Dark Allele Research Articles

Multigenerational pedigree analysis of wild individually marked black sparrowhawks suggests that dark plumage coloration is a dominant autosomal trait

AbstractThe black sparrowhawk (Accipiter melanoleucus) is a color‐polymorphic sub‐Saharan raptor, with adults occurring in two discrete color morphs: dark and light. It has previously been suggested that plumage coloration is determined by a one‐locus two‐allele system, with the light allele being dominant over the dark allele. Here, we revisit that assumption with an extended dataset of 130 individuals and pedigree information from 75 individuals spanning five generations. We test the observed offspring phenotypic ratio against the expected ratio under the Hardy–Weinberg equilibrium and find significant deviations from the expected values. Contrary to the previous assumption, our data indicate that the dark allele is in fact dominant over the light allele. Similarly, the multigenerational pedigrees obtained are incompatible with a one‐locus two‐allele system, where the light allele is dominant but are consistent with a scenario where the dark allele is dominant instead. However, without knowledge of the underlying molecular basis of plumage polymorphism, uncertainty remains, and the intra‐morph variation observed suggests that modifier genes or environmental factors may also be involved. Our study not only provides a foundation for future research on the adaptive function of color polymorphism in the species but also highlights the need for caution when drawing conclusions about the mode of inheritance in wild animal populations in the absence of genetic data, especially when one color variant is numerically much rarer than the other.

Inheritance of plumage morphs in Little Eagles Hieraaetus morphnoides in northern New South Wales

Polymorphism and inheritance of plumage colour in the Little Eagle Hieraaetus morphnoides were studied in northern New South Wales, by tallying records of parental morph combinations in breeding pairs and the morphs of their offspring in the 1980s, 2000s and 2017–2019 ( n = 41 pair combinations). The average ratio in breeding adults was 4.9 light:1 dark, with dark males outnumbering dark females (1.8:1). Light × light pairs always produced light young ( n = 32). Dark male × light female pairs variously produced light and dark offspring of both sexes ( n = 12). Light male × dark female pairs produced dark young of either sex ( n = 4) and one light young of unknown sex. One dark × dark pair produced a dark young. We conclude a Mendelian inheritance pattern with the dark morph recessive. From a small sample of mixed pairs with a dark male, the ratio of offspring morphs did not differ significantly from that expected by the Hardy–Weinberg equation, but mixed pairs with a light male produced 4 dark offspring to one light, versus the expected Hard –Weinberg ratio of 1.95 light: 1 dark. This outcome suggests a non-random transmission of the dark allele by heterozygous light males, and a similar pattern of inheritance to that in the related Booted Eagle H. pennatus .

The genetic basis and enigmatic origin of melanic polymorphism in pomarine skuas (Stercorarius pomarinus).

A key outstanding issue in adaptive evolution is the relationship between the genetics of intraspecific polymorphism and interspecific evolution. Here, we show that the pale/dark ventral plumage polymorphism that occurs in both the pomarine skua (Stercorarius pomarinus) and Arctic skua (S. parasiticus) is the result of convergent evolution at the same locus (MC1R), involving some of the same amino acid sites. The dark melanic MC1R allele in the pomarine skua is strongly divergent from the pale MC1R alleles. Whereas the dark allele is closely related to MC1R alleles in three species of great skua (S. skua, S. maccormicki, S. lonnbergi), the pale pomarine skua MC1R alleles present a star-like pattern in an intermediate position on the haplotype network, closer to alleles of the long-tailed skua (S. longicaudus). Variation at other nuclear loci confirms a close relationship between the pomarine skua and the great skuas. The plumage polymorphism in pomarine skuas might have arisen in the common ancestor of pomarine and great skuas, only being retained in pomarine skuas. Alternatively, the pale and melanic MC1R alleles may have evolved independently in different lineages and been brought together in pomarine skuas by hybridization. In this case, introgression of a pale MC1R allele into the pomarine skua from another skua lineage is most likely. Our current data do not permit us to distinguish between these hypotheses, and assaying genome-wide variation holds much promise in this regard. Nevertheless, we have uncovered an intriguing example of a functionally important allele within one species that is shared across species.

