Ecologists seek help for menaced hybrids.

Keen gardeners often cross plants of two different species to produce a hybrid bearing the best traits of both parents. Hybrids also arise in the wild between adjoining populations of different species. But even when these zones yield novel plants vulnerable to extinction, the hybrids do not qualify for protection under the U.S. Endangered Species Act.

Ecologists now hope to reverse that policy, bolstered by a new study showing that plant hybrids harbor more insects and a greater diversity of insect species than their parents. The finding suggests that plant hybrids play a vital ecological role worth protecting.

Researchers led by Thomas G. Whitham of Northern Arizona University in Flagstaff counted all the insects they could collect over a 12-minute sampling period from two species of eucalyptus trees located in adjacent forests in Tasmania, Australia. The team, which included scientists from the University of Minnesota in Minneapolis and the University of Tasmania, also sampled insects from hybrid eucalyptus trees located between the two parent species. One of the parent species is endangered.

They found twice as many insect species on the hybrid trees as on either of the parent trees. In addition, individual insects of species found on all three types of trees were three to four times more abundant on the hybrids, Whitham reported last week at a meeting of the American Institute of Biological Sciences, held in San Antonio, Texas.

Two years ago, Whitham described similar results from an eight-year study conducted along the Weber River in northern Utah, where he compared concentrations of gall aphids among narrow-and broad-leafed cottonwoods and their hybrids. In the June 23, 1989 SCIENCE, Whitham reported finding nearly all of the aphids in a zone of hybrids bearing leaves of intermediate breadth.

"It's relatively clear that the [insect] species richness is greatest in areas of [tree] hybrids," he said at last week's meeting. "Their density is also higher on hybrids than on pure parentals."

Whitham contends that his studies establish the importance of plant hybrids and demonstrate the need to conserve those threatened by extinction. "Plant hybrid zones can represent focal points of insect biodiversity, and they should be preserved for that reason alone," he asserts. "Some insect species may be so restricted to hybrid zones that the elimination of these zones that the elimination of these zones may result in the extinction of the species." He cites the gall aphids as a case in point.

Other ecologists and environmentalists seem to agree. Hybrid zones exemplify "evolution in progress," says Elaine Hoagland, executive director of the Association of Systematics Collections, a Washington, D.C.-based organization representing 80 North American botanical gardens and natural history museums. Although the association primarily seeks to preserve individual species, it is also considering lobbying for the protection of plant hybrids. "You can go overboard in trying to freeze what exists now," Hoagland explains. "You can't outlaw evolution."

Hoagland represents her association on the Endangered Species Act Reauthorization Committee, a coaliation of environmental groups drawing up changes to the 1973 Endangered Species Act for congressional consideration. The law will cease to exist if it does not gain reauthorization during the current congressional session, which will end in 1972.

David Blockstein of the American Ornithologists' Union in Washington, D.C., is a member of the reauthorization committee's working group to formulate conservation measures for all endangered hybrids, plant or animal. Recently, critics have assailed captive breeding programs for the extinct-in-the-wild red wolf, arguing that the animal is a hybrid between the gray wolf and the coyote (SN: 6/15/91, p.374). "We're looking to see if there's a need to incorporate a legal remedy [into the Endangered Species Act to protect hybrids]," Blockstein says.

In the meantime, the U.S. Fish and Wildlife Serve may loosen its strictures against hybrid preservation. Larry Shannon, chief of the agency's division of endangered species, says it will propose new regulations this fall to protect hybrids with parent species listed as endangered.