The story begins with HMS Challenger, the Royal Navy vessel whose four-year circumnavigation from 1872 to 1876 laid the foundations of modern oceanography. Along the way, the expedition’s naturalists collected butterflies at various ports of call, and some of that material reached Butler at the British Museum. In 1884 he described Catochrysops trifracta on the basis of two damaged male specimens, citing the type locality as Rat Island in the Strait of Malacca, collected on 1 September 1873. Butler noted that his material also came from the islands of St. Thomas and Bermuda in the New World, alongside the Old World localities of Ké Dulan, Ternate and Amobina, but he anchored the new species firmly in Southeast Asian waters.

His description pointed to a butterfly resembling the gram blue, Euchrysops cnejus, in the pattern of its underside, but with a distinctive difference: the row of spots across the forewing disk was broken into three parallel oblique dashes edged in white, rather than forming a single slightly irregular stripe. He also recorded only one subanal black spot on the hindwing with a pale yellow zone, barely touched with metallic scales, and a wingspan of 23 to 28 millimetres. Those characters, as the new study demonstrates, were accurate observations of the specimens — but they describe a Neotropical butterfly, not a Malayan one.

Over the following decades the name drifted through the literature in inconsistent ways. Butler himself later moved C. trifracta, along with C. cnejus and several other species distinguished by having smooth rather than hairy eyes, into his new genus Euchrysops in 1900, with C. cnejus as the type species. The species was briefly mentioned in Swinhoe’s Lepidoptera Indica in 1910 as a Malayan species allied to Indian forms. Yet the major synonymic catalogues of the era told a different story: de Nicéville in 1890 and Seitz in 1927 listed the synonyms of Euchrysops cnejus without including trifracta, Bethune-Baker’s 1923 revision of Catochrysops ignored it entirely, and even the standard reference Butterflies from the Malay Peninsula, first published by Corbet and Pendlebury in 1934, never mentioned it. The name effectively vanished from active use before reappearing, without apparent justification, as a synonym of E. cnejus in Seki and colleagues’ 1991 work on Malaysian butterflies — a listing subsequently copied by Bridges in 1994 and absorbed into most online databases.

The key to the mystery lay in the original labels and in a footnote that had been overlooked. The two syntypes of Catochrysops trifracta are preserved in the Natural History Museum in London, both bearing locality labels that read simply Rat Island — with no mention of the Malaccas at all. Thomson and Murray, in their official 1885 report on the Challenger expedition, had already flagged the problem in a footnote on page 214: the locality information given by Butler was incorrect, and the specimens actually came from Ilha Rata — Rat Island — in the Fernando de Noronha archipelago off the coast of Pernambuco, Brazil. Curiously, the same report still suggested the species seemed to be of Malayan origin, a contradiction that apparently discouraged later researchers from pursuing the point.

Fernando de Noronha’s butterfly fauna makes the South American explanation overwhelmingly likely. In their 1890 work on the natural history of the archipelago, Kirby and Ridley reported that Hemiargus hanno — then treated under the name Taurucus hanno — a lycaenid widely distributed across South America, was frequent on Rat Island and the main island. Indeed, that species appears to be the only butterfly occurring anywhere in the archipelago, according to a 1962 survey by Alvarenga. Kirby even acknowledged that the expedition’s C. trifracta had not been found again on the islands, but suggested this could reflect mislabelling of the specimens, since the genus was otherwise known only from the East Indies. Butler, meanwhile, seems to have been unaware of both the Thomson and Murray footnote and the Ridley and Kirby account when he revised his genus in 1900.

To settle the question definitively, the author of the new study compared the syntype specimens directly with reference material of both candidate species, drawing on holdings including a non-type specimen of Hemiargus hanno from Venezuela at the McGuire Centre for Lepidoptera and Biodiversity in Florida, and a non-type Euchrysops cnejus from the Philippines. The morphological evidence turned out to be unambiguous. Like H. hanno, the C. trifracta syntypes bear only a single black tornal spot on the hindwing — exactly the feature Butler described as only one subanal black spot — accompanied by blue scaling toward the margin and a small amount of orange on the inner margin. Euchrysops cnejus, by contrast, has two black tornal spots with blue scaling, each with a larger amount of orange, and these spots are visible on the upper side in both sexes, whereas the single tornal spot of H. hanno and C. trifracta is barely discernible from above.

