Colour Dimorphism Research Articles

Are the big and beautiful less bold? Differences in avian fearfulness between the sexes in relation to body size and colour

AbstractConspicuousness towards predators may influence escape behaviour (or ‘fearfulness’) among animals, with more conspicuous species initiating escape behaviour earlier. Among birds, for example, body size and colour may influence differences in escape behaviour between species, and possibly between the sexes of dimorphic species. We examined 19 bird species with varying degrees of body size and colour dimorphism (including individually marked and sexed monomorphic species), to examine whether these two potential measures of conspicuousness influence sex differences in flight‐initiation distance (FID). Starting Distance (the distance at which an observer commenced approaching a bird, which is an artefact of investigator behaviour; SD) was not correlated with dimorphism, so we used phylogenetically controlled models which explored the correlation between dimorphism and FID. Modelling indicated that only sex differences in SD correlated with sex differences in FID in these birds, and that dimorphism in either plumage or body size does not apparently correlate with sex differences in FID. These results suggest that, among the 19 bird species investigated, apparent differences in the conspicuousness to predators between the sexes do not influence escape behaviour. This suggests that either conspicuousness to predators does not influence escape distances in these species, or that sex differences in conspicuousness were too subtle to result in variation in FIDs.

Development of secondary sexual characters and their relationship to ontogeny and seasonal reproductive period in Hyphessobrycon igneus (Ostariophysi: Characiformes).

Sexual dimorphism in size, anal-fin shape and coloration of Hyphessobrycon igneus, Characidae, were examined. Males were more frequent at larger body sizes, confirming body size as a sexually dimorphic trait. Anal-fin shape and the colour of all fins were the same for females and juveniles, differing only in adult males. Likewise, only adult males had bony hooks on fin rays; larger and more sexually mature males had the most numerous and developed hooks and hooks were most developed in degree and number during peak reproductive periods. Fin hooks regressed in number and developmental degree after the reproductive period, but restarted development with the beginning of the new reproductive period without completely disappearing. Results show that bony hooks have a development and regression cycle related to reproductive seasonality.

Sexual dimorphism in shell coloration of Plectostoma (Caenogastropoda: Diplommatinidae) is caused by polyenes

Sexual dimorphism in shell coloration of Plectostoma (Caenogastropoda: Diplommatinidae) is caused by polyenes

Perianth colour dimorphism is related to germination properties and salinity tolerance in Salsola vermiculata in the Arabian deserts

We investigated the dimorphic perianth colour of Salsola vermiculata and its association with seed germination percentage, interactions with temperature, light, salinity and recovery from prior salinity exposure. Seeds with and without pink and yellow perianth were incubated at three thermal regimes, two photoperiods, and five salinity levels. Germination recovery after salinity exposure was observed on seeds that failed to germinate during the salinity study. The germination percentage and rate were significantly related to the perianth colour, the presence of perianth wings, thermal regimes and photoperiod. The presence of a perianth wing significantly reduced germination percentage and germination rate in both the pink and the yellow morph, but the yellow morph exhibited a higher germination percentage. Perianth wing removal increased germination in saline conditions. With the perianth removed, germination recovery was higher for the pink morph than for the yellow one. We suggest that by providing two different strategies for balancing germination with dormancy during favourable conditions, the presence of two morphs makes S. vermiculata more successful in highly unpredictable desert environments.

Telomere length is reflected by plumage coloration and predicts seasonal reproductive success in the barn swallow.

Individuals differ in realized fitness but the genetic/phenotypic traits that underpin such variation are often unknown. Telomere dynamics may be a major source of variation in fitness traits because physiological telomere shortening depends on environmental and genetic factors and may impair individual performance. Here, we showed that, in a population of a socially monogamous, biparental passerine bird, the barn swallow (Hirundo rustica), breeding in northern Italy, telomere length (TL) of both adult males and females positively correlated with seasonal reproductive and fledging success, as expected because long telomeres are supposed to boost performance. Telomere length was correlated with sexually dimorphic coloration in both sexes, showing for the first time in any species that coloration reliably reflects TL and may mediate mutual mate choice, leading to the observed positive assortative mating for TL in the barn swallow. Thus, TL appears to be associated with variation in a major fitness trait and may be an ultimate target of mate choice, as individuals of both sexes can use coloration to adaptively choose high-quality mates that possess long telomeres.

