BACKGROUND Studies of lizards have shown that offspring size cannot be altered by manipulating clutch size in species with a high clutch frequency. This raises a question of whether clutch frequency has a key role in influencing the offspring size-number trade-off in lizards. METHODOLOGY/PRINCIPAL FINDINGS To test the hypothesis that females reproducing more frequently are less likely to trad...

Seasonal decline in clutch size is common in birds, but the proximate mechanisms for this phenomenon have not been elucidated. The most credible model to date posits that late-laying females lay fewer eggs due to a seasonal increase in the tendency to incubate during laying, which inhibits egg production. We tested this model with free-living and laboratory American Kestrels (Falco sparverius) ...

It has been suggested that follicle-stimulating hormone (FSH) may play a role in egg size/number trade-offs in oviparous vertebrates. We tested this hypothesis in an avian species by administering porcine FSH (pFSH) to intact, captive female zebra finches (Taeniopygia guttata) during egg formation. We predicted that (1) pFSH would increase the number of ovarian follicles recruited into rapid yo...

Clutch size is a fundamental predictor of avian fitness, widely-studied from evolutionary and ecological perspectives, but surprisingly little is known about the physiological mechanisms regulating clutch size variation. The only formal mechanistic hypothesis for avian clutch-size determination predicts an anti-gonadal effect of circulating prolactin (PRL) via the inhibition of luteinizing horm...

Reproduction is thought to entail costs, but assessing survival costs associated with maturation as organisms express reproductive genes for the first time is problematic because many will die prior to expressing a phenotype. We quantified selection acting on this invisible fraction by measuring selection on predicted breeding values for clutch size estimated from a multigenerational pedigree o...

In most bird species, the timing of incubation onset may influence the degree of hatching asynchrony, which, together with variation in clutch size, affects reproductive success. In some domesticated species that usually show no hatching asynchrony, plasma prolactin concentrations in females rise with the onset of incubation and the end of laying, and this rise enhances incubation behavior and ...

In many species, empirical data suggest that temperatures less than 1 month before breeding strongly influence laying date, consistent with predictions that short lag times between cue and response are more reliable, decreasing the chance of mismatch with prey. Here we show in European starlings (Sturnus vulgaris) that mid-winter temperature ca 50-90 days before laying (8 January-22 February) s...

Understanding the variation in selection pressure on key life-history traits is crucial in our rapidly changing world. Density is rarely considered as a selective agent. To study its importance, we partition phenotypic selection in fluctuating environments into components representing the population growth rate at low densities and the strength of density dependence, using a new stochastic mode...

Phenotypic plasticity is an important mechanism via which populations can respond to changing environmental conditions, but we know very little about how natural populations vary with respect to plasticity. Here we use random-regression animal models to understand the multivariate phenotypic and genetic patterns of plasticity variation in two key life-history traits, laying date and clutch size...

Reproductive investment is typically considered in terms of size and number of propagules produced. Compared with a thorough understanding of the overall patterns and ecological correlates of avian clutch size, egg size has received less attention and the total effort invested in laying a clutch of eggs is rarely considered. We used clutch volume as an alternative estimate of reproductive inves...