Evidence for the signaling function of egg color in the pied flycatcher Ficedula hypoleuca

A recent hypothesis proposes that the bright colors, especiallyblue and green, of many avian eggs may function as signals offemale or offspring phenotypic quality or condition to malesin species with biparental care, inducing them to allocate moreeffort to their offspring. The pigment determining blue andgreen egg colors is an antioxidant whose availability for eggshellcoloring may be limited. To test the signaling function on aspecies with blue eggs, the pied flycatcher Ficedula hypoleuca,we measured egg color with a spectrophotometer on the day oflaying and obtained two principal components from their reflectancespectra that together explained 99% of variation and representedshell lightness, and hue and saturation, respectively. We alsomeasured female immunocompetence during the nestling periodthrough the response to phytohemagglutinin as a measure of cell-mediatedimmunity and the response to a tetanus vaccination as a measureof humoral immunity. The total amount of immunoglobulins inblood of females and of nestlings before fledging was also estimated.Mean within-clutch egg darkness was positively associated withboth measures of female immunocompetence, while better femalecondition was associated with colors tending away from intermediateand toward short wavelengths. Ageing female laid lighter eggs.The mean within-brood level of nestling IgY was also associatedwith mean within-clutch egg colors tending away from intermediateand toward short wavelengths. Mean egg darkness decreased linearlyduring the laying sequence, suggesting pigment limitation. Maleswere observed frequently visiting nests during the laying period,allowing them to observe eggs before the start of incubation.These results support the signaling hypothesis for explainingbright colors of avian eggs.     

Trade-offs between sexual advertisement and immune function in the pied flycatcher (Ficedula hypoleuca)

Good genes models of sexual selection assume that sexual advertisement is costly and thus the level of advertisement honestly reveals heritable viability. Recently it has been suggested that an important cost of sexual advertisement might be impairment of the functioning of the immune system. In this field experiment we investigated the possible trade-offs between immune function and sexual advertisement by manipulating both mating effort and activity of immune defence in male pied flycatchers. Mating effort was increased in a non-arbitrary manner by removing females from mated males during nest building. Widowed males sustained higher haematocrit levels than control males and showed higher expression of forehead patch height, suggesting that manipulation succeeded in increasing mating effort. Males that were experimentally forced to increase mating effort had reduced humoral immune responsiveness compared with control males. In addition, experimental activation of immune defence by vaccination with novel antigens reduced the expression of male ornament dimensions. To conclude, our results indicate that causality behind the trade-off between immune function and sexual advertisement may work in both directions: sexual activity suppresses immune function but immune challenge also reduces sexual advertisement.     

Geographical trends in the yolk carotenoid composition of the pied flycatcher (Ficedula hypoleuca)

Carotenoids in the egg yolks of birds are considered to be important antioxidants and immune stimulants during the rapid growth of embryos. Yolk carotenoid composition is strongly affected by the carotenoid composition of the female??s diet at the time of egg formation. Spatial and temporal differences in carotenoid availability may thus be reflected in yolk concentrations. To assess whether yolk carotenoid concentrations or carotenoid profiles show any large-scale geographical trends or differences among habitats, we collected yolk samples from 16 European populations of the pied flycatcher, Ficedula hypoleuca. We found that the concentrations and proportions of lutein and some other xanthophylls in the egg yolks decreased from Central Europe northwards. The most southern population (which is also the one found at the highest altitude) also showed relatively low carotenoid levels. Concentrations of ??-carotene and zeaxanthin did not show any obvious geographical gradients. Egg yolks also contained proportionally more lutein and other xanthophylls in deciduous than in mixed or coniferous habitats. We suggest that latitudinal gradients in lutein and xanthophylls reflect the lower availability of lutein-rich food items in the northern F. hypoleuca populations and in montane southern populations, which start egg-laying earlier relative to tree phenology than the Central European populations. Similarly, among-habitat variation is likely to reflect the better availability of lutein-rich food in deciduous forests. Our study is the first to indicate that the concentration and profile of yolk carotenoids may show large-scale spatial variation among populations in different parts of the species?? geographical range. Further studies are needed to test the fitness effects of this geographical variation.     