An ontogenetically stable sexual character in a montane agamid, Salea horsfieldii Gray, 1845 (Reptilia: Agamidae) from Nilgiris, India

ABSTRACTMany agamid lizards are known to show sexual dimorphism in body shape, colour and ornamentation or a combination of these traits. Adult males of Salea horsfieldii have a discontinuous dorsal crest at the nuchal region, which is a sexually dimorphic character. However, there is no information about the age or size at which this dimorphic ornamentation develops and if the species exhibits sexual shape dimorphism (SShD). The authors studied the morphology of S. horsfieldii and found that its ornamentation is an ontogenetically stable character present in all males, including juveniles. Seven morphological characters were measured to determine if they exhibited SShD at adult and juvenile stages. Analysis of covariance was used to identify differences in morphology between sexes. The results show that only adults exhibited SShD, but not juveniles. Adult males had larger head and foot lengths in comparison to females of the same size. Larger head length in adult males is a sexual fitness trait, which increases bite-force during intra-sexual combats. Although the presence of sexually dimorphic ornamentation right from the juvenile stage is rare in agamids, S. horsfieldii is an exception . The role of sexually dimorphic ornamentation at juvenile stages remains unknown and requires further investigation.

Quantifying phenotype-environment matching in the protected Kerry spotted slug (Mollusca: Gastropoda) using digital photography: exposure to UV radiation determines cryptic colour morphs

BackgroundAnimal colours and patterns commonly play a role in reducing detection by predators, social signalling or increasing survival in response to some other environmental pressure. Different colour morphs can evolve within populations exposed to different levels of predation or environmental stress and in some cases can arise within the lifetime of an individual as the result of phenotypic plasticity. Skin pigmentation is variable for many terrestrial slugs (Mollusca: Gastropoda), both between and within species. The Kerry spotted slug Geomalacus maculosus Allman, an EU protected species, exhibits two distinct phenotypes: brown individuals occur in forested habitats whereas black animals live in open habitats such as blanket bog. Both colour forms are spotted and each type strongly resembles the substrate of their habitat, suggesting that G. maculosus possesses camouflage.ResultsAnalysis of digital images of wild slugs demonstrated that each colour morph is strongly and positively correlated with the colour properties of the background in each habitat but not with the substrate of the alternative habitats, suggesting habitat-specific crypsis. Experiments were undertaken on laboratory-reared juvenile slugs to investigate whether ultraviolet (UV) radiation or diet could induce colour change. Exposure to UV radiation induced the black (bog) phenotype whereas slugs reared in darkness did not change colour. Diet had no effect on juvenile colouration. Examination of skin tissue from specimens exposed to either UV or dark treatments demonstrated that UV-exposed slugs had significantly higher concentrations of black pigment in their epithelium.ConclusionsThese results suggest that colour dimorphism in G. maculosus is an example of phenotypic plasticity which is explained by differential exposure to UV radiation. Each resulting colour morph provides incidental camouflage against the different coloured substrate of each habitat. This, to our knowledge, is the first documented example of colour change in response to UV radiation in a terrestrial mollusc. Pigmentation appears to be correlated with a number of behavioural traits in G. maculosus, and we suggest that understanding melanisation in other terrestrial molluscs may be useful in the study of pestiferous and invasive species. The implications of colour change for G. maculosus conservation are also discussed.

Pupal colour dimorphism in a desert swallowtail (Lepidoptera: Papilionidae) is driven by changes in food availability, not photoperiod

1. The swallowtail butterfly Battus polydamas archidamas Boisduval, 1936, exhibits polyphenism for pupal coloration (green and brown). It is distributed across arid regions with winter rains and is monophagous on Aristolochia plants, which emerge after the winter rains and dry out the during summer. Thus, day length does not covary positively with host plant productivity. It was hypothesised that pupal colour was driven by food availability, not photoperiod. The benefits of pupal coloration matching the colour of pupation sites in terms of field survival were also investigated to evaluate the adaptive value of pupa colour.2. Larvae were reared under a factorial array of two photoperiods (LD 10:14 h and LD 14:10 h) and two food availability regimes (leaves ad libitum and available every other day) to assess the frequency of green and brown pupae. Field survival of green and brown pupae was quantified in three commonly used habitats that differ in background coloration (cacti, rocks and shrubs).3. Food availability determined pupal colour. Larvae in the ad libitum regime resulted mostly in green pupae, while those with restricted food were mostly brown. In contrast, photoperiod did not influence pupal colour. Survival probability of pupae placed on cacti was higher than those placed on rocks and shrubs, and the lowest predation risk across habitats was for green pupae on cacti.4. Food availability plays a major role in the seasonal polyphenism for pupal colour of specialist butterflies inhabiting arid environments with winter rains.

