We’ve been wrong about how animals decide which eggs to release for decades, and a tiny shark just proved it.
April 15, 2026
Original Paper
Selective activation of LH-dependent transcriptional pathways determines ovulatory follicles in the hierarchical ovary of cloudy catshark
bioRxiv · 10.64898/2026.04.10.717848
The Takeaway
For years, biologists assumed that ovulation was a simple numbers game: if an egg grew enough hormone 'docking stations,' it would release. This is known as the LHR-threshold model, and it is the standard way we explain reproduction in almost all vertebrates, including humans. But by studying the cloudy catshark, researchers discovered that the 'winning' eggs don't actually have more receptors; they just have a unique genetic 'on-switch' that the other eggs lack. This means the body isn't just waiting for a mechanical threshold to be met, but is instead making a selective, complex decision at the molecular level. This discovery completely flips the script on our understanding of fertility and could eventually lead to entirely new ways of treating reproductive issues or designing birth control.
From the abstract
The number of offspring produced per reproductive cycle varies widely across animals and is constrained by the number of ovarian follicles that proceed to ovulation. In vertebrates, this phenomenon has been explained by a luteinizing hormone receptor (LHR)-threshold model, in which only follicles expressing sufficient levels of LHR respond to the LH surge and proceed to ovulation. Here we propose a novel mechanism that explains the difference between ovulatory (F1) and non-ovulatory (F2) follicl