The development process of turtle eggs!

Hilary holding a loggerhead turtle egg - we took this one for DNA

Blog post by: Hilary Kordecki, Sea Turtle Intern

​Go Babies Go!
 
We are well into our hatchling season having inventoried 125 nests (over halfway through all of our nests!) and well, the hatchlings got me thinking. It’s a miracle how they start off as a tiny, fertilized egg and about 55 days later, emerge as beautiful hatchlings that fit in the palm of your hand. So how do they get from a tiny embryo to a hatchling starting its two-day journey to the Sargasso Sea? I did some digging, and this is what I found.
 
Follicles are fluid-filled sacs found in the ovaries that contain immature eggs. During ovulation, the follicle ruptures and releases the egg into the coelom, a fancy word for the body cavity, where it then travels through and then down into the infundibulum. Sperm is mixed into the folds of the infundibulum and fertilize egg as it passes through into the oviduct. The oviduct is where the real magic happens. It has two different regions, all lined with secretory cells that add different layers to the embryo. The first region is the anterior glandular region which is responsible coating the embryo with albumen. This aids in maintaining the proper osmotic pressure (and subsequently gas exchanges) within the shell. The second region is the shell-forming segment which is responsible for forming the shell membrane, or chorion, around the albumen layer. This layer offers nutrients and also aids in the gas exchange. Natural levels of aragonite (more commonly known as calcium carbonate) result in crystals forming around the shell membrane. When fully formed, around the seventh day after ovulation, the large cohesive group of aragonite crystals make up the outer, leathery shell that we see. Pretty neat right? 
 
In short, the egg follows this flow chart:
Ovary --> Coelom --> Infundibulum --> Oviduct (--> anterior glandular region --> shell-forming segment)
+ aragonite crystals at the end
 
Lastly, here are some fun facts about our mother turtles!

• They have enough follicles for the whole season and any unused ones will be reabsorbed by her body
• They mate multiple times with different partners and then store the sperm in the folds of the infundibulum until egg production
  • This means that she can have multiple different fathers within a single clutch of eggs
• It’s still a mystery how exactly their ovaries manage to regulate the number of follicles released so that the average is approximately 120 follicles
• They nest on average 3-4 times a season with about 2 weeks in between nesting

Turtle on,
-Hilary
 
References:
Bolten, Alan B. & Witherington, Blair E. Loggerhead Sea Turtles. Smithsonian Institution. 2003. Print.
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Spotila, James R. Sea Turtles: A Complete Guide to Their Biology, Behavior, and Conservation. John Hopkins University Press and Oakwood Arts. 2004. Print.

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