Among vertebrates, oviparous animals lay eggs with a calcified eggshell and eggs are laid in an external environment, while viviparous animals retain eggs in oviduct until they give birth to live young. Viviparity has evolved in the lineage of snakes and lizards (squamates) over 100 times, more than all other vertebrate groups. Embryos of oviparous squamates obtain calcium from both yolk and eggshell while their viviparous counterparts lack a calcified eggshell and must obtain their calcium solely from yolk, or from yolk plus placental transfer. During embryonic development, squamates rely on calcium to build the skeleton before hatching. The extent of skeletal ossification at hatching or birth varies considerably among vertebrates. This study aims to determine if skeletal development/ossification varies in association with reduced eggshell calcium in embryos of viviparous squamate species. We studied the amount of ossification and overall size of embryos and hatchlings from an oviparous and a viviparous population of the reproductively bimodal lizard Zootoca vivipara. Previous studies suggested that limb development is delayed, and that overall size is reduced in viviparous squamates. We tested the hypothesis that viviparous embryos and hatchlings are more skeletally immature and smaller in size than oviparous embryos and hatchlings in squamates. To achieve this, specimens from both populations, spanning multiple stages of embryonic development including hatchlings, were cleared & stained to reveal skeletal cartilage and bone. Lengths of total body, humerus, femur, skull and Meckel’s cartilage were measured from photographs of cleared & stained specimens taken with a Cannon EOS 70D camera on a Motic, Leica MZ9 Compound Microscope, with a measurement reference in each picture. Photos were calibrated to the measurement reference and total length measurements were obtained using iSolutionLite® software. In addition to total measurements, the lengths of ossified portions on the humerus and femur were also measured. Preliminary results revealed that total length of the skull and body are reduced in embryos and hatchlings of viviparous specimens. Total length of the limbs and of Meckel’s cartilage are not significantly different between populations. However, it appears that the amount of ossification in the limbs is reduced in oviparous specimens. These preliminary findings do not support our hypothesis and indicate that reduction in eggshell calcium in embryos of viviparous populations does not negatively impact ossification during development but does influence overall size.
| Identifer | oai:union.ndltd.org:ETSU/oai:dc.etsu.edu:asrf-1130 |
| Date | 05 April 2018 |
| Creators | Tedder, Amanda, Pyles, Rebecca, Stewart, James R |
| Publisher | Digital Commons @ East Tennessee State University |
| Source Sets | East Tennessee State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Appalachian Student Research Forum |
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