MOUSE – SPRING 2011
Many adaptations for a given species are responses to other species, and
how the two species interact. Viewed from the perspective of a focal species, looking outward,
they can be classified broadly as: (a) resources (food or habitat), (b) competitors, (c) enemies
(predators, parasites, etc.), (d) commensals (co-livers), and (e) mutualists (mutual advantage).
– The point here is that other organisms are part of the
for our focal
species, but more interesting is the thought that our focal organism can evolve, in response to
other organisms, but can also drive the evolution in those other organisms. The possibility of
reciprocal evolutionary pressure between the players has probably contributed importantly to
the development of biodiversity on the planet, over the last 3.5 billion years.
– Coevolution can take several forms: (a) arms race, as with the wolf and the
deer, faster wolves representing a selective force for faster deer, and
; (b) diffuse
coevolution, where a response to one organism is also a response to others; (c) coordinated
radiation and speciation, where radiation in both lineages is highly correlated.
– There are different ways that species can evolve in association.
The first is uninterrupted association/concordant divergence, where the two lineages have
been locked together from the beginning. The second is by colonization, so that there has
been some lateral transfer. Futuyma gives two examples:
is always associated with aphids, and the two phylogenies, that of
and that of aphids, are coordinate. The two organisms are obligate symbiots, and
Buchnera is passed vertically through the aphid’s eggs. They are inextricably locked
together, and it would seem that the two have been associated for ~ 250 million years.
example involves the bacterium
, whose phylogeny indicates that it can
switch arthropod hosts periodically. Its phylogeny and that of the arthropods it parasitizes are
coordinate, because the bacteria can spread laterally. The pattern is thus: