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Renewed debate over what benefits females might gain from producing extra-pair offspring emphasizes the possibility that apparent differences in quality between within-pair and extra-pair offspring are confounded by greater maternal investment in extra-pair offspring. Moreover, the attractiveness of a female's social mate can also influence contributions of both partners to a reproductive attempt. Here, we explore the complexities involved in parental investment decisions in response to extra-pair offspring and mate attractiveness with a focus on the female point of view. Adult zebra finches paired and reproduced in a colony setting. A male's early-life diet quality and his extra-pair reproductive success were used as metrics of his mating attractiveness. Females paired with males that achieved extra-pair success laid heavier eggs than other females and spent less time attending their nests than their mates or other females. Extra-pair nestlings were fed more protein-rich hen's egg than within-pair nestlings. Females producing extra-pair offspring had more surviving sons than females producing only within-pair offspring. Collectively, results show that females differentially allocate resources in response to offspring extra-pair status and their social mate's attractiveness. Females may also obtain fitness benefits through the production of extra-pair offspring.

An important and understudied question in sexual selection is how females evaluate information from multiple secondary sexual traits (SSTs), particularly when expression of traits is phenotypically uncorrelated. We performed mate choice experiments on zebra finches (Taeniopygia guttata castanotis Gould) to evaluate two hypotheses: preference shifts (obstacles to choice using one trait increase chooser reliance on others) and trait synergisms (choice based on the sum/product of two or more independently varying traits). The first experiment, which employed males raised on diets that impact SST expression, supported the trait synergism hypothesis: overall, male pairing success was best predicted by synergisms involving beak color and cheek patch size. Results did not support the preference shift hypothesis. Results of a follow-up experiment that included males reared on a single diet, and in which male beak color and cheek patch size were manipulated, were also consistent with the trait synergism hypothesis. Results have implications for understanding the long-term persistence of multiple SSTs in populations and for the measurement of repeatability and heritability of mate preferences.

Developmental plasticity allows organisms to increase the fit between their phenotype and their early-life environment. The extent to which such plasticity also enhances adult fitness is not well understood, however, particularly when early-life and adult environments differ substantially. Using a cross-factorial design that manipulated diet at two life stages, we examined predictions of major hypotheses—silver spoon, environmental matching, and thrifty phenotype—concerning the joint impacts of early-life and adult diets on adult morphology/display traits, survival, and reproductive allocation. Overall, results aligned with the silver spoon hypothesis, which makes several predictions based on the premise that development in poor-quality environments constrains adult performance. Males reared and bred on a low-protein diet had lower adult survivorship than other male treatment groups; females' survivorship was higher than males' and not impacted by early diet. Measures of allocation to reproduction primarily reflected breeding diet, but where natal diet impacted reproduction, results supported the silver spoon. Both sexes showed reduced expression of display traits when reared on a low-protein diet. Results accord with other studies in supporting the relevance of the silver spoon hypothesis to birds and point to significant ramifications of sex differences in early-life viability selection on the applicability/strength of silver spoon effects. [ABSTRACT FROM AUTHOR]

