Environmental factors shape cloacal bacterial assemblages in great tit Parus major and blue tit P. caeruleus nestlings

Despite their potential ecological and evolutionary importance, factors shaping the composition of bacterial communities in wild vertebrate populations remain poorly understood. The goal of this study was to examine the relative contributions of environmental factors and genetic factors (e.g. species and common origin) to the variation of cloacal bacterial assemblages in wild bird nestlings. We conducted a partial cross-fostering experiment with two passerine species, the great tit Parus major and the blue tit P. caeruleus, sharing similar habitats and breeding biology. Nestlings of the two species were exchanged four days after hatching and cloacal bacteria were sampled nine days later. The structure of cloacal bacterial communities was determined by Ribosomal Intergenic Spacer Analysis. Our results showed that each nestling displayed a unique bacterial community. Furthermore, nestlings raised in the same nest shared significantly similar bacterial communities. The similarity of bacterial community was higher among heterospecific siblings raised within the same nest than between biological siblings raised in separate nests. Effects of common origin between species could not be detected and, if present, were dominated by nest-based short-term environmental effects. Our results show that growth conditions within nests and individually based endogenous factors have significant effects on cloacal bacteria assemblages and could affect post-fledging condition.     

Inheritance and variation in eggshell patterning in the great tit Parus major

The inheritance of patterns on avian eggshells is central to understanding the evolution of traits such as egg mimicry (e.g. in cuckoos). Yet little is known about the inheritance, or indeed function, of eggshell patterns. It has long been believed that the evolution of eggshell pattern mimicry required that patterns be determined by genes situated on the female-specific W chromosome. However, it has never been demonstrated for any bird that egg pattern traits (rather than ground colour) are female sex linked, or indeed that they are inherited. We studied the inheritance of three measures of egg-pigment patterns in a wild great tit population. Egg patterns were female specific but unrelated to female attributes such as age or condition and showed only weak environmental effects. Eggs of daughters resembled those of both their mothers and maternal grandmothers, but not of their paternal grandmothers. We conclude that this is the first demonstration of female sex-linked inheritance of avian eggshell patterning, so raising the probability that such a system operates in egg mimics and their hosts.     

Evolution and genetic structure of the great tit (Parus major) complex

The great tit complex is divided into four groups, each containing several subspecies. Even though the groups are known to differ markedly on morphological, vocal and behavioural characters, some hybridization occurs in the regions where they meet. The great tit has often been referred to as an example of a ring species, although this has later been questioned. Here, we have studied the genetic structure and phylogenetic relationships of the subspecies groups to clarify the evolutionary history of the complex using control region sequences of the mitochondrial DNA. The subspecies groups were found to be monophyletic and clearly distinct in mitochondrial haplotypes, and therefore must have had long-independent evolutionary histories. This conflicts with the ring species assignment and supports the formation of secondary contact zones of previously temporarily isolated groups. According to the phylogenetic species concept, all the subspecies groups could be considered as separate species, but if the definition of the biological species concept is followed, none of the subspecies groups is a true species because hybridization still occurs.     

Realized heritability of personalities in the great tit (Parus major)

Behaviour under conditions of mild stress shows consistent patterns in all vertebrates: exploratory behaviour, boldness, aggressiveness covary in the same way. The existence of highly consistent individual variation in these behavioural strategies, also referred to as personalities or coping styles, allows us to measure the behaviour under standardized conditions on birds bred in captivity, link the standardized measurements to the behaviour under natural conditions and measure natural selection in the field. We have bred the great tit (Parus major), a classical model species for the study of behaviour under natural conditions, in captivity. Here, we report a realized heritability of 54 +/- 5% for early exploratory behaviour, based on four generations of bi-directional artificial selection. In addition to this, we measured hand-reared juveniles and their wild-caught parents in the laboratory. The heritability found in the mid-offspring-mid-parent regression was significantly different from zero. We have thus established the presence of considerable amounts of genetic variation for personality types in a wild bird.     

Low variability and absence of phenotypic correlates of Clock gene variation in a great tit Parus major population

Studies of a range of taxa, including birds, have revealed latitudinal clines in allele length at the conserved Clock locus, a gene with known influences on behaviour and physiology. Such clines might reflect adaptation to seasonal variation, a suggestion supported by a recent within‐population analysis of blue tits Cyanistes caeruleus, which found associations between Clock genotype and timing of breeding in females. To test the generality of this pattern, we sequenced the polymorphic poly‐Q locus of the Clock gene in 521 female great tits Parus major, which were selected based on possession of extreme breeding phenotypes. In total, we identified five alleles with one allele accounting for 96% of allelic diversity in the sample set. Overall variability at the poly‐Q locus was very low, and the spatial distribution of Clock alleles across Wytham was highly homogenous. Our data further provide no evidence for a connection between Clock genotype and reproductive timing phenotype in female great tits; further, we found no effect of Clock genotype on reproductive success. Hence, these results are in contrast to the pattern found for the sympatric blue tit population inhabiting the same woodlands, suggesting that phenotypic effects of Clock are not general in passerine birds.     

