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“Relic” ant said to hail from lost past

Sept. 16, 2008
Courtesy University of Texas at Austin
and World Science staff

A bi­zarre pred­a­to­ry, blind, un­der­ground ant spe­cies dis­cov­ered in the Am­a­zon rain­for­est is probably de­scended al­most straight from the first ants, re­search­ers say.

The in­sect was un­earthed by ev­o­lu­tion­ary bi­olo­g­ist Chris­tian Ra­bel­ing of the Uni­ver­s­ity of Tex­as at Aus­tin, ac­cord­ing to sci­en­tists.

Martialis heureka (Cour­tesy C. Rabe­ling, U. Tex­as at Aus­tin)
The ant is named Mar­tialis heureka, which trans­lates roughly to “ant from Mars,” be­cause of its nev­er-be­fore-rec­orded com­bina­t­ion of traits. It lives in soil, is two to three mil­lime­ters long, pale, and has no eyes and large jaws. 

Scientists have classi­fied the crea­ture in its own new sub­fam­i­ly, one of 21 ant sub­fam­i­lies. This is the first time that a new sub­family of ants with liv­ing mem­bers has been dis­cov­ered since 1923, ac­cord­ing to the in­ves­ti­ga­tors.

“This dis­cov­ery hints at a wealth of spe­cies, pos­sibly of great ev­o­lu­tion­ary im­por­tance, still hid­den in the soils of the re­main­ing rain­for­ests,” write Ra­bel­ing and co-authors in a pa­per re­port­ing the find­ing this week in the jour­nal Pro­ceed­ings of the Na­tional Acad­e­my of Sci­ences.

Ra­bel­ing col­lect­ed what is said to be the only known spec­i­men of the ant spe­cies in 2003 from leaf-litter at the Em­presa Brasileira de Pesquisa Agropecuária in Ma­naus, Bra­zil. He and his col­leagues found that the ant was a new spe­cies, ge­nus and sub­family af­ter struc­tur­al and ge­net­ic anal­y­sis. Anal­y­sis of DNA from the an­t’s legs con­firmed its po­si­tion at the very base of the ant ev­o­lu­tion­ary tree, the re­search­ers said.

Ants are be­lieved to have evolved over 120 mil­lion years ago from wasp an­ces­tors. It’s thought that they evolved quickly in­to many dif­fer­ent lin­eages, with ants spe­cial­iz­ing to live in soil, leaf-litter or trees, or be­com­ing gen­er­al­ists. “This dis­cov­ery lends sup­port to the idea that blind sub­ter­ra­ne­an pred­a­tor ants arose at the dawn of ant ev­o­lu­tion,” said Ra­bel­ing. 

Ra­bel­ing does­n’t sug­gest that the an­ces­tor to all ants was this way, but that these adapta­t­ions arose early and have per­sisted. “Based on our da­ta and the fos­sil rec­ord, we as­sume that the an­ces­tor of this ant was some­what wasp-like, per­haps si­m­i­lar to the Cre­ta­ceous am­ber fos­sil Sphe­co­myr­ma, which is widely known as the ev­o­lu­tion­ary mis­sing link be­tween wasps and ants,” said Ra­bel­ing. 

He spec­u­lat­ed that the new ant spe­cies evolved adapta­t­ions over time to its un­der­ground habi­tat—for ex­am­ple, loss of eyes and pale col­or—while re­tain­ing some of its an­ces­tors’ char­ac­ter­is­tics. “The new ant spe­cies is hid­den in en­vi­ron­men­tally sta­ble trop­i­cal soils with po­ten­tially less com­pe­ti­tion from oth­er ants and in a rel­a­tively sta­ble mi­cro­cli­mate,” he said. “It could rep­re­sent a ‘re­lict’ spe­cies.”

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A bizarre underground, predatory, blind ant species discovered in the Amazon rainforest is probably descended almost straight from the first ants, researchers say. The insect was unearthed by evolutionary biologist Christian Rabeling of the University of Texas at Austin, according to scientists. The new ant is named Martialis heureka, which translates roughly to “ant from Mars,” because the ant has a combination of traits never before recorded. It lives in soil, is two to three millimeters long, pale, and has no eyes and large jaws. The ant also belongs to its own new subfamily, one of 21 ant subfamilies. This is the first time that a new subfamily of ants with living species has been discovered since 1923, according to the investigators. “This discovery hints at a wealth of species, possibly of great evolutionary importance, still hidden in the soils of the remaining rainforests,” writes Rabeling and co-authors in a paper reporting their discovery this week in the Proceedings of the National Academy of Sciences. Rabeling collected what is said to be the only known specimen of the ant species in 2003 from leaf-litter at the Empresa Brasileira de Pesquisa Agropecuária in Manaus, Brazil. He and his colleagues found that the ant was a new species, genus and subfamily after structural and genetic analysis. Analysis of DNA from the ant’s legs confirmed its position at the very base of the ant evolutionary tree, the researchers said. Ants are believed to have evolved over 120 million years ago from wasp ancestors. It’s thought that they evolved quickly into many different lineages, with ants specializing to lives in the soil, leaf-litter or trees, or becoming generalists. “This discovery lends support to the idea that blind subterranean predator ants arose at the dawn of ant evolution,” said Rabeling. Rabeling doesn’t suggest that the ancestor to all ants was blind and subterranean, but that these adaptations arose early and have persisted over the years. “Based on our data and the fossil record, we assume that the ancestor of this ant was somewhat wasp-like, perhaps similar to the Cretaceous amber fossil Sphecomyrma, which is widely known as the evolutionary missing link between wasps and ants,” said Rabeling. He speculated that the new ant species evolved adaptations over time to its subterranean habitat—for example, loss of eyes and pale color—while retaining some of its ancestor’s physical characteristics. “The new ant species is hidden in environmentally stable tropical soils with potentially less competition from other ants and in a relatively stable microclimate,” he said. “It could represent a ‘relict’ species that retained some ancestral morphological [structural] characteristics.”