Coevolution, Mutualism, Parasitism Reading; Smith and Smith

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Coevolution, Mutualism, Parasitism

• Reading Smith and Smith, Chapter 17 (read),
  ecological application 5 (after pp. 355, read.)

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• Coevolution occurs when one taxon exerts an
  important selective pressure on another.
• This causes an evolutionary response by the
  second taxon, which in turn, exerts a selectiv
  pressure on the first.
• Gene per gene coevolution is coevolution in the
  strictest sense, when it is possible to identify
  particular alleles in one organism that exert a
  selective pressure on particular alleles in
  another.
• Diffuse coevolution is the other extreme, when a
  general group of organisms is thought to exert
  selective pressure on another general group of
  organisms example, bees and flowering plants

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• Example or Gene Per Gene Coevolution-Wheat
  (Triticum aestivum) and Hessian Fly (Mayetiola
  destructor).
• This system has been studied extensively because
  it is of tremendous economic importance.
• The Hessian fly is an introduced species (which
  was probably introduced by Hessian mercenery
  soldiers during the American Revolutionary War).
  
• It is actually a gall midge (Cecidomyidae)-a
  group of dipterans that induce tumors in their
  plant hosts.

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• Life cycle
• There are two generations of Hessian flies per
  year, one attacks seedling winter wheat, or
  volunteer (weed) wheat. It overwinters in wheat
  stubble, emerges in spring, mates, and attacks
  wheat by depositing its eggs on the underside of
  wheat leaves. The larvae grow and inhibit the
  growth of the wheat by sucking sap and releasing
  substances which suppress its growth.

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• Resistance
• Certain alleles in wheat confer a property called
  antibiosis-toxic compounds within the wheat
  specifically act to kill the feeding larvae.
• This resistance occurs because of alleles at any
  one of 28 loci (named H1H28).
• New alleles confer very good protection against
  the fly, but as they become more common in wheat
  populations (via what strains farmers choose to
  plant, this is not strictly natural selection),
  they induce strong selective pressures on flies
  to be able to detoxify whatever it is that the
  wheat is producing to kill them.
• Thus, Hessian flies ultimately evolve immunity to
  whatever resistance alleles wheat evolves,
  causing selective pressure on wheat to evolve new
  alleles.

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• Parasite-host systems show an amazing amount of
  coevolution
• parasites can inflect significant losses of
  fitness on the host-this can cause strong
  selection for resistance
• a successful parasite produces a large number of
  offspring despite the hosts attempts to stop
  it-this causes strong selection for virulence
• additionally, there is selection for parasites to
  find new hosts
• parasites are selected to modify behavior of the
  host in such a way as to cause it to spread the
  parasite
• for some parasites, selection for increased
  virulence is tempered by the fact that dead hosts
  do not spread the disease

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Transmission Vectors

• Microscopic parasites and pathogens have an
  amazing diversity in their modes of transmission,
  and a corresponding complexity in their life
  histories-each stage has special adaptations to
  defeat the defenses of a particular host.
• The mosquito, an insect ectoparasite, is the host
  for certain stages in the life cycle for many
  different parasites, including malaria

Presumably, these complex life cycles allow
parasites to exploit ecological niches that would
not be available to them of they simply went from
one host to a similar host.
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Example

• The guinea worm, Dracunculus madeninsis, exploits
  two hosts during the course of its life cycle.
• Larvae swim in freshwater and infect a freshwater
  copepod. They feed within the still-living host,
  until it is swallowed by a human.
• In the stomach, acid dissolves the copepod, and
  the larvae emerge.

Within about a year, it (the female) has grown to
a worm that can be three feet long, living within
an artery. It will bore a painful hole to the
outside, it releases huge amounts of eggs into
the water whenever the host bathes or gets wet.
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Modification of Host Behavior

• We dont usually think of ourselves as slaves to
  our illnesses, but in many ways, parasites modify
  our behavior to increase the likelihood of
  transmission.
• A good sneeze removes the biofilm from our
  respiratory tract and allows our immune system to
  attack the function

But the bacteria that produced that biofilm were
selected to do so, and one reason was that
sneezes are excellent disease vectors.
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Host Resistance

• Hosts are not helpless when confronted with
  parasites. Nearly every organism has evolved
  sophisticated mechanisms to protect themselves.
• Passive defenses are always operational,
  frequently these guard against generalists
• Induced defenses can be triggered by particular
  parasites
• For example, the human immune system has both
  passive and induced defenses
• Every successful defense causes strong selective
  pressure on the parasite to beat the defense.

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Experiment-evolution of resistance to a
parasitoid by a sarcophagid fly

• Sarcophaga bullata is a blowfly that is the
  preferred host of the parasitoid wasp Nasonia
  vitripennis.
• In populations of hosts that have never been
  exposed to Nasonia, host mortality and the
  reproductive rate of Nasonia are very high.

