Search

Sperm competition is thought to impose strong selection on males to produce competitive ejaculates to outcompete rival males under competitive mating conditions. Our understanding of how different sperm traits influence fertilization success, however, remains limited, especially in wild populations. Recent literature highlights the importance of incorporating multiple ejaculate traits and pre-copulatory sexually selected traits in analyses aimed at understanding how selection acts on sperm traits. However, variation in a male’s ability to gain fertilization success may also depend upon a range of social and ecological factors that determine the opportunity for mating events both within and outside of the social pair-bond. Here, we test for an effect of sperm quantity and sperm size on male reproductive success in the red-back fairy-wren (Malurus melanocephalus) while simultaneously accounting for pre-copulatory sexual selection and potential socio-ecological correlates of male mating success. We found that sperm number (i.e., cloacal protuberance volume), but not sperm morphology, was associated with reproductive success in male red-backed fairy-wrens. Most notably, males with large numbers of sperm available for copulation achieved greater within-pair paternity success. Our results suggest that males use large sperm numbers as a defensive strategy to guard within-pair paternity success in a system where there is a high risk of sperm competition and female control of copulation. Finally, our work highlights the importance of accounting for socio-ecological factors that may influence male mating opportunities when examining the role of sperm traits in determining male reproductive success.

Sperm competition is thought to impose strong selection on males to produce competitive ejaculates to outcompete rival males under competitive mating conditions. Our understanding of how different sperm traits influence fertilization success, however, remains limited, especially in wild populations. Recent literature highlights the importance of incorporating multiple ejaculate traits and pre-copulatory sexually selected traits in analyses aimed at understanding how selection acts on sperm traits. However, variation in a male’s ability to gain fertilization success may also depend upon a range of social and ecological factors that determine the opportunity for mating events both within and outside of the social pair-bond. Here, we test for an effect of sperm quantity and sperm size on male reproductive success in the red-back fairy-wren (Malurus melanocephalus) while simultaneously accounting for pre-copulatory sexual selection and potential socio-ecological correlates of male mating success. We found that sperm number (i.e., cloacal protuberance volume), but not sperm morphology, was associated with reproductive success in male red-backed fairy-wrens. Most notably, males with large numbers of sperm available for copulation achieved greater within-pair paternity success. Our results suggest that males use large sperm numbers as a defensive strategy to guard within-pair paternity success in a system where there is a high risk of sperm competition and female control of copulation. Finally, our work highlights the importance of accounting for socio-ecological factors that may influence male mating opportunities when examining the role of sperm traits in determining male reproductive success.

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male–female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male–female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male-female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male-female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male-female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male-female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male-female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male-female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Why do senescence rates of fitness-related traits often vary dramatically? By considering the full aging trajectories of multiple traits, we can better understand how a species' life history shapes the evolution of senescence within a population. Here, we examined age-related changes in sex-specific survival, reproduction, and several components of reproduction using a long-term study of a cooperatively breeding songbird, the superb fairy-wren (Malurus cyaneus). We compared aging patterns between traits by estimating standardized rates of maturation, age of onset of senescence, and rates of senescence while controlling for confounding factors reflecting individual variability in life history. We found striking differences in aging and senescence patterns between survival and reproduction as well as between reproductive traits. In both sexes, survival started to decline from maturity onward. In contrast, all reproductive traits showed improvements into early adulthood, and many showed little or no evidence of senescence. In females, despite senescence in clutch size, number of offspring surviving to independence did not decline in late life, possibly due to improvements in maternal care with age. Superb fairy-wrens have exceptionally high levels of extragroup paternity, and while male within-group reproductive success did not change with age, extragroup reproductive success showed a dramatic increase in early ages, followed by a senescent decline, suggesting that male reproductive aging is driven by sexual selection. We discuss how the superb fairy-wrens' complex life history may contribute to the disparate aging patterns across different traits.

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male-female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male-female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male–female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male–female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male-female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male-female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Ornaments like plumage colours or complex song are generally regarded as male traits that are shaped by sexual selection. By contrast, the factors that shape female elaborate traits have often been overlooked, though they are expressed in females across many taxa. Understanding how trade-offs and selective pressures shape female ornamentation is crucial for advancing our understanding of trait evolution. In this thesis, I investigate the form and function of female and male plumage colour and song in the Lovely fairy-wren (Malurus amabilis), a tropical species in which females and males are both highly colourful and vocal. This was investigated over three consecutive years and field seasons in Far North Queensland, Australia. My thesis research employed field observations, behavioural experiments, and genetic analysis, to test the adaptive function(s) and mechanisms for the evolution of female and male ornamental traits. I explicitly contrast females and males so that we can address, in the light of the abundant work done on males, how females may or may not differ from males. To provide context for the ornamental traits that are exhibited by this species, I first provide a comprehensive overview of the ecology and breeding biology of the Lovely fairy-wren, since a detailed description on the species natural history prior to this work was lacking. To understand the function of plumage colouration, I studied whether plumage colour in females and males is a signal and experimentally tested if it functions in a competitive context. Additionally, I assessed whether plumage colour is sexually selected, by examining its signalling content, costs (survival), and its relationship with reproductive and paternity success. Lastly, I investigated the song function, by describing female and male song structure and examining sex-specific variation in song rate across different contexts. I also used experimental data to examine female and male responses to simulated territorial in