Environmental and genetic variation in the haematocrit of fledgling pied flycatchers Ficedula hypoleuca

We exposed females of a highly placentotrophic viviparous scincid lizard (Pseudemoia pagenstecheri) to various environmental factors during pregnancy, and quantified the effects of these treatments on their offspring. The clear result was that the phenotypes of neonatal lizards can be substantially modified by the environment that their mother experiences during gestation. Restricting prey availability to the females reduced the size of their offspring. Limiting the females' basking opportunities delayed their seasonal timing of parturition, and modified body proportions (tail length relative to snout-vent length) of the neonates. More surprisingly, female lizards that were regularly exposed to the scent of sympatric lizard-eating snakes gave birth to offspring that were heavier, had unusually long tails relative to body length, and were highly sensitive to the odour of those snakes (as measured by tongue-flick responses). The neonates' antipredator responses were also modified by the experimental treatment to which their mother was exposed. The modifications in body mass, tail length and response to snake scent plausibly reduce the offspring's vulnerability to predatory snakes, and hence may constitute adaptive maternal manipulations of the neonatal phenotype. Received: 6 July 1998 / Accepted: 5 December 1998     

Early maternal, genetic and environmental components of antioxidant protection, morphology and immunity of yellow-legged gull (Larus michahellis) chicks

Maternal effects mediated by egg quality are important sources of offspring phenotypic variation and can influence the course of evolutionary processes. Mothers allocate to the eggs diverse antioxidants that protect the embryo from oxidative stress. In the yellow-legged gull (Larus michahellis), yolk antioxidant capacity varied markedly among clutches and declined considerably with egg laying date. Analysis of bioptic yolk samples from clutches that were subsequently partially cross-fostered revealed a positive effect of yolk antioxidant capacity on embryonic development and chick growth, but not on immunity and begging behaviour, while controlling for parentage and common environment effects. Chick plasma antioxidant capacity varied according to rearing environment, after statistically partitioning out maternal influences mediated by egg quality. Thus, the results of this study indicate that egg antioxidants are important mediators of maternal effects also in wild bird populations, especially during the critical early post-hatching phase.     

Natal dispersal based on past and present environmental phenology in the pied flycatcher (Ficedula hypoleuca)

Natal dispersal allows individuals to reach suitable breeding sites. The effect of present plant phenology as a cue for dispersal into areas with favourable stages of development has been well established across avian and mammalian taxa. However, the effect of past experience is less understood. We studied the effect of past and present phenology of the environment on the direction and distance of natal dispersal in a passerine bird, the pied flycatcher (Ficedula hypoleuca). We monitored spring settlement of local recruits in six nest box plots along a 10-km stretch of a south-north gradient of plant and caterpillar food development. We found that males used both past experience of caterpillar phenology from early life and actual plant phenology during the recruitment season as independent cues for breeding settlement. Males that had experienced a mismatch with the caterpillar food peak as a nestling, and/or those that arrived late in the spring in the recruitment year, moved north of their natal site, whereas males that had experienced a better match with the caterpillars as a nestling, and/or those that migrated earlier in the spring, settled at a similar site or more to the south. In females, no such effects were found, suggesting that the usage of phenological cues is sex specific. In summary, tracking environmental phenology by natal dispersal may represent an effective mechanism for settling in new favourable areas, and may thus potentially cause rapid change of a species’ geographical breeding range in response to climate change.     

Sex-specific effects of maternal immunization on yolk antibody transfer and offspring performance in zebra finches

Trans-generational antibody transfer constitutes an important mechanism by which mothers may enhance offspring resistance to pathogens. Thus, differential antibody deposition may potentially allow a female to differentiate offspring performance. Here, we examined whether maternal immunization with sheep red blood cells (SRBC) prior to egg laying affects sex-specific yolk antibody transfer and sex-specific offspring performance in zebra finches (Taeniopygia guttata). We showed that immunized mothers deposit anti-SRBC antibodies into the eggs depending on embryo sex and laying order, and that maternal exposure to SRBC positively affects the body size of female, but not male offspring. This is the first study reporting sex-specific consequences of maternal immunization on offspring performance, and suggests that antibody transfer may constitute an adaptive mechanism of maternal favouritism.     

