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.

Selective bird predation on the peppered moth: the last experiment of Michael Majerus.

Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s ≈ 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.

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.

Frequency of renal impairment, advanced age, obesity and cancer in venous thromboembolism patients in clinical practice.

BACKGROUND: Low-molecular-weight heparin (LMWH) dosed by weight is recommended as first-line therapy for the initial treatment of venous thromboembolism (VTE) and as monotherapy for long-term treatment of cancer-related VTE. In 'special populations' such as those with renal impairment or the elderly, weight-based dosing may be excessive, and capping the dose in obese patients may lead to inadequate dosing. OBJECTIVES: We determined the frequency of 'special population' characteristics (renal impairment, advanced age, obesity) and cancer among VTE patients in clinical practice, and assessed whether these characteristics appeared to influence the type and dose of anticoagulants prescribed. METHODS: During 2004-2005, among consecutive patients with VTE at two large Canadian hospitals, the proportions with the above characteristics were calculated and treatments prescribed were determined. RESULTS: Of 524 VTE patients, 31% were aged > 75 years. Moderate renal impairment [creatinine clearance (CrCl) 30-59 mL min(-1)] was present in 20% of patients, and severe renal impairment (CrCl < 30 mL min(-1)) in 5% of patients. LMWH was prescribed to 67% of patients with severe renal impairment and to 83% of patients with moderate renal impairment. Body weight was > 100 kg in 15% of patients. Underdosing of LMWH by > 10% was documented in 36% of such patients compared with 8% of patients < 100 kg (P < 0.001). Among 26% of patients with active cancer, only one-third were prescribed LMWH monotherapy. CONCLUSIONS: In clinical practice, renal impairment, advanced age, obesity and cancer are frequently present in patients with VTE. A considerable proportion of these patients may not receive the optimal type or dose of medication to treat VTE.

Male biased sex ratio in the Mediterranean fruit fly Ceratitis capitata, an example of Y-chromosome meiotic drive.

A case of Y-chromosome meiotic drive is reported in the Mediterranean fruit fly Ceratitis capitata. It arose in an irradiated male and results in excess of males. Male excess is inherited strictly from father to son. A Y-linked factor MP (male producer) is proposed. Higher drive can be selected, but distortion declines rapidly in the absence of selection. Hybrid males from crosses between driving males and nondriving females also show drive but to a reduced extent, suggesting the action of suppressors. Sex ratio distortion is independent of postzygotic mortality, and is not associated with an obvious chromosome arrangement. Spermiogenesis in driving males is characterised by abnormalities in sperm tails and reduced numbers in some sperm cysts, whereas neighbouring cysts of the same MP testis are essentially wild type. The average number of missing sperms plus deformed sperms approximates to the average depression in female recovery among the progenies of siblings, suggesting that most of the missing or abnormal sperms would have given rise to females, that is, they would have been X-bearing. To explain the heterogeneity between neighbouring cysts, a theory is proposed that links it to variation in X-chromosome sensitivity to MP, arising by random suppression of the genetic basis of sensitivity during the six mitotic divisions in the origin of the cyst from its stem cell before meiosis.

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.

Disequilibrium in some Cepaea populations.

Phenotypic disequilibrium is a measure available, along with morph frequency, in many published sets of sample data recording the polymorphism of shell colour and pattern in the snail Cepaea nemoralis. The relation of disequilibrium to morph frequency for the colour (pink/yellow) and banding (unbanded/banded) loci has been examined for a large and widespread set of data. The direction of disequilibrium is a function of frequency at the two loci in a way that suggests that selection favours combinations of common morphs, whichever they are. This could indicate that such combinations are common because they have been selected. The data are therefore consistent with the proposal that populations are generally subject to selection of varying directions at different places and times, acting on the phenotype. In combination with migration, such selection could lead to prolonged polymorphism.

Capillary sodium dodecyl sulfate-DALT electrophoresis of proteins in a single human cancer cell.

