title: Effects of Gene Duplication, Positive Selection, and Shifts in Gene Expression on the Evolution of the Venom Gland Transcriptome in Widow Spiders.
abstract: Gene duplication and positive selection can be important determinants of the evolution of venom, a protein-rich secretion used in prey capture and defense. In a typical model of venom evolution, gene duplicates switch to venom gland expression and change function under the action of positive selection, which together with further duplication produces large gene families encoding diverse toxins. Although these processes have been demonstrated for individual toxin families, high-throughput multitissue sequencing of closely related venomous species can provide insights into evolutionary dynamics at the scale of the entire venom gland transcriptome. By assembling and analyzing multitissue transcriptomes from the Western black widow spider and two closely related species with distinct venom toxicity phenotypes, we do not find that gene duplication and duplicate retention is greater in gene families with venom gland biased expression in comparison with broadly expressed families. Positive selection has acted on some venom toxin families, but does not appear to be in excess for families with venom gland biased expression. Moreover, we find 309 distinct gene families that have single transcripts with venom gland biased expression, suggesting that the switching of genes to venom gland expression in numerous unrelated gene families has been a dominant mode of evolution. We also find ample variation in protein sequences of venom gland-specific transcripts, lineage-specific family sizes, and ortholog expression among species. This variation might contribute to the variable venom toxicity of these species.
authors.affiliation: Department of Biological Sciences, University of Massachusetts, Lowell robert_haney@uml.edu jessica_garb@uml.edu.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Haney
authors.affiliation: Department of Biology, Washington and Lee University Department of Biology, University of California, Riverside.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Clarke
authors.affiliation: Department of Biological Sciences, University of Massachusetts, Lowell.
authors.forename: Rujuta
authors.initials: R
authors.lastname: Gadgil
authors.affiliation: Department of Biological Sciences, University of Massachusetts, Lowell.
authors.forename: Ryan
authors.initials: R
authors.lastname: Fitzpatrick
authors.affiliation: Department of Biology, University of California, Riverside.
authors.forename: Cheryl Y
authors.initials: CY
authors.lastname: Hayashi
authors.affiliation: Department of Biology, Washington and Lee University.
authors.forename: Nadia A
authors.initials: NA
authors.lastname: Ayoub
authors.affiliation: Department of Biological Sciences, University of Massachusetts, Lowell robert_haney@uml.edu jessica_garb@uml.edu.
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Garb
mesh_terms: D000818:Animals; D004702:Endocrine Glands / Q000378:metabolism*; D019143:Evolution, Molecular; D005260:Female; D020440:Gene Duplication; D012641:Selection, Genetic; D013111:Spider Venoms / Q000235:genetics*; D013112:Spiders / Q000235:genetics* / Q000378:metabolism; D059467:Transcriptome
chemical_list: D013111:Spider Venoms
keywords: Latrodectus; black widow; comparative transcriptomics; gene family evolution; venomics