In late 2022 I and nine coauthors published a paper that made changes to mormyrid taxonomy based on discoveries made possible by sequencing DNA from a 19th Century holotype specimen. Here's a summary of what we did.
We had a taxonomic puzzle to solve. On the one hand we had Heteromormyrus pauciradiatus, a species described from a single odd-looking specimen in 1866 by Austrian ichthyologist Franz Steindachner (see the image of it below). The type locality was unknown apart from "Angola." No other specimens were afterwards identified to this species or to this genus. What the hell was it? A valid name on the books and a genus doing no work to organize mormyrid diversity, a sort of nomenclatural freeloader.
On the other hand we had the "Hippopotamyrus ansorgii species complex" (HaSC), a mix of described and undescribed species found in southern Africa (including the rivers of Angola). Their phylogenetic position in the mormyrid tree indicated they had been misclassified in genus Hippopotamyrus. Unfortunately the phylogenetic results also indicated that no other sequenced genus, as currently defined, could serve as their home. In other words, they were taxonomic orphans. Unless...unless...we could show that the HaSC were close relatives of Heteromormyrus pauciradiatus. If so, they could take on that formerly unshared generic name. But how to test this hypothesis?
The holotype specimen of H. pauciradiatus was preserved before using formaldehyde (which destroys DNA) was standard practice. It was preserved in "spirits," i.e. an ethanol solution of uncertain concentration. We thought, therefore, we might be able to get DNA sequences out of it. We were encouraged that other Steindachner fish types of similar age had already been successfully sequenced. The collection manager at the Naturhistorisches Museum in Vienna where the H. pauciradiatus type was housed excised some of the gill arches from the holotype and sent the sample to us. We decided to try so-called "next-generation" or "high-throughput" sequencing (also known as "shotgun" sequencing because the genome is broken up into small fragments and sequenced 150 bases at a time) instead of the older, slow and laborious Sanger sequencing method. If successful, we'd have much more than a couple short DNA sequences to show for our effort. We crossed our fingers and gave it a "shot."
The DNA from the type specimen that had sat in a jar on a shelf in the Vienna Museum since 1866 through two world wars had greatly deteriorated, as expected. But the sequences it did produce were enough to assemble a 95% complete mitochondrial genome. Mitochondria are the organelles within cells that produce chemical energy for our bodies. They come equipped with their own small, circular genomes, separate from the nuclear genome. Cells usually contain just one nuclear genome, but many mitochondria. The high number of mitogenome copies improves the chances that some mito gene sequences will persist in a degraded sample even after little trace is left of nuclear gene sequences.
With the holotype's whole mitogenome sequenced, we could compare sequences of two mito genes, cytochrome b and COI, to those from recently collected members of the HaSC from Angola and elsewhere. We found that the H. pauciradiatus holotype had identical sequences to those found in members of a group from the Lucala and Kwanza rivers of Angola informally called "K4". In other words, K4 *is* Heteromormyrus pauciradiatus. This species is embedded in the larger HaSC that with this paper are all formally reclassified in the formerly unused genus Heteromormyrus. Orphans no more!
Along the way we figured out why no one had made the connection between H. pauciradiatus and the HaSC previously: an x-ray revealed the holotype specimen had a malformed spine, missing four vertebrae relative to normal individuals. Hence its measurements were totally different from any specimen you compared it to. Alas, in 1866 there were no x-ray machines and no way for Franz Steindachner to know he was using a deformed individual as a type.
Who says taxonomy is boring? We solved a mystery and rescued orphans! We also showed that you can use next-gen sequencing on fish types with success.
The study is now published in the Open Access journal ZooKeys. It wouldn't have happened without the combined talents and efforts of all the coauthors, including Carl D. Hopkins, Stacy Pirro, Rose Peterson, Albert Chakona, Tadiwa Mutizwa, Christian Mukweze, Fahad Alqahtani, Emmanuel Vreven & Casey Dillman. Thanks to NCBI and Computercraft Corporation for supporting this research.
The publication describes no new taxa, but makes nine nomenclatural changes in Mormyridae: eight new combinations and one synonymy. These are summarized as follows:
8 New Combinations:
Hippopotamyrus ansorgii (Boulenger, 1905) --> Heteromormyrus ansorgii (Boulenger, 1905)
Hippopotamyrus pappenheimi (Boulenger, 1910) --> Heteromormyrus pappenheimi (Boulenger, 1910)
Paramormyrops tavernei (Poll, 1972) --> Heteromormyrus tavernei (Poll, 1972)
Hippopotamyrus szaboi Kramer, van der Bank & Wink, 2004 --> Heteromormyrus szaboi (Kramer, van der Bank & Wink, 2004)
Hippopotamyrus longilateralis Kramer & Swartz, 2010 --> Heteromormyrus longilateralis (Kramer & Swartz, 2010)
Hippopotamyrus macroterops (Boulenger, 1920) --> Pollimyrus macroterops (Boulenger, 1920)
Hippopotamyrus weeksii (Boulenger, 1902) --> Cyphomyrus weeksii (Boulenger, 1902)
Hippopotamyrus grahami (Norman, 1928) --> Cyphomyrus grahami (Norman, 1928)
1 Synonymy:
Hippopotamyrus harringtoni (Boulenger, 1905) --> junior synonym of Hippopotamyrus pictus (Marcusen, 1864)
Please check out the paper at https://zookeys.pensoft.net/article/90287/
and/or see this study in poster form at: https://doi.org/10.13140/RG.2.2.24304.33287