Extra‐pair paternity (EPP) has been suggested to improve the genetic quality of offspring, but evidence has been equivocal. Benefits of EPP may be only available to specific individuals or under certain conditions. Red‐winged fairy‐wrens have extremely high levels of EPP, suggesting fitness benefits might be large and available to most individuals. Furthermore, extreme philopatry commonly leads to incestuous social pairings, so inbreeding avoidance may be an important selection pressure. Here, we quantified the fitness benefits of EPP under varying conditions and across life‐stages. Extra‐pair offspring (EPO) did not appear to have higher fitness than within‐pair offspring (WPO), neither in poor years nor in the absence of helpers‐at‐the‐nest. However, EPP was beneficial for closely related social pairs, because inbred WPO suffered an overall 75% reduction in fitness. Inbreeding depression was nonlinear and reduced nestling body condition, first year survival and reproductive success. Our comprehensive study indicates that EPP should be favored for the 17% of females paired incestuously, but cannot explain the widespread infidelity in this species. Furthermore, our finding that fitness benefits of EPP only become apparent for a small part of the population could potentially explain the apparent absence of fitness differences in population wide comparisons of EPO and WPO.

The forces shaping female plumage color have long been debated but remain unresolved. Females may benefit from conspicuous colors but are also expected to suffer costs. Predation is one potential cost, but few studies have explicitly investigated the relationship between predation risk and coloration. The fairy-wrens show pronounced variation in female coloration and reside in a wide variety of habitats across Australasia. Species with more conspicuous females are found in denser habitats, suggesting that conspicuousness in open habitat increases vulnerability to predators. To test this, we measured attack rates on 3-D-printed models mimicking conspicuously colored males and females and dull females in eight different fairy-wren habitats across Australia. Attack rates were higher in open habitats and at higher latitudes. Contrary to our predictions, dull female models were attacked at similar rates to the conspicuous models. Further, the probability of attack in open habitats increased more for both types of female models than for the conspicuous male model. Across models, the degree of contrast (chromatic and achromatic) to environmental backgrounds was unrelated to predation rate. These findings do not support the long-standing hypothesis that conspicuous plumage, in isolation, is costly due to increased attraction of predators. Our results indicate that conspicuousness interacts with other factors in driving the evolution of plumage coloration.

Extra-pair paternity (EPP), where offspring are sired by a male other than the social male, varies enormously both within and among species. Trying to explain this variation has proved difficult because the majority of the interspecific variation is phylogenetically-based. Ideally, variation in EPP should be investigated in closely related species, but clades with sufficient variation are rare. We present a comprehensive multifactorial test to explain variation in EPP among individuals in 20 populations of nine species over 89 years from a single bird family (Maluridae). Females had higher EPP in the presence of more helpers, more neighbours, or if paired incestuously. Furthermore, higher EPP occurred in years with many incestuous pairs, populations with many helpers, and species with high male density or in which males provide less care. Altogether, these variables accounted for 48% of the total and 89% of the interspecific and inter-population variation in EPP. These findings indicate why consistent patterns in EPP have been so challenging to detect and suggest that a single predictor is unlikely to account for the enormous variation in EPP across levels of analysis. Nevertheless, it also shows that existing hypotheses can explain the variation in EPP well and that the density of males in particular is a good predictor to explain variation in EPP among species when a large part of the confounding effect of phylogeny is excluded.

Extra-pair paternity (EPP), where offspring are sired by a male other than the social male, varies enormously both within and among species. Trying to explain this variation has proved difficult because the majority of the interspecific variation is phylogenetically-based. Ideally, variation in EPP should be investigated in closely related species, but clades with sufficient variation are rare. We present a comprehensive multifactorial test to explain variation in EPP among individuals in 20 populations of nine species over 89 years from a single bird family (Maluridae). Females had higher EPP in the presence of more helpers, more neighbours, or if paired incestuously. Furthermore, higher EPP occurred in years with many incestuous pairs, populations with many helpers, and species with high male density or in which males provide less care. Altogether, these variables accounted for 48% of the total and 89% of the interspecific and inter-population variation in EPP. These findings indicate why consistent patterns in EPP have been so challenging to detect and suggest that a single predictor is unlikely to account for the enormous variation in EPP across levels of analysis. Nevertheless, it also shows that existing hypotheses can explain the variation in EPP well and that the density of males in particular is a good predictor to explain variation in EPP among species when a large part of the confounding effect of phylogeny is excluded.

