Description of a new species and understanding the genetic diversity of Saccocoelioides Szidat, 1954 (Haploporidae) in Middle America using mitochondrial and nuclear DNA sequences

Abstract

Members of the genus Saccocoelioides Szidat, 1954, include endoparasites from freshwater and brackish fishes from the Americas. Adult specimens were collected from the intestines of Poecilia catemaconis Miller, 1975, a poeciliid fish endemic to Catemaco Lake, and the white mullet Mugil curema Valenciennes, 1836, from Alvarado Lagoon, Veracruz, Mexico. The specimens were sequenced for three molecular markers, internal transcribed spacer 2 (ITS2) and domains D1-D3 from the large subunit (LSU) of nuclear ribosomal DNA and cytochrome c oxidase subunit 1 (cox 1) from mitochondrial DNA. The newly sequenced specimens were aligned with other sequences downloaded from GenBank. Maximum likelihood and Bayesian inference analyses were inferred with three data sets (a combination of nuclear DNA ITS2 + LSU, cox 1 alone and the concatenated cox 1+ ITS2 + LSU). The phylogenetic analyses inferred with the combined data set of the two nuclear molecular markers (ITS2 + LSU) revealed that Saccocoelioides is monophyletic and formed 11 independent lineages representing 11 valid species previously recognized plus the new lineage that is herein described as a new species named Saccocoelioides macrospinosus n. sp., however, the new species was placed in a basal polytomy in the tree. Therefore, the addition of a mitochondrial gene with a fast rate of substitution was fundamental to clarify the phylogenetic relationships of the new species. The genetic divergences estimated with the cox 1 gene were high, ranging from 8.3 to 15.5% among Saccocoelioides macrospinosus n. sp. and sister taxa. The new species has a slightly elongated body measuring 440-850 μm long and was classified in the diminutive morphotype. In addition, seven adult specimens recovered from the intestines of the banded tetra fish Astyanax aeneus Günther, 1860 from Nicaragua and Costa Rica formed a monophyletic clade with other specimens identified previously as Saccocoelioides tkachi, expanding its distribution range in other areas of Middle America.

Keywords: Digenea; ITS2; LSU; Phylogeny; Saccocoelioides; cox 1.