to 1993 in a prealpine area of western Switzerland situated at about 1400-1600 m a.s.l. Adders of two chromatic morphs (melanistic and zig-zag) are found in this locality. Body sizes of melanistic specimens (including both males and females) significantly exceeded those of zig-zag (cryptic) ones, and fecundity was higher in black than in cryptically coloured females. The existence of a dwarf mountainous "ecotype" in this alpine region is suggested. The frequency of melanism was higher in females.

Peppered moth revisited: analysis of recent decreases in melanic frequency and predictions for the future

In a recent review article by Mani published in 1990, it was shown that the changes in the frequency of the morph carbonaria can be explained through a migration-selection model and the model is capable of reproducing the decrease in the carbonaria frequency since the enactment of Clean Air Acts. In this paper new data both for carbonaria and for insularia up to 1990 for West Kirby in NW England and for Cambridge are presented. In the earlier review, the data for West Kirby extended to 1987 and for Cambridge to 1985. Data not previously published for the carbonaria and the insularia frequencies at sites in Northwood in Middlesex, Egham in Surrey and Ringwood in Hampshire are also presented. A migration-selection model was used to predict the change in the frequencies of the melanic morphs up to the year 2010. All the data are compared with the predictions of the model. It is encouraging that the data follow the theoretical predictions.