Evidence of positive selection among abalone sperm lysin and egg coat protein ZP-N motifs.

Nucleotide sequences of protein coding regions were analyzed using codeml in the PAML computer package [49]. Positive selection on lysin has been extensively studied previously (see, e.g. [46],), and results are provided here for ease of reference. Functional motifs of VERL were tested in several ways including: (i) analysis of entire repeats 1 and 2 of VERL as in [18]; (ii) by combined analyses of discrete ZP-N motifs [22] from repeat 1 and 2 of VERL; or (iii) analyzing individual ZP-N motifs from repeat 1 or 2. Tree lengths are calculated from the number of substitutions per codon. Likelihood-ratio tests of codon substitution models without -vs- with the possibility of positive selection (M8a or M8, respectively) support pervasive positive selection (ω>1) among lysin as well as the ZP-N motif of VEZP14, but evidence for VERL is weaker based on a significant test statistic only when analyzing full repeats previously shown to be under positive selection [18].