Abstract
BackgroundMygalomorph spiders represent a diverse, yet understudied lineage for which genomic level data has only recently become accessible through high-throughput genomic and transcriptomic sequencing methods. The Aptostichus atomarius species complex (family Euctenizidae) includes two coastal dune endemic members, each with inland sister species – affording exploration of dune adaptation associated patterns at the transcriptomic level. We apply an RNAseq approach to examine gene family conservation across the species complex and test for patterns of positive selection along branches leading to dune endemic species.ResultsAn average of ~ 44,000 contigs were assembled for eight spiders representing dune (n = 2), inland (n = 4), and atomarius species complex outgroup taxa (n = 2). Transcriptomes were estimated to be 64% complete on average with 77 spider reference orthologs missing from all taxa. Over 18,000 orthologous gene clusters were identified within the atomarius complex members, > 5000 were detected in all species, and ~ 4700 were shared between species complex members and outgroup Aptostichus species. Gene family analysis with the FUSTr pipeline identified 47 gene families appearing to be under selection in the atomarius ingroup; four of the five top clusters include sequences strongly resembling other arthropod venom peptides. The COATS pipeline identified six gene clusters under positive selection on branches leading to dune species, three of which reflected the preferred species tree. Genes under selection were identified as Cytochrome P450 2c15 (also recovered in the FUSTr analysis), Niemann 2 Pick C1-like, and Kainate 2 isoform X1.ConclusionsWe have generated eight draft transcriptomes for a closely related and ecologically diverse group of trapdoor spiders, identifying venom gene families potentially under selection across the Aptostichus atomarius complex and chemosensory-associated gene families under selection in dune endemic lineages.
Highlights
Mygalomorph spiders represent a diverse, yet understudied lineage for which genomic level data has only recently become accessible through high-throughput genomic and transcriptomic sequencing methods
Trapdoor spiders belong to an ancient lineage of chelicerate arthropods, the spider infraorder Mygalomorphae, which includes charismatic fauna such as tarantulas and Australian funnel web spiders [1]
The ability to carry out such studies at the species/population interface is hindered by a lack of appropriate foundational genomic datasets, as is the case for many non-model or ‘obscure model organisms’ [22]; only one mygalomorph spider genome has been partially sequenced, the tarantula Acanthoscurria geniculata (Koch, 1841), but remains in the scaffolding stage [5] and has likely been diverging from trapdoor spiders for ~114MY [14]
Summary
Mygalomorph spiders represent a diverse, yet understudied lineage for which genomic level data has only recently become accessible through high-throughput genomic and transcriptomic sequencing methods. The Aptostichus atomarius species complex (family Euctenizidae) includes two coastal dune endemic members, each with inland sister species – affording exploration of dune adaptation associated patterns at the transcriptomic level. Trapdoor spiders belong to an ancient lineage of chelicerate arthropods, the spider infraorder Mygalomorphae, which includes charismatic fauna such as tarantulas and Australian funnel web spiders [1] These spiders are Garrison et al BMC Evolutionary Biology (2020) 20:68 difficult to collect in large numbers from across their ranges, they are remarkably long-lived and take years to reach sexual maturity [3, 4], and, until recently, very few genetic markers and no genomic resources were available for the infraorder (but see [5, 6]). We have utilized RNAseq derived sequences to generate draft transcriptome assemblies, annotations, and search for gene families under selection within the A. atomarius complex; we test for positive selection in detected orthologs along branches of the species tree leading to dune endemic members.
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