Another Tortoise Adventure

Breeding management of egg-laying species such as birds and tortoises can be difficult because we often manage the incubation of the egg, as opposed to mammals where the mother takes care of the embryo. If a bird or tortoise egg does not develop, is it because the pair did not mate, the male is not producing sperm, or because the eggs were not correctly incubated? It is very important to be able to tell the difference, because the solution depends on whether it is a problem with the male or the female, or if there is a problem with how the eggs are incubated. 

To solve this conundrum, one of our lab’s research associates, Kaitlin Croyle, employed a technique to test the fertility of eggs in over a dozen bird species. She then adapted the technique for chelonians (turtles and tortoises). During the development of this technique, we worked closely with Dr. Paul Gibbons, the Chief Operating Officer of the Turtle Conservancy and Managing Director and Veterinarian of the Behler Chelonian Center. 

So, when Dr. Gibbons called and asked if we could help him figure out why their ploughshare tortoise eggs did not exhibit any signs of embryonic development, we packed our travel microscope and headed to the Chelonian Center. The ploughshare tortoises are from a small area surrounding a single bay in Madagascar. 

This species is critically endangered with only around 600 individuals left in the wild, and there is a very real possibility they will go extinct in the wild over the next 10-15 years due to poaching for the pet trade (IUCN red list 2016). 

It is easy to see why Dr. Gibbons and the Turtle Conservancy were so concerned about getting their male and female to breed and contribute to the population. While the female was laying eggs, about 2-6 eggs per clutch, there were no visible signs of a growing embryo in any of the eggs.  

Dr. Gibbons is of the opinion that the males need to see other males in order to stimulate an increase in their reproductive hormone levels so they can produce functional sperm. Our job was to confirm whether or not there was any sperm present on the membranes within the eggs, which would indicate that the male had bred the female and his sperm were capable of reaching the egg. 

Kaitlin examined one egg each from two different clutches that had been incubated for several weeks. Unfortunately, she could not confirm the presence of sperm, and this information did corroborate Dr. Gibbons’ hypothesis about male-male competition. Although we did not confirm the male’s fertility, this technique did provide some answers to help Dr. Gibbons make decisions about future steps in the Turtle Conservancy’s ploughshare conservation project. 

This collaboration with the Behler Chelonian Center and the Turtle Conservancy is just one example of why we work for the San Diego Zoo Institute for Conservation Research. Being part of an Institute where our research has a direct impact on breeding, management and the conservation of endangered species gives us a feeling of accomplishment that is hard to find anywhere else.

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