Further characters reinforce the distinction. Euchrysops cnejus carries a tail in the tornal area of the hindwing, a feature entirely lacking in both H. hanno and the trifracta syntypes. And both H. hanno and the Challenger specimens share a grey sub-basal spot at the base of the ventral hindwing cell Cu2-2A that is absent in E. cnejus — although that spot does occur in the widespread Afrotropical species E. malathana and its arid-adapted sister species E. nilotica. Taken together, the wing pattern, tornal structure and presence of the tail tell a consistent story: the syntypes represent Hemiargus hanno and neither E. cnejus nor any other member of Euchrysops.

On these grounds the study formally places Catochrysops trifracta Butler, 1884 as a junior subjective synonym of Hemiargus hanno (Stoll, 1790), with the status revised from its previous placement. Because the name trifracta was based on two syntypes and its identity needed to be fixed permanently, the author designated a lectotype: the better-preserved of the two male specimens in the Natural History Museum, London, carrying the labels Type; Rat Island 84 · 10; Catochrysops trifracta type Butler; and the registration number NHMUK010588635. A new lectotype label recording the 2022 designation will be added to the specimen in due course. This act of type designation is a standard taxonomic procedure that pins the name unambiguously to a single physical specimen, preventing future confusion.

Beyond resolving one dangling name, the case is a vivid illustration of how much biology still sleeps inside historical museum collections. The Challenger expedition’s butterflies sat mislabelled for more than a century while the same species thrived in the wild on the very islands where it was originally caught — only under a different name. The study also highlights how errors propagate through the taxonomic literature: a synonymy introduced in a 1991 field guide became entrenched in catalogues and databases simply by repetition. Correcting the record matters practically as well as academically, because Euchrysops cnejus is an Old World species and Hemiargus hanno a New World one; conflating them distorts biogeographic inference, ecological interpretation and conservation assessment alike. With the lectotype now designated and the wrong-continent error corrected, one of oceanography’s most celebrated expeditions has, at last, had its butterfly placed where it truly belongs.

Subject of Research: Taxonomic revision showing the butterfly name Catochrysops trifracta Butler, 1884 is a synonym of the Neotropical species Hemiargus hanno

Article Title: On the wrong continent: The identity of Catochrysops trifracta Butler, 1884 ( Polyommatinae , Lycaenidae ), currently a synonym of Euchrysops cnejus (Fabricius, 1798)

Article References: Espeland, M. (2022). On the wrong continent: The identity of Catochrysops trifracta Butler, 1884 (Polyommatinae, Lycaenidae), currently a synonym of Euchrysops cnejus (Fabricius, 1798). Nota Lepidopterologica, 45, 129-132. https://doi.org/10.3897/nl.45.81499

Image Credits: AI Generated

DOI: 10.3897/nl.45.81499

Keywords: taxonomy, Lepidoptera, Lycaenidae, Catochrysops trifracta, Hemiargus hanno, Euchrysops cnejus, Challenger expedition, Fernando de Noronha, lectotype designation, museum specimens, biogeography, Nota Lepidopterologica

Colistin, also called polymyxin E, occupies a special and precarious position in modern medicine. It is a cationic polypeptide that attacks the outer membrane of Gram-negative bacteria, and after decades of limited use because of kidney toxicity, it was reintroduced in recent years as a final defense against multidrug-resistant infections. With few new antibiotics in the development pipeline, clinicians increasingly depend on colistin when carbapenem-resistant pathogens strike hospital patients. The emergence of bacteria that resist this drug is therefore not a routine scientific concern but a genuine emergency in global public health, and the new study demonstrates that the ocean may be serving as an unexpected reservoir and highway for the genes responsible.

