Zoology 328

Zol. 328

Written Exercise 3

Residual yolk in reptiles is an often discussed subject. Many sources indicate that it is used for energy by the animals, while other sources claim that it is not used for anything. The ways of internalization also differs among the many different reptiles. While some are the same others vary. This paper will discuss the possibility of both while also describing what residual yolk is and how it is internalized.

As stated in Radder et al. (2007) post hatching parental care is rarely seen in reptiles. It may be explained as the reason that extra yolk is sometimes left by the mothers. It may possibly provide some value to the hatchlings. The residual yolk of the Physignathus lesueurii, Varanus rosenbergii, Amphibolurus muricatus, Calotes versicolor, Apalone mutica, and Iguana iguana were all looked at to discover what the residual yolk was used for. There were varying results between the different species.

It is stated by Troyer (1987) that Iguana iguana internalizes the yolk by drawing it into the body by contractions of the embryonic membrane. The yolk was found to have a significant role in the iguana’s growth pattern because without the residual yolk the iguana did not reach the same length as an iguana with the residual yolk.

Pezaro et al. (2013) stated that both Physignathus lesueurii and Varanus rosenbergii internalized the residual yolk in the same manner. After getting their head through the egg both species remained motionless for hours. During this time the yolk was being tightly surrounded by the amnion and internalized by both species. Only then would both species finish the hatching process. It was discovered that the hatchlings that did not internalize the yolk successfully were significantly smaller than the hatchlings that were successful.

As stated by Radder et al. (2007) the Amphibolurus muricatus draws the residual yolk into its body before completing the hatching process. It was discovered that while although...