Ecology, Life Sciences, Hypotheses, Zoology, Lead, Ponds, Principal components analysis, Eggs, Trace element contamination, Eggshell thinning, Inorganic contaminants, Maternal transfer, Calcium resorption, Fish & Wildlife Biology & Management, Amniotic eggs, Fish ponds, Metals, Calcium, Chromium, Copper, Embryogenesis, Cadmium, Manganese