A range-wide domino effect and resetting of the annual cycle in a migratory songbird.

Latitudinal differences in timing of breeding are well documented but how such differences carry over to influence timing of events in the annual cycle of migratory birds is not well understood. We examined geographical variation in timing of events throughout the year using light-level geolocator tracking data from 133 migratory tree swallows ( Tachycineta bicolor) originating from 12 North American breeding populations. A swallow's breeding latitude influenced timing of breeding, which then carried over to affect breeding ground departure.

Detection of Mycoplasma gallisepticum in House Finches ( Haemorhous mexicanus) from Arizona.

In 1994, an endemic poultry pathogen, Mycoplasma gallisepticum (MG), was identified as the causative agent of a novel disease in house finches ( Haemorhous mexicanus). After an initial outbreak in Maryland, MG spread rapidly throughout eastern North American populations of house finches. Subsequently, MG spread slowly through the northern interior of North America and then into the Pacific Northwest, finally reaching California in 2006.

The rate of telomere loss is related to maximum lifespan in birds.

Telomeres are highly conserved regions of DNA that protect the ends of linear chromosomes. The loss of telomeres can signal an irreversible change to a cell's state, including cellular senescence. Senescent cells no longer divide and can damage nearby healthy cells, thus potentially placing them at the crossroads of cancer and ageing.

Effects of age and reproductive experience on the distribution of prolactin and growth hormone secreting cells in the anterior pituitary of a passerine.

Plasma prolactin (PRL) is released from lactotrophs in the anterior pituitary. As plasma PRL levels rise during incubation in domestic fowl, the number of lactotrophs (PRL-immunoreactive, PRL-IR cells) increases while the number of growth hormone secreting cells, somatotrophs (GH-IR cells), declines. We measured plasma PRL levels using radioimmunoassay (RIA) and examined the distribution of lactotrophs and somatotrophs in the anterior pituitary of breeding and nonbreeding zebra finches of known ages with and without prior breeding experience using fluorescent immunohistochemistry (IHC).

Extent and variability of interstitial telomeric sequences and their effects on estimates of telomere length.

Telomeres often shorten with time, although this varies between tissues, individuals and species, and their length and/or rate of change may reflect fitness and rate of senescence. Measurement of telomeres is increasingly important to ecologists, yet the relative merits of different methods for estimating telomere length are not clear. In particular the extent to which interstitial telomere sequences (ITSs), telomere repeats located away from chromosomes ends, confound estimates of telomere length is unknown.

Interrelations among immune defense indexes reflect major components of the immune system in a free-living vertebrate.

Understanding the relationships among immune components in free-living animals is a challenge in ecoimmunology, and it is important not only for selecting the immune assays to be used but also for more knowledgeable interpretation of results. In this study, we investigated the relationships among six immune defense indexes commonly used by ecoimmunologists and measured simultaneously in individual free-living tree swallows. Three main axes of variation in immune function were identified using a principal components analysis, representing variation in T-cell, B-cell, and innate immunity.

Consequences of immune system aging in nature: a study of immunosenescence costs in free-living Tree Swallows.

Immunosenescence, the aging of the immune system, is well documented in humans and laboratory models and is known to increase infection risk, morbidity, and mortality among the old. Immunosenescence patterns have recently been unveiled in various free-living populations, but their consequences in the wild have not been explored. We investigated the consequences of immunosenescence in free-living Tree Swallows Tachycineta bicolor through a field experiment simulating a bacterial infection (challenge with lipopolysaccharide, LPS) in females of different ages during the nestling rearing period.

Maternal effects increase within-family variation in offspring survival.

Maternal effects are environmental components of phenotypes that complicate relationships between natural selection and evolution because they often affect phenotypes and fitness simultaneously. We studied the effects of egg size variation on juvenile survival in a population of American coots (Fulica americana). We experimentally evaluated egg size variation at three levels: across the population, within natal nests, and within foster nests.

Individual variation in baseline and stress-induced corticosterone and prolactin levels predicts parental effort by nesting mourning doves.

Endocrine systems have an important mechanistic role in structuring life-history trade-offs. During breeding, individual variation in prolactin (PRL) and corticosterone (CORT) levels affects behavioral and physiological processes that drive trade-offs between reproduction and self-maintenance. We examined patterns in baseline (BL) and stress induced (SI; level following a standard capture-restraint protocol) levels of PRL and CORT for breeding mourning doves (Zenaida macroura).

Evolutionary ecology of endocrine-mediated life-history variation in the garter snake Thamnophis elegans.

The endocrine system plays an integral role in the regulation of key life-history traits. Insulin-like growth factor-1 (IGF-1) is a hormone that promotes growth and reproduction, and it has been implicated in the reduction of lifespan. IGF-1 is also capable of responding plastically to environmental stimuli such as resource availability and temperature.

Ontogeny of innate and adaptive immune defense components in free-living tree swallows, Tachycineta bicolor.

Little is known about the development of immune function in wild animals. We investigated the ontogeny of immune defense in a free-living bird, the tree swallow. We assessed total and differential leukocyte counts, natural antibodies, complement activity, in vivo skin swelling response, and in vitro lymphocyte proliferation and compared the levels of development between nestlings and young adults.

The effects of maternal corticosterone levels on offspring behavior in fast- and slow-growth garter snakes (Thamnophis elegans).

