Larger Ornaments Research Articles

Male barn swallows use different signalling rules to produce ornamental tail feathers

The evolution of secondary sexual characters is the subject of controversial debate between those defending their role as ‘viability indicators’ and those arguing that ornaments are purely ‘attractive traits’ selected by females. Recent theoretical studies suggest that these hypotheses are not mutually exclusive, as both viability and attractiveness can contribute to improve the reproductive success of progeny and could thus simultaneously underlie female choices. If that is the case, strategies of cheaper advertisement, allowing the expression of larger ornaments for the same cost, could proliferate even in species in which honest signalling of viability prevails. Under this scenario, different males could invest a different amount of resources per ornament unit of expression, thus using different signalling rules. We studied the relationship between tail feather length (a trait that is the subject of a female mate preference) and feather mass (a measure of investment in feather production) in a barn swallow Hirundo rustica population. Different males used different and consistent signalling rules when developing ornamental feathers. That is, to produce a feather of a given length, each male used a constant amount of resources across different years, but this amount varied between males. Although the amount of material invested in feathers (feather mass) is a condition-dependent trait, the organization of this material in ornamental feathers (i.e. the signalling rules) was not. Neither survival nor risk of feather breakage was related to the signalling rules. Thus, these results suggest that both ‘viability’ and ‘runaway’ mechanisms are independent determinants of the evolution of ornamental sexual feathers in the barn swallow. A preference for long tails will ensure that females either obtain a sire with high viability, or one transferring the capability to produce longer and more attractive tails at a lower cost of production to its offspring.

Intraspecific preen oil odor preferences in dark-eyed juncos (Junco hyemalis)

Most birds possess a uropygial gland that produces a secretion, preen oil, that contains volatile compounds that may transmit information about individual attributes. However, the ability of passerine songbirds to discriminate among the odors of different individuals has not yet been demonstrated. We tested whether dark-eyed juncos (Junco hyemalis) could discriminate among preen oil odors from 1) conspecifics and heterospecifics; 2) male and female conspecifics; 3) conspecifics from same or different population or subspecies; and 4) males with large or small plumage ornaments. Our evidence suggests that juncos can discriminate between the odor of conspecifics and heterospecifics. In 2-way choice tests between conspecific odors, both males and females spent more time with male preen oil. Subjects did not discriminate between odors of individuals from their own population or a different one, and no relationship was found between choice and plumage ornaments. Unexpectedly, females spent more time with the odor of males with smaller body size, regardless of population of origin. This result was especially surprising because an analysis of preen oil volatile compounds revealed that the odors of smaller males were less male-like than the odors of larger males. We conclude that songbirds are able to detect odors from preen oil as shown by their ability to distinguish odors arising from males and females. They may also be able to distinguish among individuals of varying body size. Abstract » Full Text (HTML) Full Text (PDF) Lay Summary

Female-specific ornamentation predicts offspring quality in the striped plateau lizard, Sceloporus virgatus

When females vary in reproductive quality, they may be selected to honestly signal that quality and males may be selected to express mate choice based on this variation. In the striped plateau lizard, females with larger and more saturated orange throat patches are of higher phenotypic quality, and males preferentially associate with brighter females. Here, we assess whether this female ornament conveys fitness benefits by relating female ornamentation to offspring quality. We housed groups of male and female Sceloporus virgatus in outdoor enclosures, tracked the seasonal color development of females to determine peak ornament expression, measured offspring body condition from hatching to day 180, and measured offspring sprint speed at day 180. Although we did not eliminate the possibility of assortative mating within enclosures, we controlled for these potential effects by exposing females to small groups of similarly sized males and by including maternal body size, maternal body condition, and egg mass as covariates in our statistical models. Offspring body condition was reliably predicted by female ornament size but not by ornament color intensity or saturation. Similarly, offspring sprint speed was predicted only by ornament size and not by color intensity or saturation. Females with large ornaments tended to produce offspring with higher body condition and faster offspring than did females with small ornaments. These results are consistent with the hypothesis that males may gain fitness benefits from preferentially allocating their reproductive effort toward females with larger orange patches by producing higher quality offspring. Possible mechanisms underlying such female-ornament--offspring-quality relationships are discussed. Copyright 2009, Oxford University Press.