Discovery of androecium color polymorphism in Epimedium pubescens with habitat preference of anther/pollen color in the genus

Interspecific and intraspecific variation in flower color in natural populations provides an opportunity for us to understand the evolution and maintenance of diversity of floral traits. Compared to corolla color, little is known about the color polymorphism of sexual organs in flowering plants. To explore evolutionary transitions of androecium color and polymorphism within species, interspecific and intraspecific variation in androecium (anther and pollen) color in the genus Epimedium (Berberidaceae) was investigated. To explore the geographical patterns of anther/pollen color variation in Epimedium species, data of 45 species were collected and their phylogeny was constructed based on available DNA sequences. To investigate whether intraspecific variation in androecium color relates to habitat preference, three environmental factors were measured in the field population of Epimedium pubescens in northeastern Sichuan, China, which plants had green or yellow androecia. Vegetative and reproductive traits of this species were compared between the two color morphs. Androecium (anther and pollen) color polymorphism in field populations of Epimedium pubescens is reported here where nine populations are monomorphic with a green androecium but three populations are dimorphic with individuals having either a green or a yellow androecium. Inflorescence stalk height, stalk diameter, leaf number, flower number and spur length (as well as spur and nectar volume) were not significantly different between two morphs. Compared to the yellow morph, the green morph had relatively larger leaves and anthers, but smaller sepals. The green morph produced more pollen and larger seeds, but the same number of ovules. Seed set was not significantly different between green and yellow morph. Investigations of environmental factors in the color dimorphic populations of E. pubescens indicated that the green morph was more likely to occur in habitats with relatively lower light intensity. The distribution survey of 45 Epimedium species showed that species with a green androecium tended to appear at lower elevations. Comparative phylogenetic analysis showed that transitions from yellow to a green androecium or to androecial color dimorphism occurred at least seven times. This genus, characterized by anther color diversity and containing some species with anther color polymorphism, provides a model system in which to study the evolution and maintenance of colorful sexual organs in flowering plants.

Seasonal expression of arginine vasotocin mRNA and its correlations to gonadal steroidogenic enzymes and sexually dimorphic coloration during sex reversal in the gilthead seabream (Sparus aurata).

Arginine vasotocin is a hormone produced in the hypothalamus of teleost fish that has been shown to regulate gonad development and sexual behavior. To study the role of arginine vasotocin in the gonadal cycle of the hermaphrodite gilthead seabream, Sparus aurata, we cloned the seabream arginine vasotocin (avt) complementary DNA (cDNA). We investigated the expression of brain avt throughout the gonad cycle using real-time quantitative PCR and compared its expression levels to the expression levels of two key gonadal steroidogenic enzymes, cyp19a1a and cyp11b2. In July, when the process of sex reversal is thought to begin, avt expression was elevated over the previous 2months. Avt in the brain remained at or above the level of July until November then peaked again in December. There was no difference between males and females in the expression levels of brain avt throughout the year. However, only in ambisexual fish was the expression of the cyp19a1a gonadal aromatase correlated to the expression of avt in the brain. Cyp11b2 did not show any correlation to brain avt expression. We also found that females had more intense body coloration than males and that this intensity peaked prior to spawning. Avt expression and female coloration were positively correlated. The fact that brain avt expression was lowest during gonad quiescence, together with the observation of a correlation between brain avt with gonadal cyp19a1a and body coloration during that time suggests that avt may play a role during the process of sex reversal and spawning of the gilthead seabream.

Comparative morphology and genetics of two populations of spiny lizards (genus Sceloporus) from Central Mexico

The spiny lizard Sceloporus minor exhibits substantial variation in a variety of life history traits, but the factors promoting this variation remain unclear. We analyzed within- and between-population variation in morphological traits in two populations (El Enzuelado and La Manzana, Hidalgo, Central Mexico), and estimated the genetic distance between populations on the basis of sequence variation of the mitochondrial genes encoding a fragment of the ND4 gene, all of tRNA-His and tRNA-Ser, and a fragment of tRNA-Leu. Consistent with earlier reports, males and females exhibited marked sexual dimorphism in body size and coloration. The genetic distance between the two populations was 0.024, slightly greater than the distance measured within each population (0.015 for La Manzana and 0.003 for El Enzuelado). Maximum likelihood analysis indicated that these populations were indeed conspecific, along with other studied populations of S. minor. The morphological differences and the previously described variation in reproductive traits contrast with the limited genetic variation between populations reported herein. This suggests that a combination of both phenotypic plasticity and genes of large effect may be contributing to variation in anatomical and physiological traits in Sceloporus minor.

A new species of the genus Thrips (Thysanoptera: Thripidae) from the Western Ghats of India.

