Download Chapter 20: Coevolution and Mutualism

Chapter 17: Coevolution and
Mutualism
• Species
Interactions
Interacting species may coevolve
Biotic selective agents evolve
Species act as selective agents on each other
+/- consumer-resource
predator-prey, parasite-host, plant-herbivore
- /- competition
+/+ mutualism
trophic, seed dispersal, pollination, defense
Heliconius butterflies have big eyes
The caterpillars feed on
Passiflora leaves,,,
Passiflora leaf shapes and egg
mimics are defensive against a
visual herbivore
Two other vine genera in the
rainforest are pollinated by it
• Anguria and Gurania in squash family
• They are high canopy vines
• They have bright, red tubular flowers
with a bright yellow marking the
center
• Heliconius get pollen from them..they
use the amino acids in egg production
• Very specialized
• What about Florida firebush?
Mimicry complex
M. menophilus
M. ludovica
M. marsaeus
Northern
Peru
throughout
South
America
“Coevolution” in the strict sense
is the process whereby
• populations of
• two or more species interact,
• traits of each may evolve in
response to traits of the other
• reciprocal selective effects on traits
Coevolution is mediated by
biological agents.
• evolutionary effects of biological agents are
unlike those of physical factors
– biological factors stimulate mutual
evolutionary responses
– adaptations of organisms in response to changes
in the physical environment have no effect on
that environment
– biological agents foster diversity of adaptations
– physical agents foster convergence
Antagonists evolve in response to
each other.
• Charles Mode coined the term coevolution
in a 1958 article in Evolution:
– host and pathogen: cycling of virulent/avirulent
pathogens and susceptible/resistant hosts
• In a 1964 article in Evolution, Paul Ehrlich
and Peter Raven placed coevolution in an
ecological context
– closely related groups of butterflies tend to feed
on closely related species of plants
– specialization is associated with host plant
chemistry
Berenbaum found:
The evolutionary history
of the chemistry shows
increasing complexity
and increasing toxicity
and increasingly
specialized occurrence
The carrot family
includes Queen Anne’s
Lace,
celery, cilantro,
parsley, dill….
ONLY highly specialized
insects feed on the most
toxic ones
These are descended
from close relatives that
feed on less toxic ones
Many plants…subset of these…subset of these
Insect families such as
Swallowtail butterflies, that feed
on carrot family also feed on
distantly related
Citrus family…
Which also has
furanocoumarins!
Papilio thoas from Peru
Some other examples of coevolution
in antagonistic interactions …
• European rabbits and South
American myxoma virus in
Australia
• Houseflies and Nasonia
wasps in Pimentel’s lab
• Wheat and wheat rust in
agricultural systems: gene for
gene interaction
• specialization of scales on
individual genotypes of
ponderosa pine trees
Identifying Coevolutionary
Responses
• the evolution of strong jaws and associated
muscles by hyenas to crack the bones of their
prey is not coevolutionary, because the bones
of the prey have not evolved to resist being
eaten
• the evolution of the ability of an herbivore to
detoxify substances produced by a plant
specifically to deter that herbivore is
coevolutionary
Competition and Character
Displacement
• character traits of two closely related species
differ more in sympatric regions than in
allopatric regions
• this pattern may have arisen from strong
selective pressure for divergence in sympatry,
a process called character displacement
Mutualism (+/+): Interactions between
species that benefit both participants
• Trophic
–
–
–
–
lichen: partnership between algae and fungi
Rhizobium-plants
Mycorhizzae-plants
wood digesters in rumens…bacteria within ciliates
• Defensive
– cleaner shrimp-eels
– ants-plants
• Dispersive
– pollinators-plants
– seed dispersers-plants
Trophic Mutualism
• Trophic mutualisms usually involve
partners specialized for obtaining energy and
nutrients
Defensive Mutualism
• Defensive
mutualisms
involve species
that receive food
or shelter from
their partners in
return for a
defensive
function
Dispersive Mutualism
• Dispersive mutualisms
involve animals that:
– transport pollen in return
for rewards such as nectar
– transport and disperse
seeds in return for the
nutritional value of fruits
or other structures
associated with seeds
Coevolution?
• The term coevolution has sometimes
been used broadly to describe the close
association of certain species and
groups of species in biological
communities.
• Are these examples of coevolution?
Are close associations
coevolutionary?
• Do pairs of species undergo reciprocal
evolution or
• do “coevolved” traits arise as
responses of populations to selective
pressures exerted by a variety of
species, followed by ecological sorting?
• Are species organized into interacting
sets based on their adaptations,
coevolved or not?
Figure 17.19.The Yucca Moth and the Yucca
The Yucca Moth and the Yucca
• Yuccas (genus Yucca) and yucca moths
(genus Tegeticula)
• mutually beneficial
• obligatory
• carefully studied
Moth larvae have no other food
source and yucca plants have no
other pollinator...
• adult female yucca moths carry balls of pollen
between yucca flowers by means of specialized
mouthparts
• during pollination, the female moth deposits eggs
in the ovary of the yucca flower
• after the eggs hatch, the developing larvae feed on
some of the developing yucca seeds, not exceeding
30% of the seed crop
• the yucca exerts selective pressure on the
moths (through abortion of heavily infested fruits) to
limit moth genotypes predisposed to lay large
numbers of eggs (cheaters)
Is the Yucca/Yucca Moth
Mutualism Coevolutionary?
• Many aspects of the mutualism are present in
the phylogenetic lineage of nonmutualistic
moths within which Tegeticula evolved
– host specialization and mating on the host
plant
– traits present in the moth lineage before the
establishment of the mutualism itself,
– evidence for preadaptation
– what appear to be coevolved traits may have been
preadaptations that were critical to establishment
of the mutualism in the first place
Figure 17.20: phylogenetic analysis
Summary…idea of coevolution
• Interactions among species are major sources
of selection
• Coevolution is the interdependent evolution
of species that interact ecologically
• Consumer-resource systems give abundant
examples: host-pathogen, host-parasitoid,
plant-herbivore..
• Competition can lead to character
displacement.
Summary: mutualisms
• Mutualisms are relationships between species
that benefit both.
• Mutualisms may be trophic, defensive, or
dispersive.
• Phylogenetic analysis allows us to infer the
evolutionary history of interspecies
interactions
• Identification of coevolved relationships is
difficult, and preadaptations may complicate
evolutionary interpretation