Shifting clinal patterns of stress resistance traits in Drosophila ananassae

Drosophila ananassae, a desiccation and cold sensitive species, is abundant along the latitudinal gradient of the Indian subcontinent. Analysis of seasonally varying wild-caught flies showed two independent patterns of melanisation: (1) narrow to broad melanic stripes on three anterior abdominal segments only; (2) a novel body color pattern (dark vs. light background). We investigated the degree to which these two melanisation systems vary; first with latitude and secondly among seasons. There is a shallow latitudinal cline for percent striped melanisation as well as for frequency of body color alleles during the rainy season. The frequencies of body color alleles vary significantly across seasons in the northern populations i.e. the light allele occur abundantly (>0.94) during the rainy season while the frequency of the dark allele increases (0.22–0.35) during the dry season causing steeper clines during the dry season. By contrast, the low variations in abdominal stripes showed non-significant changes and the cline was similar across seasons. Furthermore, both types of melanisation patterns showed no plasticity with respect to temperature. The present study also investigated clines related to desiccation, heat and cold stress in D. ananassae females across seasons (rainy and dry) from nine latitudinal populations. The clines for stress related traits changes to steeper and non-linear during the dry season. Thus, latitudinal populations of D. ananassae differ in slope values of clines for stress related traits across seasons. This study reports seasonal changes in latitudinal clines of stress resistance traits as seen in a changing frequency of body color alleles of D. ananassae in northern locality, while in southern localities it remains constant. This is presumably the result of only minor seasonal changes in humidity and temperature in the South, whereas in the North seasonal climatic variability is much higher.

A Standard of AmpliType PM Typing from Aged Evidentiary Samples

In analyzing aged samples by the AmpliType PM PCR amplification and Typing kit, it was occasionally observed that color developed typing strips had dark allele dots on PM loci but no visible S dot. Since the S dot acts as a minimum dot intensity control to determine positive alleles on the PM loci, it is necessary to apply another control system. To achieve positive PM typing from a degraded DNA sample that is inferred to be derived from a single donor, a standard has been adopted wherein loci from which sufficient PCR products are observed on agarose gel can be typed. The objective determination of sufficient PCR was done by comparison between band peak height of each locus generated from a sample and that of the corresponding locus generated from two nanograms (recommended minimum quantity as template DNA) of the control DNA provided in the kit.

Floral-color polymorphism in Ipomoea purpurea: biased inheritance of the dark allele is not a general explanation for its maintenance.

A previous investigation reported the existence in a single population of the morning glory (Ipomoea purpurea) of non-Mendelian inheritance at the W locus influencing flower color. In addition, it was shown that the magnitude of biased inheritance in that population was sufficient to maintain a floral-color polymorphism at that locus at frequencies approximating those observed in natural populations. The current investigation was undertaken to determine whether this biased inheritance was characteristic of other I. purpurea populations, and thus whether it provides a general explanation for maintenance of the polymorphism. The current study found no evidence for biased inheritance in two additional polymorphic populations examined. Non-Mendelian inheritance thus seems unlikely to constitute a general explanation for the maintenance of this floral-color polymorphism in l. purpurea.

Phenotypic plasticity of abdominal pigmentation in Drosophila kikkawai: multiple interactions between a major gene, sex, abdomen segment and growth temperature.

Drosophila kikkawai is known to be polymorphic for a single autosomal locus controlling abdomen pigmentation in females. Two strains homozygous at this locus (Abdomen pigmentation, Abp) were established from a polymorphic Indian population: one was homozygous (DD) for the dark allele, the other (LL) for the light allele. A Mendelian analysis of crosses at 25 degrees C confirmed the occurrence of a major locus, with dominance of the D allele. Phenotypic variation of pigmentation according to growth temperature was then analyzed in DD and LL male and female flies, and in reciprocal F1. A slight difference was found between reciprocal F1--females from a dark mother were darker but not at all temperatures. In females, the D allele exhibited an antero-posterior gradient of increasing expression from segment 2-7, with dominance over L and an increased expression at low temperatures. In males, abdomen pigmentation was uniformly light in segments 2-5, the D allele being repressed by the sex genotype. In segment 6, the D allele was expressed but only at low temperatures, and was either recessive to L or codominant. Phenotypic plasticity that is, amount of change induced by different growth temperatures, was variable according to genotype and segment. It always corresponded to a darkening of the fly at lower temperatures, but was generally much less than in D. melanogaster. In D. kikkawai, climatic adaptation might occur more by changing the frequency of the D allele than by phenotypic plasticity.

SELECTION ON A FLORAL COLOR POLYMORPHISM IN THE COMMON MORNING GLORY (IPOMOEA PURPUREA): THE EFFECTS OF OVERDOMINANCE IN SEED SIZE.

