Spider Transcriptomes Identify Ancient Large-Scale Gene Duplication Event Potentially Important in Silk Gland Evolution.
Bottom Line: Based on phylogenetic analyses of gene families with representatives from each of the three species, we found numerous duplication events indicative of a whole genome or segmental duplication.We estimated the age of the gene duplications relative to several speciation events within spiders and arachnids and found that the duplications likely occurred after the divergence of scorpions (order Scorpionida) and spiders (order Araneae), but before the divergence of the spider suborders Mygalomorphae and Araneomorphae, near the evolutionary origin of spider silk glands.Transcripts that are expressed exclusively or primarily within black widow silk glands are more likely to have a paralog descended from the ancient duplication event and have elevated amino acid replacement rates compared with other transcripts.
Affiliation: Department of Biology, Washington & Lee University email@example.com.Show MeSH
Mentions: The observation of relaxed purifying selection in SST-containing gene families might be a byproduct of SSTs tending to be only found in spiders; 17% of SST-containing Latrodectus & Steatoda gene clusters had no observable homolog to a nonspider UniProt protein (lineage-specific). This is a much higher percentage than non-SST Latrodectus & Steatoda gene clusters (4.6%), although similar to the Latrodectus & Steatoda gene clusters containing only low expression transcripts (15%). Indeed, we found that the Latrodectus & Steatoda gene families with lineage-specific transcripts have higher omega values than those gene families with nonspider homologs. However, SST-containing Latrodectus & Steatoda gene families consistently have higher omega values (mean omega = 0.22 for SST-containing, lineage-specific families; mean omega = 0.18 for non-SST lineage-specific families; mean omega = 0.12 for SST-containing families with nonspider homolog; mean omega = 0.07 for non-SST families with nonspider homolog). Analysis of variance supports the distinction between omega values depending on the lineage-specificity and whether the Latrodectus & Steatoda gene family contains an SST, but not an interaction between the two (fig. 8; supplementary table S4, Supplementary Material online).Fig. 8.—
Affiliation: Department of Biology, Washington & Lee University firstname.lastname@example.org.