In Sum

SIS'S CHICKS Brood parasitism--tricking another mother into incubating one's eggs--is particularly common in ducks. A female duck simply lays her eggs in the nest of another duck, leaving the host mother to care for them. It's a good deal for the parasitic bird: she avoids the energetically costly business of incubating and raising her own chicks and also avoids being a sitting duck for predators.

If the host and parasite are closely related, the cost of caring for these extra offspring would be outweighed by the genetic benefit to the group. Zoologists Malte Andersson and Matti Ahlund, of Sweden's Goteborg University, studied this kin-selection hypothesis among female goldeneye ducks (Bucephala clangula,) by exploring whether the birds parasitize only individuals to which they are closely related.

Without harming the developing embryos, the researchers drew small albumen samples from goldeneye eggs and looked for genetic markers specific to each mother. Andersson and Ahlund found that the hosts and parasites were, in fact, more closely related than one would expect if nests were selected by chance. Female goldeneyes return to their birthplace to lay their eggs, so are they simply more likely to nest--and parasitize nests--in the same area, or do the ducks recognize and target their relatives? The scientists discovered that females most often parasitized the nests of their mothers and sisters and that female relatives spent more time together than random female pairs did. In addition, the more closely related the host-parasite pair, the greater the number of extra eggs a parasite laid in a host's nest--suggesting that a near-relative host was more amenable to the invasion. ("Host-Parasite Relatedness Shown by Protein Fingerprinting in a Brood Parasitic Bird," Proceedings of the National Academy of Sciences 97:24, 2000)--Kirsten L. Weir

POACHED FUNGI Processions of foliage-toting leaf-cutter ants are common in the rainforests of Central and South America. When the ants return to their nests, they don't eat the leaves they have collected but use them to feed the nutritious fungi that they cultivate in underground chambers. Now scientists have discovered a new ant species of the genus Megalomyrmex that is incapable of growing its own fungi but has evolved to steal the fungus farmers' carefully tended harvests.

Biologist Rachelle M. M. Adams, of the University of Texas at Austin, and colleagues studied this thievery-prone species both in the field and in the laboratory. Native to central Panama, it raids nests of Cyphomyrmex longiscapus ants, driving out the fungus growers and taking over the colony.

Some Megalomyrmex species invade colonies of fungus growers and live peacefully with them as parasites. But members of the newly discovered species invariably attack all the original inhabitants by pulling at their legs and antennae and perhaps by excreting venom. Unable to defend themselves, the surviving C. longiscapus ants abandon their broods and flee the nest. The predaceous invaders consume the fungus and, researchers suspect, feed the stolen larvae to their own broods.

The nest raiders may do some light gardening, maintaining healthy fungus growth for a while. But they don't add necessary nutrients to the high-maintenance gardens, so the fungi eventually become depleted and the "agro-predators" must seek out and take over a new nest. ("Agro-Predation: Usurpation of Attine Fungus Gardens by Megalomyrmex Ants," Naturwissenschaften 87, 2000)--Kirsten L. Weir

ROCK-CLIMBING FISH Salmon swim upstream to spawn, sometimes leaping over low waterfalls, but can any fish climb a wet, slippery, five-story cliff? A team of Brazilian ichthyologists, headed by Paulo A. Buckup, of the Brazilian National Museum and the Federal University of Rio de Janeiro, has observed a species of the South American darter (Characidium) that routinely performs this seemingly impossible feat.

The researchers observed the waterfall-climbing abilities of the inch-and-a-half-long fish in the swift freshwater streams of Espirito Santo in eastern Brazil. Using their two large pairs of long, flat, stiff-rayed fins, the darters cling to the base of the vertical rock surface while still underwater, then inch themselves upward with strong lateral movements. Their flat, scaleless bellies and slender, elongated bodies facilitate the process. Resting for a few minutes between each effort, they are able to gradually ascend a fifty-foot cliff beneath a waterfall. The same adaptations that enable the darters to cling and climb also enable them to recolonize upstream areas after being washed downstream by flash floods. The scientists think this behavior helps maintain populations in the isolated uplands, where, it seems, more species of darters have evolved than in the lowlands.

Other kinds of fishes, notably some tropical gobies and Asian loaches, which also have the ability to climb tall waterfalls, have independently evolved fin and body shapes similar to those of the darters. ("Waterfall Climbing in Characidium (Crenuchidae: Characidiinae) From Eastern Brazil" Ichthyological Exploration of Freshwaters 11:3, 2000)--Richard Milner

COPYRIGHT 2001 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning