There can be few topics that have attracted more debate and spread such confusion than the role of testosterone in vertebrate aggression. This is due in large part to the lack of consensus on testosterone treatment and expression of aggression, but also because social interactions increase testosterone secretion in some species but not others (e.g., Harding, 1983; Wingfield et al., 1994 ). There have been numerous attempts to define aggression, not surprisingly given the tremendous diversity of vertebrates and the enormous variety of contexts in which aggression is expressed. For example, songbirds may use a broad spectrum of behavioral traits when expressing aggression. These include song rate, song stereotypy, number of points (with wing droops and elevated tail), trill vocalizations and wing waves, flights (around the intruder), grass/substrate pulling, bill wipes, closest approach to intruder, attacks, fights, and persistence of aggression after removal of an intruder ( Sperry et al., 2003; Wingfield, 1985 ). Many of these traits involve a mixture of auditory and postural signals utilizing very different neuronal circuits. Additional sensory modalities may be used in other vertebrates adding greatly to the complexity of signals and neuronal circuits involved. For example, compare the hormone mechanisms underlying
Hormones and Behavior – Elsevier
Published: Sep 1, 2005
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