Thrips laurencei sp.n. is described from specimens collected on flowers of Hydrangea macrophylla in Western Ghats range of Tamil Nadu, India. This new species shows sexual dimorphism in colour, with the females brownish yellow with brown shadings but the males uniformly yellow.

In-ovo sexing of 14-day-old chicken embryos by pattern analysis in hyperspectral images (VIS/NIR spectra): A non-destructive method for layer lines with gender-specific down feather color

Up to now there is no economically maintainable modality for chicken sexing in early embryonic stages (first 3 d) that is suitable for large-scale application in the commercial hatcheries. Hence, the culling of male day-old chicks of layer lines is still the normal procedure.In this paper we present a non-destructive optical technique for gender determination in layer lines with gender-specific down feather color. This particular chicken strain presents a sexual dimorphism in feather color, where the female day-old chicks have brown down feathers and the males have yellow down feathers.The eggs are candled with halogen lamps and a hyperspectral camera collects the transmitted light within the spectral range from 400 nm to 1,000 nm. For data analysis and classification, common methods like principal component analysis and linear discriminant analysis are used. The accuracy of gender determination was determined for 11- to 14-day-old embryos. At 14 d of incubation (7 d before hatch) the sex can be determined with an overall accuracy of approximately 97%.

Sewall Wright, shifting balance theory, and the hardening of the modern synthesis

The period between the 1940s and 1960s saw the hardening of the modern synthesis in evolutionary biology. Gould and Provine argue that Wright's shifting balance theory of evolution hardened during this period. But their account does not do justice to Wright, who always regarded selection as acting together with drift. This paper presents a more adequate account of the development of Wright's shifting balance theory, paying particular attention to his application of the theory to the geographical distribution of flower color dimorphism in Linanthus parryae. The account shows that even in the heyday of the hardened synthesis, the balance or interaction of evolutionary factors, such as drift, selection, and migration, occupied pride of place in Wright's theory, and that between the 1940s and 1970s, Wright developed the theory of isolation by distance to quantitatively represent the structure of the Linanthus population, which he argued had the kind of structure posited by his shifting balance theory. In the end, Wright arrived at a sophisticated description of the structure of the Linanthus population, where the interaction between drift and selection varied spatially.

Bucrates lanista Rehn 1918 (Tettigoniidae: Conocephalinae): The First Record from the Brazilian Pantanal, the First Description of the Male, the First Karyotypic Report for the Genus, and the First Telomeric Hybridization of the Subfamily.

Bucrates lanista, the most southerly distributed species in the genus Bucrates Burmeister, was originally described from Brazil based on a female collected in the state of Rio Grande do Sul, but the species has not been recorded since 1918. In this work, we report that B. lanista inhabits the Pantanal Wetland in the state of Mato Grosso do Sul and, for the first time, describe the male. Individuals of B. lanista are gregarious and present a brown/green color dimorphism; this behavior and color variation are also observed in species of closely related genera. Individuals from the Pantanal vary slightly from those of Rio Grande do Sul. The karyotype was determined to be 2n♂ = 21 = 20 + X0 and 2n♀ = 22 = 20 + XX. The X chromosome is metacentric and the largest of the complement, and all of the autosomes are submetacentrics. All chromosomes solely present telomeric (TTAGG)n repeats at their ends, and some chromosomes present positive and negative DAPI bands.

Testosterone activates sexual dimorphism including male-typical carotenoid but not melanin plumage pigmentation in a female bird.

In males it is frequently testosterone (T) that activates the expression of sexually selected morphological and behavioral displays, but the role of T in regulating similar traits in females is less clear. Here, we combine correlational data with results from T and gonadotropin-releasing hormone (GnRH) manipulations in both sexes to assess the role of T in mediating sexually dimorphic coloration and morphology in the red-backed fairy-wren (Malurus melanocephalus). We show that: (1) natural variation in female expression of ornamental traits (darkened bills and red back feathers) is positively associated with age and circulating androgen titres, (2) females have the capacity to express most male-typical traits in response to exogenous T, including carotenoid-pigmented body plumage, shorter feathers, darkened bill and enlarged cloacal protuberance, but (3) appear constrained in production of male-typical melanin-pigmented plumage, and (4) low androgen levels during the pre-nuptial molt, probably because of low ovarian capacity for steroid production (or luteinizing hormone sensitivity), prevent females from developing male-like ornamentation. Thus, females appear to retain molecular mechanisms for hormonally regulated male-typical ornamentation, although these are rarely activated because of insufficient production of the hormonal signal.

