Reproductive correlates of plumage coloration of female Mountain Bluebirds

Many studies have shown that the plumage coloration of male birds can act as an honest signal of quality, indicating benefits that a female could gain from pairing with a specific male. In some species, females also display ornamental plumage, but less is known about the function and potential adaptive significance of female coloration because most research has focused on male coloration. Male Mountain Bluebirds (Sialia currucoides) display full body, ultraviolet (UV)‐blue plumage, whereas female plumage is more subdued, with blue color focused on the rump, wing, and tail. During the 2011 and 2012 breeding seasons (May–July) near Kamloops, BC, Canada, we examined coloration of the rump and tail of female Mountain Bluebirds to determine if their plumage could act as an indicator of direct reproductive benefits (e.g., enhanced parental care or reproductive success) to potential mates. We found no relationship between female plumage coloration and either provisioning rate or fledging success. However, female coloration varied with age, with after‐second‐year (ASY) females having brighter, more UV‐blue tail feathers than second‐year (SY) females. In addition, ASY females with brighter, more UV‐blue tails had larger clutches. We also observed positive assortative mating by tarsus length. Because previous work with other species suggests that female body size may be a good predictor of breeding success, males could potentially benefit from pairing with larger females. However, reproductive success did not vary with female size in our study. Although our evidence that structural plumage coloration of female Mountain Bluebirds is a signal of direct reproductive benefits for males (e.g., higher reproductive success) is limited, our results (i.e., ASY females with brighter tails than SY females, and ASY females with brighter tails having larger clutches) do suggest the potential for sexual selection to act on female coloration.     

Haemosporidian parasites depress breeding success and plumage coloration in female barn swallows Hirundo rustica

Parasites are major effectors of natural selection and also play a role in sexual selection processes. Haemosporidian blood parasites are common in vertebrates and have been shown to vary in their effects depending on both the parasite and host species, on the host trait investigated as well as on host condition and stage of infection. Here we investigated infection of adult barn swallows Hirundo rustica by Plasmodium, Leucocytozoon and Haemoproteus species during the chronic stage of infection and the consequences for host fitness traits. Prevalence was higher than 10% only for Plasmodium. Chronic stage infection by Plasmodium was associated with reduced female breeding success, but did not affect breeding dates. Infection did not affect the expression of male secondary sexual traits (tail length and melanin‐based plumage coloration), but was associated with paler coloration of females. Finally, we found a negative effect of infection by Plasmodium on feather growth rate in older but not in yearling individuals. Because feathers are moulted during wintering in sub‐Saharan Africa where infection of barn swallows by Plasmodium occurs, our results suggest that male secondary sexual traits have little potential to reveal acute‐stage infection whereas plumage coloration of females may advertise their infection status. In addition, these results suggest that infection by Plasmodium can influence the course of plumage moult. Thus, our results add to the observations of negative effects of haemosporidian infection on fitness traits in birds and provides evidence that these effects can vary among traits and in relation to age and sex.     

Structural and melanin coloration indicate parental effort and reproductive success in male eastern bluebirds

Male eastern bluebirds (Sialia sialis) have two types of ornamentalplumage coloration: a brilliant blue-ultraviolet head, back,and wings, and a patch of chestnut breast feathers. The blue-UVcoloration is produced from feather microstructure, whereasthe chestnut coloration is produced by a combination of pheaomelaninand eumelanin pigments deposited in feathers. We tested thehypothesis that plumage coloration reflects male quality ineastern bluebirds, a socially monogamous, sexually dichromaticbird. We investigated whether male ornamentation correlateswith mate quality and parental effort. We quantified three aspectsof male ornament coloration: (1) size of the patch of chestnutbreast feathers, (2) reflectance properties of the chestnutplumage coloration, and (3) reflectance properties of the blue-ultravioletplumage coloration. We found that males with larger breast patchesand brighter plumage provisioned nestlings more often, fledgedheavier offspring, and paired with females that nested earlier.Males with plumage coloration that exhibit more ultraviolethues fledged more offspring. These results suggest that plumagecoloration is a reliable indicator of male mate quality andreproductive success. Both melanin-based and structural-basedplumages appear to be honest signals of male quality and parentalcare that can be assessed by competitors or by potential mates.     

