The Effect of Formalin Fixation on Weight of Lizard Eggs

Abstract

Central to an understanding of life history and reproductive tactics (Stearns, 1976, 1977; Tinkle, 1969; Tinkle et al., 1970) and patterns of parental investment in animals (Smith and Fretwell, 1974; Brockleman, 1975; Congdon et al., 1978, 1981) is the accurate measurement of relevant reproductive characteristics. Offspring size is one such characteristic. A large number of studies have presented various kinds of data on egg size in reptiles as a relative measure of offspring size. Egg size data for reptiles are generally presented as length by width (often then used to calculate volume), egg wet weight, or egg dry weight. In many instances, wet weights of preserved eggs are presented, with no attendant information regarding time of eggs in fixative, and more importantly, correlations between weights of fixed eggs and fresh eggs. In this study, we demonstrate the effect of formalin (10% solution of 39% formaldehyde) fixation on weights of lizard eggs. The only similar comparison we know of is that of Martin (1978) where it was shown that clutch weight/total body weight ratios of lizards were significantly affected by preservation. Small samples of females of three species of lizards, Cnemidophorus septemvittatus, Sceloporus merriami and Urosaurus ornatus, were collected in or near Big Bend National Park, Brewster Co., Texas during early summer of 1981. Lizards were killed, and oviductal eggs were removed, weighed to 0.001 g, and preserved in 10% formalin, a fixative commonly used for reptiles. At three time intervals, 1 wk, 2 wk, and 24 wk, eggs were removed from fixative and reweighed. After 24 wk in formalin, the eggs were freeze dried (-60?C) to constant weight, and dry weights were taken to 0.0001 g. This allowed approximation of water content as well as dry weight. In all cases, means are presented + one standard error of the mean.