Capillary Sodium dodlecyl sulfate (SDS)-DALT an (abbreviation for Dalton) electrophoresis was applied to analysis of proteins in single HT29 human colon adenocarcinoma cells. A vacuum pulse was employed to introduce a single cell into the coated capillary. Once the cell was lysed, proteins were denatured with SDS, fluorescantly labeled with 3-(2-furoyl)-quinoline-2-carboxaldehyde (FQ), and then separated by using 8% pullulan as the sieving matrix. This method offers a few advantages for single-cell protein analysis. First, it provides reproducible separation of single-cell proteins according to their size. Based on comparison with the migration time of standard proteins, most components from a single HT29 cancer cell have molecular masses within the range of 10-100 kDa. Second, as a one-dimensional separation method, it gives fairly good resolution for proteins. Typically, around 30 protein components of a single HT29 cell were resolved, indicating that this method has similar peak capacity to SDS-polyacrylamide gel electrophoresis (PAGE). Third, this method shows high detection sensitivity and wide dynamic range, which is important because of the wide range of protein expression in living systems. Detection limits for standard proteins ranged from 10(-10) to 10(-11) M. Finally, this method provides much higher speed than classical gel electrophoresis methods, and it provides automated anlysis of cellular proteins at the single-cell level; the separation is complete in 30 min and the entire analysis takes approximately 45 min.

Two-dimensional direct-reading fluorescence spectrograph for DNA sequencing by capillary array electrophoresis.

We report a compact, two-dimensional direct-reading fluorescence spectrograph and demonstrate its application to DNA sequencing by capillary array electrophoresis. The detection cuvette is based on sheath flow, wherein the capillaries terminate in a two-dimensional array in a fluid-filled chamber that is pressurized with buffer. A thin metal plate is located downstream from the capillaries. This barrier plate has an array of holes that precisely matches the location of the capillaries. Buffer flows through the holes, drawing analyte from the capillaries in a well-defined array of thin filaments. Fluorescence is excited in the upper chamber with an elliptically shaped laser beam. The bottom chamber is sealed with a glass window and drained from the side. Fluorescence is detected by imaging the illuminated sample streams through the holes in the barrier plate. A prism is used to disperse fluorescence from each sample across a CCD camera so that the emission spectrum is monitored simultaneously from each capillary. The instrument is demonstrated in a 32-capillary configuration but can be scaled to several thousand capillaries.

Separation of proteins by sodium dodecylsulfate capillary electrophoresis in hydroxypropylcellulose sieving matrix with laser-induced fluorescence detection.

Sodium dodecyl sulfate capillary electrophoresis by using hydroxypropylcellulose as the sieving matrix was developed for separation of proteins. 3-(2-furoyl)quinoline-2-carboxaldehyde, a fluorogenic dye, was used as the pre-column reagent to label proteins, which allows the use of laser-induced fluorescence to improve the detection sensitivity. Five standard proteins within the molecular mass range of 14,000-97,000 were used to test this method and a calibration curve was obtained between the molecular mass of these proteins and their peak migration times. This method was also applied to the separation of proteins from HT29 human colon adenocarcinoma cell extracts, and, typically, nearly 30 protein components could be resolved in a 20-min separation. Similar separation patterns were observed for the cell extract proteins when three running buffer systems were employed, indicating that buffer composition did not have much influence on the separation based on HPC sieving.

Mating systems of diploid and allotetraploid populations of Tragopogon (Asteraceae). II. Artificial populations.

Polyploidization has long been recognized as an important force in the diversification of plants. Theoretical models predict that polyploids may be expected to exhibit higher rates of self-fertilization than do closely related diploid species. Wild populations of the neopolyploid Tragopogon mirus (4n) exhibited slightly higher rates of outcrossing than did populations of one of its progenitors, T. dubius (2n). In the current study, outcrossing rates in populations of T. dubius and T. mirus were estimated using artificial arrays constructed to maximize the chances of detecting outcrossing events. The artificial diploid population is more highly outcrossing (t=0.727; family-level estimates range from 0.00 to 1. 32) than the tetraploid population (t=0.591; family-level estimates range from 0.00 to 1.14), although the difference between them is not statistically significant. The results of this study, combined with those of the previous work on wild populations, suggest that mating systems in these species vary more among populations than between ploidal levels. This could be because of the relatively recent origins of the tetraploid species; there may have been insufficient time since the formations of the tetraploids for shifts in mating systems to occur.

Frequency of insularia during the decline in melanics in the peppered moth Biston betularia in Britain.

