Isolation of polymorphic tetranucleotide microsatellite markers in the satin bowerbird, Ptilonorhynchus violaceus

We isolated 13 polymorphic microsatellite markers from the satin bowerbird, Ptilonorhynchus violaceus from a genomic library enriched in (AAGG)(n) repetitive elements and characterized them in 20 individuals. The number of alleles ranged from two to 18 per locus with the observed heterozygosity ranging from 0.15 to 1.00. These markers will be useful for analysing questions concerning parentage, population genetic structure and models of speciation.

Phylogeography of an east Australian wet-forest bird, the satin bowerbird (Ptilonorhynchus violaceus), derived from mtDNA, and its relationship to morphology

Australian wet forests have undergone a contraction in range since the mid-Tertiary, resulting in a fragmented distribution along the east Australian coast incorporating several biogeographical barriers. Variation in mitochondrial DNA and morphology within the satin bowerbird was used to examine biogeographical structure throughout almost the entire geographical extent of these wet forest fragments. We used several genetic analysis techniques, nested clade and barrier analyses, that use patterns inherent in the data to describe the spatial structuring. We also examined the validity of the two previously described satin bowerbird subspecies that are separated by well-defined biogeographical barriers and tested existing hypotheses that propose divergence occurs within each subspecies across two other barriers, the Black Mountain corridor and the Hunter Valley. Our data showed that the two subspecies were genetically and morphologically divergent. The northern subspecies, found in the Wet Tropics region of Queensland, showed little divergence across the Black Mountain corridor, a barrier found to be significant in other Wet Tropics species. Biogeographical structure was found through southeastern Australia; three geographically isolated populations showed genetic differentiation, although minimal divergence was found across the proposed Hunter Valley barrier. A novel barrier was found separating inland and coastal populations in southern New South Wales. Little morphological divergence was observed within subspecies, bar a trend for birds to be larger in the more southerly parts of the species' range. The results from both novel and well-established genetic analyses were similar, providing greater confidence in the conclusions about spatial divergence and supporting the validity of these new techniques.

Genetic population structure and call variation in a passerine bird, the satin bowerbird, Ptilonorhynchus violaceus

Geographic variation in vocalizations is widespread in passerine birds, but its origins and maintenance remain unclear. One hypothesis to explain this variation is that it is associated with geographic isolation among populations and therefore should follow a vicariant pattern similar to that typically found in neutral genetic markers. Alternatively, if environmental selection strongly influences vocalizations, then genetic divergence and vocal divergence may be disassociated. This study compared genetic divergence derived from 11 microsatellite markers with a metric of phenotypic divergence derived from male bower advertisement calls. Data were obtained from 16 populations throughout the entire distribution of the satin bowerbird, an Australian wet-forest-restricted passerine. There was no relationship between call divergence and genetic divergence, similar to most other studies on birds with learned vocalizations. Genetic divergence followed a vicariant model of evolution, with the differentiation of isolated populations and isolation-by-distance among continuous populations. Previous work on Ptilonorhynchus violaceus has shown that advertisement call structure is strongly influenced by the acoustic environment of different habitats. Divergence in vocalizations among genetically related populations in different habitats indicates that satin bowerbirds match their vocalizations to the environment in which they live, despite the homogenizing influence of gene flow. In combination with convergence of vocalizations among genetically divergent populations occurring in the same habitat, this shows the overriding importance that habitat-related selection can have on the establishment and maintenance of variation in vocalizations.

Geographic variation in vocalisations of Satin Bowerbirds, Ptilonorynchus violaceus, in south-eastern Queensland

Geographic variation in the advertisement call of the male Satin Bowerbird, Ptilonorhynchus violaceus, was investigated in three populations in south-eastern Queensland. The call was found to differ significantly among the three geographically distinct populations. A discriminant function analysis using five measurements of call frequency and duration provided 100% classification success of the 25 individuals. The observed geographic variation in this call may result from adaptation to the local acoustic environment in these populations, or from genetic or cultural divergence among populations. Further research involving the acoustic properties of the habitats, population genetics and a larger number of populations is required to fully understand this pattern of call variation.

The multiple signals assessed by female satin bowerbirds: could they be used to narrow down females' choices of mates?

Female choice based on multiple male traits has been documented in many species but the functions of such multiple traits are still under debate. The satin bowerbird has a polygynous mating system in which males attract females to bowers for mating; females choose mates based on multiple aspects of males and their bowers. In this paper, we demonstrate that females use some cues to decide which males to examine closely and other cues to decide which males to mate with. Female visitation rates to bowers were significantly related to male size and the males' 'solitary' display rates, and, to a lesser extent, to the numbers of bower decorations. After controlling for female visitation rates, it was found that a male's mating success was significantly related to his size and the rate at which he 'painted' his bower with saliva and chewed up plant material.

