Out of for every single inhabitants an arbitrary attempt was removed. Animals have been anesthetized with many droplets out of liquid over loaded having chloroform and you can people, always more than 20 (except LMT, and this underwent a premier mortality inside people) was in fact separated regarding rest. The next morphological details had been quantified during the for every girls: full length; abdominal size; width out of third abdominal part; depth of one’s ovisac; period of furca; amount of setae inserted on each branch of your furca; depth out-of lead; maximum diameter and you will length ranging from material eyes; period of basic antenna; plus the proportion intestinal length ? 100/overall duration. Figure 2 illustrates these types of previously mentioned human body steps. Throughout circumstances, the same amount of people for each and every size period try integrated manageable not to prejudice performance from the sampling. Preadult citizens were thought to be better.
A few analyses was basically accomplished: very first, most of the findings was indeed categorized by kind of populace (bisexual diploid, parthenogenetic diploid and you may parthenogenetic tetraploid); regarding next study, the brand new separation criterion is the origin of your people
This multivariate procedure provides a series of variables (Z1, Z2,…), Which are linear functions of the morphological variables studied, with the form Zn = ?1X2+?2X2+… (Where ?s are the calculated discriminant coefficients and Xs casualdates the variables being considered). They maximize the ong different groups of observations defined a priori (Anderson, 1984). Thus, the first discriminant function is the equation of a line cutting across the intermixed cluster of points representing the different observations. This function is constructed in such a way that the different predefined groups will evaluate it as differently as possible. Obviously, this will not be accomplished if the number of groups is high, and subsequent discriminant functions will be needed. These analyses have been performed using a backward stepwise procedure that allows removing the different variables out of the model separately and ranking them for their relative importance in discriminating Artemia populations. Nevertheless, all described variables were kept in the model. These calculations have been performed with the help of the statistical package Statgraphics v. 3.0 (Statistical Graphics Corp., Rockville, MD) run on an IBM AT personal computer.
In Table II, the results obtained when the type of population was used as a separation factor are displayed. The two functions found give 100% separation, and both are statistically highly significant (P<0.001). Morphological characteristics allow a clear differentiation among the three groups considered (Table II, groups centroids). The morphological characteristics that most significantly contribute to the discrimination among the three groups are : lengh of first antenna, width of head and those related to the form and size of the head, the ratio abdominal length/total length in form of percentage and the width of ovisac and abdomen (Table II).
Results of the second analysis (factor of separation is population of origin) are shown in Table III and Figure 3. In this case, 12 discriminant functions are needed in order to separate thoroughly the 27 populations, but the first five of them give a cummulative separation percentage of (the four discriminant functions shown in Table III give a % cummulative separation). The first eight functions calculated are highly statistically significant (P,0.001), the ninth is also significant (P<0.05) and the last three are not significant. The morphological characteristics that most signifiantly contribute to separate the groups in this case are : distance between eyes, eye diameter, length of the first antenna and all variable related to the shape and size of the head and the length of the furca (Table III).
