Transcript Chapter 20: Coevolution and Mutualism

Plant-animal interactions
Co-evolution?
Herbivory
Plant defense
Pollination
Seed dispersal
Interactions across
the life cycle
• Conservation:
butterflies/host
plants
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Photos: Ricklefs (Economy of Nature), Bradshaw & Schemske, Kalko, http://www.inriodulce.com/links/ants.html
TODAY: Coevolution
• Definitions and issues
– Species Interactions
– Evolution by natural selection
– Fitness
– Coevolution?
• Pairwise
• Diffuse
• Geographic mosaic
• Examples (a few)
SPECIES INTERACTIONS
+/- consumer-resource
predator-prey, parasite-host,
plant-herbivore
- /- competition
+/+ mutualism
trophic, seed dispersal,
pollination, defense
Interacting species may coevolve
Biotic selective
agents evolve
Species act as
selective agents on
each other’s traits
Trait
A→A’
Trait
X→X’
Biological SELECTIVE Agents
• 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
• physical agents foster convergence
EVOLUTION
by natural selection
• Selection
= non random association of FITNESS
with traits
• Response to selection
(IF there is a genetic basis to traits)
CHANGE IN GENE FREQUENCY
ACROSS GENERATIONS
and
CHANGE IN TRAIT DISTRIBUTION
ACROSS GENERATIONS
=
FITNESS
• Representation of your
stuff in the future
– Send yourself
– Send your offspring
• Survival and reproduction
both determine your
contribution to genes (and
trait distributions) in
future population
COEVOLUTION
(in the strict sense, Janzen 1980)
• 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 or Association?
• The term “coevolution” has
sometimes been used broadly
• the close association of certain
species and groups of species in
biological communities, but…
Pairwise or Diffuse Coevolution?
• 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?
Classic references
• Charles Mode (1958) coined the term
coevolution
– host and pathogen: cycling of virulent/avirulent
pathogens and susceptible/resistant hosts
• Paul Ehrlich and Peter Raven (1964) placed
coevolution into an ecological context
– closely related groups of butterflies tend to
feed on closely related species of plants
– specialization is associated with host plant
chemistry
Geographic Mosaic Theory
(Thompson 2005)
Geographic selection mosaics: selection varies among populations because there are
geographic differences in how fitness in one species depends upon the distribution of
genotypes in another species
Coevolutionary hotspots: Interactions are subject to reciprocal selection only within
some communities. Broader matrix of coevolutionary coldspots, (where selection is nonreciprocal or where only one of the participants occurs).
Trait remixing: The genetic structure of coevolving species changes through new
mutations, gene flow across landscapes, random genetic drift, and extinction of local
populations (shifting geographic mosaic of coevolution).
http://bio.research.ucsc.edu/people/thompson/Research.html
TODAY: Coevolution
• Definitions and issues
– Species Interactions
– Evolution by natural selection
– Fitness
– Coevolution?
• Pairwise
• Diffuse
• Geographic mosaic
• Examples (a few)
HERBIVORY
Heliconius butterflies have big eyes
The caterpillars feed on
Passiflora leaves…
HERBIVORY
Passiflora leaf shapes and egg mimics are
defensive against a visual herbivore
Everything is connected: Other vines the
rainforest are pollinated by Heliconines!
• Anguria and Gurania in squash family
• high canopy vines
• bright, red tubular flowers with a
bright yellow marking the center
• Heliconius get pollen… using amino
acids in egg production
• Very specialized
• What about Florida firebush?
Photos: http://www.infojardin.com, http://www.mittanbotanicalgardens.com/shrubs.htm
Mimicry complex
M. menophilus
M. ludovica
M. marsaeus
Northern
Peru
throughout
South
America
HERBIVORY
Butterflies and host chemistry
(Ehrlich and Raven 1964)
• Papilionidae
– Papilio: Rutaceae, Umbelliferae &
coumarins
• Pieridae
– Pierinae: Capparidaceae, Cruciferae &
mustard oil glucosides
• Nymphalidae
– Danainae: Apocynaceae, Asclepiadaceae &
milky juice w/bitter glycosides
• Libytheidae: Ulmaceae, Rosaceae & ?
• Lycaenidae:
– Lycaenini: diverse families, ant-defended
Photos:http://bugguide.net/node/view/118252/bgimage, http://thelifeofyourtime.wordpress.com/page/11/,
http://www.naba.org/chapters/nabast/MonarchMilkweedSolar41705gq.jpg, http://myrmecos.net/ants/Lycaena22.JPG
Berenbaum found:
Evolutionary history
of the chemistry :
increasing complexity
and increasing toxicity
and increasingly
specialized occurrence
HERBIVORY
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
Insect families such as Swallowtail
Many plants…subset of these…subset of these
butterflies, that feed
on carrot family also feed on
distantly related
Citrus family…
Which also has furanocoumarins!
Papilio thoas from Peru
Mutualism (+/+): Interactions between
species that benefit both participants
• Trophic
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–
–
lichen: partnership between algae and fungi
Rhizobium-plants
Mycorhizzae-plants
wood digesters in rumens…bacteria within
ciliates
• Defensive
– ant-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
POLLINATION
Mimulus lewisii
Mimulus cardinalis
Bumblebee
Hummingbird
• Experimental
genetics
• Hybrid
genotypes in
field assays
• One gene (YUP)
swap = change in
pollinator?
POLLINATION
Yuccas (Yucca)
Yucca moths (Tegeticula)
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mutually beneficial
obligate for both partners
phylogenetic analysis
moth behaviors selected by
plants or pre-adapted?
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
phylogenetic analysis
Geographic mosaic:
+/+ or +/- ?
Greya politella:
friend or foe to Lithofragma parviflorum?
Photo: http://bio.research.ucsc.edu/people/thompson/HQImages.html, data Thompson and Cunningham 2002
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..
Summary: mutualisms
• Mutualisms are relationships between species that
benefit both.
• Mutualisms may be trophic, defensive, or
dispersive.
• Phylogenetic analysis helps infer the evolutionary
history of interspecies interactions
• Experimental genetics in the field can reveal how
plant-animal interactions select for different
genes and trait distributions
• Identification of coevolved relationships is
difficult, preadaptations and geographic mosaics
may complicate evolutionary interpretation