The First Mitochondrial Genome from a Hemiuroid (Didymodiclinus Sp. from Puerto Rico) Highlights Phylogenetic Volatility

The family Didymozoidae is a speciose group of fish parasites with unusual morphologic and life-history characters. In the Caribbean, juvenile didymozoids are common in demersal fishes such as snappers (Lutjanidae), but few deoxyribonucleic acid (DNA) sequences are available from these developmental stages in this region. In the present study, 1 complete and 1 partial juvenile didymozoid from a snapper (Lutjanus sp.) from Puerto Rico were characterized morphologically, and the complete ribosomal DNA operon and mitochondrial genome were sequenced. The specimens resembled the allomonilicecum morphotype, and phylogenetic analysis indicated membership in the Didymodiclininae, which comprises the genera Didymodiclinus and Paragonapodasmius. The presence of a ventral sucker excludes Paragonapodasmius, which has also not been recorded in the Atlantic region. Identification of the specimen as a member of Didymodiclinus, which is known from the broader region of our study, was generally supported in phylogenetic analysis. Mitogenome phylogenies recovered Didymodiclinus with Azygiidae, consistent with the classification of these taxa within Hemiurata. However, the position of the Hemiurata within the Digenea fluctuated radically in mitogenome trees obtained with different analytic approaches, particularly depending on whether alignments were based on amino acid translations or nucleotides. The present data have value for the study of the distribution, life history, and diversity of these parasites in the Caribbean, particularly given the negative effects of didymozoids on highly valued fishes such as tunas and groupers.