Geographic patterns of genetic differentiation and plumage colour variation are different in the pied flycatcher (Ficedula hypoleuca)

The pied flycatcher is one of the most phenotypically variable bird species in Europe. The geographic variation in phenotypes has often been attributed to spatial variation in selection regimes that is associated with the presence or absence of the congeneric collared flycatcher. Spatial variation in phenotypes could however also be generated by spatially restricted gene flow and genetic drift. We examined the genetic population structure of pied flycatchers across the breeding range and applied the phenotypic Q _ST ( P _ST)– F _ST approach to detect indirect signals of divergent selection on dorsal plumage colouration in pied flycatcher males. Allelic frequencies at neutral markers were found to significantly differ among populations breeding in central and southern Europe whereas northerly breeding pied flycatchers were found to be one apparently panmictic group of individuals. Pairwise differences between phenotypic ( P _ST) and neutral genetic distances ( F _ST) were positively correlated after removing the most differentiated Spanish and Swiss populations from the analysis, suggesting that genetic drift may have contributed to the observed phenotypic differentiation in some parts of the pied flycatcher breeding range. Differentiation in dorsal plumage colouration however greatly exceeded that observed at neutral genetic markers, which indicates that the observed pattern of phenotypic differentiation is unlikely to be solely maintained by restricted gene flow and genetic drift.     

Heritability estimates and maternal effects on tarsus length in pied flycatchers,Ficedula hypoleuca

Tarsus length has previously been shown to have an additive genetic component in some pied flycatcher populations. In addition to estimation of additive genetic variation by means of repeatability analyses at various ontogenetic stages and degrees of genetic resemblance, we explore in this paper variation among parent-offspring regressions between sexes and years, as well as the influence of hatching date, ectoparasite abundance, egg volume, and male and female condition on the tarsus length of their offspring. Mother-offspring regressions gave heritability estimates consistently higher than father-offspring regressions, although variation among years was large and both types of estimates yielded lower heritability values than those estimated by means of full-sib resemblance. This indicates that common environmental effects were inflating heritability estimates. There existed maternal effects via egg size, larger eggs fledging chicks with larger tarsi. Mean tarsus length of broods decreased with hatching date and, independently, with high loads of ectoparasitic, blood-feeding mites (Acari). The maternal effect via egg size persisted into the adulthood, and confounded the interpretation of differences between heritability slopes. We address the method of examining differences in parent-offspring regressions as a shorthand for estimating extra-pair copulation (EPC) rates. In our population, this method would give an EPC rate of 0–59%, depending on whether the analysis is performed with fledglings recruited to the breeding population or with offspring at the nest.     

Seventy new microsatellites for the pied flycatcher, Ficedula hypoleuca and amplification in other passerine birds

The pied flycatcher (Ficedula hypoleuca) is a small migratory passerine bird commonly distributed across Europe which has been the focus of considerable ecological and evolutionary research. Here, we present details of 70 microsatellite markers for the species adding to the six which are currently available. Sixty-six markers were also polymorphic in the closely related collared flycatcher (Ficedula albicollis), while 54 were polymorphic in another related passerine, the bluethroat (Luscinia svecica), and 12 were polymorphic in the more distantly related Siberian jay (Perisoreus infaustus).     

Candidate genes for colour and vision exhibit signals of selection across the pied flycatcher (Ficedula hypoleuca) breeding range

The role of natural selection in shaping adaptive trait differentiation in natural populations has long been recognized. Determining its molecular basis, however, remains a challenge. Here, we search for signals of selection in candidate genes for colour and its perception in a passerine bird. Pied flycatcher plumage varies geographically in both its structural and pigment-based properties. Both characteristics appear to be shaped by selection. A single-locus outlier test revealed 2 of 14 loci to show significantly elevated signals of divergence. The first of these, the follistatin gene, is expressed in the developing feather bud and is found in pathways with genes that determine the structure of feathers and may thus be important in generating variation in structural colouration. The second is a gene potentially underlying the ability to detect this variation: SWS1 opsin. These two loci were most differentiated in two Spanish pied flycatcher populations, which are also among the populations that have the highest UV reflectance. The follistatin and SWS1 opsin genes thus provide strong candidates for future investigations on the molecular basis of adaptively significant traits and their co-evolution.     