The mechanics of colistin resistance matter for understanding why the new results are so significant. Resistance can arise in two ways. Intrinsic resistance develops through chromosomal mutations that alter lipid A, the lipopolysaccharide component of the bacterial outer membrane that colistin targets, reducing the drug’s ability to bind. Acquired resistance, by contrast, depends on the horizontal transfer of mcr genes, usually carried on plasmids, which are mobile DNA elements that can shuttle between bacterial cells. Since the discovery of the mcr-1 gene in Escherichia coli plasmids a decade ago, researchers have identified ten mcr variants, from mcr-1 through mcr-10, and watched them disperse across continents, animal populations, and clinical settings. What remained poorly understood was how extensively these genes had colonized marine ecosystems.

To answer that question, the Brazilian team designed a natural experiment spanning roughly 330 kilometers of the Rio de Janeiro coastline plus the Fernando de Noronha Archipelago, a volcanic island group about 360 kilometers offshore in the Western Atlantic. Their sampling sites deliberately covered a gradient of human influence. At one extreme sat Bom Jesus Cove in Guanabara Bay, a tropical urban estuary receiving raw sewage, oils, and industrial contaminants from Rio de Janeiro city. At the other extreme lay the submarine caves of Fernando de Noronha, protected within a national marine park and accessible only by SCUBA diving. Between those poles, the researchers sampled the Cagarras Archipelago, a no-take marine protected area unfortunately positioned near the Ipanema submarine sewage outfall; the biodiverse waters of Arraial do Cabo, including the Gruta Azul submarine cave; and Ilha Grande Bay, one of the world’s largest tropical bays, which faces growing pressure from coastal settlements and maritime traffic.

The laboratory work was methodical and technically demanding. From 1,550 total bacterial isolates, the team focused on 308 Gram-negative bacilli identified as potential hosts of acquired colistin resistance determinants. Bacteria were cultured on Luria Bertani and MacConkey agar from water samples, washed and swabbed from pieces of floating plastic, and extracted from sponge tissue through serial dilution across four growth media. Identification proceeded by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry on a Bruker Microflex LT platform, and DNA was extracted using a thermal lysis protocol with Chelex 100 resin. Polymerase chain reaction screening then probed each strain for eight mcr variants, and any positive strains were tested further for beta-lactamase genes, quinolone resistance genes, aminoglycoside resistance genes, sulfonamide resistance genes, and class 1, 2, and 3 integron-integrase genes.

The results were striking in both breadth and detail. Of the 308 potential host strains, 101 carried at least one mcr variant, generating 128 total gene occurrences. Water samples contributed 59.4 percent of the positive strains, plastic litter 35.6 percent, and marine sponges 5.0 percent. The mcr-9 variant dominated with 33 occurrences, followed by mcr-3 with 23, mcr-2 with 18, and mcr-1 with 17. That mcr-9 topped the list is noteworthy because global metagenomic surveys have often ranked mcr-1 as the most dispersed variant. The mcr-9 gene is known to circulate on IncHI2 plasmids that interconnect human, animal, and environmental isolates, suggesting an efficient dissemination network that the ocean may now be extending.

The bacterial hosts carrying these genes were equally concerning. Among ten identified genera, Enterobacter, Acinetobacter, Vibrio, and Klebsiella predominated. Enterobacter species alone accounted for 31 strains and harbored the greatest mcr diversity, with every variant except mcr-5 and mcr-7 detected in the genus. More alarming still, mcr-positive Enterobacter was not confined to polluted Bom Jesus Cove but turned up in marine sponges and cave waters in Fernando de Noronha, an area with restricted human access. One Enterobacter hormaechei strain, isolated from a sponge in Sapata Cave, simultaneously carried mcr-2, mcr-9, and the sulfonamide resistance gene sul1. Four strains carried three mcr variants at once, including Klebsiella pneumoniae isolates from pristine sponges and from floating plastic, and an Enterobacter cloacae from Noronha water. Both K. pneumoniae and E. cloacae belong to the notorious ESKAPE group of pathogens, and their carriage of multiple resistance genes in aquatic matrices highlights the risk of waterborne transmission to humans.

