ACT Reading Apr. 2015 73G - Passage IV

Like many biologists, Andrew V. Suarez struggled

for years with the question of which colonizing organ­-

isms fail and which succeed. He studied it the hard

way-with fieldwork and lab experiments-until 1999,
₅ when he found some brown jars. He had gone to the

Smithsonian Institution National Museum of Natural

History's National Insect Collection to look for early

samples of Argentine ants collected in the United States

or at its borders. He hoped to find out how vintage
₁₀ specimens of Argentine ants were related to the existing

populations.

At the museum, among many thousands of jars of

insects labeled with taxonomic notes, locations, and

dates, Suarez ultimately found relatively few samples
₁₅ of Argentine ants. But what he found besides them was,

to his mind, far more interesting: some of the ethanol­-

filled jars were jammed with vials of ants collected at

ports of entry in the eastern U.S. from 1927 to 1985.

They were ants that border agents had picked from
₂₀ plants being shipped into the U.S. Could those ants be

identified as members of species that had failed or suc­-

ceeded as colonists, and if so, could the specimens be

used to compare the two groups?

In the jars and vials were 394 separate samples of
₂₅ ants. Suarez solicited the help of two friends, ant ecolo­-

gist David A. Holway of the University of California,

San Diego, and Philip S. Ward, guru of ant gurus, at the

University of California, Davis. Altogether they identi­-

fied 232 distinct species.

₃₀ Suarez considered the traits possessed by each of

the ant species in an attempt to see what might have

predisposed some of them to survival. He measured

whether they were big or small. He examined whether

each lived in the canopy or on the ground, and whether
₃₅ they were from one subfamily or another. He also

looked at a simpler possibility: that "survivor species"

tended to be those introduced more than once. The evi­-

dence in the jars showed, for example, that Argentine

ants had arrived at least twice. Were successes just a
₄₀ consequence of the number of tries?

When a pioneering group sets up camp and starts

living in a new place, possible futures diverge. One

species might be wiped out within a generation or two.

A second might survive, but never become common.
₄₅ Yet another species might thrive, eventually spreading

across states, continents, and even the world! Even if

surviving in a new environment is sometimes a matter

of being introduced again and again, thriving is a differ­-

ent story. Relatively few invasive species truly prevail.

₅₀ One curious thing about Argentine ants is that they

are, despite their apparent meekness, ecologically dom­-

inant. They are squishy, small, stingless wimps, as ants

go, yet somehow they have managed to overpower the

big, tough native ants.

₅₅ There's another strange thing about Argentine

ants. If you take an Argentine ant from what looks like

one colony and put it together with one from a distant

colony, they accept each other. In fact, you can perform

that trick over much of California and very few of the
₆₀ ants will fight. It is as though all of the Argentine ants

in California are part of a few huge colonies-"super­-

colonies," they've come to be called.

Biologist Ted Case joined forces with Holway and

Suarez for an experiment to test whether the lack of
₆₅ aggression among those ant colonies somehow helped

them to compete with other species. Might it simply be

that by not fighting with their neighbors, the Argentine

ants wasted less energy on war and could spend more

time on the good stuff? It turned out that, yes, aggres-
₇₀ sive ants wasted energy fighting (and dying), and so

gathered less food and fared poorly, in general. Peace

pays (at least peace with one's kin), and so Argentine

ants have made bank everyplace they have moved.

In fact, it isn't just for the Argentine ant that peace
₇₅ seems to pay. Supercolonies and the unicolonial popu­-

lations they create look to be common among invasive

ants.

Ants flash chemical badges identifying their home

nest. Without such markers, no one knows who is friend
₈₀ or foe. When the clarity of "us versus them" breaks

down, peace breaks out among colonies of an ant

species. Different nests swap workers and queens, and

the term "colony" becomes fuzzy. Experiments seemed

to show that one conglomeration of Argentine ants
₈₅ stretched the length of California, another from Italy to

Portugal ... until, in 2009, workers from those two

"colonies" (along with a third from Japan) were put

together, and they didn't fight. Thus, across the entire

globe, a few peaceful supercolonies could exist and
₉₀ expand.