The Smith-Fretwell model for optimal offspring size assumes the existence of an inverse proportional relationship (i.e., trade-off) between the number of offspring and the amount of resources invested in an individual offspring; virtually all of the many models derived from theirs make the same trade-off assumption. Over the last 30 years it has become apparent that the predicted proportionalit...

Life history theory predicts that parents will have lower Darwinian fitness if they tend clutches that are above or below the size they naturally produce. We experimentally tested for relationships between fitness and clutch size in Tree Swallow (Tachycineta bicolor) offspring and parents. Over 130 trios of nests initiated on the same day were randomly divided among reduce (-3 eggs), control (3...

We investigated the link between heterozygosity and the reaction norm attributes of reproductive performance in female house sparrows (Passer domesticus). We collected data on clutch size, egg size, hatching success and nestling survival in 2816 nesting attempts made by 791 marked individuals over a 16-year period. Pedigree analysis revealed no evidence of inbreeding. Neither parent-offspring r...

The idea that trade-offs between offspring quantity and quality shape reproductive behaviour has long been central to economic perspectives on fertility. It also has a parallel and richer theoretical foundation in evolutionary ecology. We review the application of the quantity-quality trade-off concept to human reproduction, emphasizing distinctions between clutch size and lifetime fertility, a...

Rufous bush robin, Cercotrichas galactotes, nests were experimentally parasitized in order to test which sex is responsible for egg ejection. We tested nests belonging to the same individuals (male, female or pair) in 2 consecutive years. Whether the eggs were rejected did not depend on environmental variables such as laying date and clutch size, and did not change between tests, when the two c...

Carotenoids are biologically active pigments of crucial importance for the development of avian embryos and nestlings. Thus parental ability to provide nestlings with a carotenoid-rich diet may enhance offspring fitness. However, very little is known about the possible effects of carotenoid availability in the diet on growing nestlings in natural populations. We experimentally manipulated dieta...

In Australia, the family Microhylidae consists of 19 species of Cophixalus Boettger 1892 and 5 species of Austrochaperina Fry 1912 (Hoskin 2012; Hoskin, submitted). Most of these species have highly localized distributions in the rainforests and boulder-fields of north-east Australia (Zweifel 1985; Hoskin 2004; Hoskin & Aland 2011). Australian microhylid frogs are terrestrial breeders with dire...

age at first breeding on Ural owl lifetime reproductive success and fitness under cyclic food conditions. – Journal of Animal Ecology 67: 359–369. survival in a variable environment: Ural owls and the three-year vole cycle. – Auk in press. effort and reproductive values in periodic environments. – seasonal recruitment and the evolution of the seasonal decline in Ural owl clutch size. – Manuscri...

We summarize the literature on rates of multiple paternity and sire numbers per clutch in viviparous fishes vs. mammals, two vertebrate groups in which pregnancy is common but entails very different numbers of embryos (for species surveyed, piscine broods averaged >10-fold larger than mammalian litters). As deduced from genetic parentage analyses, multiple mating by the pregnant sex proved to b...