A Survey of Texas Freshwater Turtles for Turtle Blood Flukes (Digenea: Schistosomatoidea: "Spirorchiidae"), with Comments on Morphology, Updated Phylogenies and Cryptic Species

Abstract

Turtle blood flukes (Digenea: Schistosomatoidea: “Spirorchiidae”; TBFs) are important disease agents in turtles yet are underreported in many turtle species and localities. In Texas, previous researchers documented TBF infections in only 3 of 38 turtle taxa. No TBF sequences are publicly available from Texas specimens. From 2017−2018, 96 turtles of 4 taxa were captured and searched for TBFs from 13 counties across Texas. Two hundred seventeen TBFs consisting of at least 15 species from the genera Hapalorhynchus Stunkard, 1922, Spirorchis MacCallum, 1918, Unicaecum (Stunkard, 1925) Stunkard, 1927 and Vasotrema (Stunkard, 1928) Roberts and Bullard, 2017 were recovered from the heart, kidneys, liver, lungs, mesentery and spleens of 1 Apalone spinifera emoryi (Agassiz), 7 Apalone spinifera pallida (Webb), 10 Chelydra serpentina (Linneaus) and 17 Trachemys scripta elegans (Wied). This is the first report of TBFs from A. s. emoryi and A. s. pallida. Additionally, the first TBFs from the kidneys of T. s. elegans and both the spleen and kidneys of any species of Apalone Rafinesque are reported herein. Hapalorhynchus and Vasotrema are reported from Texas for the first time. Host-induced morphological changes were found for all Vasotrema recovered, which will require redescription. In total, 6 new host records and 20 new locality records are reported, increasing the number of TBF positive counties from 5 to 16. Seventy-two new sequences were generated from 55 Texas TBFs, representing the first sequences for Vasotrema cf. brevitestis (Brooks and Mayes, 1975) Roberts and Bullard, 2017, Vasotrema longitestis (Byrd, 1939) Roberts and Bullard, 2017, and the immature Vasotrema sp. 1. Phylogenetic analysis of the large subunit ribosomal DNA (28S) recovered monophyletic clades that support the unique morphology of each genus. Three potentially cryptic species were found through phylogenetic analysis of the cytochrome c oxidase subunit 1 mitochondrial gene (cox1). Clades were designated based on pairwise comparisons of both cox1 and 28S genes but require morphological and/or further genetic identification to designate them as distinct species. Identifying cryptic freshwater TBFs will be difficult if efforts to sequence mitochondrial genes do not increase. Thirty-three turtle taxa and 238 counties remain to be searched for TBFs in Texas.