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1991; Ragnarsson, 1996; Morgan, 1997) and is the method used in all later studies
(Chapters 4, 5, 6 and 8). Body length measurements were not possible for all
individuals since many were damaged during sampling and processing. However,
lengths of all intact worms were measured to the nearest millimeter allowing
regression analysis of 5th setiger width and body length to be carried out.
Sex could be determined for sexually mature individuals only. Adult males possess a
pair of branchiae on the 2nd setiger which distinguishes them from females
(Rasmussen, 1973). The branchiae, or nuchal appendages, have been shown to be
important in copulation (Schlotzer-Schrehardt, 1987; 1991). This method of sex
determination is both a convenient and a reliable one (Rasmussen, 1973;
Gudmundsson, pers. comm.).
Each month, the number of adult female tubes containing embryos and/or larvae were
recorded. This method of assessing the reproductive status of P. elegans has been
successfully used in other studies (e.g., Morgan, 1997). Embryos and larvae present
were compared to the drawings given in Thorson (1946), Hannerz (1956) and
Rasmussen (1973). Those female tubes containing larvae were retained and preserved
in 70% ethyl alcohol. Fifty larvae per month were randomly selected from these
tubes, their general appearance were noted and their lengths measured using a
dissecting microscope fitted with an eyepiece micrometer.
Data analyses - Regression analysis was carried out, using Minitab version 10.0,
between the 5th setiger widths and lengths of all complete P. elegans individuals. The
size distributions of the larvae removed from the female tubes were tested for
differences between months using the Kolmogorov-Smimov (K-S) test. Since the K-
S test only tests for differences between pairs of distributions, this test had to be
repeated many times. These tests were not independent from each other and so a
Bonferroni correction was applied where a'=0.05/15, where 15 was the number of
tests performed. The Kolmogorov-Smirnov tests were carried out by hand using the
formula for large sample sizes given by Smimov (1948). Growth rate analysis was
carried out for P. elegans using the ICLARM software package ELEFAN (Pauly and
David, 1981; Gayanilo et al., 1989).
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