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Tramp ant caught globetrotting under false name


Tramp ant caught globetrotting under false name

December 14, 2015
Tramp ant caught globetrotting under false name
A specimen of Pheidole indica, an ant species from Asia that has been spreading across the globe under the name Pheidole teneriffana. Credit: Dr. Eli Sarnat

A century-old mystery surrounding the origin of an invasive ant species was recently solved by an international team of scientists. Since 1893, when it was first discovered as an invasive species in the Canary Islands, entomologists have been debating where this mystery species came from. While some insisted on the Mediterranean, some proposed Arabia and others argued for Africa. The correct answer? Asia.

The authors of the study, published in the open-access journal ZooKeys, solved the taxonomic puzzle by fitting together disparate pieces of evidence. “I was having a terrible time trying to distinguish this one Asian from the mysterious ant that was coming in on shipments from the Caribbean, Europe and Africa,” says Dr. Eli Sarnat, University of Illinois, about his research at the Smithsonian on tramp that were intercepted at US ports.

Tramp ants, many of which are pest species, are spread across the globe by stowing away in the cargo of ships and planes, thus posing rising environmental, food security and public health concerns.

The same day Sarnat was working on the mysterious ant in the Smithsonian, he received an email from Dr. Evan Economo, Okinawa Institute of Science and Technology (OIST). Economo and Dr. Georg Fischer, also affiliated with OIST, had included Madagascar samples of the species in a genetic analysis, and the results unexpectedly placed it within a group of Asian species. The closest genetic match to the enigmatic ant turned out to be the very same Asian species that Sarnat had found in the Smithsonian collection.

Tramp ant caught globetrotting under false name
A showing the global distribution of Pheidole indica, with the native regions in blue and the invaded regions in red. Credit: Dr. Eli Sarnat

The last piece of the riddle was discovered thanks to the painstaking work of Dr. Benoit Guénard. Guénard, a professor at the University of Hong Kong, had spent years mapping the global distributions of every ant species known to science. When he compared the ranges of the mysterious ant with the common Asian species, the two fit together like a jigsaw puzzle.

Evidence gathered from classic taxonomy, modern genetic analysis, and exhaustively researched distribution maps all pointed to the same conclusion.

“What had long been considered two different species—one found across a wide swath of Asia and the other a tramp species spread by humans across Europe, Africa, the Americas and Australia—are actually one single supertramp species,” Economo explained. “It is striking that we had these two continental super-common invaders with almost entirely complementary ranges right under our noses, yet until now no one noticed they were actually the same species,”

More information: Sarnat EM, Fischer G, Guénard B, Economo EP (2015) Introduced Pheidole of the world: taxonomy, biology and distribution. ZooKeys 543: 1-109.DOI: 10.3897/zookeys.543.6050

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Pheidole flavens-complex introduced to the southwestern Pacific

Here’s the story behind the new Bioinvasions Records article on that just came out. Christian Rabeling and Ed Wilson went to Vanuatu a few years back in 2011 because it was one of the few Melanesian islands that Wilson had never collected from. They collected all the ants they could find in a general survey and kindly sent their Pheidole to the Economo lab at OIST so that I could match them against our other Pacific Pheidole collections and Evan could include them in our phylogenetic analysis. Christian and Ev caught some great Pheidole from the island, including this beautifully spinescent endemic from the sexspinosa complex shown below (CASENT0282641).

An elegant Vanuatu endemic ant species (Pheidole epem198, CASENT0282641) from the Pheidole sexspinosa complex

But one species came out in an unexpected branch on the phylogeny. Instead of coming out with the Old World clade with all the other native Melanesian ants, this one species was reliably nested within the New World clade. It’s closest relatives on the tree were two species that had been included in Corrie Moreau’s 2008 Pheidole phylogeny and id’d as P. moerens and P. flavens–both of which are considered to be invasive.

Major worker of a species from the Pheidole flavens-complex from Espiritu Santo, Vanuatu; collection code CR111110-15, specimen code CASENT0248836. (1) Lateral view, (2) fullface view, (3) dorsal view, (4) hypostomal bridge.

Major worker of a species from the Pheidole flavens-complex from Espiritu Santo, Vanuatu; collection code CR111110-15, specimen code CASENT0248836. (1) Lateral view, (2) fullface view, (3) dorsal view, (4) hypostomal bridge.


Minor worker of a species from the Pheidole flavens-complex from Espiritu Santo, Vanuatu; collection code CR111110-15, specimen code CASENT0248835. (5) Lateral view, (6) fullface view, (7) dorsal view

We wanted to let other researchers know about the spread of this trampy species into the Pacific, so we wrote up a rapid communication article for Bioinvasions Records. The idea was to get the basic information about the new discovery out as quickly as possible, so others in the region could be on the lookout for additional incursions.

