Population Of Zebra Finches Research Articles

Patterns of conspecific brood parasitism in zebra finches

Conspecific brood parasitism (CBP) brings the obvious fitness advantage of decreased breeding costs. However, the successful development of parasitic eggs depends on appropriate timing in relation to the host's own eggs. A detailed documentation of CBP requires full knowledge of parentage. We achieved this in a captive population of zebra finches, Taeniopygia guttata, breeding in aviaries. The overall frequency of CBP was relatively high (21% of all host clutches, 5.4% of all eggs in host clutches) and comparable to what has been found in the wild in this species. A large proportion of paired females adopted a mixed strategy, laying one or two additional eggs in other nests before initiating their own clutches. Females showed a high individual consistency in whether they adopted a pure nonparasitic strategy or a mixed strategy, which is indicative of individual specialization. About 38% of all eggs laid outside a pair's own nest were incubated by host pairs and can thus be considered successfully parasitic. No paired females were purely parasitic but unpaired females used CBP as a best of a bad job strategy. Hosts were targeted during the early phase of clutch initiation with the majority of parasitic eggs laid 0-5 days before the onset of incubation and usually before the host commenced egg laying. We did not find evidence that particular types of host females were targeted. The within-female repeatability of being a host was estimated to be negative. Overall, the systematic temporal patterns indicate targeted CBP behaviour in zebra finches.

On the use of large marker panels to estimate inbreeding and relatedness: empirical and simulation studies of a pedigreed zebra finch population typed at 771 SNPs

In recent years there has been a dramatic increase in the availability of high density genetic marker data for both model and non-model organisms. A potential application of these data is to infer relatedness in the absence of a complete pedigree. Using a marker panel of 771 SNPs genotyped in three generations of an extensive zebra finch pedigree, correlations between pedigree relatedness and seven marker-based estimates of relatedness were examined, as was the relationship between heterozygosity and inbreeding. Although marker-based and pedigree relatedness were highly correlated, the variance in estimated relatedness was high. Further, the correlation between heterozygosity and inbreeding was weak, even though mean inbreeding coefficient is typical of that seen in wild vertebrate pedigrees; the weak relationship was in part due to the small variance in inbreeding in the pedigree. Our data suggest that using marker information to reconstruct the pedigree, and then calculating relatedness from the pedigree, is likely to give more accurate relatedness estimates than using marker-based estimators directly.

Low level of extrapair parentage in wild zebra finches

The captive zebra finch, Taeniopygia guttata, has become one of the key vertebrate model systems for studying a range of behavioural, physiological and neurological phenomena. In particular, this species has played a key role in developing our understanding of sexual selection and sperm competition. In contrast with the large number of studies using domesticated zebra finches, relatively few studies have focused on free-living populations of wild zebra finches. Investigating the incidence of extrapair paternity in zebra finches in the Australian desert, we found a very low level; 1.7% of 316 offspring from four of 80 broods fathered outside the pair bond. These numbers contrast with the high levels of extrapair paternity observed in domesticated aviary populations, and suggest a low level of sperm competition and sexual selection in natural populations. Our finding of such a low rate of extrapair paternity in the wild zebra finch suggests that it is one of the most genetically monogamous of all passerine species and that has important implications for future studies of this model organism in studies of sexual selection and reproductive biology. In addition, we found that 5.4% of 316 offspring were not related to either putative parent and hatched from eggs that had been dumped by intraspecific brood parasites.