Honest sexual signalling mediated by parasite and testosterone effects on oxidative balance.

Extravagant ornaments evolved to advertise their bearers' quality, the honesty of the signal being ensured by the cost paid to produce or maintain it. The oxidation handicap hypothesis (OHH) proposes that a main cost of testosterone-dependent ornamentation is oxidative stress, a condition whereby the production of reactive oxygen and nitrogen species (ROS/RNS) overwhelms the capacity of antioxidant defences. ROS/RNS are unstable, very reactive by-products of normal metabolic processes that can cause extensive damage to key biomolecules (cellular proteins, lipids and DNA). Oxidative stress has been implicated in the aetiology of many diseases and could link ornamentation and genetic variation in fitness-related traits. We tested the OHH in a free-living bird, the red grouse. We show that elevated testosterone enhanced ornamentation and increased circulating antioxidant levels, but caused oxidative damage. Males with smaller ornaments suffered more oxidative damage than those with larger ornaments when forced to increase testosterone levels, consistent with a handicap mechanism. Parasites depleted antioxidant defences, caused oxidative damage and reduced ornament expression. Oxidative damage extent and the ability of males to increase antioxidant defences also explained the impacts of testosterone and parasites on ornamentation within treatment groups. Because oxidative stress is intimately linked to immune function, parasite resistance and fitness, it provides a reliable currency in the trade-off between individual health and ornamentation. The costs induced by oxidative stress can apply to a wide range of signals, which are testosterone-dependent or coloured by pigments with antioxidant properties.

Morphological characteristics of Cape sugarbirds (Promerops cafer) from Helderberg Nature Reserve

Cape sugarbirds (Promerops cafer) are the largest nectarivores in the Western Cape and feed almost exclusively on protea nectar and associated arthropods. Helderberg Nature Reserve, Western Cape, South Africa, has a large diversity of Protea and supports breeding sugarbirds. As part of a larger study, we captured sugarbirds using mist-nets during the breeding and non-breeding season at several sites in the Helderberg Nature Reserve, Western Cape, South Africa, from 1996 to 2000. From these data (n =283 males, 272 females), we found that in both sexes, individuals with longer tails have longer wings. Males were significantly larger in mass, culmen, head, tarsus, wing and tail length than females. Males with larger mass were larger in all morphometric measurements than those with smaller mass. Mate choice and territory defence may be based on wing and tail ornament displays of male sugarbirds, thus larger males with larger ornaments could benefit through greater breeding success than smaller males.

Green swordtails alter their age at maturation in response to the population level of male ornamentation

Effects of the social environment on age at sexual maturation are assumed to require direct interactions, such as suppression of subordinates through aggression from dominants. Using green swordtails (Xiphophorus helleri), we demonstrate for the first time that females and males adjust their age at maturation in response to visual cues of male sexual ornamentation in the current environment: females matured earlier, whereas males matured later if all the mature males seen had large ornaments. Thus, age at maturation shifted in accordance with the perceived quality of mates (females) or mating competitors (males), demonstrating a capability to use visual cues from the environment to strategically adjust rates of sexual development.

Morphological characteristics of Cape sugarbirds (Promerops cafer) from Helderberg Nature Reserve

Cape sugarbirds (Promerops cafer) are the largest nectarivores in the Western Cape and feed almost exclusively on protea nectar and associated arthropods. Helderberg Nature Reserve, Western Cape, South Africa, has a large diversity of Protea and supports breeding sugarbirds. As part of a larger study, we captured sugarbirds using mist-nets during the breeding and non-breeding season at several sites in the Helderberg Nature Reserve, Western Cape, South Africa, from 1996 to 2000. From these data (n =283 males, 272 females), we found that in both sexes, individuals with longer tails have longer wings. Males were significantly larger in mass, culmen, head, tarsus, wing and tail length than females. Males with larger mass were larger in all morphometric measurements than those with smaller mass. Mate choice and territory defence may be based on wing and tail ornament displays of male sugarbirds, thus larger males with larger ornaments could benefit through greater breeding success than smaller males.

