快猫短视频

FRUIT flies accidentally introduced to the Americas two decades ago have
evolved at an unprecedented rate. The finding has rung alarm bells about the
practice of deliberately introducing animals to control pests.

鈥淭his observation of very rapid evolution may prod ecologists to realise that
invading species are not set in stone but can evolve quickly in response to
their new environment,鈥� says Raymond Huey of the University of Washington in
Seattle. He says that evolution could drastically alter the way introduced
species interact with native ones.

Huey and his colleagues discovered the unexpectedly rapid evolution while
studying the fruit fly Drosophila subobscura. A few of the flies, which
are endemic to Europe, were carried on a cargo ship to the port of Puerto Montt
in Chile in 1978. Within a year, the flies had colonised much of the Chilean
coast, and they also now inhabit much of the West Coast of the US, displacing
the native Drosophila pseudo-obscura in many areas.

Huey鈥檚 team wondered how the wingspan of the insects had changed since they
reached North America. For reasons that are unclear, the wingspans of their
European cousins increase the farther north they live, differing by up to 4 per
cent in females and 2 per cent in males. But ten years ago, a study in the flies
in America revealed no such trend.

To see if their wingspans had changed over the past decade, Huey鈥檚 team
collected flies from 11 locations in North America and 10 in Europe. Flies from
each location were bred for six generations to ensure that any differences
between them reflected their genetic make-up rather than environmental
factors.

It turned out that the wingspan of North American females had indeed changed.
Females, and to a lesser degree males, showed the same increase in wingspan with
latitude as their counterparts that have lived in Europe for around 10 000
years. And the adaptation, although similar, was achieved differently, with the
exotic flies lengthening a different part of their wing.

More shocking is the speed and scale of change. Galapagos finches are the
only other organism known to have evolved faster in nature, after a drought in
1978 led to a dramatic shift in beak size in a local population of birds. But
the flies are changing across the country. 鈥淓volution has occurred not just on a
local scale, but on a continental scale,鈥� says Huey.

Huey thinks the result should add to fears about the dangers of biological
control of pests, which is increasingly popular in the US and other New World
countries. It has gone wrong on many occasions. For instance,
Cactoblastis caterpillars released in the Caribbean have spread far beyond
their intended range, attacking rare indigenous plants
(快猫短视频,15 January, p 31).

To avoid such mistakes, ecologists have tried to draw up strict protocols to
assess the risks posed by biological control agents. But Huey says that they
have not considered that introduced species could quickly evolve new and
possibly damaging characteristics. 鈥淭hey have traditionally ignored the
possibility,鈥� he says. He urges ecologists to consider this risk in future.