Nucleotide Variation, Linkage Disequilibrium and Founder-Facilitated Speciation in Wild Populations of the Zebra Finch (Taeniopygia guttata)

The zebra finch has long been an important model system for the study of vocal learning, vocal production, and behavior. With the imminent sequencing of its genome, the zebra finch is now poised to become a model system for population genetics. Using a panel of 30 noncoding loci, we characterized patterns of polymorphism and divergence among wild zebra finch populations. Continental Australian populations displayed little population structure, exceptionally high levels of nucleotide diversity (pi = 0.010), a rapid decay of linkage disequilibrium (LD), and a high population recombination rate (rho approximately 0.05), all of which suggest an open and fluid genomic background that could facilitate adaptive variation. By contrast, substantial divergence between the Australian and Lesser Sunda Island populations (K(ST) = 0.193), reduced genetic diversity (pi = 0.002), and higher levels of LD in the island population suggest a strong but relatively recent founder event, which may have contributed to speciation between these populations as envisioned under founder-effect speciation models. Consistent with this hypothesis, we find that under a simple quantitative genetic model both drift and selection could have contributed to the observed divergence in six quantitative traits. In both Australian and Lesser Sundas populations, diversity in Z-linked loci was significantly lower than in autosomal loci. Our analysis provides a quantitative framework for studying the role of selection and drift in shaping patterns of molecular evolution in the zebra finch genome.

Use of nest-boxes by the Zebra Finch (Taeniopygia guttata): implications for reproductive success and research

Nest-boxes have been used widely and for many decades in Europe and North America to increase avian reproductive success in species management and conservation programs and to increase the amenability and efficiency with which a species can be studied. Here we describe the establishment of a breeding population of Zebra Finches using nest- boxes in semi-arid, far-western New South Wales, over three breeding seasons (2005–07). The nest-boxes were used readily by Zebra Finches, with a total of 572 breeding attempts recorded in this study. After the introduction of nest-boxes, nearly all breeding attempts were made in these artificial cavities. Zebra Finches breeding in natural nests are prone to high levels of nest predation (>60% in previous studies), but such predation was almost completely eliminated with nest-boxes, with <2% of nests being depredated. Not surprisingly, the reproductive success of pairs breeding in nest-boxes (58% of nests successfully fledged at least one young) was significantly higher than in the natural nests monitored at the same sites in a previous year, and by comparison with previous studies of the same species in other localities across Australia. Our study of the Zebra Finch, a laboratory model used throughout the world, shows the effectiveness of artificial nest-boxes at decreasing levels of predation in the wild and increasing the capacity for research.

Sexual imprinting on continuous variation: do female zebra finches prefer or avoid unfamiliar sons of their foster parents?

Sexual imprinting on discrete variation that serves the identification of species, morphs or sexes is well documented. By contrast, sexual imprinting on continuous variation leading to individual differences in mating preferences within a single species, morph and sex has been studied only once (in humans). We measured female preferences in a captive population of wild-type zebra finches. Individual cross-fostering ensured that all subjects grew up with unrelated foster parents and nest mates. Females from two cohorts (N = 113) were given a simultaneous choice between (two or four) unfamiliar males, one of which was a genetic son of their foster parents (SFP). We found no significant overall preference for the SFP (combined effect size d = 0.14 +/- 0.15). Additionally, we tested if foster parent traits could potentially explain between-female variation in preferences. However, neither the effectiveness of cooperation between the parents nor male contribution to parental care affected female preferences for the son of the foster father. We conclude that at least in zebra finches sexual imprinting is not a major source of between-individual variation in mating preferences.

Physiological, morphological and behavioural effects of selecting zebra finches for divergent levels of corticosterone

The effects of environmental stress on the physiology and behaviour of higher vertebrates has become an important avenue of research in recent years. Evidence from recent studies has suggested that the avian stress-related hormone corticosterone (CORT) may play a role in immunocompetence and sexual selection. We tested whether CORT is immunosuppressive by studying humoral and cell-mediated immune responses in populations of captive zebra finches selected for divergent peak levels of CORT. We also investigated whether selection for peak CORT has an effect on the quality of several sexually selected regions of the male zebra finch; in addition we compared morphometric parameters and the dominance ranking in males from the different selection lines. We also tested whether different components of the immune system compete for limited resources. We found that selection for divergent levels of peak CORT had little effect on humoral immunity, male sexual signal quality or dominance ranking. However, contrary to expectations, we did find a positive relationship between CORT titre and cell-mediated immunity, as well as a greater cell-mediated response in the birds selected for high CORT titre than those selected for low CORT titre. Consistent with predictions, significant negative relationships were found between both testosterone and CORT titre on humoral immunity. Birds from the low CORT lines were significantly larger in terms of skeletal size than those from the high CORT lines. Overall, our results suggest that the cell-mediated immune response is associated with a reduction in the humoral response, but only in males, and that there is no simple relationship between peak CORT levels and immune function.

