Wednesday, June 10, 2009
How fast can evolution take place? In just a few years, according
to a new study on guppies led by UC Riverside's Swanne Gordon, a
graduate student in biology.
Gordon and her colleagues studied guppies — small fresh-water fish
biologists have studied for long — from the Yarra River, Trinidad.
They introduced the guppies into the nearby Damier River, in a
section above a barrier waterfall that excluded all predators. The
guppies and their descendents also colonized the lower portion of
the stream, below the barrier waterfall, that contained natural
predators.
Eight years later (less than 30 guppy generations), the researchers
found that the guppies in the low-predation environment above the
barrier waterfall had adapted to their new environment by producing
larger and fewer offspring with each reproductive cycle. No such
adaptation was seen in the guppies that colonized the
high-predation environment below the barrier waterfall.
"High-predation females invest more resources into current
reproduction because a high rate of mortality, driven by predators,
means these females may not get another chance to reproduce,"
explained Gordon, who works in the lab of David Reznick, a
professor of biology. "Low-predation females, on the other hand,
produce larger embryos because the larger babies are more
competitive in the resource-limited environments typical of
low-predation sites. Moreover, low-predation females produce fewer
embryos not only because they have larger embryos but also because
they invest fewer resources in current reproduction."
Study results appear in the July issue of The American
Naturalist.
Natural guppy populations can be divided into two basic types.
High-predation populations are usually found in the downstream
reaches of rivers, where they coexist with predatory fishes that
have strong effects on guppy demographics. Low-predation
populations are typically found in upstream tributaries above
barrier waterfalls, where strong predatory fishes are absent.
Researchers have found that this broad contrast in predation regime
has driven the evolution of many adaptive differences between the
two guppy types in color, morphology, behavior, and life
history.
Gordon's research team performed a second experiment to measure how
well adapted to survival the new population of guppies were. To
this end, they introduced two new sets of guppies, one from a
portion of the Yarra River that contained predators and one from a
predator-free tributary to the Yarra River into the high-and
low-predation environments in the Damier River.
They found that the resident, locally adapted guppies were
significantly more likely to survive a four-week time period than
the guppies from the two sites on the Yarra River. This was
especially true for juveniles. The adapted population of juveniles
showed a 54-59 percent increase in survival rate compared to their
counterparts from the newly introduced group.
"This shows that adaptive change can improve survival rates after
fewer than ten years in a new environment," Gordon said. "It shows,
too, that evolution might sometimes influence population dynamics
in the face of environmental change."
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University of California - Riverside
Thanks to University of California - Riverside for this
article.