Females of many species can gain benefits from being choosy about their mates and even exhibit context-dependent investment in reproduction in response to the quality of their breeding situation. Here, we show that if a male house wren is provided with surplus nest boxes in his territory, his mate lays a larger clutch with a significantly higher proportion of sons. This response to a territory ...

The numbers and sizes of eggs produced by adult females ultimately determine the viability of populations, as well as the evolutionary fitness of the females themselves. Despite an enormous amount of literature on the adaptive significance of fecundity variation within and among populations, simpler questions--such as the proximate mechanisms by which a female determines her clutch size--have a...

The genetic covariance structure for life-history characters in two populations of cyclically parthenogenetic Daphnia pulex indicates considerable positive correlation among important fitness components, apparently at odds with the expectation if antagonistic pleiotropy is the dominant cause of the maintanence of genetic variation. Although there is no genetic correlation between offspring size...

Key to predicting impacts of predation is understanding the mechanisms through which predators impact prey populations. While consumptive effects are well-known, non-consumptive predator effects (risk effects) are increasingly being recognized as important. Studies of risk effects, however, have focused largely on how trade-offs between food and safety affect fitness. Less documented, and appre...

Understanding phenotypic diversity requires not only identification of selective factors that favor origins of derived states, but also factors that favor retention of primitive states. Anurans (frogs and toads) exhibit a remarkable diversity of reproductive modes that is unique among terrestrial vertebrates. Here, we analyze the evolution of these modes, using comparative methods on a phylogen...

The breeding biology of Lophortyx californicus in North America has been described by Sumner (1935), Olading (1938), Howard and Emlen (1942), Oenelly (1955), Raitt (1960) and Lewin (1963); in the Hawaiian Islands by Schwartz and Schwartz (1949) and in New Zealand by Williams (1952,1959). Much more local information has now been gathered and this paper is concerned mainly with annual and local v...

Carotenoids are important as pigments for bright coloration of animals, and as physiologically active compounds with a wide array of health-related functions. Carotenoid-dependent coloration may have evolved as a signal to conspecifics; however, factors that may limit availability of carotenoids are poorly known. We investigated how the acquisition of carotenoids may be constrained by availabil...

Theories on the evolution of clutch size are primarily influenced by examples from terrestrial animals, yet most animal phyla occur exclusively in water. Oxygen has a lower diffusion coefficient and lower solubility in water than in air, and siblings in aquatic clutches often compete for oxygen. Mitigating this competition could affect allocation of resources to offspring. Gelatinous clutches a...

We used the doubly labeled water technique to measure daily energy expenditure (DEE) during the incubation and feeding nestling stages in two populations of white-crowned sparrows (Zonotrichia leucophrys) - one montane and migratory, the other coastal and sedentary - that differ in thermal environment and clutch size. We assessed the birds' thermal environment by continuously monitoring (among ...

According to life-history theory, the development of immune function should be balanced through evolutionary optimization of the allocation of resources to reproduction and through mechanisms that promote survival. We investigated interspecific variability in cell-mediated immune response (CMI), as measured by the phytohaemagglutinin (PHA) assay, in relation to clutch size, longevity and other ...