Melanin-based coloration is a nondirectionally selected sex-specific signal of offspring development in the alpine swift

Two mutually exclusive hypotheses have been put forward to explain the evolution and adaptive function of melanin-based color traits. According to sexual selection theory melanism is a directionally selected signal of individual quality, whereas theory on the maintenance of genetic polymorphism proposes that alternative melanin-based variants achieve equal fitness. Alpine swift (Apus melba) males and females have a conspicuous patch of white feathers on the breast with their rachis varying continuously from white to black, and hence the breast varies from white to striated. If this trait is a sexually selected signal of quality, its expression should be condition dependent and the degree of melanism directionally selected. If variation in melanism is a polymorphism, its expression should be genetically determined and fitness of melanin-based variants equal. We experimentally tested these predictions by exchanging eggs or hatchlings between randomly chosen nests and by estimating survival and reproduction in relation to melanism. We found that breast melanism is heritable and that the environment and body condition do not significantly influence its expression. Between 5 and 50 days of age nestlings were heavier and their wings longer when breast feathers of their biological father were blacker, and they also fledged at a younger age. This shows that aspects of offspring quality covary positively with the degree of melanism. However, this did not result in directional selection because nestling survival and recruitment in the local breeding population were not associated with father breast melanism. Furthermore, adult survival, age at first reproduction and probability of skipping reproduction did not covary with the degree of melanism. Genetic variation in breast melanism is therefore maintained either because nonmelanic males achieve fitness similar to melanic males via a different route than producing fast-growing offspring, or because the advantage of producing fast-growing offspring is not sufficiently pronounced to result in directional selection.     

Structurally based plumage coloration is an honest signal of quality in male blue grosbeaks

We investigated the signaling function of blue plumage in maleblue grosbeaks (Guiraca caerulea) to determine if structurallybased coloration may act as a reliable signal of quality toconspecifics. Blue plumage results from the microstructureof feather barbules rather than from pigment granules, andthus it is possible that structurally based plumage ornamentsmay function differently from sexually selected ornamental coloration that is pigment based. The plumage of male blue grosbeaksreflects maximally in the blue-ultraviolet range, so most variationin plumage coloration among males is invisible to human observers.In previous research, we showed that increased area of blueplumage on the body is associated with a shift in the wavelengthof maximum feather reflectance toward the ultraviolet and withhigh intensity of light reflected at that maximum, and thatextreme expression of the male ornament is condition dependent.These observations suggest that blue plumage may be an honestadvertisement of male quality. We tested this hypothesis ina wild population of blue grosbeaks. We quantified male qualityin three broad categories. (1) Physical condition was assessed from subcutaneous fat deposits, ectoparasite load, and bodysize. (2) Territory quality was assessed from territory area,prey abundance, and predation risk. (3) Paternal investmentwas assessed from male feeding rate. We found that the bluestmales have the largest body size, maintain the largest territorieswith the greatest prey abundance, and feed nestlings in thefirst nest of the season at the highest rates. We conclude that structurally based plumage coloration functions as an honest,intraspecific signal of quality.     

Variation in effects of male plumage ornaments: the case of Iberian Pied Flycatchers

It has been proposed that mate preferences by female Pied Flycatchers Ficedula hypoleuca differ between southern (Iberian) and northern (Scandinavian) European populations. Whereas the size of the white forehead patch, but not plumage colour, has been reported to be a sexually selected trait in the former, only plumage darkness apparently acts as an ornament in the latter. In addition, northern male Pied Flycatchers become darker with age, a trend not detected until the present study in southern birds. Here we show that in an Iberian population of Pied Flycatchers breeding only a few tens of kilometres from previously studied populations, plumage darkness is associated with mating success and increases with age, whereas the size of the white forehead patch is not related to mating success and is only weakly correlated with age, trends similar to those reported for Scandinavian rather than other Iberian Pied Flycatcher populations. This represents a case of variation in sexually selected traits between geographically close populations of Pied Flycatchers that cannot be explained by sympatry with closely related species. It is proposed that differences in the identity and abundance of environmental stressors may be the cause of this regional variation in sexually selected traits.     