The co-occurrence of resistance genes painted an even darker picture. Nearly half of the mcr-positive strains, 46.5 percent, also carried other antimicrobial resistance genes or integron-integrases, with sulfonamide resistance genes, particularly sul1, the most frequent companions, followed by the beta-lactamase genes blaTEM and blaSHV. In Bom Jesus Cove, the team detected the carbapenemase gene blaKPC alongside mcr-3 in Enterobacter bugandensis and Raoultella ornithinolytica strains, a combination that effectively eliminates two of the last therapeutic options for infections caused by these organisms. Integron-integrases, genetic platforms that capture and shuffle gene cassettes, co-occurred with mcr exclusively in the polluted cove, suggesting bacterial adaptation to intense anthropogenic selective pressure. Because changes in membrane permeability in mcr-positive bacteria can reduce sensitivity to multiple drugs, these combinations can compound into true multidrug resistance, complicating treatment of hospital-associated infections.

The gradient of pollution left a measurable fingerprint on the data. In Bom Jesus Cove, 27 of 104 water-isolated strains tested positive for mcr, and 36 of 82 strains from floating plastic litter carried the genes, a prevalence of roughly 44 percent that represents the highest in the study. The finding positions plastic debris as both a reservoir and a vector for antimicrobial resistance, offering microbes a stable, drifting substrate on which biofilms can form, exchange genes, and travel with currents. At the Cagarras Archipelago, 40 percent of water-isolated strains were positive despite formal protection, a legacy of the nearby sewage outfall. Arraial do Cabo showed 36.5 percent prevalence among water isolates and Ilha Grande Bay 36.3 percent. In Fernando de Noronha, prevalence dropped to about 5 percent of candidate host strains, with two of 17 water isolates and five of 15 sponge isolates positive, proving that resistance persists even where human pressure is minimal.

What emerges from the study is a warning that antimicrobial surveillance cannot remain confined to clinics and farms. Marine sponges, submarine caves, and drifting plastic are now documented hotspots of colistin resistance, and the genes involved sit on mobile elements capable of jumping into human pathogens. The Brazilian coastline, with its juxtaposition of dense urban pollution and remote protected archipelagos, offered an ideal natural laboratory, but the pattern it revealed is almost certainly global. The researchers argue for integrated monitoring programs that treat the ocean as a critical node in the antimicrobial resistance network, alongside conservation strategies that reduce sewage discharge and plastic pollution. As colistin remains a last resort for patients out of options, every mcr gene circulating in seawater, attached to plastic, or sheltering inside a sponge represents a card stacked against future medicine, and the ocean, it turns out, is dealing them freely.

Subject of Research: Distribution of mobile colistin resistance (mcr) genes in bacteria from Brazilian marine environments

Article Title: Widespread occurrence of mobile colistin resistance genes in Brazilian marine environments

Article References: Brunelli, R. C., de Jesus Carvalho Baptista, T. V., de Oliveira Nithack Marques, M., da Silva Oliveira Alves, G., Abdon, B. B., Mello, M. P., Paranhos, R., Gallo, M. N., Vinzon, S. B., Lage, A., Sandes, J., Muricy, G., Klautau, M., Lopes, M. V., Dias, G. R., Canellas, A. L. B., & Laport, M. S. (2025). Widespread occurrence of mobile colistin resistance genes in Brazilian marine environments. Ocean Microbiology, 1(1), Article 3. https://doi.org/10.1186/s44375-025-00003-z

Image Credits: AI Generated

DOI: 10.1186/s44375-025-00003-z

Keywords: antimicrobial resistance, colistin, mcr genes, marine microbiology, plastic pollution, Guanabara Bay, Fernando de Noronha, Enterobacter, Klebsiella pneumoniae, integrons, marine sponges, One Health