General Themes: G.A. Parker, Sperm Competition and the Evolution of Ejaculates: Towards a Theory Base. A.P. Moller, Sperm Competition and Sexual Selection. W.G. Eberhard, Female Roles in Sperm Competition. J. Wright, Paternity and Paternal Care. Taxonomic Treatments: L.F. Delph and K. Havens, Pollen Competition in Flowering Plants. D.R. Levitan, Sperm Limitation, Gamete Competition and Sexual Selection in External Fertilizers. N.K. Michiels, Mating Conflicts and Sperm Competition in Simultaneous Hermaphrodites. B. Baur, Sperm Competition in Molluscs. M.A. Elgar, Sperm Competition and Sexual Selection in Spiders and Other Arachnids. L.W. Simmons and M.T. Siva-Jothy, Sperm Competition in Insects: Mechanisms and the Potential for Selection. C.W. Petersen and R.R. Warner, Sperm Competition in Fishes. T.R. Halliday, Sperm Competition in Amphibians. M. Olsson and T. Madsen, Sexual Selection and Sperm Competition in Reptiles. T.R. Birkhead, Sperm Competition in Birds: Mechanisms and Function. D.A. Taggart, W.G. Breed, P.D. Temple-Smith, A. Purvis, and G. Shimmin, Reproduction, Mating Strategies and Sperm Competition in Marsupials and Monotremes. M. Gomendio, A.H. Harcourt, and E.R.S. Roldan, Sperm Competition in Mammals. T.R. Birkhead and A.P. Moller, Sperm Competition, Sexual Selection and Different Routes to Fitness. Index.

Sperm competition and sexual selection

Food limitation is generally thought to underlie much of the variation in life history traits of birds. I examined variation and covariation of life history traits of 123 North American Passeriformes and Piciformes in relation to nest sites, nest predation, and foraging sites to examine the possible roles of these ecological factors in life history evolution of birds. Annual fecundity was strongly inversely related to adult survivaI, even when phylogenetic effects were controlled. Only a little of the variation in fecundity and survival was related to foraging sites, whereas these traits varied strongly among nest sites. Interspecific differences in nest predation were correlated with much of the variation in life history traits among nest sites, although energy trade-offs with covarying traits also may account for some variation. For example, increased nest predation is associated with a shortened nestling period and both are associated with more broods per year, but number of broods is inversely correlated with clutch size, possibly due to an energy trade-off. Number of broods was much more strongly correlated with annual fecundity and adult survival among species than was clutch size, suggesting that clutch size may not be the primary fecundity trait on which selection is acting. Ultimately, food limitation may cause trade-offs between annual fecundity and adult survival, but differences among species in tecundity and adult survival may not be explained by differences in food abundance and instead represent differing tactics for partitioning similar levels of food limitation. Variation in fecundity and adult survival is more clearly organized by nest sites and more closely correlated with nest predation; species that use nest sites with greater nest predation have shorter nestling periods and more broods, yielding higher fecundity, which in turn is associated with reduced adult survival. Fecundity also varied with migratory tendencies; short-distance migrants had more broods and greater fecundity than did neotropical migrants and residents using similar nest sites. HowevEr, migratory tendencies and habitat use were confounded, making separation of these two effects difficult. Nonetheless, the conventional view that neotropical migrants have fewer broods than residents was not supported when nest site effects were controlled

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Avian Life History Evolution in Relation to Nest Sites, Nest Predation, and Food

The application of molecular genetic techniques has revolutionized our view of avian mating systems. Contrary to prior expectations, birds are only very rarely sexually monogamous, with ‘extra-pair offspring’ found in approximately 90% of species. Even among socially monogamous species, over 11% of offspring are, on average, the result of extra-pair paternity (EPP). Based on over 150 molecular genetic studies of EPP in birds, we review two topical areas: (i) ecological explanations for interspecific variation in the rate of EPP; and (ii) evidence bearing on the adaptive function of EPP. We highlight the remaining challenges of understanding the relative roles of genes and ecology in determining variation between taxa in the rate of extra paternity, and testing for differences between extra-pair offspring and those sired within-pair.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-294X.2002.01613.x

Extra pair paternity in birds: a review of interspecific variation and adaptive function.

▪ Abstract It has recently been argued that the paradox of helping behavior in birds has been solved (73). This optimism may be premature. I argue that there is no obvious dichotomy between cooperative societies based on natal philopatry and the formation of extended families, and those formed via recruitment of unrelated individuals into coalitions. Tests of the effect of helping behavior suggest that kinship may have been overemphasized for male helpers but underestimated for females. The first studies applying molecular techniques to resolve genealogy in these societies suggest that reproductive sharing occurs commonly across all types of social organization. Incest avoidance may be an important constraint on sharing in families, but molecular techniques have thus far been inappropriate to assess its importance. The interests of males and female helpers may be quite different because females often have less opportunity to inherit a territory vacancy on the death of the breeder, less opportunity to cour...