Carotenoid plumage hue and chroma signal different aspects of individual and habitat quality in tits

We hypothesized that Blue Tits Cyanistes caeruleus and Great Tits Parus major from low quality habitat (small woods) would have less yellow ventral plumage than those from high quality habitat (large woods) because they moult faster and/or their diet contains fewer carotenoids. They moult faster because they moult later in the season and are subject to more rapidly shortening daylengths. We tested this using a database of the plumage coloration (chroma, hue and lightness) of birds breeding in woods of different sizes, by manipulating the speed of moult in captive Blue Tits, and by counting the abundance and size of caterpillars (the major source of dietary carotenoids) in the diet of nestlings. In accordance with our hypothesis, juveniles of both species (which moult about three weeks later than adults) were about 8% less saturated in colour (lower chroma) than adults, but there was no significant difference in chroma between habitats. However, both species did differ significantly in hue between large and small woods. Blue Tits forced to moult faster in captivity, at a rate similar to that caused by a month's delay in the start of moult, had yellow flank feathers that were 32% less saturated in colour than those allowed to moult more slowly. Blue Tit nestlings in large woods consumed 47% more caterpillar flesh (per gram of faecal material voided) than those in small woods, and Great Tit pulli 81% more. When habitat effects were controlled for in ANOVAs, Blue Tits mated assortatively on the basis of flank hue and Great Tits on the basis of flank lightness. Flank colour therefore has the capacity to provide information about the potential quality of both habitats, and individual birds, to potential colonists and sexual partners.     

The evolution of bill coloration and plumage dimorphism supports the transference hypothesis in dabbling ducks

Bright coloration in male birds is typically thought to be drivenby sexual selection (female choice or male-male competition).Bird species often vary in the intensity of bright coloration,but few studies have addressed this cross-species variation.Potentially this variation could result from either variationin female preferences or in the relative costs of male traits. Speciesof dabbling ducks vary in the presence of bright male plumageand bill coloration. I tested the transference hypothesis forornament evolution in dabbling ducks using a phylogenetic studyof character evolution. The transference hypothesis makes threepredictions: (1) a costly male ornamental trait is the ancestralcondition, (2) a less costly male ornamental trait is the derivedcondition, and (3) gains in the less costly trait are associatedwith losses or absence of the more costly male trait. All threeof these predictions were satisfied in this study of the evolutionof plumage dimorphism and bright bill coloration in the dabblingducks, given that bright plumage coloration is more costly thanbright bill coloration.     

Revealing the colourful side of birds: spatial distribution of conspicuous plumage colours on the body of Australian birds

In many species of birds, different body parts often display very different colours. This spatial distribution of coloured plumage patches may be determined, among other factors, by the balance between being cryptic to predators, and conspicuous to intended receivers. If this is the case, ventral and anterior body parts in birds – which are less visible to predators but more prominent to conspecifics – should present more conspicuous and sexually dichromatic plumage colours. Here, I test these predictions using reflectance spectrometric measurements of standardised plumage patches across males and females for nearly an entire avifauna (Australian landbirds, n = 538 species). My data show that, as predicted, conspicuous and sexually dichromatic colours are mainly located near the head, while the plumage of the back is the most cryptic. One clear exception to this pattern is the conspicuous rump coloration. In many species, this patch can be concealed by wings, and therefore exposed only when necessary. In addition, conspicuous rump coloration could deflect or confuse predators in case of attack. However, there is considerable variation across species, and this makes position on the body a very poor predictor of plumage elaboration (R² < 0.02). Future studies should try to determine whether differences between species in the distribution of colours across the plumage are due to variation in ecological factors (predation risk, habitat, etc.).     

Divergent patterns of age-dependence in ornamental and reproductive traits in the collared flycatcher

