Mothers are predicted to overproduce male or female eggs when the relative fitness gains from one sex are higher and outweigh the costs of manipulation. However, in birds such biases are often difficult to distinguish from differential embryo or chick mortality. Using a molecular technique to identify the sex of early embryos, we aim to determine the effect of maternal nutrition on zebra finch ...

A13STRACT.--We studied the nesting biology of the Green-rumped Parrotlet (Forpus passerinus) in the llanos of Venezuela. Clutch size averaged 7 eggs (range: 5-10), and eggs were typically laid daily or every other day over 7-16 days (• = 10). Incubation began with the first egg. Clutches hatched over 2-14 days (œ = 8.6) and fledged over 4-17 days (œ = 9.7). An average of 5.7 chicks hatched (ran...

Parental care is an advantageous reproductive behavior, as the fitness of the caregiver is increased through improving the chances of its offspring's survival. Parental care occurs in a variety of teleost fishes. The body size of parental fish and the size of their brood can affect nest abandonment decisions, where compared with smaller fish with smaller broods, larger fish with larger broods t...

A .—We studied the relationships among weather, reproductive success, and population density over 21 years (1980–2000) in a resident Song Sparrow (Melospiza melodia) population in coastal scrub habitat. Our goals were to test potential relationships between annual variation in weather and reproductive success, to evaluate whether reproductive success is density dependent, and to explore the eff...

Postcopulatory sexual selection may select for male primary sexual characteristics like sperm morphology and sperm motility, through sperm competition or cryptic female choice. However, how such characteristics influence male fertilization success remains poorly understood. In this study, we investigate possible correlations between sperm characteristics and paternity success in the socially mo...

The Shiner Perch (Cymatogaster aggregata Gibbons) exhibits a viviparous reproductive mode and long-term female sperm storage, two biological features that may predispose this fish species for both intense sperm competition and frequent multiple paternity within broods. To test these hypotheses, we used polymorphic microsatellite markers to identify sires and quantify paternal contributions to t...

The typical pattern in hymenopteran species is that females are produced from fertilized eggs but that males arise parthenogenetically from unfertilized eggs (arrhenotoky). In some species, however, unfertilized eggs can yield diploid female offspring through the process of thelytokous parthenogenesis. Indeed, it is puzzling why such asexual mutants have not outreproduced their sexual counterpa...

I examined the effects of the parasitic larval nematode, Eustrongylides ignotus, on male mate choice in the western mosquitofish, Gambusia affinis. I hypothesized that parasite presence influences male mate choice either directly (via reduction in male mating behavior due to presence of parasite in females) or indirectly (via reduction in male mating behavior due to reduced condition of infecte...