Evolution of helping behavior in cooperatively breeding birds

Avian fat storage is associated with both benefits and costs. Although the benefits of maintaining higher energetic reserves have long been considered, the associated costs have received far less attention. Spatial and temporal patterns of fat storage, together with experimental data, indicate that birds are capable of actively regulating their energetic reserves at levels below physiological or environmental maxima. This regulation implies that fat storage entails a cost. Evidence of potential costs are reviewed and discussed under the following headings: mass-dependent metabolism, mass-dependent predation risk, mass-dependent risk of injury, mass-dependent foraging, pathological costs and reproductive costs. Although the evidence that fat storage is costly is convincing, key empirical data are lacking. We indicate the sorts of data which need to be gathered and suggest ways in which this might be done. We go on to discuss the interaction of these costs and their relevance to between-individual patterns of fat storage and the interpretation of ‘condition indices’. Because many of the purported costs of fat storage are dependent upon changes in body mass, or wing loading, our review is also relevant to other phenomena which may involve mass-dependent costs, such as gonadal hypertrophy, transport of food items and primary moult.

The ecological costs of avian fat storage

Behavioral ecologists generally agree that animals derive benefits from familiarity with spaces that they inhabit or visit, yet site familiarity is rudimentary or lacking in most models of habitat selection. In this review, I examine evidence for the occurrence of site familiarity and its fitness benefits, describe the difficulty of measuring site familiarity, note its omission from the influential ideal free and ideal despotic models, and use a literature search to test an assumption of the ideal models that has become widespread in habitat selection theory: that animals behave without regard for site familiarity. I find little support for such “familiarity blindness” in vertebrates. Next I discuss how the study of public information has drawn attention away from site familiarity and point out that both kinds of information are likely to be important in habitat selection. I proceed to examine current models of initial settlement (exploration and settlement of prebreeders on first territories) and optional resettlement (site fidelity or dispersal by established breeders following a period of prospecting) and find that the latter include only basic forms of site familiarity. Hence, I develop the concept that an inhabited space holds a unique “private value” to an animal based on its familiarity with the space and offer a simple model for optional resettlement based on private value that generates several novel predictions, including site fidelity based on cumulative breeding site familiarity and high site fidelity among species with complex territories.

Making habitat selection more “familiar”: a review

POSTPONEMENT of dispersal and breeding to assist in rearing others' young may be favoured if helpers' contributions to the production of close kin exceed their likely reproductive success had they dispersed1,2. Young adult stripe-backed wrens (Campylo-rhynchus nuchalis) remain in natal groups and greatly enhance reproductive success of close kin. Long-term behavioural observations suggest that only the dominant male and female in a group breed3; however, extra-pair parentage has been confirmed biochemically in apparently monogamous birds4,5, including some social species6,7. DNA fingerprinting of wren groups shows that behaviourally dominant males sometimes share paternity with auxiliary males previously thought to be nonproductive, whereas dominants are the only reproductives among females. Reproduction by auxiliary males (but not females) helps explain the long tenure of males in helper status and the contrasting combativeness of females in competition for breeding positions outside the natal group8,9, but reproduction by auxiliaries cannot alone explain helping behaviour.

Shared paternity revealed by genetic analysis in cooperatively breeding tropical wrens

We examined correlates of extra-pair fertilization (EPF) success in the hooded warbler (Wilsonia citrina), a species where females pursue extra-pair matings. The good genes hypothesis predicts that females choose extra-pair mates with morphological or behavioral traits that reflect differences in male genetic quality. EPFs were common, as 35.3% (42/119) of broods contained extra-pair young (EPY) and 26.7% (95/356) of nestlings were the result of EPFs. There was a strong skew in male EPF success which increased the variance in annual male mating success 2–3 fold. However, male morphology did not predict EPF success, as extra-pair males were not older or larger than the males they cuckolded. Likewise, there were no significant correlations between the proportion of extra-pair young in a brood and male size or age. The good genes hypothesis predicts that high-quality males will be consistently preferred as genetic mates, but the number of young sired by a male with his social mate was not consistent from one year to the next. There was a significant negative correlation between female age and proportion of EPY produced, which could result if older females obtain higher-quality social mates. We found no strong evidence that females choose extra-pair mates for good genes, but females may use behavioral rather than morphological cues to assess relative male quality.

https://www.jstor.org/stable/pdfplus/4601307.pdf

Correlates of extra-pair fertilization success in hooded warblers

Correlates of dominance in wintering white-throated sparrows: age, sex and location

Most of the behavioral components of what we now term social dominance behavior have long been recognized in animals. Darwin, in his treatise on the emotions of humans and animals, described in detail the suite of behaviors that characterize dominant and subordinate animals, although he did not use those terms (Darwin, 1965). Hoffer (1882, in Wilson, 1975) actually described stable dominance relationships in bumblebees, but his behavioral findings did not stimulate further research. The formal scientific investigation of social dominance relationships in animals began with Thorleif Schjelderup-Ebbe’s studies of captive groups of domestic chickens (Gallus domesticus) in the early 1920s (Schjelderup-Ebbe, 1922). Schjelderup-Ebbe observed that among any two individuals within a group there existed a “peck-right” relationship: a fundamental behavioral asymmetry whereby one of the pair could consistently peck the second and thus force it to yield its position, while the second bird rarely, if ever, was able to gain such an advantage over the first.

Walter H. Piper

Papers

Making habitat selection more “familiar”: a review

Shared paternity revealed by genetic analysis in cooperatively breeding tropical wrens

Correlates of extra-pair fertilization success in hooded warblers

Correlates of dominance in wintering white-throated sparrows: age, sex and location

Social Dominance in Birds