Speckled eggs: water-loss and incubation behaviour in the great tit Parus major

Many small passerine birds worldwide lay white eggs speckled with red, brown and black protoporphyrin pigment spots (maculation). Unlike some patterns of avian eggshell pigmentation which clearly serve a crypsis or signalling function, the ubiquity of maculation among passerines suggests that its origins lie in another function, not specific to any particular ecological or behavioural group. Elsewhere, we have presented evidence that protoporphyrin pigments serve a structural function related to eggshell thickness and calcium availability: eggshell maculation in the great tit Parus major increases with decreasing soil calcium levels, pigments demarcate thinner areas of shell, and both the pigment intensity and distribution are related to shell thickness. Here we show that maculation also affects the rate of water loss from the egg during incubation (≈ Mass Loss per Day or MLD, which is critical to egg viability), but not that of unincubated eggs. We also demonstrate, both by observation and experiment, that the effect of female incubation behaviour on MLD compensates in some way for variation in egg characteristics, and that differences between females in the degree of such compensation are related to differences in clutch maculation. Our results suggest that, while a principal function of maculation in this species may be to strengthen the eggshell, it may also reduce eggshell permeability when large amounts of pigment are used, and that this necessitates a behavioural adjustment from the female during incubation. We discuss these findings and make further testable predictions from our model.     

Seasonal and lifetime reproductive consequences of inbreeding in the great tit Parus major

Inbreeding depression has been hypothesized to drive the evolutionof mating systems and dispersal. Some studies have shown thatinbreeding strongly affects survival and/or fecundity, but otherstudies suggest that fitness consequences of inbreeding areless detrimental or more complex. We studied consequences ofmating with a relative in a population of great tits (Parusmajor) with a high local recruitment rate. Genotypic informationfrom microsatellite markers was used to calculate coefficientsof kinship, and fitness was measured as seasonal and lifetimereproductive success. We show that mating with a relative affectsseasonal reproductive success, as was found in other studiesof the same species. However, these effects do not result ina lifetime fitness reduction, suggesting that individuals mayhave scope for avoidance of inbreeding after inbreeding depression.Several explanations are proposed as compensatory mechanisms.Although individuals are more likely to divorce after experiencinginbreeding depression, we show that divorce alone cannot explainthe compensation for inbreeding depression in subsequent breedingattempts in our study. We conclude that the costs of matingwith a relative in the short term do not necessarily imply lifetimefitness consequences.     

Offspring sex ratio is related to male body size in the great tit (Parus major)

Sex allocation theory predicts that the allocation of resourcesto male and female function should depend on potential fitnessgain realized through investment in either sex. In the greattit (Parus major), a monogamous passerine bird, male resourceholdingpotential (RHP) and fertilization success both depend on malebody size (e.g., tarsus length) and plumage traits (e.g., breaststripe size). It is predicted that the proportion of sons ina brood should increase both with male body size and plumage traits,assuming that these traits show a father—offspring correlation. Thiswas confirmed in our study: the proportion of sons in the brood increasedsignificantly with male tarsus length and also, though not significantly,with the size of the breast stripe. A sex ratio bias in relationto male tarsus length was already present in the eggs because(1) the bias was similar among broods with and without mortalitybefore the nestlings' sex was determined, and (2) the bias remainedsignificant when the proportion of sons in the clutch was conservativelyestimated, assuming that differential mortality before sex determinationcaused the bias. The bias was still present among recruits.The assumption of a father—offspring correlation was confirmedfor tarsus length. Given that both RHP and fertilization successof male great tits depend on body size, and size of father andoffspring is correlated, the sex ratio bias may be adaptive.     

Paternal leakage of mitochondrial DNA in the great tit (Parus major)

Animal mitochondrial DNA is normally inherited clonally from a mother to all her offspring. Mitochondrial heteroplasmy, the occurrence of more than one mitochondrial haplotype within an individual, can be generated by relatively common somatic mutations within an individual, by heteroplasmy of the oocytes, or by paternal leakage of mitochondria during fertilization of an egg. This biparental inheritance has so far been reported only in mice, mussels, Drosophila, and humans. Here we present evidence that paternal leakage occurs in a bird, the great tit Parus major. The major and minor subspecies groups of the great tit mix in the middle Amur Valley in far-eastern Siberia, where we found a bird that possessed the very distinct haplotypes of the two groups. To our knowledge this is the first report of paternal leakage in birds.     