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• In a series of experiments conducted during the
  1960s, David Pimentel showed that Sarcophaga
  could evolve increased resistance to Nasonia in
  response to selective pressure.
• Treatment 1-remove all flies that survive attack
  by Nasonia, add constant new flies.
• Treatment 2-flies that survive attack are allowed
  to reproduce, the rest are new

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• Result-in the treatment where survivors were
  allowed to reproduce, the reproductive rate of
  Nasonia went from 135 offspring per female to 35,
  with correspondingly high increases in the
  survivorship of Nasonia.
• How do insects defend against parasitoids?
• many insect larvae have special cells that can
  encapsulate a parasitoid larva-they recognize the
  attacker, and surround it with a layer of tough,
  melanin-containing cells.
• Some parasitoids beat this defense
• Ichneumenoid parasitoids have special polyDNA
  viruses, harmless to the wasp, that concentrate
  in their venom, and can destroy the potential of
  the hosts to defend themselves.
• A parasitoid is the ultimate transmission vector
  for a virus, once the infected host is killed,
  viruses enter the pupating parasitoid larvae, and
  have perfect transportation to a new host!

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Other Forms of Parasitism

• Brood parasitism occurs when members of one
  species rob members of another species of their
  reproductive effort, rather than taking energy or
  nutrients directly from the host.
• It can be interspecific or
• intraspecific.
• Interspecific brood parasitism
• can be obligate or facultative.
• It is particularly common
• in birds, wasps, and bees.

Cuckoo wasp
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• Species of birds that suffer frequent brood
  parasitism will eject strange eggs from their
  nests.
• Species of birds that have, historically, lacked
  brood parasites, lack defenses.
• Example-after millennia of isolation from
  cowbirds, Kirtlands warbler (Dendroica
  kirtlandi) lacks behavioral defenses against the
  parasitic cowbird.

Brown-headed cowbird
Kirtlands warbler (50birds.com)
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Examples

• Intraspecific brood parasitism.
• Certain females of the barn swallow (Hirundo
  rustica) lay eggs in the nests of their
  neighbors, rather than building their own nests.
  Adult barn swallows may build nests, parasitize,
  or do both.
• Interspecific brood parasitism.
• Females of the cuckoo wasp, Trichrisius tridens,
  enter the nests of bees and wasps, laying their
  eggs on the provisions that have been provided
  for the development of the nest-builders egg.
  The T. tridens larvae hatches first and destroys
  the larvae of the host, then devours the
  provisions for itself. Cuckoo wasps have evolved
  heavy armor to avoid being stung and killed by
  their hosts. Some hosts dig false burrows to
  deceive cuckoo wasps.

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Kleptoparasitism-is where animals steal some
important resource from each other.

• Example of intraspecific kleptoparasitism-Certain
  females of the great golden digger wasp (Sphex
  ichneumenoides) will enter the nests of
  conspecific females, effectively taking them over
  and saving the trouble of digging their own.
• If they encounter the original female, the two
  will fight ferociously.
• Example of interspecific kleptoparasitism-Black
  headed gulls (Larus ridibundus) parasitize flocks
  of golden plovers (Pluvialis apricaria) and
  lapwings (Vanellus vanellus) in the English
  countryside. They harass unwary birds until they
  drop the worms they have just extracted from the
  soil.

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Slave-Making in Ants

• Slave making is an interesting form of parasitic
  behavior among social insects, where it is the
  lifetime effort of worker ants that is, in fact,
  stolen.
• If abducted and transported as larvae, worker
  ants of most species will emerge as adults and
  serve the colony into which they emerge, even if
  it is a colony of a different species of ant.
• Thus, an ant colony can increase its fitness (in
  terms of the number of reproductives it produces)
  by abducting workers of another species and
  enslaving them.

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• Example Colonies of Formica sanguinea will raid
  colonies of Formica fusca, and abduct their
  workers for use as slaves. Colonies of
  victimized species have evolved defenses against
  slave makers, including abandoning nests and
  moving the colony to avoid being victimized.

Formica sanginea, (which is also an aphid farmer).
Formica fusca
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• Similar behaviors are sometimes seen in bees and
  wasps, but in those taxa, queens of a related
  species will take over the entire colony of the
  host species and enslave it, for instance,
  Polistes nimphus is a parasitic paper wasp, which
  will take over colonies of the closely related
  Polistes dominulus. This is called social
  parasitism.

Polistes dominulus
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How important is parasitism?

