Patterns of variability are consistent across signal types in the treefrogDendropsophus ebraccatus

Abstract

Animal signal characteristics vary at multiple levels, and this variation can be related to the selective forces acting on signal structure. However, the effectiveness of selection acting on any one signal type may depend on selective forces acting on the same characteristics in other signal types, particularly if the signals share a common physical production mechanism. In anurans, signal variability has been related to the potential for various forms of selection by female choice on the characteristics of male advertisement calls. The significance of variability in the characteristics of another vocalization type, the aggressive call, is less well understood. In the present stiudy, within- and between-male variability was measured in several characteristics of both advertisement and aggressive calls in the treefrog Dendropsophus ebraccatus. Many characteristics of both call types were repeatable within males. Fine-temporal and spectral characteristics generally had low variation within males, whereas gross-temporal characteristics were more variable. Unexpectedly, there were strong correlations between both measures of variability and mean values of the call characteristics of advertisement and aggressive calls. Thus, despite potentially conflicting selection pressures acting on advertisement and aggressive calls, the characteristics of individuals' calls were consistent across these two signal types. The potential forces responsible for consistency across call types are discussed, including morphological constraints and behavioural syndromes that act across different signalling contexts. In general, it is argued that measurements of variability made across multiple signal types, as in the present study, can provide important insights into the evolution of signal structure in organisms with complex signal repertoires. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 131–145.