Sexual Dimorphism In Coloration Research Articles

SEXUAL DIMORPHISM AND PARENTAL ROLES IN THE THORN-TAILED RAYADITO (FURNARIIDAE)

Sexual dimorphism, mating system, and parental care are known for only a few species of the large passerine family Furnariidae. We conducted a study of sexual dimorphism in morphology, coloration, and parental roles during incubation and chick-rearing in the Thorn-tailed Rayadito (Aphrastura spinicauda), a characteristic resident ovenbird of the southern temperate rainforests of Chile and Argentina. Through molecular sexing, morphological measurements, and spectrophotometric analysis of body plumage and rectrices of reproductive adults captured on Chiloé Island (southern Chile), we determined that males were between 2% and 10% larger than females in mass, tarsus length, and wing length, while no difference was found for the length of the bill or the two longest central rectrices and their characteristic spines, or in plumage coloration. Heavy males were paired with heavy females and light males with light females. Males and females participated equally in all reproductive activities during the incubation and nestling phases, except removal of nestling feces, in which females were twice as active as males. In a study of habitat use on Navarino Island (extreme southern Chile) we found that the extended graduated tail, with rectrices that end in spines, which gives the species its name, was not used as a support while foraging and could be related to another function such as sexual or social signaling. The absence of sexual dimorphism in plumage and parental roles in rayaditos may be related to the use of the long, graduated tail as a signal of quality by both sexes, although this hypothesis requires confirmation through future mate choice studies.

Testosterone increases bioavailability of carotenoids: insights into the honesty of sexual signaling.

Androgens and carotenoids play a fundamental role in the expression of secondary sex traits in animals that communicate information on individual quality. In birds, androgens regulate song, aggression, and a variety of sexual ornaments and displays, whereas carotenoids are responsible for the red, yellow, and orange colors of the integument. Parallel, but independent, research lines suggest that the evolutionary stability of each signaling system stems from tradeoffs with immune function: androgens can be immunosuppressive, and carotenoids diverted to coloration prevent their use as immunostimulants. Despite strong similarities in the patterns of sex, age and seasonal variation, social function, and proximate control, there has been little success at integrating potential links between the two signaling systems. These parallel patterns led us to hypothesize that testosterone increases the bioavailability of circulating carotenoids. To test this hypothesis, we manipulated testosterone levels of red-legged partridges Alectoris rufa while monitoring carotenoids, color, and immune function. Testosterone treatment increased the concentration of carotenoids in plasma and liver by >20%. Plasma carotenoids were in turn responsible for individual differences in coloration and immune response. Our results provide experimental evidence for a link between testosterone levels and immunoenhancing carotenoids that (i) reconciles conflicting evidence for the immunosuppressive nature of androgens, (ii) provides physiological grounds for a connection between two of the main signaling systems in animals, (iii) explains how these signaling systems can be evolutionary stable and honest, and (iv) may explain the high prevalence of sexual dimorphism in carotenoid-based coloration in animals.

Carotenoid coloration in great black‐backed gull Larus marinus reflects individual quality

Carotenoids are a large group of biochemicals, with similar properties, synthesised by bacteria, fungi, algae and plants. Vertebrates obtain these biologically active pigments through the diet, and they are a disproportionately common component of animal colour signals and play important roles in immune functions and as antioxidants. Carotenoids are believed to be a limited resource and because of the trade‐off between allocation of carotenoids to signals and to other functions, carotenoid based signals are often thought to be handicap signals. The purpose of this study was to investigate the signalling potential of carotenoid‐based tissue coloration in the great black‐backed gull Larus marinus. The intensity of carotenoid‐based coloration in bill, gape and eye‐ring coloration was investigated in relation to body condition, reproductive parameters, levels of immune activity, and sexual dimorphism. In males there was a positive relationship between colour intensity and body condition, but in females no such relationship was found. However, females with high colour intensity had larger eggs and clutches. Additionally, females with high red scores tended to have high density of circulating lymphocytes. There was no sexual dimorphism in coloration and there was a negative relationship between colour intensity and sampling time, which indicates that this coloration is most intensely expressed early in the breeding season. The results in this study suggest that carotenoid‐based coloration in great black‐backed gull are partly condition dependent and reveal information about individual quality in both males an females. Hence, it might have evolved as an important signal for assessing the quality of potential mates.