Over the last three decades the frequency of the dark melanic form carbonaria of the peppered moth Biston betularia has declined in Britain. Data have been examined which show the intermediate phenotype insularia, controlled by alleles at the same locus, to have increased or remained level in frequency. Phenotype frequency of insularia does not always track allele frequency accurately because it is recessive to its alternative when carbonaria is common but dominant to the alternative when typical is common. It is shown that if insularia fitness lies between that of carbonaria and typical, and melanics replace typicals or vice versa, there will be a rise and fall in insularia allele frequency during a transitory period. The path followed is strongly affected by initial gene frequencies. During the high melanic period in Britain, differences in insularia frequency between localities may have been influenced by history of arrival of the novel morphs as well as by local selective conditions.

Fractal fiber optics.

Analysis of the geometry of recursive tilings has led to the development of a new class of highly ordered optical composites that exhibit fractal surface character. These objects are, we believe, the first engineered fractal objects. The mathematics of tiling and examples of fractal fiber array devices are reviewed.

Phenotypic variability and heterozygosity at an esterase locus in the mosquito Aedes aegypti.

Populations of the yellow fever mosquito, Aedes aegypti L. are polymorphic for esterase alleles. This could be because the alleles are neutral or because selection protects the polymorphism, as had been concluded from a study of allele frequencies. A test has been carried out to look for possible associations of esterase heterozygosity with speed of development, body size and spine number symmetry in two spine rows. Heterozygotes were found to be larger and slower growing than homozygotes, but there was no difference in degree of asymmetry. There were fewer heterozygotes and a greater deficiency compared with expectation in insects reared at higher temperatures. It is concluded that different genotypes do differ in fitness.

What can be learnt about selection from gene frequency distribution?

Polymorphism has been studied at the Esterase 6 locus in the Yellow Fever mosquito Aedes aegypti (L.) in laboratory stocks. At least 12 alleles are present, with up to four coexisting in a stock. The allele frequency distribution is quite sharply peaked at a mode of about 0.25. The experimental data are compared with the results of simulation based on two models, one in which the initial global distribution is taken to be the stationary distribution obtained from the neutral model assuming M = 4 mu Ne = 1 and the other in which the initial global distribution is generated from the experimental populations studied. The results suggest that the patterns observed are not likely to arise through random fluctuation of frequencies in neutral alleles, but that some kind of selection maintains polymorphism, either in the wild or in the laboratory, or both.

Postindustrial melanism in the peppered moth.

New data show the geographical pattern of frequency of the melanic morph carbonaria of the peppered moth, Biston betularia, in 1983-84. These frequencies are compared with data from 1952 to 1970. After 20 years of smoke control, the area of high melanic frequency has contracted to the northeast. The change indicates a disadvantage to carbonaria of about 12 percent compared with 20 years ago. Computer simulations, which do not include the assumption of heterozygote advantage, provide a good match to the surface for the period 1952 to 1970, and also the 1983-84 surface. Experiments on visual predation have been criticized as giving unrepresentative estimates of selection but they permit satisfactory simulations to be made.

A note on estimating selection pressures on insecticide-resistance genes.

It is useful to be able to measure selection pressures acting on resistance genes in insect vectors of disease, since it is thus possible to predict future changes in frequency and to consider ways to minimize development of resistance. This note describes a method for estimating the selection coefficients, given two or more post-selection phenotype frequencies and knowing the number of generations between them.The method is applied to published data on Anopheles labranchiae under selection with DDT. The relative fitness (1-s) of the susceptibles compared with resistants was estimated by this method to be 31-38%. This was an annual estimate, but if the number of generations per year is known, it is also possible to calculate a value per generation. A computer program for making these estimates is given. The calculations depend on the gene being effectively recessive, i.e., on the heterozygote being killed by the dose applied in the field.Another approach to estimation of selection is by determining the deviation in gene frequency from the Hardy-Weinberg expectations. By this method, the relative fitness (1-s) of the susceptibles in a population of A. funestris under dieldrin selection in the north of the United Republic of Cameroon has been estimated to be 40%. There are difficulties with this method, however, because population mixing may result in deviations that mimic the effect of selection. Examples are discussed for A. gambiae, where population mixing may occur and heterozygote deficiencies for the dieldrin resistance gene have been observed.For both methods of estimation, it is essential to know the real effective dominance of the resistance gene in the wild, i.e., whether the resistance heterozygote is killed or not. This factor is important in the control of resistance.