Metabolic costs of heat solicitation calls in relation to thermal need in embryos of American white pelicans

Oxidative stress mediates physiological costs of begging in magpie (Pica pica) nestlings

BACKGROUND

Theoretical models predict that a cost is necessary to guarantee honesty in begging displays given by offspring to solicit food from their parents. There is evidence for begging costs in the form of a reduced growth rate and immunocompetence. Moreover, begging implies vigorous physical activity and attentiveness, which should increase metabolism and thus the releasing of pro-oxidant substances. Consequently, we predict that soliciting offspring incur a cost in terms of oxidative stress, and growth rate and immune response (processes that generate pro-oxidants substances) are reduced in order to maintain oxidative balance.

METHODOLOGY/PRINCIPAL FINDINGS

We test whether magpie (Pica pica) nestlings incur a cost in terms of oxidative stress when experimentally forced to beg intensively, and whether oxidative balance is maintained by reducing growth rate and immune response. Our results show that begging provokes oxidative stress, and that nestlings begging for longer bouts reduce growth and immune response, thereby maintaining their oxidative status.

CONCLUSIONS/SIGNIFICANCE

These findings help explaining the physiological link between begging and its associated growth and immunocompetence costs, which seems to be mediated by oxidative stress. Our study is a unique example of the complex relationships between the intensity of a communicative display (begging), oxidative stress, and life-history traits directly linked to viability.

Ontogeny of vocalizations and movements in response to cooling in chickens fetuses

Bird incubation demands a balance between parental needs for foraging with fetal needs for heat provision and protection so that any means of communication between the fetus and the parents would have an adaptive value. The aim of the study was to investigate whether putative avenues of feto-maternal communication would correlate to physiological changes caused by environmental alterations. Oxygen consumption was used as an indicator of fetal well being. The frequency, duration, intensity and composition of fetal vocalizations and the frequency and intensity of movements were used to evaluate the potential for communicating fetal status quo. Fetuses of broiler chickens (Gallus gallus domesticus) at three developmental stages (day 18, internally pipped and externally pipped) were challenged by a stepwise reduction in ambient temperature down to 30 degrees C. A drop in oxygen consumption in response to lowered temperatures was found in all stages. No differences correlating with temperature variations were found in any of the variables associated with fetal vocalization, even if externally pipped fetuses vocalized more than internally pipped fetuses. Movement occurrence and movement intensity, however, increased initially and decreased at temperatures below 35.0-35.5 degrees C. Considering that the lower limit of optimal development is between 35 and 36 degrees C, the results suggest that fetal movements can be of potential use to the incubating parent to assess and protect the well-being of the fetus.

Are chicken embryos endotherms or ectotherms? A laboratory exercise integrating concepts in thermoregulation and metabolism

This investigative laboratory exercise uses the different relations between ambient temperature and metabolic rate in endotherms and ectotherms as a core concept to answer the following question: What thermoregulatory mode is employed by chicken embryos? Emphasis is placed on the physiological concepts that can be taught with this exercise, including methods for measuring rates of oxygen consumption, the relation between oxygen consumption and metabolic rate, the influence of temperature on metabolic rate, and the differences between endotherms and ectotherms both in the overall magnitude of metabolic rate and in the shape of the relation between metabolic rate and ambient temperature. Included in this article are respirometer designs suitable for teachers working with a wide variety of budgets and available equipment, specific laboratory protocols for collecting data, sample data, thought questions with sample answers, and suggestions for classroom implementation as a 1-, 2- or 3-wk laboratory exercise that can be taught at a variety of undergraduate levels.