A New Species of Hanging-Parrot (Aves: Psittacidae: Loriculus) from Camiguin Island, Philippines

A new species of Hanging-Parrot or Colasisi, Loriculus, is described from a series of 23 specimens (19 males, 4 females) collected in the 1960s on Camiguin Island, Camiguin Province, Philippines, at elevations between 300 and 1350 m. The new species lacks sexual dimorphism in plumage coloration, which distinguishes it from all other members of the L. philippensis group and all other Loriculus. The overall color pattern of the new species appears most like females of L. p. worcesteri and L. p. apicalis but differs in plumage characteristics (the width and extension of the orange-scarlet crown patch, the amount and intensity of blue in the face and thighs, and the intensity of the blue in the tail above inner edges and the tail below). In addition, males of the new species are larger than males of nearby populations of L. philippensis, having significantly longer tails and wing chords. Nothing is known about the habits of the new species; however, the small size of the island of Camiguin, coupled with extensive deforestation, makes the status of the new species a significant conservation concern.

SEXUALLY DIMORPHIC BODY PLUMAGE IN JUVENILE CROSSBILLS

Sexual dimorphism in color and pattern of contour feathers is rare in juvenile songbirds. We describe how captive-bred juvenile males of Scottish Crossbill (Loxia scotica) and nominate Red Crossbill (L. curvirostra curvirostra) can be differentiated from females prior to prebasic molt by an unstreaked patch on the males' upper breast. There may be a functional relationship between sexual dimorphism and the formation of pair bonds or breeding while the birds are still in juvenile plumage. Sexually dimorphic Red Crossbills and Bearded Tits (Panurus biarmicus) are known to form pair bonds, and even breed successfully, while still in juvenile plumage.

Correlates of timing of spring migration in birds: a comparative study of trans-Saharan migrants

The evolution of migratory strategies in birds is likely to have been influenced by ecological as well as socio-sexual factors in both wintering and breeding areas. In this comparative study, we analysed timing of spring passage of 38 long-distance migratory bird species that winter south of the Sahara desert and breed in Europe, in relation to wintering and breeding latitudes, moult strategy, nesting site (open vs. cavity), and sexual dimorphism in size and coloration, which may reflect intensity of sexual selection. We employed a large data set consisting of more than 190 000 individuals ringed during spring migration in the Mediterranean Sea. We found that the species that migrated earlier were those wintering farther north, nesting in cavities and showing the largest degree of sexual size dimorphism (SSD). However, sexual dichromatism was not related to migration date. Among passerine species, moulting wing-feathers in Africa delayed migration. We found no support for the energetic constraint hypothesis, which proposes that early arrival selects for large male size, since early arriving species were not larger than late arriving ones. Thus, the observed associations suggest that variation in migration schedules at the interspecific level may have evolved in relation to ecological factors and SSD, possibly reflecting the intensity of mating competition. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 199–210.

The mbuna cichlids of Lake Malawi: a model for rapid speciation and adaptive radiation

