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Testing Benefits of Being in a group

1. Experiment by Gamberale and Tullberg, 1998.

2. Tested how naive chicks respond to solitary or grouped prey of two types.a. Aposematic, distasteful preyb. Cryptic, palatable prey

2. Prey were the larvae of two different bug species.

Tesing Fisher’s Model

Being in a group reduces attack rates of aposematic prey. (Gamberale and Tullberg, 1998).

Cryptic, palatableAposematic

Grey = solitaryBlack = grouped

Tesing Fisher’s Model

1. Fisher’s model assumes that kin groups evolve first, which then allows the evolution of warning colors.

2. Sillen-Tullberg (1988) analyzed independent origins of warning colors and of larval groupings.

3. Warning coloration evolves before groupings. This is opposite expectation from Fisher’s model.

4. Possible solution: Bright colors may give direct advantages. If some insects are released unharmed, then bright colors may result in fewer subsequent attacks from the same predator. (Sillen-Tullberg, 1985).

5. Thus, aposematism may be able to evolve due to direct benefits. Grouping evolves afterwards to reinforce predator learning.

Coral Snake

California Mountain King Snake

Mimicry

Batesian Mimicry

1. Henry Walter Bates (1852)

2. Three-player system a. Model: noxious/dangerous prey b. Mimic: palatable prey c. Predator: the signal-receiver

3. Model uses aposematic coloration as a warning of its defenses or unpalatability to predators.

a. Honest signal

4. A Batesian mimic gains protection by convergence upon the aposematic signal of the model.a. Dishonest signal

Batesian Mimicry

5. Selection favors the mimic when it is rare as compared to the model species. Fitness is negatively frequency-dependent.

6. Model species experiences increased mortality as the number of mimics in the system increase.

a. Due to predators relaxing the association of the aposematic signal with a secondary defense.

7. If mimics become common, the system is unstable and selection promotes signal divergence between model and mimic.

Model species on left, mimic species on right, from Greene, 1981

Batesian MimicryColoration of the model changes over time, mimics selected to keep up.

Batesian Mimicry by Ensatina

1. Prediction: A Batesian mimic should gain protection from predators by resembling the model.

Mimic = Yellow-eyed Ensatina Model = Pacific Newt

Not Mimic = E. e oregonesis

Batesian Mimicry by Ensatina

1. Test: Compare predation rates between Batesian mimics and closely related species that do not mimic.

2. Kuchta (2005) deployed clay salamander replicas in the field and recorded attack rates.

3. Models with yellow and orange aposematic colors were depredated less than models lacking the colors.

4. Suggests that E. e. xanthoptica benefits from aposematic coloration.

Batesian Mimicry by Ensatina

1. Kuchta et al, 2008 conducted feeding trials using Western Scrub-Jays.

2. Jays were first presented with the model (newt). Then presented with either the presumed mimic (E. e.

xanthoptica) or a control subspecies lacking the postulated aposematic colors (E. e. oregonensis).

3. No newts were eaten. Some Ensatina salamanders were eaten.

4. The median time to contact was 315 sec for the mimic and 52 sec for the control.

5. Mimicking the newts confers protection from a bird predator.

Batesian Mimicry by Ensatina

Mimic (black line) is more likely to survive than a salamander lacking coloration similar to the toxic newts.

Mullerian Mimicry

Heliconius erato on the left H. melpomene on the right.

Apheloria clade millipedes on top.Brachoria clade millipedes on bottom.

Mullerian Mimicry

1. Proposed by Fritz Muller (1878) to explain why unrelated distasteful butterfly species share a single warning color.

2. Mullerian mimics share aposematic signals due to the mutual benefit of spreading the selective burden of educating predators that they are distasteful.

3. In this case, signals are standardized and the predator avoids all models.

4. Mullerian mimics give honest signals.

Testing Mullerian Mimicry

1. Experiment by Alatalo and Mappes, 1996. Tested how the Great Tit, Parus major, learns to avoid aposematic signals.

2. Prey were evolutionarily novel. Fat-filled rye straws or almond slivers. Controls for prior experience of predators.

3. Prey either palatable or unpalatable (treated with chloroquine).

4. Prey either cryptic (pluses) or aposematic (squares) on a background of plus symbols.

Testing Mullerian Mimicry

1. Experiment 1: Does grouping help aposematic straw prey?

2. Result: Avoidance of aposematic prey increased over successive trials (solitary and grouped). Grouped prey were avoided faster than solitary prey. a. Supports Fisher’s hypothesis.

3. Experiment 2: The same predators were tested on new prey (almond slivers), but with the same symbols (Mullerian mimics).

Testing Mullerian Mimicry

1. Result: Aposematic prey were still avoided, despite being a different “species.”a. Supports predator avoidance of Mullerian mimics.

Fat-filled straw prey Almond prey

The Poisonous Pitohuis

Top = Hooded Pitohuis, Pitohui dichrous

Bottom = Variable Pitohui, P. kirhocephalus

Mullerian Mimicry in Pitohui kirhocephalus Coloration?

1. Hypothesis 1: Different populations share coloration because of common ancestry.

2. Hypothesis 2: Different populations share coloration because of convergent evolution leading to Mullerian mimicry.

Testing Mullerian Mimicry

Test 1: Verified that there was resemblance among P. dichrous and P. kirhocephalus.

