Siddharth Kulkarni, Hannah Wood, Gustavo Hormiga

In the last decade and a half, advances in genetic sequencing technologies have revolutionized systematics, transforming the field as studying morphological characters; a few genetic markers have given way to genomic data sets in the phylogenomic era. A plethora of molecular phylogenetic studies on many taxonomic groups have come about, converging on, or refuting prevailing morphology or legacy-marker-based hypotheses about evolutionary affinities. Spider systematics has been no exception to this transformation and the interrelationships of several groups have now been studied using genomic data. About 50,500 extant spider species have been described so far, all with a conservative body plan, but innumerable morphological and behavioral peculiarities. Inferring the spider tree of life using morphological data has been a challenging task. Molecular data have corroborated many hypotheses of higher-level relationships, but also resulted in new groups that refute previous hypotheses. In this review, we discuss recent advances in the reconstruction of the Spider Tree of Life and highlight areas where additional effort is needed with potential solutions. We base this review on the most comprehensive spider phylogeny to date, representing 131 of the currently known 132 (99%) spider families. To achieve this sampling, we combined a legacy data set of six Sanger-based markers with newly generated and publicly available genome-scale data sets. We find that some inferred relationships between major lineages of spiders (such as Austrochiloidea, Palpimanoidea, Synspermiata, etc.) are robust across different classes of data. However, several surprising new hypotheses have emerged with different classes of molecular data. We identify and discuss the robust and controversial hypotheses and compile this blueprint to design future studies targeting systematic revisions of these problematic groups. We offer an evolutionary framework to explore comparative questions such as evolution of venoms, silk, webs, morphological traits, and reproductive strategies.