AbstractMbuna, the dominant fishes on the rocky shores of Lake Malawi, have become a major ‘model system’ for the study of rapid speciation and adaptive radiation. At least 295 putative species are known, of which more than 200 remain undescribed. There is no good evidence for monophyly in the mbuna, rather mitochondrial DNA phylogenies indicate that they are polyphlyetic with respect to benthic feeding cichlids of the generaAulonocara,Alticorpusand some species ofLethrinops. Male mbuna hold territories for 18 months or more and breed year‐round. All species are maternal mouthbrooders, but females do not guard free‐swimming young. Mbuna are polygamous (both sexes). There is sexual dimorphism in size, colour and fin length, and many species show within‐population colour polymorphism. Mbuna genera are largely differentiated on the basis of head, jaw and tooth morphology, but congeneric species are generally distinguished by male colour. Many morphologically specialized forms have broad diets and often feed on common easily obtainable resources. While it is likely that dietary and habitat niche partitioning contributes to species coexistence, this has never clearly been demonstrated under experimental conditions. Populations on spatially separated habitat patches are often genetically differentiated, probably because most species are specialized for life on rocky shores, and lack a dispersal phase in their life histories. Males seem to disperse more than females, but are able to home several kilometres back to their territories. Some closely related ecologically equivalent allopatric populations are differentiated in male colour. Those tested have been shown to mate at least partially assortatively. Sexual selection acting on male colour seems the most plausible mechanism for initial species divergence. The same colour forms seem to have arisen several times, suggesting frequent parallel evolution. The main conservation threat to mbuna at present seems to be translocation of species within the lake as a result of the aquarium trade. However, deleterious effects on indigenous populations are not documented. In the long run, sedimentation, pollution, introduction of alien species and the development of targeted food fisheries could be more serious threats.

Sexual dimorphism in the Neotropical lizard, Tropidurus torquatus (Squamata, Tropiduridae)

Abstract We describe the sexual dimorphism in coloration, body shape, and body size in Tropidurus torquatus, a widely distributed lizard species in central Brazil. Adult males have colored patches varying from yellow to yellow-and-black, and black on the abdomen, ventral aspect of the thighs, and pre-cloacal flap. Adult females lack ventral colored patches. During ontogeny, there is a gradual darkening of the patches, but no modification either in patch size or color is associated with the reproductive cycle. Adult males have wider heads and thinner bodies than females of the same body size. Males and females grow at the same rate prior to sexual maturity, but males take longer to reach sexual maturity, maturing at a larger body size than females.

Coat colour variation in the banded palm civet Hemigalus derbyanus and in Owston's civet Chrotogale owstoni

ABSTRACT 1. Coat colour variation was studied in two viverrid species belonging to the subfamily Hemigalinae, on the basis of museum specimens and observations of live animals. 2. In both species, polymorphism and ontogenetic colour change occur, and in the Owston's civet, sexual dimorphism in coat colour was identified.

Molecular sexing of prey remains permits a test of sex-biased predation in a wintering population of western sandpipers

Population sex ratios in monogamous birds are often male biased. One factor that can affect population sex ratios is sex-biased predation. However, most estimates of sex-biased predation in birds have focused on species with obvious sexual colour dimorphism or body size dimorphism. Data on sexually monomorphic birds are generally lacking. In the present study, we adopt a PCR-based sexing procedure to help test for sex-biased predation in a wintering population of western sandpipers (Calidris mauri), a shorebird that shows only subtle sexual size dimorphism. Specifically, by comparing the a priori determined sex ratio of live birds wintering at a site in western Mexico to the molecular estimate obtained from depredated birds at this same site, we were able to perform a population-specific test for sex bias in predator-induced mortality. The proportion of females estimated from living (ca. 25%) versus dead (ca. 24%) individuals was in fact not significantly different, indicating that the strong male bias in this population is not due to differential predation. However, molecular sexing of prey remains is a hitherto unexploited test of sex-biased predation in birds, and is potentially applicable to any species for which prey remains can be gathered. We discuss our results in the context of alternate ecological hypotheses for population sex biases.

Sexual dimorphism in Liolaemus occipitalis (Iguania, Tropiduridae)

The sexual dimorphism in size, morphology and color of the lizard Liolaemus occipitalis Boulenger, 1885 was studied. Thirty-two adult males and twenty-eight adult females were sampled from a population in the Jardim do Éden beach, near Tramandaí, Rio Grande do Sul, Brazil. Size related sexual dimorphism occurred in all compared body dimensions. The largest female was 59.6 mm in snout-vent length, and the largest male was 69.3 mm. Males and females also presented differences in ventral and dorsal color pattern, and in the presence of pre-cloacal pores. The results suggest that, in Liolaemus occipitalis, sexual dimorphism in size is determined by sexual selection, competition between males and by the high energetic cost for females a few months after hatching.

