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Steroid hormones effect changes in both neuroanatomy and aggressive behavior in animals of various taxa. However, whether changes in neuroanatomy directly underlie changes in aggression is unknown. We investigate this relationship among steroid hormones, neuroanatomy, and aggression in a free-living vertebrate with a relatively simple nervous system, the(More)
The neuropeptide arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin (AVP) are neuromodulators known to be steroid sensitive and associated with social behaviors in a number of vertebrate taxa. However, the role of AVT/P in the regulation of aggression remains unclear and contrasting effects of this peptide on aggression are seen in(More)
Testosterone is usually thought to be the major sex steroid regulating adult male territorial aggression in vertebrates. However, recent evidence has suggested a role for progesterone, as well as testosterone, in the organization of the two male reproductive phenotypes of tree lizards (Urosaurus ornatus), which differ in adult levels of territorial(More)
The neural mechanisms by which steroid hormones regulate aggression are unclear. Although testosterone and its metabolites are involved in both the regulation of aggression and the maintenance of neural morphology, it is unknown whether these changes are functionally related. We addressed the hypothesis that parallel changes in steroid levels and brain(More)
The regulation of hatching in oviparous animals is important for successful reproduction and survival, but is poorly understood. We unexpectedly found that RU-486, a progesterone and glucocorticoid antagonist, interferes with hatching of viable tree lizard (Urosaurus ornatus) embryos in a dose-dependent manner and hypothesized that embryonic glucocorticoids(More)
Adolescent abstainers have largely been ignored in the literature. This article describes the reasons for not drinking of 2366 Israeli Jewish, Moslem, Druze and Christian adolescents in the north of Israel in the winter of 1994. It analyzes the findings by religious group, religiosity (secular versus religious Jews), location and gender of Jews, and school(More)
1. Maternal investment in egg quality can have important consequences for offspring fitness. For example, yolk antioxidants can affect embryonic development as well as juvenile and adult phenotype. Thus, females may be selected to advertise their yolk antioxidant deposition to discriminatory males via ornamental signals, perhaps depending on the(More)
Testosterone (T) induces singing behavior and mediates changes in the sizes and neuroanatomical characteristics of brain regions controlling singing behavior (song control regions, SCRs) in songbirds. These effects may require the enzymatic conversion of T into androgenic and estrogenic metabolites by brain tissues and can be modulated by factors such as(More)
Indicator models of sexual selection suggest that signal honesty is maintained via costs of ornament expression. Carotenoid-based visual signals are a well-studied example, as carotenoids may be environmentally limited and impact signaler health. However, not all bright yellow, orange and red ornaments found in vertebrates are carotenoid-based; pteridine(More)
Long-term captivity can result in abnormal behavior and physiology in many vertebrates. Here, we examine whether semi-natural, outdoor captive environments can offer a compromise, allowing much of the experimental control afforded by captivity, while providing the environmental conditions essential for normal behavior and physiology. We first determined(More)