Habitat type and density influence vocal signal design in satin bowerbirds

This study provided a thorough test of the acoustic adaptation hypothesis using a within-species comparison of call structure involving a wide range of habitat types, an objective measure of habitat density and direct measures of habitat-related attenuation. The structure of the bower advertisement call of the satin bowerbird was measured in 16 populations from throughout the species' range and related to the habitat type and density at each site. Transmission of white noise, pure tones and different bowerbird dialects was measured in five of six habitat types inhabited by satin bowerbirds. Bowerbird advertisement call structure converged in similar habitats but diverged among different habitats; this pattern was apparent at both continent-wide and local geographical scales. Bowerbirds' call structures differed with changes in habitat density, consistent with the acoustic adaptation hypothesis. Lower frequencies and less frequency modulation were utilized in denser habitats such as rainforest and higher frequencies and more frequency modulation were used in the more open eucalypt-dominated habitats. The white noise and pure tone transmission measurements indicated that different habitats varied in their sound transmission properties in a manner consistent with the observed variation in satin bowerbird vocalizations. There was no effect of geographical proximity of recording locations, nor was there the predicted inverse relationship between frequency and body size. These findings indicate that the transmission qualities of different habitats have had a major influence on variation in vocal phenotypes in this species. In addition, previously published molecular data for this species suggest that there is no effect of genetic relatedness on call similarity among satin bowerbird populations.

Imitating the neighbours: vocal dialect matching in a mimic-model system

Vocal mimicry provides a unique system for investigating song learning and cultural evolution in birds. Male lyrebirds produce complex vocal displays that include extensive and accurate mimicry of many other bird species. We recorded and analysed the songs of the Albert's lyrebird (Menura alberti) and its most commonly imitated model species, the satin bowerbird (Ptilonorhynchus violaceus), at six sites in southeast Queensland, Australia. We show that each population of lyrebirds faithfully reproduces the song of the local population of bowerbirds. Within a population, lyrebirds show less variation in song structure than the available variation in the songs of the models. These results provide the first quantitative evidence for dialect matching in the songs of two species that have no direct ecological relationship.

Visual effects in great bowerbird sexual displays and their implications for signal design

It is often assumed that the primary purpose of a male's sexual display is to provide information about quality, or to strongly stimulate prospective mates, but other functions of courtship displays have been relatively neglected. Male great bowerbirds (Ptilonorhynchus nuchalis) construct bowers that exploit the female's predictable field of view (FOV) during courtship displays by creating forced perspective illusions, and the quality of illusion is a good predictor of mating success. Here, we present and discuss two additional components of male courtship displays that use the female's predetermined viewpoint: (i) the rapid and diverse flashing of coloured objects within her FOV and (ii) chromatic adaptation of the female's eyes that alters her perception of the colour of the displayed objects. Neither is directly related to mating success, but both are likely to increase signal efficacy, and may also be associated with attracting and holding the female's attention. Signal efficacy is constrained by trade-offs between the signal components; there are both positive and negative interactions within multicomponent signals. Important signal components may have a threshold effect on fitness rather than the often assumed linear relationship.

Illusions vary because of the types of decorations at bowers, not male skill at arranging them, in great bowerbirds

Many animals use extended phenotypes to attract mates, but the availability of suitable resources in the environment can affect the size and form of these signals, with unknown consequences for honest signalling. In some populations of the great bowerbird, Ptilonorhynchus nuchalis, males arrange decorations by size, with smaller decorations placed closer to the bower entrance than larger decorations. This may create a more even background pattern from the female's viewpoint within the bower than if decorations were arranged randomly. Males show consistent, individual variation in the size-distance gradient, which could reflect variation among males in the cognitive skills needed to arrange decorations. We examined whether individual consistency in gradient characteristics is related to a male's skill at decoration arrangement or the types of decorations at bowers. We paired 18 males and switched bower decorations between pairs. We measured gradient characteristics before switching and 4 and 8 days after switching. Gradient characteristics after switching were related to those of the bower from which decorations were received, not to those of the male's own bower before switching. Gradient characteristics were also related to the types of decorations received, including bones and snail shells. These results suggest that variation among males in the size-distance gradient is explained by differences in the availability of decorations at bowers, not the cognitive skills required to arrange decorations. Although variation in gradient characteristics could indicate the male's ability to locate and transport particular decorations, it could also reflect local availability of objects, with no relationship to male quality.

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