Taxonomic recommendations for British birds: second report

Taxonomic recommendations for British birds: second report

Sexual colour dimorphism in ranid frogs from New Guinea: Description of two new species (Amphibia, Anura, Ranidae)

Sexual colour dimorphism in ranid frogs from New Guinea: Description of two new species (Amphibia, Anura, Ranidae)

A NEW SPECIES OF LIOLAEMUS FROM SOUTHERN BRAZIL (IGUANIA: TROPIDURIDAE)

We describe a new species of the genus Liolaemus from Rio Grande do Sul, Brazil. The morphology of the new species, L. arambarensis sp. nov, is compared to other species of Liolaemus of the “wiegmannii” group. The new species is distinguished from others members of this group by a dorsal color pattern with a medium dorsal white stripe and two dorsolateral stripes, two rows of juxtaposed brown marks resembling triangles, delimited by a white bar; nasal scales oriented dorsally; a complete row of dorsally oriented lorilabial scales between the subocular and supralabial scales; a moderate number of scales around the mid-body; flat temporal scales; flat head scales; and a transversely divided frontal. Liolaemus arambarensis sp. nov. is omnivorous, oviparous, and exhibits sexual dimorphism in color and size. Resumo Uma nova especie do genero Liolaemus do Rio Grande do Sul, Brazil e descrita neste trabalho. A morfologia da nova especie, L. arambarensis sp. nov, e comparada as especies de Liolaemus do grupo “wie...

Perspective: female remating, operational sex ratio, and the arena of sexual selection in Drosophila species.

As commonly observed among closely related species within a variety of taxa, Drosophila species differ considerably in whether they exhibit sexual dimorphism in coloration or morphology. Those Drosophila species in which male external sexual characters are minimal or absent tend, instead, to have exaggerated ejaculate traits such as sperm gigantism or seminal nutrient donations. Underlying explanations for the interspecific differences in the presence of external morphological sexual dimorphism versus exaggerated ejaculate traits are addressed here by examining the opportunity for sexual selection on males to occur before versus after mating in 21 species of Drosophila. Female remating frequency, an important component of the operational sex ratio, differs widely among Drosophila species and appears to dictate whether the arena of sexual selection is prior to, as opposed to after, copulation. Infrequent female mating results in fewer mating opportunities for males and thus stronger competition for receptive females that favors the evolution of male characters that maximize mating success. On the other hand, rapid female remating results in overlapping ejaculates in the female reproductive tract, such that ejaculate traits which enhance fertilization success are favored. The strong association between female remating frequency in a given species and the presence of sexually selected external versus internal male characters indicates that the relationship be examined in other taxa as well.

PERSPECTIVE: FEMALE REMATING, OPERATIONAL SEX RATIO, AND THE ARENA OF SEXUAL SELECTION IN DROSOPHILA SPECIES

As commonly observed among closely related species within a variety of taxa, Drosophila species differ considerably in whether they exhibit sexual dimorphism in coloration or morphology. Those Drosophila species in which male external sexual characters are minimal or absent tend, instead, to have exaggerated ejaculate traits such as sperm gigantism or seminal nutrient donations. Underlying explanations for the interspecific differences in the presence of external morphological sexual dimorphism versus exaggerated ejaculate traits are addressed here by examining the opportunity for sexual selection on males to occur before versus after mating in 21 species of Drosophila. Female remating frequency, an important component of the operational sex ratio, differs widely among Drosophila species and appears to dictate whether the arena of sexual selection is prior to, as opposed to after, copulation. Infrequent female mating results in fewer mating opportunities for males and thus stronger competition for receptive females that favors the evolution of male characters that maximize mating success. On the other hand, rapid female remating results in overlapping ejaculates in the female reproductive tract, such that ejaculate traits which enhance fertilization success are favored. The strong association between female remating frequency in a given species and the presence of sexually selected external versus internal male characters indicates that the relationship be examined in other taxa as well.