Incubation temperature affects multiple measures of immunocompetence in young wood ducks (Aix Sponsa)

Parental effects play a vital role in shaping offspring phenotype. In birds, incubation behaviour is a critical parental effect because it influences the early developmental environment and can therefore have lifelong consequences for offspring phenotype. Recent studies that manipulated incubation temperature found effects on hatchling body composition, condition and growth, suggesting that incubation temperature could also affect energetically costly physiological processes of young birds that are important to survival (e.g. immune responses). We artificially incubated wood duck (Aix sponsa) eggs at three biologically relevant temperatures. Following incubation, we used two immunoassays to measure acquired immune responses of ducklings. Ducklings incubated at the lowest temperature had reduced growth, body condition and responses to both of our immune challenges, compared with those from the higher temperatures. Our results show that incubation temperatures can be an important driver of phenotypic variation in avian populations.     

Pre-laying nutrition mediates maternal effects on offspring immune capacity and growth in the pied flycatcher

We have aimed at detecting prelaying maternal effects on nestling antibody defences and growth through experimental food supplementation of female pied flycatchers Ficedula hypoleuca and subsequent exchange of whole clutches with control nests. The levels of immunoglobulins and the mass and size of chicks at 12 days of age were ascertained. This is the first study controlling for maternal incubation effects by exchanging eggs rather than nestlings. Our prediction is that the females' availability of pre-laying nutritional resources affects offspring immune capacity and growth through maternal effects in the eggs when conditions during incubation and rearing are controlled for. Nestling immunoglobulin Y (IgY) levels and tarsus length were indeed positively associated with maternal food supplementation at laying. The only rearing environmental effect detected was that of mite infestation which affected both IgY levels and growth of nestlings. Nestlings that recruited to the population in the subsequent 2 years had higher IgY levels than those that did not. Maternal adaptations for allocating resources to eggs play an important role in moulding offspring phenotypes and may affect their survival prospects.     

Variation of lymphoid activity in the spleen of a migratory bird,the pied flycatcher (Ficedula hypoleuca; Aves,passeriformes)

The size and microscopic structure of the spleen of the migratory pied flycatcher (Ficedula hypoleuca) show marked changes during the reproductive cycle. Upon the spring return to their northern breeding sites, the birds have a small spleen with little lymphoid activity and a poorly developed red pulp. During the breeding period the volume of red and white pulp increases, the number and distinctness of lymphoid follicles (germinal centres) in the white pulp increase, and groups of cells with intensely basophilic cytoplasm, probably B cells (plasma cells), appear. The findings suggest that the immune system of the adult pied flycatcher is activated during periods when it is bound to the nest. Young flycatchers beginning their autumn migration also show a marked increase of lymphoid activity in the spleen.     

Development of the auditory sensitivity and formation of the acoustically guided defensive behavior in nestlings of the pied flycatcher Ficedula hypoleuca

Age dynamics of generation of the evoked potentials (EP) in the field L of caudal nidopallium (the higher integrative center of the avian auditory system) and development of the auditory-guided defensive behavior were studied in control and visually deprived pied flycatcher Ficedula hypoleuca nestlings. It was shown that the rhythmically organized monofrequency signals with sound frequency 3.5 kHz and higher produced the defensive behavior as the auditory sensitivity to these frequencies matured. After 9 days, the species-specific alarm signal produced more effectively the defensive behavior than the tonal signals. The rhythmically organized sound with filling frequency 0.5 kHz, occupying the less low-frequency diapason than the feeding signal, produced the effect opposite to the alarm signal to increase the nestling mobility. At the initial stage of the defensive behavior development the auditory threshold fell markedly in the frequency diapason corresponding to the frequency diapason of the alarm signal (5–6 kHz), which seemed to facilitate involvement of this diapason signals in the defensive integration. The auditory EP generation thresholds in the whole studied diapason were lower in the visually deprived nestlings than in the normally developing one; however, the ability of the acoustic signals to suppress alimentary reactions fell significantly.     

