Figure 6

The distribution of pairwise synonymous divergence ( dS ) for toxins compared to nontoxins. The histogram shows the null distribution of d S for pairs of nontoxin orthologs identified by means of a reciprocal blast search. The vertical line denotes the cutoff for the 95th percentile for the nontoxins. The d S values for the toxins are plotted below the histogram, and those toxin comparisons with values exceeding the 95th percentile for nontoxins are indictated with triangles and labeled with the names of the two sequences compared. The P value is based on a Wilcoxon rank sum test and shows a significant difference between the average d S of toxins and nontoxins. Comparisons with d S>0.1 were excluded from the analysis. If the distributions were the same between toxins and nontoxins, we expected to see 1.5 toxins exceeding the threshold instead of the seven that were observed. Six of these seven toxin pairs were C-type lectins, a toxin class that showed a 100-fold reduction in expression in C. horridus relative to C. adamanteus. The CTLs above the threshold may represent a failure to find the true ortholog in the C. horridus transcriptome due to low coverage.