The past 30 years of immunological research have revealed much about the proximate mechanisms of maternal antibody transmission and utilization, but have not adequately addressed how these issues are related to evolutionary and ecological theory. Much remains to be learned about individual differences within a species in maternal antibody transmission as well as differences among species in transmission or utilization of antibodies. Similarly, maternal-effects theory has generally neglected the mechanisms by which mothers influence offspring phenotype. Although the environmental cues that generate maternal effects and the consequent effects for offspring phenotype are often well characterized, the intermediary physiological and developmental steps through which the maternal effect is transmitted are generally unknown. Integration of the proximate mechanisms of maternal antibody transmission with evolutionary theory on maternal effects affords an important opportunity to unite mechanism and process by focusing on the links between genetics, environment and physiology, with the ultimate goal of explaining differences among individuals and species in the transfer of immune function from one generation to the next.

Whole-genome sequencing projects are increasingly populating the tree of life and characterizing biodiversity1–4. Sparse taxon sampling has previously been proposed to confound phylogenetic inference5, and captures only a fraction of the genomic diversity. Here we report a substantial step towards the dense representation of avian phylogenetic and molecular diversity, by analysing 363 genomes from 92.4% of bird families—including 267 newly sequenced genomes produced for phase II of the Bird 10,000 Genomes (B10K) Project. We use this comparative genome dataset in combination with a pipeline that leverages a reference-free whole-genome alignment to identify orthologous regions in greater numbers than has previously been possible and to recognize genomic novelties in particular bird lineages. The densely sampled alignment provides a single-base-pair map of selection, has more than doubled the fraction of bases that are confidently predicted to be under conservation and reveals extensive patterns of weak selection in predominantly non-coding DNA. Our results demonstrate that increasing the diversity of genomes used in comparative studies can reveal more shared and lineage-specific variation, and improve the investigation of genomic characteristics. We anticipate that this genomic resource will offer new perspectives on evolutionary processes in cross-species comparative analyses and assist in efforts to conserve species.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Abstract.-This article, which focuses on hormones and the diverse effects they have on behavior and physiology, raises evolutionary questions that hormonal studies appear especially well suited to address. These include the endocrine basis for life-history trade-offs, the role of hormones in adaptive alterations in social organization and mating systems, and whether natural selection acts on traits or organisms. The article also shows how phenotypic engineering by hormonal manipulations can reveal the evolutionary significance of phenotypic variation. By generating rare or novel phenotypes, we can attempt to determine the shape of fitness profiles in nature. To illustrate phenotypic engineering, we manipulated plasma testosterone in a freeliving bird, the dark-eyed junco (Junco hyemalis), and measured the effects of the treatment on behavior, including allocation of time to mate attraction and parental behavior as well as use of space, and on physiology, including regulation of body mass, corticosterone, and molt. We compared treated males to controls for various correlates of fitness, including territory acquisition, mate acquisition, mate retention, physical condition of the mate, apparent reproductive success, extrapair fertilizations, and survival. The results to date appear to indicate that selection is relatively indifferent to a broad range of phenotypes, while extreme deviations from the norm are selected against.The objective of this article is to describe the potential that studies of hormones have to increase understanding of the consequences of variation in behavior and physiology and thus understanding of the evolution of life histories, social organization, and mating systems. We begin by reviewing some basic facts about the action of one hormone, testosterone, in birds. Our aim is to illustrate a few principles, including (1) that hormones are secreted in response to stimuli that are generated both internally and externally, (2) that hormones have multiple targets and diverse effects, and (3) that the complexity of hormonal action leaves ample room for variation on which natural selection can act.We then pose four interconnected questions that relate hormones to the evolutionary process and that provide fruitful avenues for research: (1) How might hormones form the mechanistic bases for trade-offs in life histories? (2) What is the role of hormones in the evolution of inter-and intraspecific variation in social organization and mating systems? (3) Does natural selection act on organisms or on traits? (4) What is the evolutionary significance of phenotypic variation in hormonally mediated traits? From the recent literature we give examples of studies that address o...

When selection on males and females differs, the sexes may diverge in phenotype. Hormones serve as a proximate regulator of sex differences by mediating sex-biased trait expression. To integrate these perspectives, we consider how suites of traits mediated by the same hormone in both sexes might respond to selection. In male birds, plasma testosterone (T) varies seasonally and among species according to mating system. When elevated experimentally, it is known to enhance some components of fitness and to decrease others. We report that female T also varies seasonally and co-varies with male T. Female T is higher in relation to male T in sexually monomorphic species and is higher absolutely in females of species with socially monogamous mating systems, which suggests adaptation. We also consider the effect of experimentally elevated T on females and whether traits are sensitive to altered T. We hypothesize that sensitive traits could become subject to selection after a natural change in T and that traits with opposing fitness consequences in males and females could constrain dimorphism. Results from birds, including the dark-eyed junco (Junco hyemalis), reveal many sensitive traits, some of which appear costly and may help to account for observed levels of sexual dimorphism.

The sex ratio of Dark—eyed Juncos wintering in the eastern and central United States and Canada varies clinally along a latitudinal gradient. The percentage of @V @V among both museum skins and live—caught birds is °70% in the south, 20% in the north. When abundance according to latitude is also considered, an average ♀ appears to winter farther south than an average ♂ and hence probably tends to migrate farther. Latitude alone is an excellent predictor of sex ratio (r2 = 85%), and latitude plus 13 other measures of climate explain virtually all the variation (r2 = 96.6%). Extreme measures of climate, as compared to mean measures, are equally predictive. Principal component analysis indicates that snowfall, temperature, and latitude are the most important climatic variables associated with sex ratio. Because ♂ ♂ average larger than ♀ ♀ and are concentrated northward, mean wing length increases with latitude and is significantly correlated with climatic measures that vary with latitude. Further, larger birds within each sex may select higher altitudes as wintering sites. Sex ratio does not vary measurably with date in wintering populations. Among possible explanations for clinal variation in sex ratio are sex—associated differences in (1) advantages of early arrival on the breeding or wintering grounds, (2) impacts of inter— and intrasexual competition, and (3) effects of low temperature and intermittent food availability. Comparison of ♂ ♂ and ♀ ♀ with respect to potential fasting endurance, a size—related metabolic parameter, indicates that at 0 degrees C an average ♂ should be able to fast 4% longer (1.6 h) than an average ♀ at standard metabolic rates. An extremely heavy 7 ♂ might endured fasting up to 29% (10.7 h) longer than a very light ♀. These differences may confer greater survival ability upon the ♂ at latitudes where snow cover can often preclude feeding.