InTERACTIonS Among SPECIES 325
Predators and parasites have evolved some extraordinary adaptations for captur-
ing, subduing, or infecting their victims (FIGURE 13.5). Defenses against predation
and parasitism can be equally impressive, ranging from cryptic patterning to the
most versatile of all defenses: the vertebrate immune system, which can generate
antibodies against thousands of foreign compounds. The CRISPR-Cas mechanism
in some bacteria is also an elaborate system of recognizing and defending against
foreign invaders—that is, viruses. Many such adaptations appear to be directed at a
variety of different enemies or prey species, so the coevolution, if any, has probably
been diffuse.
R. A. Fisher, one of the founders of evolutionary genetics, suggested that a spe-
cies’ environment, such as the climate, is constantly changing, but “probably more
important than the changes in climate will be the evolutionary changes in progress
in associated organisms” [25]. This idea is expressed by the Red Queen hypothesis,
named by paleontologist Leigh Van Valen [79] for the Red Queen whom Alice meets
in Lewis Carroll’s Through the Looking-Glass: each species has to run (i.e., evolve) as
fast as possible just to stay in the same place (survive) because interacting species
also continue to evolve. The dynamics of Red Queen coevolution may take several
forms, including escalation and oscillation. In the long term, the dynamics may lead
to indefinite coexistence of enemy and victim species, a switch by the enemy to a
different victim species, or extinction of one or both species [1, 56].
An evolutionary arms race, also called escalation, may occur if the capture rate
of the prey by the predator increases with the difference between the defensive
trait of a prey species and a corresponding character in a predator. Then the char-
acteristics of both species that affect their interaction evolve in one direction: for
example, greater speed of gazelles and of pursuit predators such as cheetahs (FIG-
URE 13.6). This can lead to extinction or to a stable point when the costs of increas-
ing the trait (e.g., speed, or a plant’s defensive chemicals) become too great.
The Japanese camellia (Camellia japonica) and the camellia weevil (Curculio
camelliae) present a dramatic example of escalatory coevolution. The camellia’sFIGURE 13.5 Predators and para-
sites have evolved many extraordi-
nary adaptations to capture prey or
infect hosts, and prey have elaborate
counteradaptations. (A) This tropical
net-casting spider (Deinopis subrufa)
holds an expandable web that it uses
to quickly envelope slowly flying
insects that pass by. (B) The larva of a
parasitic trematode (Leucochloridium)
migrates to the eyestalk of its inter-
mediate host, a land snail, and turns it
a bright color to make the snail more
visible to the next host in the parasite’s
life cycle, a snail-eating bird such as a
thrush. (C) Katydids (Tettigoniidae) of
the genus Mimetica have an extraor-
dinary resemblance to leaves, includ-
ing what looks like leaf venation and
damage by herbivores. (B, photo by P.
Lewis, courtesy of J. Moore.)Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_13.05.ai Date 11-02-2016Trematode-
infected
eyestalkNormal
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