• Parasites have a pervasive effect on the
  populations of plants and animals.
• A growing body of evidence supports the notion
  that many parasites effective agents of
  population regulation, acting in many of the same
  ways as top predators, but more ubiquitous.
• Parasite induced mortality may interact with
  limitation of resources to produce population
  control. Populations that are under nutritional
  stress are frequently more susceptible to
  parasite-induced mortality.

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• Microparasites which are transmitted from one
  individual to the next typically require dense
  populations of hosts to sustain themselves.
• Hosts develop immunity to most microparasites.
  This causes the disease to burn through its
  supply of susceptible individuals in a local area
  (it will grow exponentially, at first), and
  unless it can infect a new area, it will go
  extinct.
• Long-term persistence is facilitated by
  long-lived infective stages, by the physiological
  ability to avoid inducing immunity in the host,
  or by evolving so quickly that subsequent
  generations of the parasite can attack previously
  immune individuals.

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• The more virulent diseases spread more quickly,
  but generally require denser populations of hosts
  to persist-over time.
• If a disease kills the host too quickly, that
  population of the parasite dies before begetting
  new populations of parasites. Thus, there is
  interdemic selection in favor of reduced
  virulence, but within hosts themselves, there is
  selection for increased virulence, because
  virulent individuals make more copies of
  themselves. Thus, diseases frequently evolve a
  balance, such that transmission rate is balanced
  with virulence.
• There is an old saying, a good parasite does not
  kill the host. In fact, this is only true if
  the parasite relies on living hosts for
  transmission.
• A good parasite does not kill the host before it
  has infected more hosts.

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Example-the Black Death

• Historically, human populations have been kept in
  check both by resource limitation and by disease.
• In medieval Europe, circa 1346, populations were
  close to an all-time high, and widespread famines
  periodically killed thousands.
• Filthy, crowded conditions combined with poor
  nutrition to create perfect conditions for an
  outbreak of Yersinia pestis, a disease that is
  not primarily a parasite of humans.
• In many places, the human population was reduced
  from 40-65, and did not recover for centuries
  because of repeated outbreaks.
• The disease required dense populations of humans,
  rats, and fleas, because it was both epidemic and
  epizootic.

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• Yersinia pestis is a bacterium, normally a
  parasite of rodents, especially rats and marmots.
• It is transmitted among rodent hosts by fleas,
  mostly the rat flea, Xenopsylla cheopis.
• In Central Asia, in 1345, a particularly nasty
  strain jumped from Marmots to Mongols.
• The Mongols transmitted it to the Genoese, who
  spread it to Europe.
• In Europe, it went back in forth from rat-human
  transmission, to a human-human form (pneumonic
  plague).
• Eventually, it ran out of human hosts, but
  persisted in rodent populations, facilitating
  later outbreaks

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http//www.insecta-inspecta.com/fleas/bdeath/Path.
html
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• In general, macroparasites, which generally rely
  on animal transmission vectors, and usually have
  more complex life cycles, can parasitize
  populations that are much less dense, and persist
  exist at much lower population levels.
• They require an efficient means of infecting each
  host in their life cycle.
• Because they rely on indirect transmission, they
  do not burn through all the available hosts.
  Instead, a few individuals harboring huge
  parasite loads cause the parasite to persist in a
  local are for large amounts of time.
• Parasites survival depends upon keeping a few of
  these disease bags around-which means prolific
  reproduction.

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Effect of Parasite on Distribution of the Host

• It is thought that parasites have enormous
  potential effects on the distribution of hosts,
  though our reasons for thinking this are
  indirect most of what persists today are
  parasite-host systems that are coevolved and
  permit the existence of both species.
• Cases of introduced parasites suggest that
  parasites can easily eliminate a host from major
  areas of the range, or drive it entirely extinct.
• Examples Dutch elm disease, chestnut blight

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Mutualism

• Mutualisms are ecological interactions in which
  both partners benefit (at least some of the time
  at least), either in terms of an increased
  potential for population growth, or because they
  are able to live in environments that are
  unavailable to them otherwise.
• Mutualisms fall along a continuum from
  facultative to obligate.
• Mutualistic symbioses are mutualisms in which
  both partners live in, on, or in very close
  proximity to each other.
• Mutualisms run the gamut from chance ecological
  interactions, to interspecific interactions that
  have coevolved over millions of years, in which
  one partner cannot hope to survive without the
  other.

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Pollination

• One of the most ubiquitous and important
  mutualistic interactions in terrestrial
  communities involves animal pollination in
  angiosperms.
• Angiospersms are either wind pollinated (no
  mutualism) or animal pollinated.
• Animal pollination is generally mutualistic,
  though it can be parasitic.
• Animal partners include bees, butterflies and
  moths, flies, beetles, thrips, hummingbirds,
  bats, and occasionally other animals.
• These mutualisms range from obligate to
  facultative.

