![]() ![]() ![]() The species of Atta in particular are among the scourges of tropical agriculture. Since they attack most kinds of vegetation, including crop plants, they are serious economic pests. Many of the species gather pieces of fresh leaves and flowers to nourish the fungus gardens, and Atta and Acromyrmex rely on this source exclusively. In the vast subtropical and tropical zones in between, attines are among the dominant ants. One species, Trachymyrmex septentrionalis, ranges north to the Pine Barrens of New Jersey, while in the opposite direction several species of Acromyrmex penetrate to the cold temperate deserts of central Argentina. The Attini are an enormously successful group where they exist. Also, fungus-growing ants forage above ground, often even in trees, while fungus-growing termites are primarily subterranean. This is possible because attines utilize insect excrement and fresh plant material for the most part, while the macrotermitines use dead plant material. The latter is more likely to be the case, meaning that if attines were to be introduced today into the range of the macrotermitines, or vice versa, the two kinds of insects could coexist with little interference. ![]() No one can be sure whether this complementary global pattern is due to a mutual preemption involving competitive exclusion of one group by another or whether it is simply one more accidental outcome reflecting the extreme rarity of the evolutionary origin of fungus gardening. In Africa, southern Asia, and other parts of the Old World tropics, the Attini are replaced by fungus-growing termites (Macrotermitinae), which in their turn do not occur in the New World. Extinct but modern-looking species of Trachymyrmex (Baroni Urbani, 1980) and Cyphomyrmex (Wilson, 1985h) have been found in the Dominican amber, which is believed to be either late Oligocene or early Miocene in age. Exactly when the event occurred is open to conjecture, but it was almost certainly prior to the Miocene Epoch. It is conceivable that fungus growing originated only once in a single ancestral attine living in South America during that continent's long period of geological isolation from late Mesozoic times to approximately four million years ago. Besides their unique behavior and the many peculiar behavioral and physiological changes associated with it, the Attini are distinguished from other ants by a distinctive combination of anatomical traits, including the shape of the antennal segments a less-than-absolute tendency toward hard, spinose, or tuberculate bodies and a proportionately large, casement-like first gastral segment. The Attini are a morphologically distinctive group limited to the New World, and most of the 12 genera and 190 species occur in the tropical portions of Mexico and Central and South America. Members of the myrmicine tribe Attini share with macrotermitine termites and certain wood-boring beetles the sophisticated habit of culturing and eating fungi. Altruism and the origin of the worker caste ![]()
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