Developmental stress impairs song complexity but not learning accuracy in non-domesticated zebra finches (Taeniopygia guttata)

Food restrictions early in life can have adverse effects on the development of adult avian song structure. Nutritional deficiencies during brain development are thought to impair the growth of neural circuits responsible for learning and production of song in adulthood. Thus, the quality of song may reflect the quality of the singer due to the costs associated with neural development early in life. Recent investigations have focused on domesticated laboratory strains of zebra finches where early dietary deficiencies have significantly reduced the complexity of song and its sexual attractiveness. Domesticated zebra finches may be more sensitive to the early effects of moderate under-nutrition on song complexity than their non-domesticated counterparts. In an aviary experiment with non-domesticated zebra finch stock, we found that song complexity when measured by a linear combination of six variables was reduced in food-restricted birds, with syllable rate and maximum syllable frequency as the principal variables affected. The restriction had no effect on learning accuracy when song phrases of experimental birds were compared to those of their fathers.This result demonstrates that early nutrition may differentially affect the development of neural processes that influence learning accuracy and song complexity. While the finding of negative effects of dietary restriction on song complexity is robust for zebra finches and is not an artefact of domestication, it does not explain why some nutritionally stressed populations of wild zebra finches have more complex songs than those from other regions of Australia characterised by greater food availability.

Basal metabolic rate: heritability and genetic correlations with morphological traits in the zebra finch

Studies of genetic variation in metabolic traits have so far not focused on birds. In our study population of captive zebra finches we found evidence for a significant heritable genetic component in basal metabolic rate (BMR). Heritability of all morphological traits investigated (body mass, head length, tars length and wing length) was significantly larger than zero. All traits were positively phenotypically correlated. Eight of 10 genetic correlations presented in this study differed significantly from zero, all being positive, suggesting the possibility of correlated responses to any selection acting on the traits. When conditioned on the genetic variance in body mass, the heritability of BMR was reduced from 25% to 4%. Hence, our results indicate that genetic changes in BMR through directional selection are possible, but the potential for adaptation independent of body mass may be limited.

Development of polymorphic microsatellite markers for the zebra finch (Taeniopygia guttata)

AbstractTo study the population genetics as well as the mating system of captive zebra finch (Taeniopygia guttata) populations, we developed primers for 12 microsatellite loci and screened them in 529 individuals from two successive generations of a single captive population. All markers were polymorphic with five to 14 alleles per locus. We checked all markers for Mendelian inheritance in 307 offspring whose parents were known for sure. Four markers showed evidence for the presence of null alleles. Once allowing for null alleles, we found no mismatches between offspring and parents, suggesting a very low rate of mutation. Average observed and expected heterozygosities across the eight loci showing no evidence for null‐alleles was 0.819 and 0.812, respectively.

Simple sequence repeats in zebra finch (Taeniopygia guttata) expressed sequence tags: a new resource for evolutionary genetic studies of passerines