Dumbacher and Fleischer. 2001.Phylogenetic Evidence for Colour Pattern Convergence in Toxic Pitohuis: Müllerian Mimicry in Birds?

Evolution of Pitohui Coloration

Test 2: Phylogenetic reconstruction. Shows one example of Mullerian mimicry through convergence, but shared ancestry explains most populations.

Mullerian Mimicry in Poison Frogs?

Dendrobates imitator

Dendrobates variabilis Dendrobates fantasticus Dendrobates ventrimaculatus

Evolution of Poison Frog Coloration

Phylogenetic reconstruction is consistent with Dendrobates imitator being a Mullerian mimic.

D. ventrimaculatus

D. variabilis

D. fantasticus

D. imitator

D. imitator

D. imitator

Symula et al. 2001

1. Brood parasites lay their eggs in other species’ nests.

2. The parasite benefits by not raising young.

3. Prey suffer cost of raising young not their own (often at the expense of their own offspring).

4. This can give rise to coevolutionary arms races.

Host and parasite interaction: brood parasites

1. Female cuckoos (Cuculus canorus) lay eggs in nest of host species. Females specialize on one species and lay eggs that closely match host’s eggs.

2. Cuckoo chick hatches and removes all eggs and chicks of host.

3. Host feeds cuckoo chick as its own and has zero fitness for breeding year.

Cuckoos versus hosts

Cuckoos versus hosts

1. Different host-races of the common cuckoo lay distinctive eggs, which often match the eggs of the species that they parasitize.

2. A female cuckoo will wait near a host nest, then will remove one host egg, and quickly lay her own egg. This can take less than 10 seconds!

3. The cuckoo will typically lay her egg in the afternoon, during the hosts’ laying period.

Cuckoos versus hosts

4. Hypothesis: Cuckoo egg-laying tactics are adaptations to circumvent host defenses.

5. Experiment: Add a model cuckoo egg to a reed warbler nest and see if they accept it or not.

6. Results: Hosts reject eggs:a. that are a poor matchb. that are laid before the host starts layingc. if host is alerted to cuckoo presence on their nest

1. Host birds have evolved to be able to discriminate between their own and parasitic eggs.

a. Discrimination may not be perfect.

2. Varying degrees of mimicry between cuckoo host races and the host eggs. a. Need to measure the degree of visual overlap accounting for avian vision (birds have 4 color vision cones, human have 3)

3. How discriminating host is (their egg rejection rate) is correlated with how closely cuckoo egg matches host species.

4. This suggest that there is a coevolutionary arms race between cuckoos and hosts.

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Hosts vs cuckoos

1. Given high cost of parasitism (zero reproductive success), hosts evolve in response to cuckoos.

2. Favored hosts reject odd eggs and exhibit mobbing behavior at cuckoos.

3. Unsuitable hosts (seed diet or cavity nesting) show little to no rejection of eggs unlike their own and no aggression towards cuckoos near their nests.

4. Isolated populations of favored hosts show less rejection of non-mimetic eggs.

a. Meadow pipits in Iceland (no cuckoos) vs. in Great Britain (with cuckoos).

Host Counter-adaptations

1. An African warbler (Prinia subflava) shows a high diversity of egg markings within single species.

a. Able to independently vary background color, marking size, variation in markings, and marking dispersion.

2. Cuckoos have developed mimetic eggs but aren’t able to target host individuals with similar eggs.

3. Parasite lays eggs randomly and suffers high rate of rejection

Host Counter-adaptations

1. If size and color are used to reject odd eggs why don’t hosts use the same cues for the chick stage?

a. The reason could be the costs of making a mistake when imprinting on offspring.

2. Since cuckoos don’t lay an egg until after the host starts laying, the host almost always imprints on its own egg.

a. Cost of mistaken imprinting are low.

3. Hosts could be parasitized on their first breeding and then would imprint on a cuckoo chick and always reject its own offspring.

a. Cost of mistaken imprinting is high.

4. However, hosts of bronze-cuckoos (Chalcites spp.) in Australia regularly reject cuckoo chicks.

5. Bronze-cuckoos developed mimetic chicks.

Egg vs. Chick rejection

1. At start of arms race new hosts exhibit little to no rejection of foreign eggs.

2. In response to parasitism, host evolves egg rejection and more variation in egg markings.

3. In response to rejection cuckoos evolve egg mimicry.

4. If egg mimicry is very good and parasitism levels low, it may be best for the host to accept to avoid cost of rejecting own eggs.

Likely Sequence of the Coevolutionary Arms Race

1. Antagonistic interactions between predators and prey lead to evolution of adaptations and counter-adaptations.

a. ‘Red Queen’ coevolution results in tactics changing, but relative success of each party staying the same.

2. Crypsis and polymorphisms can reduce prey profitability and detection.

3. Aposematism is an effective warning signal for non-palatable or toxic prey.

4. Aposematism has promoted evolution of both honest and dishonest mimicry systems.

a. Batesian mimicry: a palatable species mimics an unpalatable species.b. Mullerian mimicry: an unpalatable species mimics an unpalatable species.

5. Prey defenses are costly and often involve trade-offs in their production and use.

6. Brood parasites and hosts appear to be in successive stages of coevolution.

Summary