External incubation alters the composition of squamate eggshells

Area of Science:

• * Zoology
• * Herpetology
• * Biochemistry

Background:

• * Reptile eggshells are crucial for embryonic development, providing calcium and protection.
• * The composition and changes in eggshell mass during incubation are not fully understood.
• * Understanding eggshell dynamics offers insights into reproductive strategies and the evolution of viviparity.

Purpose of the Study:

• * To quantify calcium and protein content changes in Eumeces (skink) and Opheodrys (snake) eggshells during incubation.
• * To analyze amino acid composition, specifically desmosine and isodesmosine, in relation to incubation.
• * To explore potential mechanisms and physiological significance of eggshell constituent mobilization.

Main Methods:

• * Analysis of calcium and protein content in eggshells at oviposition and post-hatching.
• * Comparison of amino acid profiles (including desmosine and isodesmosine) between pre- and post-incubation eggshells.
• * Comparative analysis across different geographic populations (Missouri and Michigan Eumeces).

Main Results:

• * Significant reductions (17-41%) in calcium concentration and content were observed in both species' eggshells post-incubation.
• * Protein content also decreased substantially (22-86%) following incubation.
• * Eumeces eggshells from Michigan lacked desmosine and isodesmosine, and desmosine concentrations decreased post-incubation in both Missouri and Michigan Eumeces.

Conclusions:

• * Eggshells of Eumeces and Opheodrys undergo significant calcium and protein loss during incubation.
• * Observed changes in amino acid composition, particularly desmosines, suggest active mobilization processes.
• * The study outlines potential pathways for material mobilization, relevant to squamate reproductive physiology and the evolution of reptilian viviparity.