BackgroundPasserines (perching birds) are widely studied across many biological disciplines including ecology, population biology, neurobiology, behavioural ecology and evolutionary biology. However, understanding the molecular basis of relevant traits is hampered by the paucity of passerine genomics tools. Efforts to address this problem are underway, and the zebra finch (Taeniopygia guttata) will be the first passerine to have its genome sequenced. Here we describe a bioinformatic analysis of zebra finch expressed sequence tag (EST) Genbank entries.ResultsA total of 48,862 ESTs were downloaded from GenBank and assembled into contigs, representing an estimated 17,404 unique sequences. The unique sequence set contained 638 simple sequence repeats (SSRs) or microsatellites of length ≥20 bp and purity ≥90% and 144 simple sequence repeats of length ≥30 bp. A chromosomal location for the majority of SSRs was predicted by BLASTing against assembly 2.1 of the chicken genome sequence. The relative exonic location (5' untranslated region, coding region or 3' untranslated region) was predicted for 218 of the SSRs, by BLAST search against the ENSEMBL chicken peptide database. Ten loci were examined for polymorphism in two zebra finch populations and two populations of a distantly related passerine, the house sparrow Passer domesticus. Linkage was confirmed for four loci that were predicted to reside on the passerine homologue of chicken chromosome 7.ConclusionWe show that SSRs are abundant within zebra finch ESTs, and that their genomic location can be predicted from sequence similarity with the assembled chicken genome sequence. We demonstrate that a useful proportion of zebra finch EST-SSRs are likely to be polymorphic, and that they can be used to build a linkage map. Finally, we show that many zebra finch EST-SSRs are likely to be useful in evolutionary genetic studies of other passerines.

Quantitative genetics and behavioural correlates of digit ratio in the zebra finch

A recent study on a captive zebra finch population suggested that variation in digit ratio (i.e. the relative length of the second to the fourth toe) might be an indicator of the action of sex steroids during embryo development, as is widely assumed for human digits. Zebra finch digit ratio was found to vary with offspring sex, laying order of eggs within a clutch, and to predict aspects of female mating behaviour. Hence, it was proposed that the measurement of digit ratio would give insights into how an individual's behaviour is shaped by its maternal environment. Studying 500 individuals of a different zebra finch population I set out to: (1) determine the proximate causes of variation in digit ratio by means of quantitative genetics and (2) to search for phenotypic and genetic correlations between digit ratio, sexual behaviour and aspects of fitness. In contrast to the earlier study, I found no sexual dimorphism in digit ratio and no effect of either laying order or experimentally altered hatching order on digit ratio. Instead, I found that variation in digit ratio was almost entirely additive genetic, with heritability estimates ranging from 71 to 84%. The rearing environment (from egg deposition to independence) explained an additional 5-6% of the variation in digit ratio, but there was no indication of any maternal effects transmitted through the egg. I found highly significant phenotypic correlations (and genetic correlations of similar size) between digit ratio and male song rate (positive correlation) as well as between digit ratio and female hopping activity in a choice chamber (negative correlation). Rather surprisingly, the strength of these correlations differed significantly between subsequent generations of the same population, illustrating how quickly such correlations can appear and disappear probably due to genotype-environment interactions.

Seasonal variation in body mass and fat of Zebra Finches in south-eastern Australia

In order to detect seasonal acclimatisation on body mass and fat reserves, patterns in mean monthly dawn body mass and body fat were investigated in a population of Zebra Finches, Taeniopygia guttata, for 17 months in the extreme south-eastern part of their distribution. Mass and fat were lowest in the cold (non-breeding) months and highest in the warmer (breeding) months, resulting in a maximum annual amplitude in body mass of 8% in males and 14% in females. Both sexes increased in body mass and fat at the onset of the breeding season, but there were no significant sex differences. The pattern of winter ‘slimming’ and summer ‘fattening’ in Zebra Finches stands in striking contrast to that of small, non-migrant, Northern Hemisphere passerines that make substantial mass increases in winter, rather than summer. However, our findings are consistent with studies on laboratory Zebra Finches. Winter mass loss could be an adaptive response to reduce energetic costs, including those of flight, and it could reduce predation risk associated with frequent travelling in search of dispersed winter food. In a multiple regression analysis, day length, minimum ambient temperature and breeding activity were significant predictors of body mass in males, but not in females. Breeding activity was the most significant predictor, but was positively correlated with day length and temperature. Competitive mating may be a factor in regulating increases in male mass during the breeding season, but further investigations are needed.

