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| Filistriatus gen. nov. Girard (A) Filistriatus plebeius (Broussonet 1782), Fresh specimen (USNM 471329) in lateral view. Neurocranium in dorsolateral view of: (B) F. bifurcus (Motomura, Kimura & Iwatsuki 2001); (C) F. sexfilis (Valenciennes 1831);(D) Polydactylus virginicus (Linnaeus, 1758); (E) Leptomelanosoma indicum (Shaw, 1804) in Girard et Chovanec, 2025. |
Abstract
DNA sequencing continues to revolutionize our understanding of biodiversity, ecology, and evolution. While analyzing sequence data allows us to address countless questions, most of the world’s vertebrate museum specimens have been historically inaccessible for genetic sampling. This is partially due to the absence of modern genetic samples and/or the impact formalin has on DNA during the preservation of specimen vouchers. Recent studies have shown successful extraction of DNA from historic museum specimens using additional chemicals and/or exposing the sample(s) to heat, with these advances enhancing the possibility of capturing genomic information from type specimens, characterizing genetic diversity within species complexes, and incorporating rare samples into phylogenetic analyses. However, questions remain about the reliability of these data and utility of historic DNA in modern phylogenetic analyses. In this study, we use a commercial extraction kit that targets formalin-fixed, paraffin-embedded samples to successfully extract DNA from historic museum specimens of threadfin fishes (Teleostei: Polynemidae). These specimens represent rare, genetically uncharacterized taxa that have yet to be included in a phylogenetic analysis. Low-depth shotgun sequencing is then used to sequence mitochondrial loci from the historic samples. The resulting sequence data are assembled, validated, and incorporated into a newly generated mitochondrial dataset that is simultaneously analyzed with a previously published ultraconserved-element dataset to construct a phylogenetic framework. We then explore new and previously described morphological variation within this new evolutionary framework for threadfins, identifying several shared characters that warrant revision of the generic-level classification. These findings add to the growing body of literature that demonstrates sequencing historical DNA from museum specimens and analyzing these data with complementary datasets of molecular markers from modern genetic samples can provide reliable and comprehensive assessments of biodiversity, ecology, and evolution across fishes and other vertebrates.
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| Morphology relating to the monophyly of Filistriatus gen. nov. (A) Fresh specimen of Filistriatus plebeius gen. nov. (USNM 471329) in lateral view. (B) Neurocranium of F. bifurcus gen. nov. (USNM 76627) in dorsolateral view. (C) Neurocranium of F. sexfilis gen. nov. (CSIRO C261) in dorsolateral view. (D) Neurocranium of P. virginicus (FMNH 104648) in dorsolateral view. (E) Neurocranium of L. indicum (USNM 357716) in dorsolateral view. Left frontal and medial supraorbital canal commissure colored in (B–E), with isolated colored frontals below each whole neurocranium. Arrow I indicates dark stripes along the longitudinal scale rows above the lateral line. Faint stripes also present along the longitudinal scale rows below the lateral line. Arrow II indicates reduced lateral pore of the supraorbital canal. Arrow III indicates reduced medial commissure of sensory canal on the dorsal surface of the frontal. Arrow IV indicates pronounced lateral pore of the supraorbital canal that is visible when viewing the side of the neurocranium. Arrow V indicates elevated medial commissure of sensory canal. Scale bars = five mm. |
Taxonomic modifications to the Polynemidae
Filistriatus gen. nov. Girard
Diagnosis: a genus of small-to-moderately-sized threadfins differentiated from all other genera of the Polynemidae by the following combination of characters: 7–9 dark stripes along the longitudinal scale rows above the lateral line, 7–9 faint stripes along the longitudinal scale rows below the lateral line, reduced lateral pore of the supraorbital canal, reduced sensory canal commissure on the dorsal surface of the frontal, 5–6 free pectoral-fin rays, and 54–72 lateral-line scales.
Type species: Polynemus sexfilis Valenciennes 1831
Included species: Polydactylus bifurcus Motomura, Kimura & Iwatsuki 2001,
Polydactylus plebeius (Broussonet 1782),
Polydactylus sexfilis (Valenciennes 1831),
Polydactylus siamensis Motomura, Iwatsuki & Yoshino 2001.
Etymology: the generic name refers to the thread-like fin rays of the pectoral fin and the diagnostic stripes along the lateral flanks [fili (Latin) = thread and striatus (Latin) = striped]. Gender masculine.
Remarks: “Polydactylus” siamensis was characterized by several longitudinal dark stripes along the flank, 5 pectoral filaments, and 54–58 lateral-line scales (Motomura, Iwatsuki & Yoshino, 2001). Although we could not sample this taxon in this study, the species has the diagnostic characters of Filistriatus. The species is also reassigned to the new genus.
Matthew G. Girard and Kevin R. Chovanec. 2025. Unlocking the Genomic Potential of Historical and Formalin-fixed Specimens: Phylogenetic insights from Museum-preserved Threadfin Fishes (Teleostei: Polynemidae). PeerJ. 13:e20029. DOI: doi.org/10.7717/peerj.20029 [September 30, 2025]