An analysis of pre- and post-hatching maternal effects mediated by carotenoids in the blue tit

Maternal effects increase phenotypic plasticity in offspring traits and may therefore facilitate adaptation to environmental variability. Carotenoids have been hypothesized to mediate costs of reproduction in females as well as maternal effects. However, assessing potential transgenerational and population consequences of environmental availability of carotenoids requires a better understanding of mechanisms of maternal effects mediated by these antioxidant pigments. Manipulating dietary availability of carotenoids to egg-laying female blue tits and subsequently cross-fostering nestlings between female treatments allowed us to specifically investigate the relative importance of maternal effects through egg carotenoids and through post-hatching care mediated by antioxidants in females. Nestling body size and mass and plasma antioxidants were not significantly affected by pre- or post-hatching maternal effects mediated by antioxidants, although both types of maternal effects in interaction explained the variation in growth, as measured by wing length. Development of the ability to mount a cell-mediated immune response as well as its temporal dynamics was influenced by both pre- and post-hatching maternal effects, with an advantage to nestlings originating from, or reared by, carotenoid-supplemented females. In addition, nestlings reared by carotenoid-fed females had a lower blood sedimentation rate, indicating that they may have been less infected than nestlings from controls. Finally, prehatching maternal effects in interaction with nestling plasma carotenoid levels affected the development of carotenoid-based plumage. Maternal effects mediated by carotenoids may thus act as a proximate factor in development and phenotypic plasticity in traits associated with nestling fitness, such as immune response and ability to metabolize and use antioxidants, and ultimately participate in the evolution of phenotypic traits.     

Individual color variation and male quality in pied flycatchers (Ficedula hypoleuca): a role of ultraviolet reflectance

Bright coloration of males in many animal species has inspiredresearchers for more than a century. In this field study, weinvestigated whether color variation between individuals isrelated to individual quality in pied flycatcher (Ficedulahypoleuca) males in terms of arrival time at the breeding sites.In addition to traditional visual color scoring, plumage color was measured using spectroradiometric measurements between 320and 700 nm. This range includes the near-ultraviolet wavebandfrom 320 to 400 nm. Males that arrived earlier at breedingsites had higher proportional UV reflectance in the crown andmantle. The proportional UV reflectance in the crown and mantlewas not related to traditionally scored general brownness inmales. However, adult males had a higher proportion of ultravioletin the plumage than yearling males or females. These resultssuggest that in pied flycatcher males, the UV reflectance ofplumage may be positively correlated with individual quality.     

Access to multiple mates increases fecundity but does not affect per‐offspring maternal investment in a marine gastropod

Females of many organisms mate more than once and with more than one male, suggesting that polyandry confers some advantage to the female or her offspring. However, variation in maternal investment in response to mate choice and mate number can confound efforts to determine if there are benefits of polyandry. Access to multiple mates could increase maternal investment in offspring via a number of different mechanisms. Few studies have determined if investment is influenced by mate choice and number, and data are particularly lacking for marine invertebrates. This study was designed to determine if maternal investment and offspring size increase with access to increasing numbers of mates in the protandrous intertidal slipper snail Crepidula cf. marginalis. Virgin female slipper limpets were exposed to one, three, or five potential mates and their fecundity, egg size, and hatchling size were measured for multiple clutches. Treatment had a significant effect on fecundity, with fecundity increasing with the number of potential mates. Treatment did not have an effect on the size of eggs or hatchlings, on the variation in egg size or hatchling size within broods, or on the frequency of oviposition. Treatment did alter the variation in average offspring size among females, but not in the way predicted by theory. The main result, that access to multiple mates does not have an effect on per offspring maternal investment, makes C. cf. marginalis an ideal candidate to study the effects of polyandry on offspring fitness without having to take into account confounding effects of variation in maternal investment.