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• Advantages to wind pollination-straightforward,
  effective when plants grow in dense stands, range
  of species is not affected by availability of
  mutualist pollinators.
• Disadvantages-uses a lot of pollen (energetically
  expensive), can be unreliable.
• Advantages to animal pollination-depending upon
  pollinators, can be reliable over moderately long
  distances, reduces amount of pollen plant needs
  to produce and thus is easier on the energetic
  cost of sex.
• Disadvantages- requires the existence of a
  pollinator, incentive must be provided to
  pollinator for their services.

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Pollination Syndromes

• Pollinators fall into several general categories.
  
• The selective pressures exerted by these
  pollinators causes flowers to evolve certain sets
  of characteristics to attract the type of
  pollinators most likely to increase the plants
  fitness.

This is an Indonesian corpse flower, the
worlds largest inflorescence (Amorphophallus tit
anum). It smells like dead people to
attract carrion beetles and flies
www.loc.gov
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Pentstemon digitalis, a bee pollinated plant.
Melittid bees are commonly specialized to feed
on Pentstemon, though the flowers will accept
any bee this is a Megachile bee.
www.clc.edu
Pentstemon barbatus This is a great hummingbird
plant. borderlandnews.com
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• Fungus gnats-smells like mushroom, flowers not
  terribly showy
• Moths strong smell, open at night, white
• Hummingbirds usually red, long corolla, exserted
  anthers, dilute nectar
• Short-Tongued Bees short corolla,
  purple-yellow-bee purple, concentrated nectar
• Long-Tongued Bees longer corolla,
  purple-yellow-bee purple-white, landing platform,
  concentrated nectar
• Butterflies long corolla
• Bats-Big flowers, musky scent, dull colored, open
  at night, copious dilute nectar
• Carrion Beetles-smell like rotting flesh, weird
  looking

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Example-Melittid Bees

• The melittid bees are a family that includes
  about 100 species worldwide.
• Some are specialist pollinators (ie., obligate
  mutualists, others are generalists-facultative
  mutualism)
• All melittids are solitary bees.
• Ecological specialized species have life cycles
  timed to synchronize with the plants they forage
  upon. The bees are inactive as resting pupae for
  the rest of the year

Macropis steironematis from the UIC greenhouse,
foraging upon catnip Nepeta catara.
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Example Caullauthidium is a small solitary
bee. Males defend the flowers upon which females
specialize (Pentstemon).
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• Pentstemon flowers provide pollen, a rich source
  of protein that the female bees use to provision
  nests, and concentrated nectar, which is an
  important food source for both adults and larvae.
• Pentstemon also have eliaphores-which provide
  energy-rich oils along with pollen as provisions
  for developing larvae.
• Most flowers in the genus are either white or
  purple, a color which is attractive to bees.
  Melittids are fairly large, generally, and
  Pentstemon flowers have a landing pad to make
  it easier to get in and get out.
• In return for nectar and oil, the flower gets an
  efficient pollinator. Melittid bees are very
  active, and can fly great distances, and will
  visit the same type of flower in search of
  resources-thus ensuring efficient pollination.
• On t
• I.

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• The mutualism is assymetric. Although
  Callauthidium specializes in Pentstemon, Bee
  pollinated species of Pentstemon will accept many
  different floral visitors.
• Other bees in the same family, such as Macropis,
  will visit many types of flowers.
• It is possible that the ecological specialization
  of some species of bees results from
  interspecific competition,
• OR it is possible that the only way for a species
  to carve out a particular ecological niche is to
  specialize-specialists that are active only a
  short period of time are not limited to habitats
  where flowers are continuously available all
  summer long.
• Specialization is definitely a factor limiting
  their range, since the right type of floral
  resource must be present for the bee to occur.

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• On the flowers end, it is not likely that the
  flowers evolved specialization per se, it is more
  likely that the most effective pollinators exert
  sufficient selective pressure that the flower
  evolves certain traits that make it most suitable
  for a particular species of pollinator.
• Remember the bumblebee snapdragon study?
  (Freeman and Herron, pp. 75) Note that the
  yellow color was selected against and the white
  color-spotted color scheme was favored. Bees are
  especially attracted to flowers with patterns.
• OR it is also possible that there is indeed
  selection for specialization, to increase the
  efficiency of pollination and avoid wasting
  floral resources..

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Seed Dispersal

• A major class of plant/animal mutualisms involves
  seed dispersal. Certain plants, with heavy
  seeds, rely upon animals to disperse them.
• There is a great section in your book on seed
  dispersal (pp 328-330)
• Why is Clarks nutcracker the only seed predator
  that effectively acts as a mutualist to the
  whitebark pine?.