Sexual ornaments are predicted to honestly signal individual condition. We might therefore expect ornament expression to show a senescent decline, in parallel with late-life deterioration of other characters. Conversely, life-history theory predicts the reduced residual reproductive value of older individuals will favor increased investment in sexually attractive traits. Using a 25-year dataset of more than 5000 records of breeding collared flycatchers (Ficedula albicollis) of known age, we quantify cross-sectional patterns of age-dependence in ornamental plumage traits and report long-term declines in expression that mask highly significant positive age-dependency. We partition this population-level age-dependency into its between- and within-individual components and show expression of ornamental white plumage patches exhibits within-individual increases with age in both sexes, consistent with life-history theory. For males, ornament expression also covaries with life span, such that, within a cohort, ornamentation indicates survival. Finally, we compared longitudinal age-dependency of reproductive traits and ornamental traits in both sexes, to assess whether these two trait types exhibit similar age-dependency. These analyses revealed contrasting patterns: reproductive traits showed within-individual declines in late-life females consistent with senescence; ornamental traits showed the opposite pattern in both males and females. Hence, our results for both sexes suggest that age-dependent ornament expression is consistent with life-history models of optimal signaling and, unlike reproductive traits, proof against senescence.     

Contrasting patterns of selection on the size and coloration of a female plumage ornament in common yellowthroats

Females often possess ornaments that appear smaller and duller than homologous traits in males. These ornaments may arise as nonfunctional by‐products of sexual selection in males and cause negative viability or fecundity selection in females in proportion to the cost of their production and maintenance. Alternatively, female ornaments may function as signals of quality that are maintained by sexual or social selection. In a 4‐year study of 83 female common yellowthroats (Geothlypis trichas) and their 222 young, we found strong viability and fecundity selection on the yellow bib, a carotenoid‐based plumage ornament that is a target of sexual selection in males. Females with larger bibs were older, larger and more fecund than females with smaller bibs. However, bib size positively covaried with bib total brightness and carotenoid chroma, aspects of bib coloration that were under negative viability and fecundity selection. Females with more colourful bibs laid fewer eggs in their first clutch, were more likely to suffer total brood loss due to predation and were less likely to return to the study area. Selection against bib coloration limits the value of bib size as a quality indicator in females and may constrain the elaboration of bib attributes in males.     

The role of maternal and paternal effects in the evolution of parental quality by sexual selection

Genetic models of maternal effects and models of mate choice have focused on the evolutionary effects of variation in parental quality. There have been, however, few attempts to combine these into a single model for the evolution of sexually selected traits. We present a quantitative genetic model that considers how male and female parental quality (together or separately) affect the expression of a sexually selected offspring trait. We allow female choice of males based on this parentally affected trait and examine the evolution of mate choice, parental quality and the indicator trait. Our model reveals a number of consequences of maternal and paternal effects. (1) The force of sexual selection owing to adaptive mate choice can displace parental quality from its natural selection optimum. (2) The force of sexual selection can displace female parental quality from its natural selection optimum even when nonadaptive mate choice occurs (e.g. runaway sexual selection), because females of higher parental quality produce more attractive sons and these sons counterbalance the loss in fitness owing to over-investment in each offspring. (3) Maternal and paternal effects can provide a source of genetic variation for offspring traits, allowing evolution by sexual selection even when those traits do not show direct genetic variation (i.e. are not heritable). (4) The correlation between paternal investment and the offspring trait influenced by the parental effects can result in adaptive mate choice and lead to the elaboration of both female preference and the male sexually selected trait. When parental effects exist, sexual selection can drive the evolution of parental quality when investment increases the attractiveness of offspring, leading to the elaboration of indicator traits and higher than expected levels of parental investment.     

Variation in melanin pigmentation of a sexually selected plumage trait and its adaptive value in the Common Snipe Gallinago gallinago

There is increasing evidence that melanin‐based plumage coloration correlates with different components of fitness and that it may act as a social or sexual signal of individual quality. We analysed variation in melanin pigmentation in the outermost tail feathers of the Common Snipe Gallinago gallinago. During courtship flights, male Snipe use their outermost tail feathers to generate a drumming sound, which plays a role in territory establishment and mate choice. As the outermost tail feathers are displayed to females during these flights, we predicted that conspicuous variation in their rusty‐brown (pheomelanin‐based) coloration may act as an honest signal of individual quality. To test this prediction, we spectrophotometrically measured brightness (an indicator of total melanin content) and red chroma (an indicator of pheomelanin content) of the outermost tail feathers in 180 juvenile and adult Common Snipe. An age‐related decline in feather brightness was found exclusively in females, suggesting that melanization could have evolved by natural selection to camouflage incubating birds. In both sexes, brightness of the tail feathers was inversely correlated with their structural quality (as measured with mass–length residuals), suggesting that melanization could increase mechanical properties of feathers and, in males, enhance the quality of courtship sonation. Red chroma positively correlated with total plasma protein concentration, supporting our prediction that pheomelanin pigmentation of tail feathers may act as an honest signal of condition. Our study indicated that variation in the melanin‐based coloration of the outermost tail feathers in the Common Snipe could have evolved as a result of several different selection pressures and it emphasizes the complexity of the processes that underlie the evolution of melanin‐based plumage coloration in birds.     

