Sitting in natural history collections around the world are single specimens collected 50, 100, or even 200 years or more ago. In some cases, these rare specimens are the type specimens for their species—the material from which a species is first described and to which later collections are compared.
Genomic sequencing of type specimens is a valuable source of information. Researchers can understand the evolutionary history of the species, clearly link a species with its genetic code, and uncover its taxonomic affiliations.
However, sequencing of relic specimens is precarious because extracting DNA can destroy irreplaceable specimens. What’s more, degraded DNA doesn’t always yield usable results.
A collaboration between evolutionary biologists and museum curators has assembled a complete mitogenome using non-destructively extracted DNA from a single butterfly leg that happens to be attached to a rare type specimen collected at least 140 years ago.
Led by Jian Zhang at the University of Texas (UT) Southwestern Medical Center and David Lee at the Natural History Museum, the new study is published in Genome.
Based on the mitogenome, made possible by next generation sequencing, the authors propose a taxonomic move for the butterfly genus Malaza to a new monotypic subfamily, Malazinae.
Malaza fastuosus—or Lavish Malaza for its large size and beautiful patterning—is one of three species in its genus of skipper butterfly, all endemic to Madagascar.
The Malaza fastuosus type specimen used in the study lacks both a head and its original abdomen, making a complete morphological analysis impossible.
“Because most animals were described a long time ago, 100–250 years ago, these type specimens are old. And for many of them, morphology is not sufficient to attribute present day specimens to it. Primary types may be damaged, or there may be cryptic species in this group. Thus, genomic sequencing solves these problems, and quite beautifully,” says senior author Dr. Nick Grishin, Professor of Biochemistry at UT Southwestern Medical Center.
To avoid damage and to leave any remaining DNA in the leg viable for future work, the butterfly’s foreleg was removed and incubated whole in extraction buffer.
Though the extracted DNA was degraded and produced relatively short fragments when sequenced, a sufficiently high number of reads were produced to connect them into a continuous sequence with high confidence.
Asked how old a specimen this method may work on, Grishin says, “I think we can cover any extant specimens; I do not see a conceptual problem.” The oldest specimen Grishin has successfully sequenced, part of yet-unpublished work, was collected sometime prior to 1777.
With the establishment of the new Malazinae subfamily, M. fastuosus moves outside of the subfamily Hesperiinae (Family Hesperiidae).
Its highly distinct morphology and newly sequenced mitogenome support the revised phylogenetic placement. The authors note that additional studies are needed to “firmly establish phylogenetic affinities of Malaza.”
The new subfamily represents an ancient lineage which today survives only in Madagascar. “It was already our hunch that Malaza represents an evolutionarily highly distinct lineage that probably belonged to no existing skipper butterfly subfamily from Madagascar,” Grishin says.
Malaza fastuosus was chosen because it is the type species for its genus—every genus has one designated species considered to be representative of the genus at large. “[S]uch type species serve rather like anchor points for stable nomenclature. For example, other species might really belong elsewhere, so such an unambiguous selection helps stabilize the genus,” Grishin explains.
This work is part of a larger project aiming to sequence type specimens for all butterfly genera, with more than 1500 primary type specimens sequenced so far.
Read the paper: The mitogenome of a Malagasy butterfly Malaza fastuosus (Mabille, 1884) recovered from the holotype collected over 140 years ago adds support for a new subfamily of Hesperiidae (Lepidoptera) in Genome.
