Gene Expression and Evolution in the Smalltooth Sawfish,Pristis pectinata

Summary Sawfishes (Pristidae) are large, highly threatened rays named for their tooth-studded rostrum, which is used for prey sensing and capture. Of all five species, the smalltooth sawfish, Pristis pectinata , has experienced the greatest decline in range, currently found in only ∼20% of its historic range. To better understand the genetic underpinnings of these taxonomically and morphologically unique animals, we collected transcriptomic data from several tissue types, mapped them to the recently completed reference genome and contrasted the patterns observed with comparable data from other elasmobranchs. Evidence of positive selection was detected in 79 genes in P. pectinata , several of which are involved in growth factor/receptor tyrosine kinase signaling and specification of organ symmetry, suggesting a role in morphogenesis. Data acquired also allow for examination of the molecular components of P. pectinata electrosensory systems, which are highly developed in sawfishes and have likely been influential in their evolutionary success.