Transcriptomics illuminate the phylogenetic backbone of tiger beetles

Phylogenomics is progressing rapidly, allowing large strides forward into
our understanding of the tree of life. In this study, we generated
transcriptomes from ethanol-preserved specimens of 13 tiger beetle species
(Coleoptera: Cicindelinae) and one Scaritinae outgroup. From these 14
transcriptomes and seven publicly available transcriptomes, we recovered
an average of 2538 loci for phylogenetic analysis. We constructed an
evolutionary tree of tiger beetles to examine deep-level relationships and
examined the extent to which the composition of the dataset, missing data,
gene tree inconsistency and codon position saturation impacted
phylogenetic accuracy. Ethanol-preserved specimens yielded similar numbers
of loci to specimens originally preserved in costly reagents, showcasing
more flexibility in transcriptomics than anticipated. The number of loci
and gene tree inconsistency had less impact on downstream results than
third codon position saturation and missing data. Our results recovered
tiger beetles as sister to Carabidae with strong support, confirming their
taxonomic status as an independent family within Adephaga. Within tiger
beetles, phylogenetic relationships were robust across all nodes. This new
phylogenomic backbone represents a useful framework for future endeavours
in tiger beetle systematics and serves as a starting point for the
development of less costly target capture toolkits to expand the taxonomic
breadth of the future tiger beetle tree of life.