Features of the Retinotopic Representation in the Visual Wulst of a Laterally Eyed Bird,the Zebra Finch (Taeniopygia guttata)

The visual wulst of the zebra finch comprises at least two retinotopic maps of the contralateral eye. As yet, it is not known how much of the visual field is represented in the wulst neuronal maps, how the organization of the maps is related to the retinal architecture, and how information from the ipsilateral eye is involved in the activation of the wulst. Here, we have used autofluorescent flavoprotein imaging and classical anatomical methods to investigate such characteristics of the most posterior map of the multiple retinotopic representations. We found that the visual wulst can be activated by visual stimuli from a large part of the visual field of the contralateral eye. Horizontally, the visual field representation extended from -5° beyond the beak tip up to +125° laterally. Vertically, a small strip from -10° below to about +25° above the horizon activated the visual wulst. Although retinal ganglion cells had a much higher density around the fovea and along a strip extending from the fovea towards the beak tip, these areas were not overrepresented in the wulst map. The wulst area activated from the foveal region of the ipsilateral eye, overlapped substantially with the middle of the three contralaterally activated regions in the visual wulst, and partially with the other two. Visual wulst activity evoked by stimulation of the frontal visual field was stronger with contralateral than with binocular stimulation. This confirms earlier electrophysiological studies indicating an inhibitory influence of the activation of the ipsilateral eye on wulst activity elicited by stimulating the contralateral eye. The lack of a foveal overrepresentation suggests that identification of objects may not be the primary task of the zebra finch visual wulst. Instead, this brain area may be involved in the processing of visual information necessary for spatial orientation.     

Structural Variation in the Zebra Finch Distance Call

The distance calls (DC) of free-living and recently captured zebra finches (ZF) were investigated in order to establish the extent of variation in the structure within and between individuals, colonies, sexes, geographic localities and subspecies. Most work was carried out on the Australian subspecies P. g. castanotis in south-eastern Australia. The calls were analysed sonographically and analysis of two frequency and two temporal parameters were undertaken. The spectral structure of the calls was also assessed subjectively. The main findings are as follows:

• 1 Each individual has its own uniquely structured DC. The calls of males are more distinct than those of females.
• 2 The differences between individuals are sufficiently large to expect that they could probably be perceived by individuals.
• 3 The DCs differ between the sexes. The female call is significantly longer. In P. g. castanotis the male call has two elements — a tonal element followed by a noise element; it also has fewer harmonics. The differences could be detected by ear. The Timor subspecies is thought to have lost the noise element.
• 4 Adjacent colonies have DCs that are not significantly different.
• 5 DCs from different and distant geographic localities are not significantly different except for a few locations where distinct local forms of the DC exist. The changing composition of colonies is thought to erode the development of dialects.
• 6 The DCs of both subspecies have the same basic complex tone with the same harmonic configuration. The calls of males are of the same duration in both subspecies but those of females are longer in P. g. castanotis. The calls of P. g. guttata have a higher fundamental frequency, fewer harmonics and a higher emphasized frequency (FMA).
• 7 The DC in P. g. castanotis is probably used to keep pairs together in the large flocks. It may also be used to detect relatives.

     

A Test of Inbreeding Avoidance in the Zebra Finch

Optimal-outbreeding theory suggests that the genetic relatedness of individuals may be an important factor in mate choice. Several studies have demonstrated that matings between individuals of intermediate genetic relatedness tend to produce more offspring than those between more closely or distantly related mates. Inbreeding avoidance has been studied in captive zebra finches, Poephila guttata. Slater & Clements (1981) found a preference for closely related individuals, while Evans-Layng (1987), in a different design, found a preference for less related mates. Our study examines patterns of mate choice in small flocks of zebra finches of known genetic relatedness. 13 flocks of 9 birds (3 females and 6 males) were released into separate aviaries and left until pairs had formed. 6 of these flocks consisted of siblings and nonrelatives and 7 consisted of cousins and nonrelatives. The degree of genetic relatedness of the individuals used did not affect mate choice, while factors such as male age and experience were correlated with mating success. There was a marginally significant trend for sibling pairs to take longer to lay eggs, although no overall difference in clutch size among sibling pairs, cousin pairs and genetically unrelated pairs was detected. We conclude, then, that there is no evidence of inbreeding avoidance in captive zebra finches.     

Gaze Strategy in the Free Flying Zebra Finch (Taeniopygia guttata)

Fast moving animals depend on cues derived from the optic flow on their retina. Optic flow from translational locomotion includes information about the three-dimensional composition of the environment, while optic flow experienced during a rotational self motion does not. Thus, a saccadic gaze strategy that segregates rotations from translational movements during locomotion will facilitate extraction of spatial information from the visual input. We analysed whether birds use such a strategy by highspeed video recording zebra finches from two directions during an obstacle avoidance task. Each frame of the recording was examined to derive position and orientation of the beak in three-dimensional space. The data show that in all flights the head orientation was shifted in a saccadic fashion and was kept straight between saccades. Therefore, birds use a gaze strategy that actively stabilizes their gaze during translation to simplify optic flow based navigation. This is the first evidence of birds actively optimizing optic flow during flight.     