Sexual selection and extrapair fertilization in a socially monogamous passerine, the zebra finch (Taeniopygia gullata)

We investigated paternal exclusion rate (the percentage of young reared by a male that were not his genetic offspring), and behavioral and reproductive variables influencing this rate, in a freely breeding laboratory population of zebra finches (Tae-niopygia guttala castanotis), a socially monogamous grassfinch. Prior to the experiment, each male founder was fitted with either two red bands (creating a phenotype previously demonstrated to be attractive to females) or two green bands (unattractive to females) as part of a unique combination of four leg bands. The overall paternal exclusion rate was 28%, as determined by multilocus, minisatellite DNA fingerprinting of 278 offspring reared by 26 males and their mates. Mean exclusion rates were 16% and 40% for red- and green-banded males, respectively. Exclusion rates were directly proportional to rates of female participation in unforced extrapair copulations (UEPCs) with red-banded males that occurred when females were fertile. Rates of fertile, forced extrapair copulations (FEPCs) and fertile UEPCs involving green-banded males either failed to influence exclusion rate or varied inversely with exclusion rate, indicating that extrapair fertilization (EPF) is under female control. Effort devoted by males to seeking EPFs increased exclusion rate. Results suggest that males place greater effort into seeking fertile versus infertile EPCs and that unattractive males accrue fitness gains through high parental investment (PI), whereas attractive males benefit through decreased PI and increased allocation to EPF.

Constraints on the Evolution of Attractive Traits: Selection in Male and Female Zebra Finches

We examined natural and sexual selection in a laboratory population of zebra finches (Taeniopygia guttata), with a principal focus on bill color. Previous studies indicated that females prefer males with redder bills, whereas males prefer females with less red bills. For male red bill color, both the selection differential and selection gradient coefficients were significantly positive with fitness (the number of offspring surviving to independence), which was primarily due to differences in the time to the first nest and in reproductive rate but not to differences in survival. In contrast, for female red bill color, there was significant negative selection, which was due to differences in most stages of reproductive and survival selection but not to differences in the time to the first nest. There were no significant correlations between male or female bill color and offspring weight or postfledging survival. All male plumage color traits (breast band, cheek patch, flank patch) showed nonsignificant selection for increase in size due to both the time to the first nest and for reproductive rate but showed selection for decrease in size due to survival. Tarsus length was the only male trait to show significant selection for decrease in size. The opposing selection on red bill color between the sexes indicates that the positive genetic correlation between male and female red bill color may constrain the evolutionary rate of red bill sexual dichromatism.

Survivorship, dispersal and sex ratios of Zebra Finches Taeniopygia guttata in southeast Australia

Membership of three permanent breeding colonies of Zebra Finches Taeniopygia guttata studied in farmland changed continually due to arrival and departure of birds from distant colonies. Sixty‐six percent of adults stayed for less than 1 month, and many that stayed longer disappeared for extended periods. Over 78% of adults captured were hatched in other colonies and only 23% made a breeding attempt in their natal colony. There was no sex‐biased natal dispersal or philopatry, but there were sex differences in the timing of dispersal. Sex ratios at the end of parental care were variable and may depend on food resources. Adult ratios were slightly male‐biased. Annual losses of adults ranged from 72 to 82% across colonies, but mortalities and dispersal were heavily confounded by high adult mobility. The oldest bird was more than 5 years old. A total of 67% of young were lost between fledging and nutritional independence at 35 days of age, and only 20% of fledglings survived to day 80, the age of first breeding. Artificial supplies of seed at baited walk‐in traps prolonged the stay of dispersing adults from other colonies, enhanced the survivorship of young hatched in the colony and possibly affected the secondary sex ratio. In this southeast part of their Australia‐wide distribution, Zebra Finch populations appear to be highly mobile over a very large home range with extensive free interchange of members among a number of permanent breeding colonies. High mobility may be adaptive for exploiting patches of seed and water in a highly erratic environment.

