SEM image of P. barbatus (Image: C.-P. Strehl)
|Mayr , 1868|
About 60 species are known that are distributed in deserts and steppe areas of the New World (North, Central and South America) and can be divided into at least two subgenera : Pogonomyrmex sensu stricto (G. Mayr, 1868) and Ephebomyrmex (WM Wheeler, 1902). The name of the genus comes from the Greek and refers to a beard-like (Gr. Pogon = beard) structure below the head of most representatives of the subgenus sensu stricto , the Psammophore (see picture: Pogonomyrmex barbatus ). The representatives of the subgenus Ephebomyrmex , whose name was derived from the Greek name for a beardless youth (ephebos), and generally has smaller individuals and colonies , lack this structure .
The first Pogonomyrmex species arose within the subfamily Myrmicinae probably around 30 million years ago in the dry phases of the Oligocene , when the first grasses emerged. The closest related genera are Myrmica and Hylomyrma .
Pogonomyrmex species feed on occasionally preyed insects or other animals. The main source of food for the colonies, however, is seeds, which are mostly collected from surrounding grasses and can be stored in underground food stores (up to 2 m deep). Representatives of this genus are therefore among the so-called harvest ants . In most Pogonomyrmex species, the grinding of the hard seed coats is made easier by the presence of strong mandible muscles, which give them a characteristic, beefy head.
Workers and queens have a sting that can be used several times and can also pierce human skin. Males are stingless. The sting of the representatives of most Pogonomyrmex species is painful for humans. The species Pogonomyrmex maricopa is one of the species with the lowest lethal dose ( LD50 ) of an insect venom ever measured in mice . The strength of the poison may be used to defend the underground seed stores from gerbils. Lizards of the genus Phrynosoma are immune to the poison and one of the main predators. The venom of some species of Pogonomyrmex has been considered hallucinogenic by some North American Indians . H. the perception-changing means used.
The mating behavior of the monogynous North American P. sensu stricto species was well investigated by Bert Hölldobler in the 1970s. In P. sensu stricto species there are unusually high mating frequencies of queens for eusocial Hymenoptera , which should lead to the offspring of a queen having several fathers within a colony and thus a low degree of relationship to one another (see also: kinship selection ). For Pogonomyrmex occidentalis , these high mating frequencies of the queens of Blaine J. Cole and Diane C. Wiernasz could also be detected for the first time in 1999 by means of genetic fingerprints. Since then, multiple mating has also been genetically proven in many other sensu stricto species (including P. badius , P. barbatus , P. rugosus ). Cole and Wiernasz also showed for P. occidentalis that the lower kinship among nest mates resulting from the multiple pairing of the queens correlates with faster growth of the entire colony. Possible explanation of the two scientists: the lower intracolonial relationship causes a higher genetic variability, which in turn enables Pogonomyrmex (a) better protection against parasites or (b) more efficient work performance of the entire colony.
A multiple pairing has so far only been detected for the representatives of the subgenus sensu stricto , but not so far for the subgenus Ephebomyrmex . Nevertheless, the genetic variability of the colonies seems to be increased in Ephebomyrmex species as well , since several queens can lay eggs (functional polygyny ).
- Arthur C. Cole jr .: Pogonomyrmex harvester ants. The University of Tennessee Press (1968)
- Hölldobler and Wilson : The Ants. Harvard University Press, 1990, ISBN 3764351527
- Christoph-Peter Strehl: "Evolution of colony characteristics in the harvester ant genus Pogonomyrmex"; University of Würzburg, 2005; URN: urn: nbn: de: bvb: 20-opus-14324