Geographic and Temporal Variation of the Male Zebra Finch Distance Call

Temporal and geographic variation of acoustic signals can provide insights into dispersal patterns, population history and speciation. Vocalizations that are transmitted from one generation to the next are of particular value in this respect because they can reveal patterns of gene flow, effectively behaving as population markers. The male zebra finch Taeniopygia guttata distance call is one such vocalization; sons learn their father's distance call in the first 40 d of life and it is individually stereotyped thereafter. We investigated geographic variation in the zebra finch by comparing the structure of distance calls recorded from 61 males from six populations across the continent‐wide range of the Australian subspecies T. g. castanotis. Intra‐population variation was high, in many cases greater than the variation among all males recorded, possibly because of population interchange. However, three of six call variables measured, including the newly discovered modulated element, varied geographically although the pattern of distance call variation did not agree with that of geographic proximity of populations. The proportion of calls with a modulated element increased dramatically over 7 yr in central Australia but there was no change over a similar period of time in south‐eastern Australia where no calls contained the element. The findings suggest that interchange among widely separated populations may be commonplace in Australian zebra finches, with the possible exception of those from south‐eastern Australia.     

Undirected Song Encourages the Breeding Female Zebra Finch to Remain in the Nest

Wild zebra finches sing frequently during the breeding season, but the vast majority of song is of the undirected song type that is not directed at any individual, and the function of which is obscure — it appears to be ignored by all potential recipients. It is sung close to the nest-site, has a peak in production during the egg-laying period, and diminishes thereafter. The incidence of undirected song is positively correlated with extra-pair courtship, a finding consistent with the hypothesis that it is a means of advertising availability for extra-pair matings. Typically, undirected song occurred outside the nest when the female was inside, and a positive relationship was found between the amount of singing given by the male during the 5-min interval immediately after the female entered the nest and the time she subsequently spent inside the nest. Keeping the partner inside the nest during her fertile period is an advantage to the male: it serves as a form of paternity protection against other males and it allows him opportunities to pursue his own extra-pair matings. Occupancy of the nest during laying is also a means of guarding against intraspecific brood parasitism, which was high at this colony.     

Molecular Phylogenetic Analysis of Zebra Finch Basic Helix-Loop-Helix Transcription Factors

The zebra finch (Taeniopygia guttata) is an established organism for developmental, behavioral, and neurological research. In this study, we conducted a genomewide survey using the zebra finch genome project databases and identified 86 bHLH sequences in silico in the zebra finch genome. Phylogenetic analysis revealed that 85 proteins belong to 38 families with 29, 18, 18, 3, 11, and 6 bHLH members in supergroups A, B, C, D, E, and F, respectively. One orphan member belonged to none of these groups. Comparisons of zebra finch with chicken and human bHLH repertoires suggested that both humans and birds have a number of lineage-specific bHLH members. Chromosome distribution patterns and phylogenetic analysis suggest that the zebra finch bHLH members should have arisen through gene duplication. This study provides useful information for further research using zebra finch as a model system.     

Discovery of the First Germline-Restricted Gene by Subtractive Transcriptomic Analysis in the Zebra Finch,Taeniopygia guttata

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Posthatch Oral Estrogen Exposure Impairs Adult Reproductive Performance of Zebra Finch in a Sex-Specific Manner

We determined whether short-term, posthatch oral exposure to estradiol benzoate (EB) or the industrial surfactant octylphenol (OP) could impair the reproductive performance of zebra finches. If so, naturally occurring phytoestrogens and xenoestrogens might influence reproduction in wild populations. Chicks were given oral administration of 10 or 100 nmol EB per gram of body mass (earlier work showed the latter to be the minimum oral dose required to maximally masculinize female song nuclei) or an equimolar amount of OP daily from 5 through 11 days of age. Canola oil was used as a vehicle and control. Reproductive testing was done either in individual pair cages or in communal cages that permitted self-selection of mates, N = 10 pairs per group. Pairs consisted of EB-treated males and females, EB-treated males paired with canola-treated females, vice versa, and canola-treated males and females. Posthatch EB treatment produced sex-specific impairments in reproduction that, in some instances, were additive when both sexes were treated. Egg production was reduced and egg breakage was increased in 100 nmol/g EB-treated male and female pairs. The incidence of missing eggs was increased in 10 nmol/g EB-treated male and female pairs. Candled fertility was reduced in both groups containing 100 nmol/g EB-treated males. The number of hatched chicks was severely reduced in all EB-treated groups. No adverse effects of OP treatment were detected. These significant treatment effects (all P < 0.05) show that posthatch EB treatment profoundly disrupts the reproductive performance of zebra finches, suggesting that exposure to estrogens in the wild could impair the reproductive performance of wild populations.     

