Malurus

Abstract: Cooperative breeding systems are characterized by nonbreeding helpers that assist breeders in offspring care. However, the benefits to offspring of being fed by parents and helpers in cooperatively breeding birds can be difficult to detect. We offer experimental evidence that helper effects can be obscured by an undocumented maternal tactic. In superb fairy-wrens (Malurus cyaneus), mothers breeding in the presence of helpers lay smaller eggs of lower nutritional content that produce lighter chicks, as compared with those laying eggs in the absence of helpers. Helpers compensate fully for such reductions in investment and allow mothers to benefit through increased survival to the next breeding season. We suggest that failure to consider maternal egg-investment strategies can lead to underestimation of the force of selection acting on helping in avian cooperative breeders.

Abstract: IN a small proportion of bird species (<3%), offspring delay their dispersal beyond the time when they are reproductively capable, remain on their natal territory, and usually assist the resident breeders, normally their parents, to raise other young1–3. This pattern of social organization and care-giving behaviour, most frequently termed cooperative breeding, is controversial with respect to why offspring delay their dispersal2–8. In this study we investigate the interaction between habitat limitation, habitat quality, and sex ratio in influencing dispersal decisions in a population of superb fairy-wrens (Malurus cyaneus). We show that every non-breeding male (31 of 32; 96.9%) given the opportunity, dispersed and bred. The sex ratio was male-biased and although males did not disperse into vacant but previously occupied territories in the absence of females, the reintroduction of females prompted dispersals. Our data suggest that young males delay their dispersal in response to a limited number of mates and secondarily to habitat limitation.

Abstract: Dispersal influences evolution, demography, and social characteristics but is generally difficult to study. Here we combine long-term demographic data from an intensively studied population of superb fairy-wrens (Malurus cyaneus) and multivariate spatial autocorrelation analyses of microsatellite genotypes to describe dispersal behavior in this species. The demographic data revealed: (1) sex-biased dispersal: almost all individuals that dispersed into the study area over an eight-year period were female (93%; n = 153); (2) high rates of extragroup infidelity (66% of offspring), which also facilitated local gene dispersal; and (3) skewed lifetime reproductive success in both males and females. These data led to three expectations concerning the patterns of fine-scale genetic structure: (1) little or no spatial genetic autocorrelation among females, (2) positive spatial genetic autocorrelation among males, and (3) a heterogeneous genetic landscape. Global autocorrelation analysis of the genotypes present in the study population confirmed the first two expectations. A novel two-dimensional local autocorrelation analysis confirmed the third and provided new insight into the patterns of genetic structure across the two-dimensional landscape. We highlight the potential of autocorrelation analysis to infer evolutionary processes but also emphasize that genetic patterns in space cannot be fully understood without an appropriate and intensive sampling regime and detailed knowledge of the individuals genotyped.

Abstract: Superb fairy-wrens Malurus cyaneus are small, sexually dichromatic, co-operatively breeding birds of southeastern Australia. Groups typically consist of a single female, an unrelated dominant male and several male helpers. Although all males care for the offspring, 76% of all offspring produced on territory are sired by males from outside the group (Mulder et al. 1994); this is the highest known frequency of extra-pair paternity of any bird (Westneat & Webster 1994). In order to understand this remarkable system it is essential to understand the distribution of paternity. Although multilocus DNA fingerprinting has allowed partial success in assigning paternity (Mulder et al. 1994), this technique is time-consuming, inefficient and demands relatively large blood samples from individuals. We describe a microsatellite-based, genotyping system for the superb fairy-wren which facilitates efficient determination of paternity. We also discuss the ubiquitous but largely ignored problem of paternity assignment in species with male philopatry. Initially, pBluescript libraries enriched for either (CA)n dinucleotide or (TTTC)n tetranucleotide repeats were con