During embryonic development, viviparous offspring are exposed to maternally circulating hormones. Maternal stress increases offspring exposure to corticosterone and this hormonal exposure has the potential to influence developmental, morphological and behavioral traits of the resulting offspring. We treated pregnant female garter snakes (Thamnophis elegans) with low levels of corticosterone after determining both natural corticosterone levels in the field and pre-treatment levels upon arrival in the lab.

Decoupling morphological development from growth in periodically cooled zebra finch embryos.

Temperature affects growth and development, and morphometry can provide a quantitative description of how temperature changes affect the resulting phenotype. We performed a morphometric analysis on zebra finch (Taeniopygia guttata) embryos that were either exposed to periodic cooling to 20 or 30 degrees C throughout incubation over a background temperature of 37.5 degrees C, or were incubated at a constant temperature of 37.

Telomerase activity is maintained throughout the lifespan of long-lived birds.

Telomerase is an enzyme capable of elongating telomeres, the caps at the ends of chromosomes associated with aging, lifespan and survival. We investigated tissue-level variation in telomerase across different ages in four bird species that vary widely in their life history. Telomerase activity in bone marrow may be associated with the rate of erythrocyte telomere shortening; birds with lower rates of telomere shortening and longer lifespans have higher bone marrow telomerase activity throughout life.

A laboratory exercise to illustrate increased salivary cortisol in response to three stressful conditions using competitive ELISA.

Perceived stress activates the hypothalamus-pituitary-adrenal axis, resulting in the release of glucocorticoids into the systemic circulation. Glucocorticoids cause the elevation of blood glucose, providing the necessary energy for the organism to cope with stress. Here, we outline a laboratory exercise that uses a competitive ELISA kit to illustrate the response of salivary cortisol concentrations to three stressful conditions.

Immunosenescence in some but not all immune components in a free-living vertebrate, the tree swallow.

A wide diversity of free-living organisms show increases in mortality rates and/or decreases in reproductive success with advancing age. However, the physiological mechanisms underlying these demographic patterns of senescence are poorly understood. Immunosenescence, the age-related deterioration of immune function, is well documented in humans and laboratory models, and often leads to increased morbidity and mortality due to disease.

Longer telomeres associated with higher survival in birds.

Differences in individual quality and survival within species are a major focus in evolutionary ecology, but we know very little about the underlying physiological mechanisms that determine these differences. Telomere shortening associated with cellular senescence and ageing may be one such mechanism. To date, however, there is little evidence linking telomere length and survival.

Periodic cooling of bird eggs reduces embryonic growth efficiency.

For many bird embryos, periodic cooling occurs when the incubating adult leaves the nest to forage, but the effects of periodic cooling on embryo growth, yolk use, and metabolism are poorly known. To address this question, we conducted incubation experiments on eggs of zebra finches (Taeniopygia guttata) that were frequently cooled and then rewarmed or were allowed to develop at a constant temperature. After 12 d of incubation, embryo mass and yolk reserves were less in eggs that experienced periodic cooling than in controls incubated constantly at 37.

Cell-mediated immunosenescence in birds.

The phytohaemagglutinin (PHA) skin test response, used to assess cell-mediated immunity, is known to vary with many social and energetic factors, but the effects of age have received little attention. We found that the PHA response of immature birds was lower than those of the youngest breeding adults and were decreased in adults. Whenever possible, age should be included as a covariate when the PHA skin test is used to assess immunocompetence in ecological immunology.

Telomerase expression is differentially regulated in birds of differing life span.

Cellular senescence caused by telomere shortening has been suggested as one potential causal agent of aging. In some tissues, telomeres are maintained by telomerase; however, telomerase promotes tumor formation, suggesting a trade-off between aging and cancer. We predicted that telomerase activity should vary directly with life span.

Telomeres shorten more slowly in long-lived birds and mammals than in short-lived ones.

We know very little about physiological constraints on the evolution of life-history traits in general, and, in particular, about physiological and molecular adjustments that accompany the evolution of variation in lifespan. Identifying mechanisms that underlie adaptive variation in lifespan should provide insight into the evolution of trade-offs between lifespan and other life-history traits. Telomeres, the DNA caps at the ends of linear chromosomes, usually shorten as animals age, but whether telomere rate of change is associated with lifespan is unknown.

The natural history of telomeres: tools for aging animals and exploring the aging process.

We have been exploring the use of telomere length as a technique to age animals. If telomere restriction fragments (TRFs) shorten predictably with age in a particular tissue, then measurement of TRFs will allow estimation of ages of animals when age cannot be measured directly. This would be particularly useful in population studies where tissue samples can be collected, but age of individuals or age structure of the population is otherwise unknown.

Calibrating the telomere clock in common terns, Sterna hirundo.

Field biologists often work with animals for which there are no prior history. A marker of an animal's age would offer insight into how age and experience affect reproductive success and other life history parameters. We previously reported that length of telomere restriction fragments shorten predictably with age in the captive zebra finch (Taeniopygia guttata).

Telomere length provides a new technique for aging animals.

Field biologists often work with animals for which there is no prior history. A marker of an animal's age would offer insight into how age and experience affect reproductive success and other life history parameters. Telomere length shortens with age in cultured cells and mouse and human tissues.

Physiological condition and reproductive consequences in adelie penguins.

Animals must make "decisions" (e.g., when or whether to breed, the effort to put into a breeding episode) by integrating physiological, environmental and social inputs.