The most frustrating part of this study was trying to get a name on the species. Unfortunately, the taxonomy of P. flavens and its close relatives like P. moerens and P. exigua is a super sticky mess, rife with infra-specific names, lost holotypes, and inaccurate determinations. It seems like these taxonomic morasses plague trampy species (like P. flavens and friends) much more often than your average ant species.

Why is it that trampy species so often belong to species-complexes? What are species-complexes, anyways? I suppose I’d define them as geographically distinct populations that are somewhere on the continuum of streching from a recently coalesced species radiation on one end to a network of geographically isolated groups with some low amount of gene flow still persisting. For the taxonomist or even the molecular systematist there is no clear way to know whether to call these things five geographically isolated species or one widespread species.

Whatever the population on Vanuatu turns out to be, it doesn’t match the neotype of P. flavens or the syntypes of P. moerens, so for now we have to settle for calling it a member of the flavens-complex and hope that someone tries to untangle this taxonomic knot in the near future.

EM Sarnat, C Rabeling, EP Economo & EO Wilson (2014) First record of a species from the New World Pheidole flavens-complex (Hymenoptera: Formicidae) introduced to the southwestern Pacific. Bioinvasions Records 3: 301-307. | PDF


The Ants of Fiji – Print and PDF out now

Figure 1. Photographs of Fijian ants. A) Acropyga sp. FJ02 (endemic) carrying mealybug. B) Hypoponera eutrepta (endemic) carrying larva. C) Tetramorium lanuginosum (introduced). D) Camponotus dentatus (endemic). E) Odontomachus simillimus (Pacific native). F) Camponotus polynesicus (endemic).

The print and full color, open-access pdf versions of the Ants of Fiji (Sarnat & Economo, 2012) are now available. The 400-page monograph reviews the entire known Fijian ant fauna, and includes the results of a recently completed archipelago-wide biodiversity inventory. A total of 187 ant species representing 43 genera are recognized here with an illustrated key to genera, synopses of each species, keys to species of all genera, and a species list. The work is heavily illustrated with specimen images, distribution maps, and habitat elevation charts.


Sarnat, E.M. & Economo, E.P. (2012) Ants of Fiji. University of California Publications in Entomology, 132, 1-398. [pdf]


Expert from the introduction section

Biologists have long sought to document and understand the unique evolution and ecology of island biotas. Oceanic archipelagos are often adorned with spectacular evolutionary radiations and unique ecosystems. These distinctive faunas, however, are highly vulnerable to human activities, climate change, and introduction of exotic species. Among island ant faunas, perhaps nowhere are these themes so prominently on display as in the Fijian archipelago.

The Fijian terrestrial biota was assembled during approximately 20 million years of over-water colonization, in situ evolution and speciation, and more recently through the arrival of species as stowaways on canoes, galleys and battleships (Figure 1). Today’s Fijian ant fauna is characterized by extreme geographic isolation from source areas, differentiation and pattern formation among islands, and contemporary invasions. The list of species occurring in Fiji, which continues to grow, includes both widespread dominant species and rare taxonomic oddities.

The motivation of this study is to provide an update to W. M. Mann’s (1921) monograph The Ants of the Fiji Islands, published 89 years ago. At the time, Mann lamented that the insect fauna of Fiji had been almost entirely neglected, and the limited knowledge accrued in the years since his publication is even more lamentable. With the recent collection of a large number of ant specimens in recent years, and a surge of interest in biodiversity research and conservation in Fiji, the opportunity has arrived to synthesize the taxonomy of the Fijian ant fauna for new generations of biologists. Our goal is to provide a resource that will allow a scientist to collect an ant specimen anywhere in Fiji and connect it to information on its taxonomy, geographic distribution, habitat distribution and natural history. With 187 species distributed over seven islands of moderate size, and hundreds of smaller islands, the system represents a diverse yet tractable fauna that can be useful for testing hypotheses in evolutionary biology, island biogeography, community ecology, invasion biology and other disciplines.

It would be remiss to conclude this introduction without a note of recognition and thanks to the people of Fiji. Mann (1921) wrote in the introduction of his own treatise on Fijian ants, “I shall remember the native Fijians…as the kindliest, most hospitable folk I have known.” Eighty-nine years later, we both share those sentiments and add our admiration for the Fijians’ thoughtful stewardship of their native lands. We hope this small study will be useful for scientific discovery and conservation of Fiji’s fascinating natural heritage in the generations to come.