Attractive males provide less parental care in two populations of the common yellowthroat

Male ornaments may be signals of direct or indirect benefits to females that mate with those males. One important direct benefit to females is the level of male parental assistance they receive when provisioning young. Three main hypotheses attempt to explain the relationship between male ornament size and parental care. The good parent hypothesis predicts that males with larger ornaments will provide more care, while the differential allocation and trade-off hypotheses predict that they will provide less care. We examined the relationship between male ornamentation and parental care in two populations of common yellowthroats, Geothlypis trichas, in which the sexually selected male ornament differs. More ornamented males provided less parental care in both populations, contrary to the good parent hypothesis. However, females did not feed their nestlings more frequently when mated with more ornamented males, which is an additional prediction of the differential allocation hypothesis. Our results are most consistent with the trade-off hypothesis, which suggests that more ornamented males provide less care because they spend relatively more of their effort in pursuing extrapair mates or defending their territories from other males.

Experimental evidence that female ornamentation increases the acquisition of sperm and signals fecundity

Mate choice can lead to the evolution of sexual ornamentation. This idea rests on the assumption that individuals with more elaborate ornaments than competitors have higher reproductive success due to gaining greater control over mating decisions and resources provided by partners. Nevertheless, how the resources and quality of sexual partners that individuals gain access to are influenced by the ornamentation of rival individuals remains unclear. By experimentally concealing and subsequently revealing female ornaments to males, we confirm in the fowl, Gallus gallus, that female ornamentation influences male mating decisions. We further show, by manipulating the relative ornament size of females, that when females had larger ornaments than competitors they were more often preferred by males and obtained more sperm, especially from higher quality males, as measured by social status. Males may benefit by investing more sperm in females with larger ornaments as they were in better condition and produced heavier eggs. Female ornament size also decreased during incubation, providing a cue for males to avoid sexually unreceptive females. This study reveals how inter-sexual selection can lead to the evolution of female ornaments and highlights how the reproductive benefits gained from mate choice and bearing ornaments can be dependent upon social context.

Consequences of complex signaling: predator detection of multimodal cues

Animals often evolve complex signals to enhance their detectability by intended receivers. But signals that are more detectable by intended receivers may also be more likely to be intercepted by others, including predators. Courtship signaling in male Schizocosa ocreata wolf spiders (Lycosidae) includes morphological traits (prominent foreleg tufts) and active behaviors that together produce a complex signal with simultaneous broadcast of visual and seismic components. Females respond more readily to males with large tufts and are more likely to respond when multiple modalities (visual and seismic) are present in a complex signal. These spiders cooccur with active predators that may intercept these conspicuous courtship signals and use them as hunting cues. We used video/seismic playback to experimentally isolate and manipulate aspects of the complex signal produced by male S. ocreata. We found that increasing the size of a visual signal (male tufts) and increasing the complexity of the courtship signal by adding a second modality (visual plus seismic versus visual alone) increased the speed with which a common predator, the jumping spider Phidippus clarus (Salticidae), responded to playbacks of courting male S. ocreata. These results indicate that the benefits of increased signaling efficacy of large visual signaling ornaments and complex, multimodal signaling may be countered by increased predation risks.

Mate choice for indirect benefits displayed by a large ornament: simulations using a neural network

I analysed mate choice for indirect genetic benefits displayed by an ornament theoretically by means of a neural network model. In particular, the fitness of a choosy female was compared to that of a nonchoosy one under various ecological conditions such as variation in ornament size between males, the cost of searching, the heritability of the ornament and a correlation between ‘good genes’ and the phenotypic expression of the ornament. Females were allowed to choose between either six or 43 males with ornaments of various sizes. They were allowed to compare males until the largest of the presented males was chosen. I found that choosiness was favoured with increasing variation in ornament size between males, combined with a high heritability of the ornament, a very high correlation between the ‘good genes’ and the phenotype, and low search costs. In general, as the correlation between the ‘good genes’ and the phenotype decreased the variance in expected fitness of choosy females increased. The results suggest that the conditions favouring this type of mate choice are restrictive and apply only to a small set of species.