Variation in Song Structure within and among Populations of Australian Zebra Finches

AsTmAcT.-Zebra Finch (Taeniopygia guttata castanotis) songs from 33 colonies in two geographic zones of Australia (central and southeastern) were investigated in order to describe variation from macrogeographic to microgeographic levels. Canonical discrimination classified songs according to 31 measurements of the song phrase and clearly distinguished those from the two zones. Songs from regions within the southeastern zone fell into two groups on element sequence and frequency of element types. The two song groups came from habitats that differ in aridity and tree cover; both factors affect dispersal. Song variation within and among colonies in a region occurred in the frequency of labile elements. Movements of birds among colonies are extensive, but patterns are still far from clear. Despite resemblance in song structure between sons and their fathers, dispersal to and from colonies prevents the formation of colony-specific versions of the song. Received 9 March 1992, accepted 30 November 1992.

Constraints on the evolution of attractive traits: genetic (co)variance of zebra finch bill colour.

We estimated the heritability and genetic correlation between male and female bill colour in a laboratory population of zebra finches (Taeniopygia guttata) in order to examine the potential genetic constraints on the evolution of a sexually dimorphic trait. The heritability estimates of bill colour from regressions of offspring on single parents ranged from h2 = 0.34 to 0.73 and all but one of these estimates were significantly greater than zero. The restricted maximum likelihood heritability estimates for full- and half-siblings were significant for females (h2 = 0.48) but not significant for males (h2 = 0.45). The maximum likelihood estimates indicate that there is little dominance genetic variance for bill colour. The large genetic correlation between male and female bill colour (rg = 0.91) combined with opposing selection on male and female bill colour indicates that the evolution to sex-specific optima may proceed very slowly.

Heritability of selectively advantageous foraging behaviour in a small passerine

I measured the heritability of foraging patch choice in a laboratory population of zebra finches (Taeniopygia guttata). Mothers and offspring were tested for their ability to discriminate between four foraging patches which provided four different rates of energy gain. Use of a foraging patch with a high rate of energy gain has been shown to confer a selective advantage on zebra finches in a similar experimental system. In this population of zebra finches there was a large amount of variation in foraging patch choice behaviour both within and among individuals. I determined that foraging patch choice was a phenotypically labile trait with a degree of stereotypy or repeatability, much lower than those typically recorded for morphological traits. The mating behaviour of zebra finches required that heritability be determined from a mother—offspring regression, which showed that narrow sense heritability of foraging patch choice was approximately 0.346. This heritability was significantly different than zero, as was heritability when it was limited by repeatability to 0.246. Foraging patch choice, a behaviour that has a demonstrated fitness consequence, had a heritable component in this laboratory population of zebra finches.

Zebra Finch Incubation: Brood patch, Egg Temperature and Thermal Properties of the Nest

Incubation was investigated in a wild population of Zebra Finches Taenropygia gurtata in northern Victoria and comparisons made with wild-caught birds. A data logger recorded temperature readings from thermocouples inside eggs, nests, nesting bushes and exposed positions adjacent to nesting bushes. Both sexes incubate but only the female has a brood patch; this forms at the start of incubation and regresses soon after eggs hatch. Females incubated at night and both sexes shared incubation during the day. There were no consistent differences in the temperature of developing eggs heated by the two sexes nor did the sexes differ in their ability to rewarm cold eggs; fluctuations in incubation temperature also did not differ consistently between the sexes. Incubation began the day the fourth egg was laid for clutches ≥ 5 or the day the last egg was laid for smaller clutches. Hatching was more synchronous in the wild than in captivity. The ability of the nest to maintain a temperature differential was limited: air temperatures in the roof of the nesting chamber of enclosed roosting and breeding nests followed ambient temperatures closely when conditions were mild but the nest provided an insulating effect that ameliorated low temperatures.