Mimicry Related Predation on Two Viceroy butterflies

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Mimicry Related Predation on Two Viceroy
butterflies

• Karina Alvarez
• Chantal Steinlage

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Abstract

• In the eastern united states the mimetic viceroy
  butterfly (Limenitis archippus) exhibits clinical
  variation in wing color, ranging form a tawny
  orange in the north to a dark mahogany (L. a.
  Floridensis) in Florida. Geographic distribution
  of these two sub species are roughly coincident
  with the ranges of the viceroys two eastern
  mimicry models the monarch (Danaus plexippus) in
  the north and the queen (D. gilippus) in the
  south. This coincidence has historically been
  attributed to model-switching. Presumably,
  southern viceroy butterflies have switched from
  mimicking the monarch to mimicking the locally
  predominant queen, due to selective pressures
  exerted by visual foraging predators. As an
  initial test of this hypothesis, I sought
  evidence of selective predation on light and dark
  viceroys by captive red-winged black birds
  previously exposed to either monarch of queens.
  Results were consistent with the model switching
  hypothesis Queen conditioned birds
  preferentially avoided the dark, queen like L. a.
  Floridensis, and monarch condition birds avoided
  to a lesser degree the light l. a. archippus
  phenotype. I propose that this differential
  predation, while perhaps asymmetrical,
  demonstrates the selective mechanism responsible
  for the evolution of regional viceroy races, and
  that geographic model switching explains the
  large scale modern day correlation between Danaus
  biogeography and viceroy wing color.

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Outline

• I. Abstract
• II. Outline
• III. Introduction
• A. Two assumptions and two predictions
• B. Questions experiment hopes to answer
• Methods
• A. Experimental Protocol
• 1. Three phases

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Introduction

• Defensive mimicry is the imitation of a prey
  species by another prey species, with consequent
  protection form the educated predator.
• One of the most common cases of this is the
  viceroy butterfly, Limenitis archippus, and its
  model the monarch butterfly, Danaus plexippus
• Studies have suggested that the viceroy monarch
  relationship is Mullerian and not Batesian as
  once thought, however the accuracy of the viceroy
  mimic assures us that their relationship will
  remain an example of defensive mimicry.
• Not all viceroys resemble the monarch
• The tawny orange L. a. archippus is a monarch
  mimic ( has the same distribution as the monarch)
• The dark mahogany L. a. floridensis resembles the
  Florida queen (Danaus gilippus berenice)
• In the desert the L. a obsoleta coexists with the
  similarly colored striated queen , D. gilippus
  strigosus.

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Introduction Continued

• The phenotypic and the distributional correlation
  that the 3 pairs of butterflies exhibited points
  to the conclusion that the viceroy populations in
  different states have evolutionarily switched
  from one danaine mimicry model to another.
• This is called the Model-switching hypothesis. It
  implies that the directional selection imposed by
  visually selective predators having previous
  experience with distasteful danaines, has
  resulted in the evolution of regional viceroy
  races that are adapted to mimic the locally
  dominant danaine

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Two assumptions and Two predictions

• The model switching hypothesis as it applies to
  viceroys is based on two assumptions
• 1. predators can become conditioned to avoid
  given danaine color after an experience with in
  palatability
• 2. the color pattern aversion exhibited by
  danaines-conditioned predators extends to
  viceroys as well as danaines
• Assuming that these conditions are met the model
  switching hypothesis leads us to two predictions
• 1. Predators can discriminate against various
  viceroy phenotypes a
• 2. predators selectively attack viceroys avoiding
  those phenotypes similar to the locally
  predominant danaines

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What questions will the experiment answer ?

• The experiment wants to answer the following
  questions
• 1. Are birds capable of discriminating between
  light and dark viceroys?
• 2. if so, is the ability to discriminate
  translated into selective predation? ( do birds
  exposed to queens of monarchs preferentially
  avoid dark or light viceroys)

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Methods

• The predators used were male red-winged
  blackbirds.
• The monarchs and queens used in the experiment
  were collected as adults and frozen until used
  for the experiment
• 16 birds were used 8 received monarchs and 8
  received queens
• The monarch birds were exposed to moderately
  unpalatable monarchs. The queen birds were
  exposed to moderately unpalatable queens.
• The viceroy used in this experiment were
  collected as adults and also frozen untill used
  in the experiment.