Male reproductive senescence: the price of immune-induced oxidative damage on sexual attractiveness in the blue-footed booby

In animals, male reproduction is commonly a function of sexual attractiveness, based on the expression of sexually dimorphic traits that advertise genuinely the male's quality. Male performance may decline with age because physiological functions underlying sexual attractiveness may be affected by senescence. Here we show that a sexual signal (foot colour) declines with age, due probably to the deleterious effects of oxidative damage. We found that in the blue-footed booby Sula nebouxii foot colour during courtship was less attractive in senescent than in middle-aged males. In addition, we increased reactive oxygen species experimentally by immunizing males with lipopolysaccharide, a bacterial cell wall component that induces marked oxidative stress in animals. The immune system activation induced greater lipid peroxidation and invoked changes on colour expression (less attractive), particularly in senescent males. These results support the idea that oxidative stress affects reproductive senescence, and suggest that oxidative damage might be a proximal mechanism underlying age-reproductive patterns in long-lived animals.     

Sexual coloration and sperm performance in the Australian painted dragon lizard,Ctenophorus pictus

Theory predicts trade‐offs between pre‐ and post‐copulatory sexually selected traits. This relationship may be mediated by the degree to which males are able to monopolize access to females, as this will place an upper limit on the strength of post‐copulatory selection. Furthermore, traits that aid in mate monopolization may be costly to maintain and may limit investment in post‐copulatory traits, such as sperm performance. Australian painted dragons are polymorphic for the presence or absence of a yellow gular patch (‘bibs’), which may aid them to monopolize access to females. Previous work has shown that there are physiological costs of carrying this bib (greater loss of body condition in the wild). Here, we show that male painted dragons use this bright yellow bib as both an inter‐ and intrasexual signal, and we assess whether this signal is traded off against sperm performance within the same individuals. We found no relationship between aspects of bib colour and sperm swimming velocity or percentage of motile sperm and suggest that the bib polymorphism may be maintained by complex interactions between physiological or life‐history traits including other sperm or ejaculate traits and environmental influences.     

The relationship of egg size and incubation temperature to embryonic development time in univoltine and multivoltine aquatic insects

1. We used published data to investigate the combined influence of egg size and incubation temperature on embryonic development time for a broad assortment of aquatic insects at four different incubation temperatures (10, 15, 20 and 25 °C).
2. Embryonic development time (EDT) was positively correlated with egg size at each of the four temperatures, but with different relationships for univoltine and multivoltine aquatic insects. The relationships of embryonic development time to egg size expressed in degree-days did not significantly differ in slope ( P >0.50) or intercept ( P >0.05) for either univoltine or multivoltine aquatic insects at each of the four temperatures.
3. The relationship of embryonic development time (degree-days) to egg mass in multivoltine aquatic insects (EDT=885×0.19, P <0.0001, r 2=0.48) is similar in slope and intercept to that for other oviparous animals (i.e., zooplankton, fish, amphibians and reptiles), and to the relationship of embryonic development time to neonate mass in mammals. Univoltine species on average require 3–5 times longer to develop (EDT=14190×0.29, P <0.001, r 2=0.29) than most other animals of equivalent egg mass, but the relationship of embryonic development time to egg mass is similar in slope to that of most other animals. Together, these relationships provide a basis for evaluating differences in embryonic development time among aquatic insects.     

