On the Evolutionary History of Philometridae (Nematoda: Dracunculoidea): Integrative Taxonomy Reveals Evidence of Character Diversification and Host–Parasite Cophylogenetic Patterns

(1) Background: Integrative taxonomy has been important in the comprehension of relationships among nematode parasites. Philometridae is a highly diverse family of these organisms, but poorly-known regarding genetic characterization and evolution. An integrative taxonomic analysis was performed to improve the knowledge of the evolutionary history of Philometridae. (2) Methods: Phylogenies were reconstructed based on genetic sequences alone and integrated with morphological/life history traits, which were phylogenetically mapped. The host–parasite cophylogeny was evaluated. (3) Results: Previously unpublished 28S rDNA sequences are given for some species. The phylogeny from this marker, although limited by data scarcity, showed similar patterns as that from 18S rDNA. Clades shared common features related to the structure of the esophagus and of the tail in males (especially the gubernaculum), site of infection, habitat, host taxa and geographic origin; most of these features were phylogenetically informative. The integrative phylogeny was better resolved. A cophylogenetic signal was present mainly in clades of freshwater species. (4) Conclusions: The speciation process in Philometridae is not unique or uniform; host capture, host–parasite co-evolution and allopatric (especially in freshwater) events may be occurring simultaneously in different lineages, places and times. Cases of plesiomorphy retention probably occur. Evolutionary convergence of poorly-informative characters is suggested, even though they are important for species diagnosis.