Description
Sharks are members of elasmobranch fish characterized by a cartilaginous skeleton. Sharks are distributed throughout the world’s oceans. It's often the case that a shark species is the apex predator in their environment. However, despite the crucial ecological role sharks play, much yet is to be discovered regarding their reproductive propensities. The intent of this study is to use maternal risk-management theory as a theoretical framework for understanding the natural selection pressures that have shaped pup number, relative pup size, pup diversity, and diverse brooding tactics in sharks (oviparity, viviparity, and oviviviparity). This study analyzed data on 123 species of sharks using multivariate statistics. The maternal risk management model predicts that pup size and pup number per litter were independent maternal investments. Shark species in which offspring are threatened by predators produce a larger litter size. In contrast, shark species in which offspring are vulnerable to patchy distribution of food are threatened by starvation. In this study we found that pup size and pup number were independent. Furthermore, female size was a predictor of pup size but not pup number. Phylogeny explained a small fraction of variation in pup number. However, phylogeny did explain a larger fraction of variation in pup size. Predation pressures were found to predict the number of pups per breeding event across shark species. Additionally, both female size at maturity and prey scarcity were found to predict the size of pups at birth. Prey scarcity was also found to predict a female shark’s size at maturity.
Multiple Reproductive Adaptations Ameliorate Pup Mortality by Predation in Elasmobranchii Sharks
Sharks are members of elasmobranch fish characterized by a cartilaginous skeleton. Sharks are distributed throughout the world’s oceans. It's often the case that a shark species is the apex predator in their environment. However, despite the crucial ecological role sharks play, much yet is to be discovered regarding their reproductive propensities. The intent of this study is to use maternal risk-management theory as a theoretical framework for understanding the natural selection pressures that have shaped pup number, relative pup size, pup diversity, and diverse brooding tactics in sharks (oviparity, viviparity, and oviviviparity). This study analyzed data on 123 species of sharks using multivariate statistics. The maternal risk management model predicts that pup size and pup number per litter were independent maternal investments. Shark species in which offspring are threatened by predators produce a larger litter size. In contrast, shark species in which offspring are vulnerable to patchy distribution of food are threatened by starvation. In this study we found that pup size and pup number were independent. Furthermore, female size was a predictor of pup size but not pup number. Phylogeny explained a small fraction of variation in pup number. However, phylogeny did explain a larger fraction of variation in pup size. Predation pressures were found to predict the number of pups per breeding event across shark species. Additionally, both female size at maturity and prey scarcity were found to predict the size of pups at birth. Prey scarcity was also found to predict a female shark’s size at maturity.
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