Sources of calcium for the agamid lizard Psammophilus blanfordanus during embryonic development
We determined the sources of calcium for the developing embryo and the parallel changes in eggshell structure in the Indian agamid lizard Psammophilus blanfordanus. The developing eggs were opened at 0 (freshly laid), 10, 20, 30, 35, 38, and 40 days of incubation and at hatching (day 41) and subjected to chemical and structural analyses. The oval and flexible-shelled eggs had undergone significant changes in size (40% increase in length, 68% increase in breadth and 315% increase in weight) from laying to hatching. The fresh eggshell contained 2.76 mg (12.51%) calcium whereas the hatched eggshell had only 1.02 mg (7.20%), or a 63% reduction from its original content. The yolk + fluids fraction provides only 0.47 mg to the 1.76 mg of calcium in the hatchling, the rest being resorbed from the eggshell during development. The fresh eggshell (62 µm thick) had a rough granular structure in its calcareous layer with near uniform rectangular/polygonal fields made up of globules of varying sizes. The membrane layer had a multilayered mat of interwoven, irregularly oriented and bifurcated, fibres of uneven thickness. The spherical globules were absent at several places in the hatched eggshell as a result of eggshell calcium utilisation by the developing embryo. Hence, like that of most reptiles, the eggshell of Psammophilus blanfordanus also acts as a secondary source of calcium for the developing embryo. The embryo utilizes the eggshell calcium towards the end of development.
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