Female egg investment in relation to male sexual traits and the potential for transgenerational effects in sexual selection

Life-history theory predicts that individuals should increase their reproductive effort when the fitness return from reproduction is high. Females mated with high-quality males are therefore expected to have higher investment than females mated with low-quality males, which could bias estimates of paternal effects. Investigating the traits females use in their allocation decisions and the aspects of reproduction that are altered is essential for understanding how sexual selection is affected. We studied the potential for differential female allocation in a captive population of a precocial bird, the Chinese quail, Coturnix chinensis. Females paired with males with large sexual ornaments laid larger, but not more, eggs than females paired with males with small sexual ornaments. Furthermore, female egg mass was also significantly positively affected by male testis size, probably via some unknown effect of testis size on male phenotype. Testis size and ornament size were not correlated. Thus, both primary and secondary male sexual traits could be important components of female allocation decisions. Experimental manipulation of hormone levels during embryonic development showed that both male and female traits influencing female egg size were sensitive to early hormone exposure. Differences in prenatal hormone exposure as a result of maternal steroid allocation to eggs may explain some of the variation in reproductive success among individuals, with important implications for non-genetic transgenerational effects in sexual selection.

Humoral immune response in relation to senescence, sex and sexual ornamentation in the barn swallow (Hirundo rustica).

Performance of animals may decline with age. The effects of senescence, however, may differ between the sexes because of differences in physiology and behaviour. Acquired immunity provides hosts with efficient mechanisms of anti-parasite defence, but the effect of senescence on immunocompetence has never been studied in natural populations. In the barn swallow (Hirundo rustica), primary antibody response to an antigen during one breeding season declined with age in females, while secondary response during the following breeding season declined with age in both sexes. Parasite-mediated sexual selection theory posits that male secondary sexual characters reveal resistance to parasites. Males with large tail ornaments had stronger primary response, retained larger antibody levels until the following year, but did not differ in secondary response compared with short-tailed males, as predicted if ornamentation reflects resistance to parasites. This is the first study showing that immunocompetence declines with age in any vertebrate under natural conditions.

Sophisticated sperm allocation in male fowl.

When a female is sexually promiscuous, the ejaculates of different males compete for the fertilization of her eggs; the more sperm a male inseminates into a female, the more likely he is to fertilize her eggs. Because sperm production is limited and costly, theory predicts that males will strategically allocate sperm (1) according to female promiscuity, (2) saving some for copulations with new females, and (3) to females producing more and/or better offspring. Whether males allocate sperm in all of these ways is not known, particularly in birds where the collection of natural ejaculates only recently became possible. Here we demonstrate male sperm allocation of unprecedented sophistication in the fowl Gallus gallus. Males show status-dependent sperm investment in females according to the level of female promiscuity; they progressively reduce sperm investment in a particular female but, on encountering a new female, instantaneously increase their sperm investment; and they preferentially allocate sperm to females with large sexual ornaments signalling superior maternal investment. Our results indicate that female promiscuity leads to the evolution of sophisticated male sexual behaviour.

Immune response of male barn swallows in relation to parental effort, corticosterone plasma levels, and sexual ornamentation

Life-history theory posits trade-offs between fitness components. Reproduction negatively affects physiology and immune system functioning, and the effect of this form of stress may be mediated by glucocorticosteroids. We manipulated brood size of barn swallows (Hirundo rustica) to study the effect of stress arising from reproductive effort on corticosterone levels of males. We also measured T-cell--mediated immunocompetence by intradermally injecting birds with phytohemagglutinin, which is mitogenic to T-lymphocytes. The results confirmed the prediction of a negative effect of parental effort on lymphoproliferative response. We found no covariation between immune response and corticosterone levels. Males with long tails, an ornament currently under directional sexual selection, had a relatively large T-cell response to the mitogen, consistent with models of parasite-mediated sexual selection predicting higher levels of immune defense in highly ornamented males. In addition, males with large sexual ornaments had relatively low corticosterone levels at the end of the parental period. These results can be reconciled with the hypothesis proposing a trade-off between parental activities and adaptive immunity and suggest that highly ornamented males are less exposed or less susceptible to stress arising from parental effort. Copyright 2002.

