Reproductive Biology and Phylogeny of Chondrichthyes

Chondrichthyan fishes successfully utilize a remarkably diverse and complex array of reproductive modes, all of which result in the production of a small number of relatively large offspring. Internal fertilization and an adaptable reproductive tract, coupled with mechanisms for endocrine regulation, facilitated evolution of oviparity and diverse viviparous strategies. Since chondrichthyans are anamniotes, the morphological and physiological mechanisms recruited for specific reproductive modes involve the yolk sac and uterine specializations and not an amnion, chorion or allantois. Reproduction is either totally reliant on yolk stores as lecithotrophy or the mother augments yolk stores, via a variety of mechanisms, as matrotrophy. Internal fertilization is universal in chondrichthyan fishes and, as such, requires a suite of biological activities, including behavioral, morphological and physiological mechanisms, to ensure successful copulation and fertilization. This volume correlates available data and ideas concerning the development, reproductive morphology, function and phylogeny of chondrichthyan fishes. The information presented and discussed is fundamental to our understanding of oogenesis, spermatogenesis, gestation, regulation of reproductive tract function, sperm storage, nutrient provision, placentation, phylogeny and are pertinent to our concepts of the origin of live bearing in general. New and exciting data is presented including the idea that yolk sac viviparity is the plesiomorphic state rather than oviparity.