Infestation of Research Zebra Finch Colony with 2 Novel Mite Species

A zebra finch (Taeniopygia guttata) housed in a neuroscience laboratory was observed to have numerous feather mites. Subsequently, similar mites were found on other birds in the animal facility and research space. The most abundant mite was a novel, undescribed species in the genus Neocheyletiella. Whereas known Neocheyletiella mites have previously been characterized as skin parasites of various birds worldwide, the species on the zebra finches is unique because it lives and builds nests in the feathers. Infrequent specimens of a ‘true’ feather mite, a new species of Megninialges, were present also. Although multiple treatments using a pyrethrin spray were effective in eradicating the mites, topical ivermectin later was found to be more efficacious, better tolerated by the birds, and less labor intensive. This case highlights the general dearth of information regarding ectoparasites in zebra finches, even though these are the most frequently used songbirds in biomedical research. The mite epizootic also underscores the diverse pathogens possible in zebra finches that arrive from outside sources and why ongoing health monitoring of finch colonies is warranted.Zebra finches (Taeniopygia guttata) are increasingly popular as animal models in biomedical research, especially in the fields of neurobiology and behavior.^2,7 Many investigators using these birds maintain inhouse, closed breeding colonies. When birds need to be imported, they are provided by colleagues or are obtained from a limited number of pet-bird dealers that often buy zebra finches from ‘backyard’ breeders. A primary concern about any outside supplier, as has been noted by other authors,¹ is that little (if any) health monitoring of the birds might be done prior to shipment. Birds can arrive at research institutions infected with various parasites and potentially pathogenic bacteria, among other agents. Depending on many factors, such as parasite burden, infections can cause immediate morbidity and mortality or can be clinically silent. This report describes an epizootic of feather mites that presumably went undetected for some time. The 2 mite species observed in the finches had not previously been described by entomologists, and the most prevalent mite was sufficiently novel to justify the assignment of a scientific name. The infestation reinforces why vigilant diagnostic testing, and perhaps prophylactic treatment, of newly arrived zebra finches should occur before their release into the regular colony and why continued health surveillance of an established group of zebra finches is invaluable.     

The use of muscle protein for egg production in the Zebra Finch Taeniopygia guttata

Pectoral muscle can be an important source of protein for birds. During egg formation Zebra Finches Taeniopygia guttata are able to compensate for nutritional inadequacies in their diet by utilization of the protein in their flight muscles. This analysis of flight muscle sarcoplasm supported earlier observations of protein depletion during egg production. However, SDS gel electrophoresis of the sarcoplasm produced no evidence to support a previous suggestion of the existence of a high molecular weight storage protein, and it is thought that the original observation may have arisen as an artefact of experimental methodology. During laying, protein removal from the sarcoplasm occurred over a range of different proteins and was not confined to any one specific protein band. Additionally, the protein band most reduced over the course of laying did not contain elevated levels of the amino acids most limiting to egg production. These results indicate that during laying, flight muscle sarcoplasm contributes towards the nutrient requirements of egg production from general protein reserves, rather than from a specific storage protein containing elevated levels of limiting amino acids.     

The importance of green seed in the nitrogen nutrition of the Zebra Finch Taeniopygia guttata

Abstract Australian grass-finches are widely reported to consume large quantities of green seed when it becomes available, and the opportunistic breeding of wild Zebra Finches in the arid zone has been correlated with the occurrence of rain. In this study, green and ripe seeds were harvested from seven pasture and weed grasses grown in experimental plots and, along with three cereal flours and whole-egg powder, were analysed for the amino-acid composition of their protein. The relative levels of ten amino acids essential in the diets of growing birds were compared between samples using a cluster analysis dendrogram generated from Raabe's Similarity Index. The protein of all green seeds clustered with whole egg, and away from all but one of the ripe seeds and seed products. Green and ripe seed profiles were found to be significantly different by a two-sample multivariate test of significance (Hotelling's T²). Histidine, lysine, phenylalanine and threonine were the amino acids most different. Of these four amino acids, lysine and threonine (along with methionine) were potentially limiting in ripe seeds when compared with whole-egg protein. In green seeds, lysine was only marginally limiting, threonine was no longer limiting, but methionine was still limiting when compared with whole-egg protein. These results indicate that the benefit of green vs ripe seed in the diet of breeding Zebra Finches is partly a higher level of the limiting essential amino acid, lysine, and partly a higher intake and throughput of soft green seed and consequent greater extraction of limiting essential amino acids.     

Zebra Finch Mates Use Their Forebrain Song System in Unlearned Call Communication

Unlearned calls are produced by all birds whereas learned songs are only found in three avian taxa, most notably in songbirds. The neural basis for song learning and production is formed by interconnected song nuclei: the song control system. In addition to song, zebra finches produce large numbers of soft, unlearned calls, among which “stack” calls are uttered frequently. To determine unequivocally the calls produced by each member of a group, we mounted miniature wireless microphones on each zebra finch. We find that group living paired males and females communicate using bilateral stack calling. To investigate the role of the song control system in call-based male female communication, we recorded the electrical activity in a premotor nucleus of the song control system in freely behaving male birds. The unique combination of acoustic monitoring together with wireless brain recording of individual zebra finches in groups shows that the neuronal activity of the song system correlates with the production of unlearned stack calls. The results suggest that the song system evolved from a brain circuit controlling simple unlearned calls to a system capable of producing acoustically rich, learned vocalizations.