Developmental stress, and individual variation in response to it, can have important fitness consequences. Here we investigated the consequences of variable dietary protein on the duration of growth and associative learning abilities of zebra finches, Taeniopygia guttata, which are obligate graminivores. The high-protein conditions that zebra finches would experience in nature when half-ripe seed is available were mimicked by the use of egg protein to supplement mature seed, which is low in protein content. Growth rates and relative body proportions of males reared either on a low-protein diet (mature seed only) or a high-protein diet (seed plus egg) were determined from body size traits (mass, head width, and tarsus) measured at three developmental stages. Birds reared on the high-protein diet were larger in all size traits at all ages, but growth rates of size traits showed no treatment effects. Relative head size of birds reared on the two diets differed from age day 95 onward, with high-diet birds having larger heads in proportion to both tarsus length and body mass. High-diet birds mastered an associative learning task in fewer bouts than those reared on the low-protein diet. In both diet treatments, amount of sub-adult head growth varied directly, and sub-adult mass change varied inversely, with performance on the learning task. Results indicate that small differences in head growth during the sub-adult period can be associated with substantial differences in adult cognitive performance. Contrary to a previous report, we found no evidence for growth compensation among birds on the low-protein diet. These results have implications for the study of vertebrate cognition, developmental stress, and growth compensation.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2006.01.017 Byline: Nancy Tyler Burley, Valerie S. Foster Abstract: The occurrence and significance of variation in apparent mate choice within populations are poorly understood. While one possible explanation for variation is that individuals differ in their mate preferences, an alternative possibility is that individuals vary in their mate selectivity or 'choosiness': that is, some individuals may be willing to accept less attractive mating partners than are others. This latter possibility is likely to result from bidirectional mate choice and differential mating access of high- versus low-quality mating partners. Here we altered the physical condition of female zebra finches, Taeniopygia guttata castanotis, through modest trimming of their flight feathers to explore the possibility that individuals adjust selectivity in response to their own condition. We compared the selectivity of individuals with clipped versus intact wing feathers. Female finches spent less time associating with attractive males when their wings were clipped than when wings were intact. To ascertain whether their choices were influenced by the behaviour of stimulus males that perceived their altered status, we performed a companion experiment that measured male mate choice of females with clipped versus intact wings; no discrimination against clipped females was found. Collectively, these results indicate that a female's mate selectivity is dynamically adjusted based on her assessment of her own condition or mate-getting ability. Future studies that investigate the relationship between realized and ideal mate preferences are necessary to better understand preference functions and the genetic basis of mate preferences. Author Affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, U.S.A. Article History: Received 22 July 2005; Revised 18 September 2005; Accepted 27 January 2006 Article Note: (miscellaneous) MS. number: A10213

We experimentally examined the responses of captive Zebra Finches (Taeniopygia guttata) to intraspecific brood parasitism by adding two eggs to clutches at the onset (early treatment), in the middle (midtreatment), or at the end (late treatment) of egg laying. A comparison group was derived from nonparasitized nesting attempts of the same pairs. Experimentally parasitized nests were abandoned before hatching could have occurred at a much higher rate than were unmanipulated nests; most of the abandonment occurred in early-treatment nests. Females in the early treatment also appeared to curtail egg laying. A smaller proportion of eggs in experimentally parasitized nests survived, but survival of host and parasite hatchlings in such nests was equivalent. Within nests containing both host and parasite young, host young were heavier at day 10 posthatching; the cause of mass differences was not ascertained. Egg loss occurred relatively more frequently in manipulated than in unmanipulated nests, suggesting that clutch enlargement taxes parental capabilities.

Red-banded male zebra finches, Taeneopygia guttata, are very attractive to females and engage in unforced extra-pair copulations more frequently than green-banded males that are unattractive to females. Red-mated females avoid extra-pair courtship more than mates of green-banded males. Band color does not affect male involvement in forced extra-pair copulations. Red-banded males' paternity confidence and ability to obtain extra-pair fertilizations are greater than that of green-banded males.

Examines the relation of bill color in determining the preference of mates of male and female zebra finches. Sexual dichromatism of zebra finches; Selection of birds in the study; Sexual selection as dominant influence on the selection on male bill color.

Presents an experimental evidence that two avian species from a linage devoid of crested species have mate preferences for opposite-sex conspecifics wearing artificial white crests. Historical perspective; Measuring of aesthetic preferences; Results and discussion.

A stage model traces key behavioural tactics and life-history traits that are involved in the transition from promiscuity with no parental care, the mating system that typifies reptiles, to that typical of most birds, social monogamy with biparental care. In stage I, females assumed increasing parental investment in precocial young, female choice of mates increased, female-biased mating dispersal evolved and population sex ratios became male biased. In stage II, consortships between mating partners allowed males to attract rare social mates, provided a mechanism for paternity assessment and increased female ability to assess mate quality. In stage III, relative female scarcity enabled females to demand parental investment contributions from males having some paternity certainty. This innovation was facilitated by the nature of avian parental care; i.e. most care-giving activities can be adopted in small units. Moreover, the initial cost of care giving to males was small compared with its benefit to females. Males, however, tended to decline to assume non-partitionable, risky, or relatively costly parental activities. In stage IV, altriciality coevolved with increasing biparental care, resulting in social monogamy. Approaches for testing behavioural hypotheses are suggested.