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Experimental Protocol

• The birds in the experiment were placedin cages
  with a one way glass and had opaque partitions
  between the birds
• The four day experiment has 3 phases
• 1. model conditioning trial
• 2. mimic choice trials ( light vs. dark)
• 3. solo light and dark viceroy presentations

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3 phases

• Model-conditioning trials the birds were exposed
  to the danaines before the viceroys
• After being deprived of food for 1.75 hrs. they
  were given 2 or 3 danaine models with two or
  three unpalatable butterflies
• Mimicry choice trails were intended to
  demonstrate whether birds selectively attacked
  light or dark phenotypes.
• Birds were presented with two trials on day 2. in
  each trial one light and one dark viceroy was
  presented.
• Solo viceroy presentation each bird on day 4
  were offered four viceroys 2 light and two dark.

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Experiment 1 Queen as Model

• Treatment of Queen Models
• Birds readily attacked and ate the controlled
  species treated the queens as moderately
  unpalatable
• All eight red wings readily attacked the first
  queen offered, indicated no preexisting aversion
  to the queens color pattern
• Some birds developed conditioned aversions to the
  taste or color pattern of the queens.
• Decreases in the mean response score from Day 1
  to Day 4 suggest that 6 of the 8 birds were
  developing conditioned aversions to the taste or
  appearance of queens by Day 4
• Supports hypothesis that queens can act as models
  in a mimicry system

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Experiment 1 Queen as Model

• Response to Viceroy mimics
• Each bird was presented with two choice trials
  involving simultaneous presentation of a light
  and dark viceroy
• Birds preferentially attacked the light viceroy,
  rejecting the dark one
• Support prediction that red wings can
  discriminate between viceroy morphs and that they
  selectively attack the phenotype least like the
  danaine to which they have been exposed.
• Birds tended to avoid the more queen like viceroy
  phenotype

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Experiment 2 Monarch as Model

• Treatment of monarch models
• Birds treated the monarchs presented during model
  conditioning trials as moderate unpalatable
• Monarchs did not appear to differ in palatability
  from the sampled queens, at least with respect to
  red winged blackbird predators.
• All 8 red wings readily attacked the first model
  offered indicating no pre-existing aversion to
  the monarchs color pattern appeared to develop
  aversions to the taste or color pattern of the
  monarchs
• All 8 birds exhibited a dec. from day 1 to day 4
  in monarch response score (monarchs were being
  attacked less vigorously as the experiment
  progressed).

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Experiment 2 Monarch as Model

• Response to viceroy mimics
• Birds showed no significant preference for dark
  over light viceroys
• Explanations birds receiving monarchs as models
  exhibited a clear preference for dark viceroys as
  opposed to light
• Birds preferentially avoided the viceroy
  phenotype most like the monarch models to which
  they had been exposed.

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Variations in Bird Response

• Individual red wings variated in their treatment
  of monarchs and queen models
• Some birds ate every danaine while others didnt
• due to individual variation in taste sensitivity
• natural variation in prey palatability
• differences in birds experience
• differences in birds sensory physiology

www.southern-exposures.net/page/rwblackbirds.htm
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Discussion

• Unpalatability of danaines
• Monarchs and queens were both moderately
  unapalatable to the red winged blackbirds
• Monarchs and queens from the populations examined
  are sufficiently unpalatable and considered
  potential models in the mimicry relationship

• Danaines as mimicry models
• Red wings varied in their responses to monarchs
  and queens
• Both danaines elicited less vigorous attacks as
  the experiment progressed
• Both monarchs and queens were sufficiently
  unpalatable to promote conditioned aversions in
  some birds

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Discussion

• Selective attacks on viceroy phenotypes
• Queen and monarch conditioned birds differed in
  their treatment of light and dark viceroy
  phenotypes
• Queen conditioned birds performed better

• Inferences
• A birds propensity to attack light vs. dark
  viceroys depends upon its recent experience with
  monarchs and queens.
• Study represents an indirect assessment of
  selective predation in a lab setting
• Suggests that in nature
• Where monarchs predominate, natural selection
  favors lighter monarch like viceroy phenotype
• In the queens more southern range, dark viceroys
  should have the selective advantage

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Proposed Experiment

• Conduct an experiment in an area populated by
  both Monarchs and Queens
• Prediction viceroys will exhibit intermediate
  wing color
• Mixed mimicry
• Conduct experiment in Northern Florida Southern
  Georgia
• Observe results with different avian predator
  fauna