Different environments lead to a reversal in the expression of weapons and testes in the heliconia bug,Leptoscelis tricolor (Hemiptera: Coreidae)

In many species, males invest both in weapons used in competitions for access to mates and testes size to increase competitive chances for fertilizations. The expression of weapons and testes can be sensitive to environmental factors experienced during development. However, relatively few studies have examined the effects of discrete, natural developmental environments on the expression of these traits in wild populations. In the present study, we examined the development of these primary and secondary sexual traits for the Heliconia bug, Leptoscelis tricolor (Hemiptera: Coreidae) across two different natural host plants, Heliconia mariae and Heliconia platystachys. Development on H. platystachys resulted in increased investment in weapons and reduced investment in testes, whereas development on H. mariae resulted in the opposite pattern. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●● , ●●–●●.     

Impact of increasing temperatures and exposure duration on egg hatch in the hemlock looper,Lambdina fiscellaria

As the growing season is expected to begin earlier under climate change, insects should initiate reproduction several days or weeks earlier than they used to. In eastern Canada, hemlock looper (HL) Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) females generally oviposit in September, with eggs entering an obligatory diapause quickly after their deposition. We therefore simulated an early start of the HL reproduction cycle of 2, 4, 6, or 8 weeks to examine the extent to which freshly laid eggs from two populations (island and mainland) can withstand exposure to four temperature conditions (15, 20, 25 °C, or fluctuating temperature in an outdoor insectary), with all treatments ending on 1 September 2007. On this date, half the eggs from each population were immediately incubated at 15 °C, while the rest were stored in an outdoor insectary until their incubation at 15 °C the following spring. In a separate experiment, the effect of temperature on pre‐diapause duration was determined from the number of days required for eggs to change colour after oviposition. The pre‐diapause phase was completed faster as temperature increased. Regardless of incubation date and population, percent hatch decreased significantly after 6‐8 weeks of exposure to 25 °C or in the outdoor insectary. Under most treatments, the odds of dying as pharate larvae increased with exposure duration. When eggs were incubated at 15 °C immediately after treatment, time to hatch and diapause duration remained constant over treatments, except at 25 °C when they both decreased. After 8 weeks of exposure to 15 or 20 °C, eggs transferred outdoors were more likely to hatch precociously than those exposed to 25 °C or insectary conditions. Globally, mortality seemed greater among eggs stored outdoors than among those kept indoors. Most eggs that survived the winter hatched synchronously after incubation in spring. Overall, larger eggs from the island population survived better than smaller eggs from the mainland population.     

The effect of size and sex ratio experiences on reproductive competition in Nicrophorus vespilloides burying beetles in the wild

Male parents face a choice: should they invest more in caring for offspring or in attempting to mate with other females? The most profitable course depends on the intensity of competition for mates, which is likely to vary with the population sex ratio. However, the balance of pay‐offs may vary among individual males depending on their competitive prowess or attractiveness. We tested the prediction that sex ratio and size of the resource holding male provide cues regarding the level of mating competition prior to breeding and therefore influence the duration of a male's biparental caring in association with a female. Male burying beetles, Nicrophorus vespilloides were reared, post‐eclosion, in groups that differed in sex ratio. Experimental males were subsequently translocated to the wild, provided with a breeding resource (carcass) and filmed. We found no evidence that sex ratio cues prior to breeding affected future parental care behaviour but males that experienced male‐biased sex ratios took longer to attract wild mating partners. Smaller males attracted a higher proportion of females than did larger males, securing significantly more monogamous breeding associations as a result. Smaller males thus avoided competitive male–male encounters more often than larger males. This has potential benefits for their female partners who avoid both intrasexual competition and direct costs of higher mating frequency associated with competing males.     

On the heritability of blue‐green eggshell coloration

Abstract Avian blue‐green eggshell coloration has been proposed as a female signal of genetic or phenotypic quality to males. However, little is known about the relative importance of additive genetic and environmental effects as sources of eggshell colour variation in natural populations. Using 5 years of data and animal models, we explored these effects in a free‐living population of pied flycatchers. Permanent environmental and year effects were negligible, although year environmental variance (V_Year) was significant for all but one of the traits. However, we found high–moderate narrow‐sense heritabilities for some colour parameters. Within‐clutch colour variability showed the highest coefficient of additive genetic variation (i.e. evolvability). Previous evidence suggests that eggshell colour is sexually selected in this species, males enhancing parental effort in clutches with higher colour variability and peak values. Eggshell colour could be driven by good‐genes selection in pied flycatchers although further genetic studies should confirm this possibility.