Colour vision in diurnal birds falls into two discrete classes, signified by the spectral sensitivity of the violet- (VS) or ultraviolet-sensitive (UVS) short wavelength-sensitive type 1 (SWS1) single cone. Shifts between sensitivity classes are rare; three or four are believed to have happened in the course of avian evolution, one forming UVS higher passerines. Such shifts probably affect the expression of shortwave-dominated plumage signals. We have used genomic DNA sequencing to determine VS or UVS affinity in fairy-wrens and allies, Maluridae, a large passerine family basal to the known UVS taxa. We have also spectrophotometrically analysed male plumage coloration as perceived by the VS and UVS vision systems. Contrary to any other investigated avian genus, Malurus (fairy-wrens) contains species with amino acid residues typical of either VS or UVS cone opsins. Three bowerbird species (Ptilonorhynchidae) sequenced for outgroup comparison carry VS opsin genes. Phylogenetic reconstructions render one UVS gain followed by one or more losses as the most plausible evolutionary scenario. The evolution of avian ultraviolet sensitivity is hence more complex, as a single shift no longer explains its distribution in Passeriformes. Character correlation analysis proposes that UVS vision is associated with shortwave-reflecting plumage, which is widespread in Maluridae.

Urbanisation has created an environment with a broad spectrum of habitats of differing quality for birds. Understanding habitat characteristics is necessary for effective conservation of species in urban environments. We investigated the vegetation requirements of a small, shrub-nesting, Australian bird, the Superb Fairy-wren (Malurus cyaneus), and the relative quality of urban habitats in the Illawarra region of New South Wales. Vegetation was assessed in three different habitats: suburban sites within Superb Fairy-wren territories (n = 20 sites), suburban sites where Fairy-wrens were absent (n = 20), and rural–woodland edge in which Fairy-wrens were present (n = 17). This third habitat represents a habitat assumed to be the best possible habitat for this species within the landscape. We analysed structure and floristics of the vegetation. The three habitats were significantly different from each other both in vegetation structure and floristic composition. While there was some variability in habitat selection in suburban areas, Superb Fairy-wrens were largely restricted to areas that have a dense layer of native shrubs surrounding grassy areas. They were absent from suburban sites where there were either few shrubs in total or sites with exotic shrubs, regardless of abundance. It was predicted that non-suburban habitats (habitat located on the rural–remnant edge) would be of a higher quality than suburban habitats (habitat within residential housing) owing to a prevalence of native vegetation. However, these sites were dominated by a single exotic species, Lantana (Lantana camara). Despite this plant replacing native vegetation, it was an important habitat feature. Either this plant or native shrubs must be available for this species to colonise a site.

Urbanisation has created an environment with a broad spectrum of habitats of differing quality for birds. Understanding habitat characteristics is necessary for effective conservation of species in urban environments. We investigated the vegetation requirements of a small, shrub-nesting, Australian bird, the Superb Fairy-wren (Malurus cyaneus), and the relative quality of urban habitats in the Illawarra region of New South Wales. Vegetation was assessed in three different habitats: suburban sites within Superb Fairy-wren territories (n = 20 sites), suburban sites where Fairy-wrens were absent (n = 20), and rural–woodland edge in which Fairy-wrens were present (n = 17). This third habitat represents a habitat assumed to be the best possible habitat for this species within the landscape. We analysed structure and floristics of the vegetation. The three habitats were significantly different from each other both in vegetation structure and floristic composition. While there was some variability in habitat selection in suburban areas, Superb Fairy-wrens were largely restricted to areas that have a dense layer of native shrubs surrounding grassy areas. They were absent from suburban sites where there were either few shrubs in total or sites with exotic shrubs, regardless of abundance. It was predicted that non-suburban habitats (habitat located on the rural–remnant edge) would be of a higher quality than suburban habitats (habitat within residential housing) owing to a prevalence of native vegetation. However, these sites were dominated by a single exotic species, Lantana (Lantana camara). Despite this plant replacing native vegetation, it was an important habitat feature. Either this plant or native shrubs must be available for this species to colonise a site.

Urbanisation has created an environment with a broad spectrum of habitats of differing quality for birds. Understanding habitat characteristics is necessary for effective conservation of species in urban environments. We investigated the vegetation requirements of a small, shrub-nesting, Australian bird, the Superb Fairy-wren (Malurus cyaneus), and the relative quality of urban habitats in the Illawarra region of New South Wales. Vegetation was assessed in three different habitats: suburban sites within Superb Fairy-wren territories (n = 20 sites), suburban sites where Fairy-wrens were absent (n = 20), and rural–woodland edge in which Fairy-wrens were present (n = 17). This third habitat represents a habitat assumed to be the best possible habitat for this species within the landscape. We analysed structure and floristics of the vegetation. The three habitats were significantly different from each other both in vegetation structure and floristic composition. While there was some variability in habitat selection in suburban areas, Superb Fairy-wrens were largely restricted to areas that have a dense layer of native shrubs surrounding grassy areas. They were absent from suburban sites where there were either few shrubs in total or sites with exotic shrubs, regardless of abundance. It was predicted that non-suburban habitats (habitat located on the rural–remnant edge) would be of a higher quality than suburban habitats (habitat within residential housing) owing to a prevalence of native vegetation. However, these sites were dominated by a single exotic species, Lantana (Lantana camara). Despite this plant replacing native vegetation, it was an important habitat feature. Either this plant or native shrubs must be available for this species to colonise a site.