Published online by Cambridge University Press: 10 August 2009
CHAPTER SUMMARY
The wide diversity of alternative tactics of reproduction found among vertebrates offers a unique opportunity to study the endocrine mechanisms underlying the phenotypic variation of reproductive traits. Here, we first assess the existing conceptual frameworks on the mechanisms underlying the expression of alternative reproductive tactics (ARTs) by reviewing the available data on hormone levels in alternative phenotypes and on the effects of hormone manipulations in different vertebrate taxa. We then highlight recent studies that have opened new avenues of research on the neuroendocrine basis of ARTs, such as the use of functional genomics to study differential gene expression between morphs. Finally, we stress the need to integrate the study of ARTs with the mechanisms underlying the expression of alternative phenotypes and with functional studies of ARTs. Only such an integrative approach will allow a comprehensive understanding of the evolution and development of ARTs.
INTRODUCTION
Setting the scene
According to the classic paradigm of the endocrine control of vertebrate reproduction, the hypothalamus–pituitary–gonadal (HPG) axis controls gonadal maturation, the expression of secondary sexual characters, and reproductive behavior (Figure 7.1A). However, in some species there are males in which gonadal maturation and sperm production are dissociated from the expression of behavioral and morphological male traits (i.e., secondary sexual characters). They are males with male alternative reproductive tactics (ARTs), and they offer unique opportunities to study the proximate mechanisms of reproduction (Figure 7.1B).
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