Evolution__3rd_Edition

640 PART 5 / Macroevolution
Coevolution occurs ...
. . . but its relative contribution to
macroevolution is unknown
Summary
stimulate research, and it likely accounts for some fraction of macroevolution. Just how
large a fraction that is remains to be seen.
22.9 Both biological and physical hypotheses should be
tested on macroevolutionary observations
1 Coevolution occurs when two or more lineages
reciprocally influence each other’s evolution. Coadaptation
between species, such as in any example of mutualism,
is probably but not necessarily the result of
coevolution.
2 Insects and flowering plants have influenced each
other’s evolution. Adaptations concerned with phytophagy
(animals feeding on plants) and pollination
provide examples. The evolutionary relations of flowering
plants and insects are sometimes fully coevolutionary.
In other cases, evolution may be sequential,
Coevolution is one of several general processes that can account for evolution on a large
scale a that is, macroevolution a as well as on a small scale. No one doubts its importance
in microevolution, for instance in the evolution of mutualists or of parasites and
their hosts. However, unanswered microevolutionary questions remain, such as the
question of whether evolution in plants and insects is more often sequential evolution
or fully reciprocal coevolution.
The contribution of coevolution to macroevolution is more controversial. Coevolution
is not the only macroevolutionary force. Many macroevolutionary events are
likely caused by changes in the physical environment a climatic change, or tectonic
change, or asteroid impacts such as we look at in Chapter 23. Evolutionary biologists
are interested in the relative contribution of physical and biological factors, and their
interaction, in driving macroevolution.
One way to dramatize the issue is to ask a grand (and unanswered) question: if
change in the physical environment ceased, do you think that evolution would soon
come to a stop? If physical factors dominate evolution, it surely would, perhaps after a
short period during which the species adjusted to the final permanent physical conditions.
In the Red Queen view of evolution, the coevolutionary and biological relations
between species might have a life of their own and evolution would carry on much as
before after the cessation of physical environmental change. The question in its general
form is too difficult for us to answer yet, but it puts under a spotlight many of the ideas
that we need to examine to understand macroevolution.
as plant evolution influences insect evolution but not
vice versa.
3 Taxa of insects and flowering plants that interact
with each other may show cophylogenies, or mirrorimage
phylogenies. Deviations from cophylogenies
can be caused by host shifts. For instance, an insect
species may colonize a new plant species that is chemically
but not phylogenetically similar to the plant
species it currently lives on.
4 Insects and flowering plants may have promoted
each other’s diversification, from the Cretaceous to the
..