The pdm3 Locus Is a Hotspot for Recurrent Evolution of Female-Limited Color Dimorphism in Drosophila

Sex-limited polymorphisms are an intriguing form of sexual dimorphism that offer unique opportunities to reconstruct the evolutionary changes that decouple male and female traits encoded by a shared genome. We investigated the genetic basis of a Mendelian female-limited color dimorphism (FLCD) that segregates in natural populations of more than 20 species of the Drosophila montium subgroup. In these species, females have alternative abdominal color morphs, light and dark, whereas males have only one color morph in each species. A comprehensive molecular phylogeny of the montium subgroup supports multiple origins of FLCD. Despite this, we mapped FLCD to the same locus in four distantly related species-the transcription factor POU domain motif3 (pdm3), which acts as a repressor of abdominal pigmentation in D.melanogaster. In D.serrata, FLCD maps to a structural variant in the first intron of pdm3; however, this variant is not found in the three other species-D.kikkawai, D.leontia, and D.burlai-and sequence analysis strongly suggests the pdm3 alleles responsible for FLCD originated independently at least three times. We propose that cis-regulatory changes in pdm3 form sexually dimorphic and monomorphic alleles that segregate within species and are preserved, at least in one species, by structural variation. Surprisingly, pdm3 has not been implicated in the evolution of sex-specific pigmentation outside the montium subgroup, suggesting that the genetic paths to sexual dimorphism may be constrained within a clade but variable across clades.

Temperature-dependent colour change is a function of sex and directionality of temperature shift in the eastern fence lizard (Sceloporus undulatus)

Sexually dimorphic colour traits are widespread across taxa, but relatively little is known about how and why these features change with body temperature. To examine whether sex and directionality (warming vs. cooling) influence temperature-dependent colour change, we used spectrophotometry to characterize ventral and dorsal coloration in eastern fence lizards (Sceloporus undulatus), a species with temperature-dependent conspecific signals (ventral patches). In general, we found that skin colour (hue) in both sexes changed with temperature. Only ventral patch colour in males changed visibly to human observers; ventral patch hue decreased (green to blue shift) with an increase in body temperature. Male dorsal colour also changed with temperature, with cooler males exhibiting a longer-wavelength hue (red shift) than that exhibited by warmer males. Female dorsal hue changed in a manner paralleling that of males, and female ventral hue trended in the same direction: overall, warmer females tended to exhibit shorter-wavelength hues. However, the magnitude of male ventral patch colour change was highly dependent upon temperature sequence; the colourful badges of males that were progressively warmed changed from green to blue, whereas those of males that were cooled over the same time period did not change hue. Notably, only the coloration of male ventral patches was dependent on the directionality of temperature change; no other measured skin surfaces in either sex exhibited similar temperature-directionality dependence. These results are considered in the context of models for badge colour production in Sceloporus, as well as in hypotheses for the functional significance of ventral patch coloration.

Effect of bright wing color of males on other males in Favonius taxila (Lepidoptera: Lycaenidae) with sexual dimorphism in wing color

AbstractTo examine the effect of wing colors of Favonius taxila males on other males, an intact bright butterfly model or a dull butterfly model whose wing scales had been dislodged was placed in a potential territory, and the behavior of invading males was recorded. The invader showed decreased probability of landing there with a bright model in place compared with a dull model, and exhibited complex flights with frequent turning for a bright model, in contrast to simple flights with relatively linear paths for a dull model. These results support the idea of intrasexual selection in which bright colors of males' wings have evolved through male–male interactions.

Genetic Architecture of Conspicuous Red Ornaments in Female Threespine Stickleback.

Explaining the presence of conspicuous female ornaments that take the form of male-typical traits has been a longstanding challenge in evolutionary biology. Such female ornaments have been proposed to evolve via both adaptive and nonadaptive evolutionary processes. Determining the genetic underpinnings of female ornaments is important for elucidating the mechanisms by which such female traits arise and persist in natural populations, but detailed information about their genetic basis is still scarce. In this study, we investigated the genetic architecture of two ornaments, the orange-red throat and pelvic spine, in the threespine stickleback (Gasterosteus aculeatus). Throat coloration is male-specific in ancestral marine populations but has evolved in females in some derived stream populations, whereas sexual dimorphism in pelvic spine coloration is variable among populations. We find that ornaments share a common genetic architecture between the sexes. At least three independent genomic regions contribute to red throat coloration, and harbor candidate genes related to pigment production and pigment cell differentiation. One of these regions is also associated with spine coloration, indicating that both ornaments might be mediated partly via pleiotropic genetic mechanisms.