03/16/2023
By Rick Hochberg

The Kennedy College of Sciences, Department of Biology, invites you to attend a master’s thesis defense by Stephanie Meyer on “Nanomechanical Properties of Resting Eggshells of Rotifers.”

Defense Date: Thursday, March 30, 2023
Time: 2 to 3 p.m.
Location: Via Zoom
Thesis/Dissertation Title: Nanomechanical Properties of Resting Eggshells of Rotifers.

Committee:

  • Advisor Rick Hochberg, Biology, UML
  • Thiago Q. Araujo, Biology, UML
  • Alison Hamilton, Biology, UML
  • Robert Wallace, Biology, Ripon College, WI
  • Elizabeth Walsh, Biology, University of Texas El Paso

Abstract: Rotifers are microscopic, planktonic animals that play important roles in freshwater food webs. They have complex lifecycles that include both asexual and sexual phases in a population (called cyclical parthenogenesis). The sexual phase leads to the production of diapausing (resting) embryos that are resistant to adverse environmental conditions. This multi-species study investigated the nanomechanical and structural properties of resting eggshells. These properties include hardness, elasticity, and various ultrastructural features. Scanning electron microscopy was used to study eggshell topography; transmission electron microscopy was used to study shell ultrastructure; and atomic force microscopy was used to measure nanomechanics. I used these data to determine if eggshell structure gave insights into properties that may be important in a shell’s ability to withstand abrasion and external forces. Most shells were externally ornamented and contained multiple internal layers, some of which contained air spaces (likely for dispersal). Hardness values did not correlate with ultrastructural features (including thickness) of the eggshells but did show a modest correlation with the number of shell layers. The presence of air spaces did not appear to have an impact on Young’s Modulus of elasticity. Elasticity values were 2.25 Megapascals (Mpa) to 34.16 Mpa. Hardness values had a range of 1.09E-2 Gigapascals (Gpa) to 2.28E-2 Gpa. These values are in line with or higher than values of eggshells from much larger (vertebrate) animals. In total, these data are interpreted to mean that rotifer resting eggshells are not very stiff but instead may flex under pressure without cracking. These eggshells probably evolved nanomechanical properties to withstand being buried under sediments for weeks, months, and years to permit embryos to diapause without disruption.