The great tit (Parus major) – a misclassified ring species

The great tit (Parus major) has been considered to be the most typical example of an avian ring species. The terminal taxa of the ring (major and minor sectors) are supposed to be reproductively isolated in a zone of secondary contact in the middle Amur valley, Siberia. Our study combines molecular markers (cytochrome‐b), bioacoustic analyses and morphological characters to judge the ring species status of the great tit complex. Despite a notable percentage of intermediately coloured birds in the mixed population of middle Amur, a lack of mitochondrial introgression between the major and minor sectors and a small number of true hybrids among voucher specimens from this area suggest at least a partial reproductive barrier between both sectors. In contrast, variation of morphological and especially acoustic characters along the ring‐shaped area and the phylogenetic structure of the P. major group do not match the ring species concept. Bioacoustic and molecular data (cytochrome‐b sequences) reveal two large and closely related subspecies blocks, the sectors major and bokharensis in the Western Palaearctic and central Asia, and the sectors minor and cinereus in the Eastern Palaearctic and South‐east Asia, respectively. The two western sectors diverged only recently (0.5 Mya) and they were separated from the eastern group by Pleistocene events about 1.5 Mya. Songs from allopatric regions of the two subspecies blocks differ distinctly in frequency parameters and element composition. In the area of secondary contact, males of all phenotypes share the same frequency range of song, close to the range of the typical minor song. Hybrids and major males sing mixed repertoires of typical major and minor strophe types as well as mixed strophes. In contrast, phenotypic minor males display only pure minor strophes. Differences in mate choice and mating success based on repertoire size are believed to uphold the reproductive barrier between major and minor birds in the area of sympatry. Taxonomic consequences suggest three separate species in the Parus major complex: Parus major s.s. (including the very closely related bokharensis sector), Parus minor and Parus cinereus. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 153–174.     

Variation in personality and behavioural plasticity across four populations of the great tit Parus major

1. Interest in the evolutionary origin and maintenance of individual behavioural variation and behavioural plasticity has increased in recent years. 2. Consistent individual behavioural differences imply limited behavioural plasticity, but the proximate causes and wider consequences of this potential constraint remain poorly understood. To date, few attempts have been made to explore whether individual variation in behavioural plasticity exists, either within or between populations. 3. We assayed 'exploration behaviour' among wild-caught individual great tits Parus major when exposed to a novel environment room in four populations across Europe. We quantified levels of individual variation within and between populations in average behaviour, and in behavioural plasticity with respect to (i) repeated exposure to the room (test sequence), (ii) the time of year in which the assays were conducted and (iii) the interval between successive tests, all of which indicate habituation to novelty and are therefore of functional significance. 4. Consistent individual differences ('I') in behaviour were present in all populations; repeatability (range: 0.34-0.42) did not vary between populations. Exploration behaviour was also plastic, increasing with test sequence - but less so when the interval between subsequent tests was relatively large - and time of year; populations differed in the magnitude of plasticity with respect to time of year and test interval. Finally, the between-individual variance in exploration behaviour increased significantly from first to repeat tests in all populations. Individuals with high initial scores showed greater increases in exploration score than individuals with low initial scores; individual by environment interaction ('I × E') with respect to test sequence did not vary between populations. 5. Our findings imply that individual variation in both average level of behaviour and behavioural plasticity may generally characterize wild great tit populations and may largely be shaped by mechanisms acting within populations. Experimental approaches are now needed to confirm that individual differences in behavioural plasticity (habituation) - not other hidden biological factors - caused the observed patterns of I × E. Establishing the evolutionary causes and consequences of this variation in habituation to novelty constitutes an exciting future challenge.     

Yolk carotenoids increase fledging success in great tit nestlings

Avian mothers can influence offspring phenotype through the deposition of different compounds into eggs, such as antibodies, hormones and antioxidants. The concentration of carotenoids in yolk is larger than in maternal plasma, suggesting an important role of these compounds for offspring development. Since carotenoids have to be acquired from the diet, they may be available in limiting amounts to the mothers. Here, we investigated the role of egg carotenoids for offspring growth by experimentally increasing the concentration of yolk lutein, the main carotenoid in great tit (Parus major) yolk. We subsequently measured body condition, oxidative stress, immune response, plumage colouration and fledging success. Lutein increased body mass soon after hatching and fledging success, but did not affect tarsus length, oxidative stress, immune response and plumage colouration. The higher content of yolk lutein could have increased body mass by reducing oxidative stress caused by high metabolic rates of rapidly growing embryos or by promoting cell differentiation and proliferation. The positive effect of lutein on fledging success seems to be mediated by its influence on body mass 3 days post-hatch, since these two traits were correlated. The finding that our treatment did not affect traits measured later in the nestling period, except for fledging success, suggests that yolk lutein has short-term effects that are essential to increase survival until fledging. Our study shows the positive effect of yolk lutein on offspring survival in the great tit, and therefore suggests an important role of carotenoid-mediated maternal effects.     

