Meeting Abstract

4.4  Monday, Jan. 4  Precise measurement of growth using multiple fluorochrome markers, the cubed root of weight and a new growth function JOHNSON, A.S.*; ELLERS, O; Bowdoin College; Bowdoin College ajohnson@bowdoin.edu

Fluorochromes have been widely used to mark growing calcitic structures. We present images from a size range (3.9–44.3 mm in diameter) of growing sea urchins that were marked by both immersion and injection using the fluorochromes: tetracycline, calcein, calcein blue and alizarin complexone. These fluorochromes appear as distinct, differently colored lines deposited in skeletal structures with as little as three days separating marks. We show that the marking process, even with multiple fluorochromes, has only a short-term negative impact on growth rate, with no measurable differences in growth rate after three months and no effect on gonad production. To enable us to test for potentially small differences in growth caused by the fluorochromes, we had to develop new methods for quantifying size more precisely. Specifically, we use the cubed root of weight as a measure of size and show that this is more precise then simply measuring a single linear dimension. Analysis of small differences in growth is also made possible by the use of a residuals analysis relative to a fitted function, which describes the rate of growth as a function of linear size. We invented a new function, called the gamma function, which provides a good description of growth rate as a function of size for sea urchins. The early lag phase, which has been noted previously in urchins, had heretofore been described by the Tanaka function, which is more complicated to fit. The fluorochrome images are beautiful and reminiscent of Deutler’s (1926) famous sketches of growth lines in urchins.