Understanding the processes that maintain genetic variation in natural populations is a major focus of evolutionary biology. Theoretical investigations have shown that more than a dozen processes can explain the maintenance of genetic variation (see Hartl 1980 for a summary), whereas experiments with laboratory populations indicate that at least some of these processes can operate under some conditions (e.g., Dobzhansky 1948; Dobzhansky and Pavlovsky 1953; Ehrman 1967; Powell and Wistrand 1978; Jones and Probert 1980; Cavender and Clegg 1981). Nevertheless, detailed studies of the selective forces acting to maintain genetic variation in natural populations are rare. The study reported here is part of an ongoing examination of the selective forces acting to maintain genetic variation at a locus influencing floral pigment intensity in the common morning glory, Ipomoea purpurea. This locus (designated W) is polymorphic in natural populations throughout the southeastern United States. Plants homozygous for the w allele have white flowers with pigmented rays (i.e., whites). Heterozygous plants have lightly pigmented flowers with dark rays (i.e., lights), and homozygotes for the W allele have darkly pigmented flowers with even darker rays (i.e., darks) (Ennos and Clegg 1983; Epperson and Clegg 1988). In natural populations, frequencies of the white allele generally range from 0 to 0.4, with a mean of about 0.1 (Epperson and Clegg 1986). Previous work has shown that when white (ww) plants are in the minority, they are undervisited by bees (Brown and Clegg 1984; Epperson and Clegg 1986; Rausher et al. 1993). This undervisitation results in higher selfing rates for white plants, without an associated reduction in the contribution of whites to the outcross pollen pool (i.e., no pollen discounting, Rausher et al. 1993; Iwao 1995). Moreover, inbreeding depression is minimal or absent in North American populations that have been examined (Pear 1983; S. M. Chang, pers. comm. 1996). These observations indicate that the white allele should enjoy a transmission advantage, and thus increase in frequency, when rare (Fisher 1941) and may explain the protection of the white allele in natural populations. It is unclear, however, what forces operate to protect the dark allele. In the absence of any other selective forces acting on the W locus, a combination of genetic drift and active protection of the white allele is expected to result in the fixation of the white allele. The high frequency of the dark allele (0.6-1) in most natural populations therefore suggests the action of other selective forces favoring the dark allele.

SELECTION ON A FLORAL COLOR POLYMORPHISM IN THE TALL MORNING GLORY (IPOMOEA PURPUREA): TRANSMISSION SUCCESS OF THE ALLELES THROUGH POLLEN.

The W locus, a codominant locus influencing floral pigment intensity in the tall morning glory, Ipomoea purpurea, is polymorphic throughout the southeastern United States. Previous studies suggest that this polymorphism is actively maintained by balancing selection, and that increased selfing accompanied by lack of pollen discounting ("Fisher effect") may act to protect the white allele when it is rare. Processes that act to protect the dark allele and thus stabilize the polymorphism in conjunction with the Fisher effect have not been previously detected. The goal of this study was to determine whether any of three such processes might operate in I. purpurea. Estimates of breeding system parameters in a large experimental population in which the white allele was in higher than normal frequency (0.5) provided little evidence that either dark- or light-flowered plants were more successful as pollen parents than white-flowered plants. In addition, no evidence was found for a transmission bias favoring the dark allele in the ovules produced by light heterozygotes. In contrast, a strong transmission bias favoring the dark allele in pollen of heterozygotes was observed. A simple model using parameter estimates derived from this and previous studies indicates that a balance between the Fisher effect and biased transmission in heterozygote pollen could account for many properties of the polymorphism.

Effects of a locus affecting floral pigmentation in Ipomoea purpurea on female fitness components.

A locus influencing floral pigment intensity in the morning glory, Ipomoea purpurea, is polymorphic throughout the southeastern United States. Previous work has suggested that the white allele at this locus has a transmission advantage during mating because of the effect of flower color on pollinator behavior. The experiment described here was designed to determine whether other effects of the W locus may contribute an opposing selective advantage to the dark allele. Dark homozygotes were vegetatively smaller and produced fewer flowers, seed capsules and seeds than either light heterozygotes or white homozygotes. In addition, dark homozygotes produced smaller seeds than heterozygotes, and there is some indication that white homozygotes also produced smaller seeds than heterozygotes. Pleiotropic effects on seed number thus do not seem to contribute to selection opposing the mating advantage associated with the white allele. However, pleiotropic effects on seed size might contribute to overdominance that could stabilize the W locus polymorphism.

Genetic analysis of color dimorphism in the Drosophila montium subgroup.

Four Drosophila species, D. baimaii, D. bicornuta, D, burlai and D, truncata, belonging to the montium species subgroup, were examined for the abdominal tergite coloration. Females show dimorphsim, light or dark, in coloration. In all species examined, the color dimorphism is regulated by two alleles of a single autosomal locus and the dark allele is dominant. Males of the first three species show monomorphic tergite coloration, either light or dark, while males of the fourth species, D. truncata, show the light/dark color dimorphism. Here again it is controlled by two alleles of a single autosomal gene and the dark allele is dominant.