ソグディアナにおける絹織物の使用と生産

The present article presents a discussion on the silk fabrics which were used and produced in Sogdiana. The Sogdians were not only traders, but also users of Chinese and Persian brocades. On Sogdian mural paintings we can see Sogdians with clothes made of polychrome silks (_??_jin). At the same time the Sogdians were producers of brocade, and it is suggested here that one group of that kind of textiles unearthed in Turfan was manufactured in Sogdiana. In this article the so-called “Zandaniji” silks are not mentioned, because their identification with actual textiles is problematic.The Sogdian wall paintings from Pendzhikent, Afrasiab and Varakhsha show a series of patterned textiles which became popular there from the 6th to the first half of the 8th centuries (Fig. 1-2). In the 6th and 7th centuries textiles were patterned with small ornaments. From the second half of the 7th century large ornaments came into fashion, and in the Afrasiab mural, datable from around 660, the costumes are filled with Sasanian patterns (animal motifs encircled in pearl roundels). Chinese damask (_??_ ling) and Tang rosette silks (_??__??__??__??__??_ bao xiang hua wen jin) appear in the paintings of the early 8th century. In the murals from the middle of the 8th century animal motifs in medallions are no longer to be seen and are replacecd by flowers (Marshak 2001).In two cases it is possible to determine the place of origin of the textiles depicted on murals. Firstly, as monochrome damask and Tang rosette silks are specific products of China, those depicted on the murals are surely Chinese. Secondly, studying the textile motifs in the Afrasiab painting (Fig. 2, Left), M. Mode had identified them as Sasanian textiles. In his opinion, Senmurv (mythical creature), which is one of the animals represented on brocades in the Afrasiab mural, is a motif specific to Sasanian art. When comparable animals are depicted in Sogdian art (wall paintings and silver vessels) they are not the Senmurv, but winged camels or winged lions. The brocades with various animal motifs on the Afrasiab painting have an unity, and all of them are undoubtedly Sasanian.

Sexually selected traits and adult survival: a meta-analysis.

Traits correlated with male mating success are likely to be subject to sexual selection. Sexually selected characters are thought to be costly to develop and maintain. If males do not vary their investment in sexual traits in relation to their ability to bear the costs, there should be a negative relationship between male longevity or survival and the expression of sexual traits. In particular, a negative relationship is predicted by pure Fisherian models for the evolution of sexual ornaments. The same should also be true for traits that evolve via pleiotropy (e.g., due to sensory exploitation or bias) with no subsequent evolution of condition dependent modification. We collected information on the relationship between traits correlated with male mating rate and estimates of adult male survivorship or life span. In total we obtained 122 samples from 69 studies of 40 species of bird, spider, insect, and fish. In a meta-analysis we calculated the average sample size weighted correlation between trait expression and adult survival. Analyses at the level of samples, studies, and species revealed significant positive relationships (r = 0.08, 0.10, and 0.13, respectively; all P < 0.001). The unweighted correlation at the species level was r = 0.24. In general, males with larger ornaments or weapons, greater body size, or higher rates of courtship showed greater survivorship or longevity. This finding is inconsistent with pure Fisherian models or other models that do not incorporate condition or quality dependent trait expression. It suggests that male investment in sexually selected traits is not fixed but varies in relation to the ability to pay the underlying costs of expressing these characters. Hence, many secondary sexual characters are likely to be condition dependent in their expression.

