2 No evidence for lateral gene transfer from salmonids to Schistosomes ( or vice 3 versa ) 4

12 13 A study in 2004 in number 8 of this journal concluded that in the past some sort of 14 lateral gene transfer occurred from the salmonids to the schistosomes 1. Schistosomes 15 are parasitic helminths that cause a severe disorder called bilharziosis or 16 schistosomiasis in humans and several animals. The deduction of gene transfer was 17 based on the analysis of an EST library for Schistosoma japonicum (Adult SjC 7/94, 18 GenBank accession number BU712912) and on PCR on genomic and cDNA of S. 19 mansoni and S. japonicum. The study identified salmon transposon-like sequences in 20 schistosomes, and these sequences were deposited in GenBank as schistosomes-21 specific, salmon-like repeats (GenBank accession numbers AY834394 to AY834403). 22 Naturally, the report stirred up a considerable interest in the scientific community 23 since the evolutionary conclusions were far-reaching 2-4. Nowadays, schistosomatidae 24 are parasitic helminths of mammals and birds, and a relation to fish that would be 25 close enough to allow for gene transfer made it necessary to reconsider the 26 evolutionary history of these blood-flukes. We show here that we find no evidence for 27 the proposed transfer of repetitive sequences from salmonids to S. mansoni and S. 28 japonicum. 29 We re-sequenced the genomes of female and male S. mansoni using the Genome 30 Analyzer II (Illumina) by single end sequencing according to the manufacturers 31 protocol. We obtained a total of 17,955,578 reads (~645 Mb). Sequences are available 32 at the NCBI sequence read archive (study accession number SRA012151.6). These 33 sequences were aligned to the 1278 repeats (total number of bp: 1,305,387) in the 34 r e p e a t m a s k e r d a t a b a s e o f S. m a n s o n i 35 mology_evidence/sma1.repeats.gz) that includes the above-mentioned Sm_salmonid 37 repeat (GenBank AY834402) but not the other putative salmon-like repeats. A total of 38 2,810,622 reads (15.66 %) aligned to the repeats database (2-fold coverage). The 39 Sm_salmonid sequence was the only one that did not match with any of the sequence 40 reads. In other words, among roughly 18 million sequence bits of 36 bp, not a single 41 read correspond to the 419 bp long previously in S. mansoni identified sequence of 42 putative salmonid origin. We then used Blast searches for GenBank accession 43 numbers AY834402, AY834401, AY834399, …