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The next morning Janet was so much calmer, and at breakfast spoke so decidedly of going to her mother’s, that Mrs Pettifer and Mrs Raynor agreed it would be wise to let her know by degrees what had befallen her husband, since as soon...

Abstract In a population of stream-resident stickleback from British Columbia, females frequently have orange-red throats which are conspicuous to the human eye and, according to two straightforward physical measures of coloration, are more intensely red than the throats of anadromous females. Stream and anadromous males from these populations, however, do not differ for a reflectance-based index of red chroma. This suggests that exceptional female red coloration in the stream population has not evolved as a byproduct of the evolution of exceptional coloration in males. In contrast to results for female lateral barring in another threespine stickleback population, red is not strongly associated with reproductive readiness and unlikely to function strictly as a signal of readiness to mate. Larger stream females have more intensely red throats though this pattern was significant only in one year and according to one technique. With these findings and the extensive literature already available for this species, the threespine stickleback becomes a promising model system for studying the evolution of female secondary sexual characters in species with conventional sexual dimorphism.

Male green anoles (Anolis carolinensis) court females by extending a bright red throat fan, called a dewlap. The dewlap is larger in males than in females who do not display the structure in the context of courtship. The ceratohyoid muscle and second ceratobranchial cartilage which control dewlap extension are significantly larger in male than in female anoles. Neurons innervating the ceratohyoid muscle were retrogradely labeled by injecting the muscle with fast blue and were found to be located in the vagal portion of nucleus ambiguus (Amb X), as well as in the region containing the glossopharyngeal portion of nucleus ambiguus (Amb IX) and the ventral portion of the motor nucleus of the facial nerve (nVIImv). Cells in both areas were larger in males than in females. These parallels between structure and function provide the opportunity to study mechanisms of sexual differentiation of brain and behavior.

Male anoles extend a bright red throat fan, called a dewlap, during both courtship and aggressive encounters. Female anoles perform this behavior less often than males and only in aggression towards both sexes. The cartilage, muscle fibers, and motoneuron somata controlling the display are larger in males than females. In the present study, we used the Golgi technique in an effort to characterize more completely the morphology of these dewlap motoneurons, and to investigate whether the dendritic arborization is different between the sexes. In addition to describing the morphology, we report that the length of processes, and numbers of primary processes and branch points are comparable in males and females. This similarity in arborization represents an intriguing contrast to other sexually dimorphic neuromuscular systems.