The effects of testosterone on a viral infection in greenfinches (Carduelis chloris): an experimental test of the immunocompetence-handicap hypothesis

The immunocompetence-handicap hypothesis suggests that the honesty of quality signals could be guaranteed if testosterone (T) suppresses immune function while enhancing male ornaments. In addition, it has been proposed that the cost of enhancing ornaments should be highest for males with small ornaments. Recently, the assertion that T causes obligate immunosuppression has been questioned. In this study, we tested whether elevated T levels would increase susceptibility to a viral infection, and whether this hypothesized effect would be most pronounced in males with small ornaments. We surgically inserted T implants into 15 male greenfinches (Carduelis chloris) and control implants into a further 15 males. All birds were then infected with a naturally occurring virus (Sindbis virus, Alphavirus genus), and each bird's daily viraemia (blood virus concentration) was measured for seven days. The specific antibody response was measured for eight weeks. T-implanted males did not exhibit increased viraemia or decreased antibody response, and males with small and large ornaments did not respond differently to T implantation. We did, however, find that T implantation decreased viraemia early in the course of the infection and increased viraemia late in the infection. Thus, our results demonstrate that T may act both to increase and to decrease viraemia.

Sexual selection and the evolution of costly female preferences: spatial effects.

Models of Fisher's runaway process show that if there is a cost to female preference, no preference or male trait exaggeration will evolve. Surprisingly, this is true no matter how small the cost, which reveals that these models of Fisher's process are structurally unstable (Bulmer 1989). Here a model of Fisher's runaway process is presented to demonstrate that costly female preference evolves very easily when space is explicitly included in the model. The only requirement is that the optimal male phenotype changes across the species' range. The model shows that the spatial average of the female preference and male trait reach an evolutionary equilibrium that is identical to those of nonspatial models, but that the preference and male trait can deviate greatly from these averages at any point in space. For example, if random mating results in the lowest cost to females, then at equilibrium the spatial average preference will be zero. Nevertheless, there will be some locations at which females prefer males with larger ornaments and others where they prefer males with smaller ornaments. Results also show that the structural instability of nonspatial models of Fisher's process is less of a problem in spatial models. In particular, many of the main qualitative features of cost-free spatial models of Fisher's process remain valid even when there are small costs of female preference. Finally, the model shows that abrupt changes in the optimal male phenotype across space can result in an amplification of this pattern when preference has a small cost, but it can also result in a pattern similar to reproductive character displacement. Which of these occurs depends on the magnitude of the cost of female preference. This suggests that some patterns of reproductive character displacement in nature might be explained simply by sexual selection rather than by hybrid dysgenesis and reinforcement.

SEXUAL SELECTION AND THE EVOLUTION OF COSTLY FEMALE PREFERENCES: SPATIAL EFFECTS

Models of Fisher's runaway process show that if there is a cost to female preference, no preference or male trait exaggeration will evolve. Surprisingly, this is true no matter how small the cost, which reveals that these models of Fisher's process are structurally unstable (Bulmer 1989). Here a model of Fisher's runaway process is presented to demonstrate that costly female preference evolves very easily when space is explicitly included in the model. The only requirement is that the optimal male phenotype changes across the species' range. The model shows that the spatial average of the female preference and male trait reach an evolutionary equilibrium that is identical to those of nonspatial models, but that the preference and male trait can deviate greatly from these averages at any point in space. For example, if random mating results in the lowest cost to females, then at equilibrium the spatial average preference will be zero. Nevertheless, there will be some locations at which females prefer males with larger ornaments and others where they prefer males with smaller ornaments. Results also show that the structural instability of nonspatial models of Fisher's process is less of a problem in spatial models. In particular, many of the main qualitative features of cost-free spatial models of Fisher's process remain valid even when there are small costs of female preference. Finally, the model shows that abrupt changes in the optimal male phenotype across space can result in an amplification of this pattern when preference has a small cost, but it can also result in a pattern similar to reproductive character displacement. Which of these occurs depends on the magnitude of the cost of female preference. This suggests that some patterns of reproductive character displacement in nature might be explained simply by sexual selection rather than by hybrid dysgenesis and reinforcement.Corresponding Editor: J. Mallet