Media release

From: The Royal Society

The adaptability of facultative parthenogenesis and ‘multiple embryos per eggcase’ as alternative reproductive strategies in Chondrichthyes

Sharks, rays, and their relatives, are a fascinating case study for investigating reproductive biology. Several 'rare' cases of parthenogenesis (or so called 'virgin birth') have been reported in sharks and rays over the last two decades, but we have little understanding of how frequent this behaviour is, or why it occurs. Similarly, most egg laying species produce only one embryo per egg, but in some shark and ray species there are up to 8 embryos per eggcase. Again, we have very little understanding of why this might be, or how frequent this behaviour is. In this article I summarise the the potential causes and consequences of these 2 unusual reproductive strategies, ultimately determining that they likely represent evolved adaptations. I then consider the contexts under which these traits may be beneficial, their potential consequences for conservation and extinction vulnerability, and finally open questions in the field.