9 research outputs found
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Effects of eggshell removal on embryonic skeletal development in the American alligator (Alligator mississippiensis)
The eggshell of reptiles is essential for not only protecting the embryo, but can also serve as source of calcium for embryonic skeletal development. Whereas embryonic lepidosaurs and chelonians rely on their yolk sac for calcium during development, embryonic archosaurs mobilise eggshell calcium supply to both the embryo and the yolk sac. By the time archosaurs hatch, their residual yolk sacs have a calcium content equal or greater than at time of oviposition, which is used to support post-hatching growth. To date, no study has looked into how removal of the calcareous eggshell affects embryonic development in archosaurs. I tested how the removal of the calcareous eggshell affects embryonic and hatchling growth and biomechanic function of the skeleton in embryos and hatchlings of the American alligator (Alligator mississippiensis). Experimental eggs had their eggshell manually peeled, while control eggs were sham handled but otherwise not altered. Sampling of eggs occurred on a weekly basis until the end of incubation. Embryos, yolk sacs, and eggshells were removed and analyzed for morphological, histological and biomechanical parameters. Results show that at the time of eggshell peeling yolk sac calcium reserves were sufficient for experimental embryos to develop, but animals hatched in diminutive state. Serial clearing and staining of embryos revealed that onset of bone mineralization was similar for both treatment groups. Growth trajectory of experimental hatchlings parallelled that of control animals, without compensatory growth. Experimental hatchlings were observed to have flexible lower jaws and produced a weaker bite force than control hatchlings. Cross-sections of the mandible and femoral mid-diaphysis had a significantly reduced cross-sectional area in experimental hatchlings. I conclude that loss of the calcareous eggshell during incubation leads to severe constraint on growth and biomechanics of the alligator skeleton
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Effect of Embryonic Calcium Constraint on PostHatching Growth and Bone Microstructure in the American Alligator (Alligator mississippiensis)
Among oviparous reptiles, archosaurs lay eggs with the thickest and most rigid eggshells. During embryonic development, archosaurs mobilize eggshell calcium to the yolk sac, and upon hatching rely on this calcium reservoir to supplement their dietary calcium intake. This additional source of calcium may have allowed archosaurs to achieve high post-hatching growth rates. We tested this hypothesis by incubating eggs of the American alligator, and following posthatching growth for over two months. The calcareous eggshells were either experimentally peeled or shamhandled with the fibrous shell membrane left intact in both treatment groups. At hatching, experimental animals were significantly smaller than controls. There was considerable variation in growth rates within both groups, but overall control animals grew significantly faster than experimental ones. Standardized to bone length, femora and lower jaws of three month-old experimental animals had smaller cross-sectional area, second moment of area, and polar moment of inertia. Cortical thickness was decreased, as was lacunar density. Incomplete osteone formation resulted in prominent vascular spaces in the lower jaws of experimental alligators. Considering a lower bone mineral content in the experimental group, these results suggest that insufficient calcium supply exerts negative feedback on bone tissue growth, and archosaurs cannot compensate for decreased material stiffness by augmenting the geometric properties of skeletal elements, even those critical to locomotion or feeding. We propose that selective forces on post-hatching survival drove the evolution of ever-thicker and mineralized eggshell of archosaur eggs. Eggshell and bone microstructure of extinct archosaurs may contain clues to their calciumhandling strategies
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Embryonic Responses To Carbonic Anhydrase Inhibition And Exogenous Calcium Supplementation In Eggs Of The American Alligator
: During incubation, embryonic archosaurs mobilize calcium from the eggshell, and deposit it in the yolk and the skeleton. Previous experiments on eggs of the American alligator (Alligator mississippiensis) demonstrated that removal of the calcareous eggshell results in embryonic growth retardation. So far, no experiments have ascertained the role of carbonic anhydrase in eggshell calcium mobilization, nor the importance of calcium provenance to embryonic crocodilians. We conducted two experiments to test whether (i) carbonic anhydrase (CA) inhibition has similar effects on the embryo as eggshell removal, and (ii) exogenous calcium supplementation can rescue the original embryonic phenotype. To inhibit CA, we applied topical acetazolamide (150-600 µg/day AZA in DMSO vehicle). As exogenous sources of calcium, we used 0.1M CaCO3 solution and calcite sand. We found AZA reduced embryonic wet mass after five weeks of treatment, with a significant dose-dependent response. Calcium supplementation of eggs with the eggshell removed yielded mixed results. Spraying with CaCO3 solution partially rescued the phenotype, with alligator embryos being intermediate in wet mass between control and non-treated experimental siblings. Egg incubation in calcite sand, however, did not restore normal embryonic growth trajectory. This suggests alligator embryos can potentially obtain calcium from environmental sources, with presence of aqueous calcium especially important
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Effects of Eggshell Removal on Embryonic Skeletal Development and Post-Hatching in the American Alligator (Alligator mississipiensis)
Embryonic archosaurs (crocodilians and birds) are known to sequester calcium from their heavily mineralized eggshell and use it to mineralize their developing skeleton. In order to test the importance of eggshell calcium to embryonic growth, we studied growth of embryos and hatchlings of the American alligator with and without the calcareous eggshell. The outer eggshell layer was manually removed early in incubation, and embryos (n=6) were sampled at weekly intervals until hatching. The experimental and shamhandled control eggs were incubated at 30ºC and 100% relative humidity. Results show that experimental (“shellless”) embryos were significantly smaller in body mass and length than their clutch-sibling controls. Under identical rearing conditions, experimental hatchlings did not demonstrate catch-up growth despite ad infinitum diet and remained significantly smaller than control hatchlings. Observation of biting behavior revealed that experimental hatchlings had more compliant lower jaws and generated weaker bite forces. Our results suggest that yolk calcium reservoir is sufficient for healthy development, but eggshell calcium is required for normal embryonic growth. We posit that increased calcium absorption during development allows the embryo to hatch at larger size, which ultimately allows greater force development during predation
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Importance of the Cakareous Eggshell to Normal Development in the American Alligator
Crocotilians and birds lay heavily mineralized eggs as opposed to the leathery eggs of other amniotes. The mineralized layer of experimental American alligator eggs was removed and experimental eggs were incubated alongside control eggs. Results show that experimental hatchlings were smaller and hard larger yolk sacks than hatchlings
Application of Operando X-ray Diffraction and Raman Spectroscopies in Elucidating the Behavior of Cathode in Lithium-Ion Batteries
\u3ci\u3eDrosophila\u3c/i\u3e Muller F Elements Maintain a Distinct Set of Genomic Properties Over 40 Million Years of Evolution
The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have greater transposon density (25–50%) than euchromatic reference regions (3–11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% vs. 11–27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density and types of transposons affect the degree of local heterochromatin formation. F element genes have lower estimated DNA melting temperatures than D element genes, potentially facilitating transcription through heterochromatin. Most F element genes (~90%) have remained on that element, but the F element has smaller syntenic blocks than genome averages (3.4–3.6 vs. 8.4–8.8 genes per block), indicating greater rates of inversion despite lower rates of recombination. Overall, the F element has maintained characteristics that are distinct from other autosomes in the Drosophila lineage, illuminating the constraints imposed by a heterochromatic milieu