The genetics of mimetic colour polymorphism in the large narcissus bulb fly, Merodon equestris Fab. (Diptera: Syrphidae).

Genetical studies have revealed six gene loci concerned with body hair colour inMerodon equestris. These are: (i)Bulborum. Darkens all the thorax including the scutellum except the anterior. The dark allele is dominant. (ii) The modifier U. In conjunction withbulborumthis produces the morphsubvalidus. This is characterized by some sexual dimorphism. These are certain sex differences in the degree of darkening of the second abdominal segment and the female shows a degree of darkening of the anterior thorax. The dominant dark allele only expresses itself when the dominant allele ofbulborumis present. (iii) The modifier V. In conjunction with the dominant alleles ofbulborumand the modifier U only the dominant allele of the modifier V gives the sexually dimorphic colour typevalidus. The second abdominal segment is more or less completely blackened and in the female only the anterior of the thorax is completely blackened. (iv)Equestris. The dominant allele produces a black thoracic band likebulborumexcept that the scutellum is coloured. (v)Transversalis. Expression is limited to the female, although the locus is inherited autosomally. There is a black band on the third abdominal segment. (vi) Ground colour. There are three alleles determining the distribution of orange and yellow over the thorax and abdomen. They are YOYO, OOYY and OOOO, the letters referring to yellow or orange coloration from the anterior of the thorax to the abdomen tip. The dominance is simple: YOYO is dominant to OOYY and OOOO and OOYY is dominant to OOOO. Within the colour types YOYO and OOYY there are colour variants YYYO, YOYY, YYYY and OOOY, OOYO respectively. Orange is dominant to yellow in the YOYO category and yellow dominant to orange in the OOYY category. The OOOO can be regarded as a universal recessive and can be treated as a separate category or as a variant of the OOYY category. Linkage has been detected between three of the loci. These areequestris, bulborumand ground colour and the order of mention is the order of linkage on the chromosome. Linkage, however, is not very strong so that some recombination occurs. Some aspects of the population genetics of the colour polymorphism have been studied using such little data as are available. Linkage disequilibrium has been found in the field for the linked genesbulborumand ground colour appears to be strongly maintained. A listing of potential models for the 34 colour types ofM. equestrisreveals that the colour types most commonly occurring, and maintained at high frequency and in linkage disequilibrium, are the best mimics of bumble bees in the United Kingdom. Some aspects of the evolution of the colour polymorphism in Europe, particularly in relation to the related species M.flavusare discussed. The chromosome number found confirms that found by other workers (2n= 12) and polytene chromosomes have been demonstrated in a variety of tissues

DENSITY AND DISTRIBUTION OF DROSOPHILA POLYMORPHA AND ITS COLOR ALLELES IN SOUTH AMERICA

A balanced polymorphic condition, perhaps more than any other type of variation in nature, demands equal attention from the ecological as well as the genetic viewpoints. The reasons for this are well known and have been attractively presented by Sheppard (1958). One of the inherent advantages in the study of a polymorphism is that the problem of mutation rate is a negligible one, permitting closer scrutiny into other phases of population dynamics that affect gene frequencies. The discovery of a new allele at the color locus in Drosophila polymorpha Dobzhansky and Pavan in South America (Heed and Blake, 1963) has led to the present report on the population structure of the species in its natural habitat. The chief difference throughout the distribution of polymorpha is that the populations in the extreme northeastern faunistic limit of South America (Trinidad) are monomorphic light, while in most of Brazil, three main abdominal phenotypes exist which are light and dark and one that is intermediate between these two (da Cunha, 1949). The second main difference is that the gene controlling the light abdomen in the north is usually not the same gene that controls the light abdomen in Brazil. This is apparent because the northern light allele is dominant, or nearly so, to the dark allele from the south, whereas the southern light allele, when heterozygous with the dark gene, produces an intermediate phenotype. Another area in South America that has been collected extensively for Drosophila is Colombia. Until the present report, only the two alleles for the light abdomen were known from the area. The first section of the Results is an analysis of a small number of polymorpha females and their descendants received in March, 1962, from El Colegio, Colombia. The data indicate that the population contains all three alleles, and it is the first to be so reported. Furthermore, it is very possible that the dominant light allele is present in many of the populations analyzed by da Cunha (1949) from southern Brazil, and his data are reviewed with this in mind. What ecological conditions correspond to .the change in gene frequencies and the change in phenotypic proportions? The information at hand allows two important aspects of the environment of polymorpha to be measured: its population density, and the relative abundance of closely related species. These observations are presented in the second and third sections of the Results, and indicate that correlations of a general nature may be made. In addition, information on the color variation in the cardini species group as a whole, of which polymorpha is a member, is reviewed and classified.