Uterine and eggshell structure and histochemistry in a lizard with prolonged uterine egg retention (Lacertilia, Scincidae, Saiphos)

Abstract

The eggshell of lizards is a complex structure composed of organic and inorganic molecules secreted by the oviduct, which protects the embryo by providing a barrier to the external environment and also allows the exchange of respiratory gases and water for life support. Calcium deposited on the surface of the eggshell provides an important nutrient source for the embryo. Variation in physical conditions encountered by eggs results in a tradeoff among these functions and influences eggshell structure. Evolution of prolonged uterine egg retention results in a significant change in the incubation environment, notably reduction in efficiency of gas exchange, and selection should favor a concomitant reduction in eggshell thickness. This model is supported by studies that demonstrate an inverse correlation between eggshell thickness and length of uterine egg retention. One mechanism leading to thinning of the eggshell is reduction in size of uterine shell glands. Saiphos equalis is an Australian scincid lizard with an unusual pattern of geographic variation in reproductive mode. All populations retain eggs in the uterus beyond the embryonic stage at oviposition typical for lizards, and some are viviparous. We compared structure and histochemistry of the uterus and eggshell of two populations of S. equalis, prolonged egg retention, and viviparous to test the hypotheses: 1) eggshell thickness is inversely correlated with length of egg retention and 2) eggshell thickness is positively correlated with size of shell glands. We found support for the first hypothesis but also found that eggshells of both populations are surprisingly thick compared with other lizards. Our histochemical data support prior conclusions that uterine shell glands are the source of protein fiber matrix of the eggshell, but we did not find a correlation between size of shell glands and eggshell thickness. Eggshell thickness is likely determined by density of uterine shell glands in this species.

A Structurally Enhanced, Ergonomically and Human–Computer Interaction Improved Intelligent Seat’s System

“…The new structure is inspired by a common object in daily lives: the eggshell. For the embryo, the eggshell is an important structure [6]. Firstly, the eggshell forms a chamber with safety for the new developing embryo.…”

“…Thus, we decided to make the back rest and seat bottom hollow [6]. This does not reduce the strength and stiffness of the material but reduces the material costs.…”

“…It is a tiny chip, and one that will soon be remarkably easy to add to nearly any device: inside the frame of a VR (virtual reality) helmet, the bezel of a smart watch, or the chassis of your phone [6]. Some devices with chips are shown in Figure 8.…”

“…The gestures don't have to be huge and exaggerated: one doesn't need to wave like a madman in front of the Kinect [6]. They can be as small as they are in real life.…”

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