Components of variance underlying fitness in a natural population of the great tit Parus major

Traits that are closely associated with fitness tend to have lower heritabilities (h2) than those that are not. This has been interpreted as evidence that natural selection tends to deplete genetic variation more rapidly for traits more closely associated with fitness (a corollary of Fisher's fundamental theorem), but Price and Schluter (1991) suggested the pattern might be due to higher residual variance in traits more closely related to fitness. The relationship between 10 different traits for females, seven traits for males, and overall fitness (lifetime recruitment) was quantified for great tits (Parus major) studied in their natural environment of Wytham Wood, England, using data collected over 39 years. Heritabilities and the coefficients of additive genetic and residual variance (CVA and CVR, respectively) were estimated using an "animal model." For both males and females, a trait's correlation (r) with fitness was negatively related to its h2 but positively related to its CVR. The CVA was not related to the trait's correlation with fitness in either sex. This is the third study using directly measured fitness in a wild population to show the important role of residual variation in determining the pattern of lower heritabilities for traits more closely related to fitness.     

Egg yolk carotenoids in relation to habitat and reproductive investment in the great tit Parus major

Maternal allocation of antioxidants to egg yolk has been shown to affect early embryonic development and nestling survival. In environments with high levels of anthropogenic pollution, antioxidants (such as carotenoids) are important to protect the body from elevated oxidative stress. Thus, female allocation of antioxidants to yolk may be traded off against self-maintenance. Here we investigate maternal reproductive investment with respect to yolk carotenoid content and composition in relation to subsequent female condition and carotenoid status in urban and rural great tits Parus major. We found no differences between the urban and rural populations in total yolk carotenoids, egg mass, clutch size, hatching success, or female carotenoid status. Interestingly, however, rural eggs contained more zeaxanthin, a more potent antioxidant than lutein, which suggests that rural embryos have better antioxidant protection than urban embryos. Whether rural females actively transfer more zeaxanthin to the yolk or whether it passively reflects differences in dietary access or uptake needs to be further investigated. This highlights the importance of carotenoid identity and composition in future studies of carotenoid physiology, ecology, and signaling.     

Caterpillar abundance in the territory affects the breeding performance of great tit Parus major minor

The effects of caterpillar food supply on the breeding performance of a population of the Japanese great tit Parus major minor were investigated. Since more than 90% of the food items in our study site were caterpillars living on trees, we estimated the food availability using 20 frass traps per hectare. The sampling error of this method was about 10% on average, which was accurate enough to detect differences between territories. Food abundance at laying in each territory affected the timing of egg laying. However, food amount after hatching was correlated with clutch size. No relationship was found between fledgling quality and food availability, probably because the effects of local variation in food abundance could be canceled out by parental effort such as extending the foraging area. There was a significant negative correlation between the length of the nestling period and food availability. We suggest that parent tits decide the timing of fledging at the point where two factors, predation risk before fledging and additional improvement of nestling quality, are balanced. Food availability just after fledging affected the length of post-fledging parental care; it seems that fledglings in “poor” territories would have had difficulty in finding food and hence needed to depend on their parents longer than those in “rich” territories. Received: 10 June 1997 / Accepted: 29 December 1997     

Ultraviolet reflectance of plumage for parent-offspring communication in the great tit (Parus major)

Ultraviolet (UV) reflectance has been implicated in mate selection.Yet, in some bird species the plumage of young varies in UVreflectance already in the nest and long before mate choiceand sexual selection come into play. Most birds molt the juvenilebody plumage before reaching sexual maturity, and thus, someconspicuous traits of the juvenile body plumage may rather haveevolved by natural selection, possibly via predation or parentalpreference. This second hypothesis is largely untested and predictsa differential allocation of food between fledging and totalindependence, which is a time period of 2–3 weeks whereoffspring mortality is also highest. Here, we test the predictionthat parents use the individual variation in UV reflectanceamong fledglings for differential food allocation. We manipulatedUV reflectance of the plumage of fledgling great tits Parusmajor by treating chest and cheek feathers with a lotion thateither did or did not contain UV blockers and then recordedfood allocation by parents in an outdoor design simulating postfledgingconditions. The visible spectrum was minimally affected by thistreatment. Females were found to feed UV-reflecting offspringpreferentially, whereas males had no preference. It is the firstevidence showing that the UV reflectance of the feathers ofyoung birds has a signaling function in parent–offspringcommunication and suggests that the UV traits evolved via parentalpreference.