7 - Reproduction strategies

Elasmobranchs are an evolutionarily conserved group that has success- fully survived for over 400 million years. The permanence of elasmobranch populations has largely depended on the reproductive strategies of the population, as the primary requirement for successful propagation of any species and their individuals is the ability to reproduce. In vertebrates, reproductive strategies are regulated by the brain-gonadal axis, which controls the synthesis of reproductive hormones triggering all aspects related to reproduction. This chapter details the different reproductive strategies employed by elasmobranchs, from the wider range of reproductive modes including oviparity (egg-laying) and different forms of viviparity (live- bearing); followed by a description of the different reproductive cycles, from seasonal to continuous, displayed by both sexes. Finally, the role of reproductive hormones in both females and males regulating gametogenesis and the different reproductive cycles are discussed. The endocrine control of the elasmobranch reproductive strategies are preserved throughout vertebrate evolution, however they are distinct within this group.