Browsing by Author "Kennamer, Robert A."

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    Incubation temperature and social context affect the nest exodus of precocial ducklings
    Hope, Sydney F.; Kennamer, Robert A.; van Montfrans, Schuyler G.; Hopkins, William A. (2019-03)
    The environments that animals experience during development have important fitness consequences. In birds, parents influence the developmental environment of their offspring through incubation. Subtle changes in incubation temperature affect offspring morphology and physiology, such as growth, immune function, and thermoregulation, yet little is known about how it may affect critical early-life behaviors. Because expression of behavior can be influenced by the social environment, the effect of incubation temperature on behavior may be context-dependent. We investigated whether incubation temperature and social context influence a critical early-life task in wood ducks (Aix sponsa). Wood ducks nest in tree cavities and, shortly after hatching, ducklings must jump and climb out of the cavity. Failure to exit the nest is fatal. In 2 experiments, we incubated eggs at different mean temperatures and examined the nest exodus of ducklings individually and in mixed-incubation temperature pairs. When tested individually, ducklings incubated at 35.8 degrees C and 37.0 degrees C were similar to 2.5 times more successful at exiting the nest, and jumped and climbed more often, than those incubated at 35.0 degrees C. However, in an experiment conducted the following year, we found that social interactions mitigated these effects and there was no difference in nest exodus success when ducklings incubated at 35.0 degrees C and 36.0 degrees C were tested together in pairs. This may be because, when in pairs, ducklings incubated at the low-temperature experience social enhancement whereas those incubated at the high temperature maintain similar behaviors. These results advance our understanding of how parental effects influence offspring behaviors and performance within different social contexts.
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    Limited Support for Thyroid Hormone or Corticosterone Related Gene Expression as a Proximate Mechanism of Incubation Temperature-Dependent Phenotypes in Birds
    Hope, Sydney F.; Buenaventura, Christopher R.; Husain, Zahabiya; DuRant, Sarah E.; Kennamer, Robert A.; Hopkins, William A.; Thompson, Christopher K. (Frontiers, 2019-07-05)
    The conditions that animals experience during early development can have profound consequences for health and fitness. In birds, one of the most important aspects of development is egg incubation temperature. A small decrease in average temperature leads to various impacts on offspring phenotype, such as smaller body sizes, slower growth rates, and less efficient metabolic activity. Little is known, however, about the proximate mechanisms underlying these incubation temperature-induced phenotypic changes. Two important hormones which could play a proximate role are thyroid hormone and corticosterone, which mobilize stored energy reserves and coordinate the normal growth of tissues, particularly in the brain. Previous research shows that circulating blood concentrations of both hormones are influenced by incubation temperature, but the mechanism by which incubation temperature may lead to these changes is unknown. We hypothesized that incubation temperature induces changes in thyroid hormone and corticosterone regulation, leading to changes in expression of hormone-sensitive genes in the brain. To test this, we incubated wood duck (Aix sponsa) eggs at three different temperatures within the natural range (35.0, 35.8, and 37.0 degrees C). We measured mRNA expression of thyroid hormone-related neuroendocrine endpoints (deiodinase 2/3, thyroid hormone receptor alpha/beta, neural regeneration related protein, and Krueppel-like factor 9) in newly hatched ducklings and corticosterone-related neuroendocrine endpoints (mineralocorticoid receptor, glucocorticoid receptor, cholecystokinin, and brain-derived neurotrophic factor) in 15 day-old ducklings using qPCR on brain tissue from the hippocampus and hypothalamus. Contrary to our predictions, we found that mRNA expression of thyroid hormone-related endpoints in both brain areas were largely unaffected by incubation temperature, although there was a trend for an inverse relationship between mRNA expression and incubation temperature for several genes in the hypothalamus. We also found that mineralocorticoid receptor mRNA expression in the hypothalamus was lower in ducklings incubated at the low relative to the high temperatures. This study is the first to evaluate the effects of incubation temperature on mRNA expression of neuroendocrine endpoints in the developing avian brain and suggests that these particular endpoints may be largely resistant to changes in incubation temperature. Thus, further research into the proximate mechanisms for incubation temperature-induced developmental plasticity is needed.