Sexing on down and feather colour in the Dandarawi Egyptian breed

1. The study was on a population of the Egyptian local strain Dandarawi. Hatching records were obtained from three lines over two generations (1996 and 1997). Sex ratios were calculated using a total of 5822 1-d-old chicks. 2. Sex could be identified at hatch by down colour. Female chicks showed a black spot on the head or irregular strips on the back, whereas males had no marks on head and back. At 8 weeks of age, progeny could be easily sexed by feather colour, which was black and white for males and brown for females. The sexual dimorphism in feather colour at that age is due to the presence of the autosomal recessive wild type allele CO*N. Accuracy for autosexing at hatching time was 89.02% for males and 92.42% for females. 3. Sex ratio deviated significantly from the expected value, 1: 1, in one line (line E) where the number of female chicks exceeded that of males, over the two generations. Chicks of both sexes exhibited the same survival rate up to 8 weeks of age.

Initial Mate Recognition in the British Cabbage Butterfly, Pieris rapae rapae

Abstract Visual features of the wing color, with special reference to the UV (ultraviolet) color, of the British subspecies of the cabbage butterfly, Pieris rapae rapae and its mating behavior were investigated. Both sexes of the British subspecies were found to lack UV color and differed only slightly in color in the visible color range, with female wings more yellowish. It follows that they show only slight sexual dimorphism in wing color. It was shown that the initial mate recognition was mediated visually, based on the wing color. Males discriminated between the sexes visually, but only marginally and were occasionally observed to approach other males mistakenly. The resting males approached by female-searching males displayed a flutter response, deterring the approaching males from attempting to copulate with them; i.e. it functioned as “mechanical isolation mechanism” against maladaptive copulatory attempts between males. The results are discussed in terms of the comparative ethology of the mating b...

Evolution of sexual dichromatism: contribution of carotenoid- versus melanin-based coloration

In birds, carotenoid-based plumage coloration is more dependent on physical condition and foraging abilities and less constrained developmentally than is melanin-based coloration. Thus, female mate choice for honest signals should result in more intense sexual selection on carotenoid- than on melanin-based plumage coloration. Using variation in sexual dimorphism as an indirect measure of the intensity of sexual selection, we tested the prediction that variation in sexual dimorphism is driven more by change in carotenoid-based coloration between males and females than by change in melanin-based coloration. Examination of historical changes in carotenoid- versus melanin-based pigmentation in 126 extant species of Cardueline finches supported this prediction. We found that carotenoid-derived coloration changed more frequently among congeners than melanin-based coloration. In both sexes, increase in carotenoid-based coloration score, but not in melanin-based coloration score, was strongly associated with increase in sexual dichromatism. In addition, sexual dimorphism in carotenoid-based coloration contributed more to overall dichromatism than dimorphism in melanin-based plumage. Our results supported the hypothesis that melanin-based and carotenoid-based coloration have fundamentally different signal content and suggest that combining melanin-based and carotenoid-based coloration in comparative analyses is not appropriate.

Evolution of sexual dichromatism: contribution of carotenoid- versus melanin-based coloration

In birds, carotenoid-based plumage coloration is more dependent on physical condition and foraging abilities and less constrained developmentally than is melanin-based coloration. Thus, female mate choice for honest signals should result in more intense sexual selection on carotenoid- than on melanin-based plumage coloration. Using variation in sexual dimorphism as an indirect measure of the intensity of sexual selection, we tested the prediction mat variation in sexual dimorphism is driven more by change in carotenoid-based coloration between males and females than by change in melanin-based coloration. Examination of historical changes in carotenoid- versus melanin-based pigmentation in 126 extant species of Cardueline finches supported this prediction. We found that carotenoid-derived coloration changed more frequently among congeners than melanin-based coloration. In both sexes, increase in carotenoid-based coloration score, but not in melanin-based coloration score, was strongly associated with increase in sexual dichromatism. In addition, sexual dimorphism in carotenoid-based coloration contributed more to overall dichromatism than dimorphism in melanin-based plumage. Our results supported the hypothesis that melanin-based and carotenoid-based coloration have fundamentally different signal content and suggest that combining melanin-based and carotenoid-based coloration in comparative analyses is not appropriate.