Sharks and rays, members of the ancient group known as chondrichthyans, have long fascinated scientists with their evolutionary adaptations. A recent study by Joel Harrison Gayford, a marine biologist at James Cook University, Australia, sheds light on two rare and unusual reproductive strategies that could help explain the long-term survival of these marine predators.
Published in the Royal Society Open Science journal, Gayford’s research focuses on the evolutionary significance of facultative parthenogenesis and multiple embryos per egg case (MEPE) in chondrichthyans—a group that also includes skates and chimaeras.
Diverse Reproduction in Chondrichthyans
Unlike most animals, which typically reproduce through one consistent method, chondrichthyans display a remarkable diversity of reproductive strategies. Some species lay eggs (oviparity), others give birth to live young (viviparity), and some have placental connections to their offspring. Certain species even consistently give birth to twins.
This reproductive diversity is believed to be a key factor in the evolutionary success of sharks and rays, which have existed for hundreds of millions of years—longer than many other life forms on Earth.
Facultative Parthenogenesis: Reproducing Without Males
One of the rare reproductive strategies highlighted in the study is facultative parthenogenesis, where females can produce offspring without mating with males. While this phenomenon is known in other animal groups, it is surprisingly frequent in some shark species. Interestingly, some female sharks choose parthenogenesis even when males are available, possibly due to a preference for cloning their own genetics over using suboptimal male DNA.
This self-reproduction method may offer an evolutionary backup in environments where males are scarce, ensuring the survival of the species.
Multiple Embryos Per Egg Case (MEPE): A High-Risk, High-Reward Strategy
The second strategy examined is MEPE, where a single egg case contains several embryos. While this method reduces energy expenditure and effort for the mother, it also increases risk. If the egg case is discovered by a predator, all embryos could be lost at once. Despite this risk, the strategy may offer evolutionary benefits under certain ecological conditions—though more research is needed to fully understand its advantages.
Why These Strategies Matter for Evolutionary Biology
Gayford’s findings contribute to a growing body of knowledge about evolutionary adaptability in marine species. By studying these rare reproductive methods, scientists can better understand how marine animals like sharks and rays have thrived across geological eras.
Conclusion
The study emphasizes that reproductive flexibility may be key to the long-term survival of sharks, rays, and other chondrichthyans. Whether through self-cloning or producing multiple embryos at once, these unusual strategies reveal just how adaptable and resilient these marine creatures can be.
Reference:
- Joel Harrison Gayford. The adaptability of facultative parthenogenesis and ‘multiple embryos per eggcase’ as alternative reproductive strategies in Chondrichthyes. Royal Society Open Science (2025). DOI: 10.1098/rsos.242030