Structure and Function of Elasmobranch Egg Capsules

Tom Koob and I are intersted in the amazing biomechanical, biochemical, and evolutionary aspects of the chondrichthian egg capsule. Egg-laying, or oviparity has evolved at least 4 times in the cartilaginous fishes, and an embryo may spend as long as three years in the capsule before hatching. The capsular material is relatively impermeable to oxygen, so the embryo requires a flow of oxygenated water through the capsule as it develops. Small slits open up in the sides of the capsule to allow flow. In the case of skates and chimaeroids the embryo actively pumps water through the capsule by undulating its tail. In sharks the capsule water is passively pumped through the capsule by currents around it. We are investigating the tradeoffs between active and passive flow, the metabolic costs of pumping, the evolution of the capsule shape, and the hydrodynamics of the egg capsule.