Fixation and preservation contribute to distortion in vertebrate museum specimens: a 10-year study with the lizard Anolis sagrei

Preservation of museum specimens depends on chemical fixation and preservation, processes that might distort the original material. Relatively few studies have examined the effects of preservation in potentially susceptible soft-bodied taxa, such as herpetofauna, and those that have rarely extend over more than a few months. We collected six common morphological measurements from the same set of radiographed specimens of the Neotropical lizard Anolis sagrei over nearly 10 years to investigate whether morphometric changes result from fixation in formalin and/or subsequent long-term preservation in ethanol. Snout-vent length declined by 3.5% on average over 10 years, starting almost immediately with fixation and continuing to decline during fluid preservation, eventually levelling off at 40 weeks and beyond. The mostly ossified component of snout-vent length, spine length, declined by 2% on average, but the decline did not begin until fluid preservation commenced and continued throughout the duration of the study. Other characters showed significant decline over the course of the study. Our findings suggest caution when combining fresh and preserved specimens or specimens of different preservation ages, because a decline in snout-vent length but not in other allometrically proportional characters will introduce error when correcting characters for body size in preserved animals.