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Topic 11: Convergence

� What is convergence?

� How can convergence be detected?

� Do we see convergence?

� What are the classic herp examples?

� Have they been formally studied?

What is convergence?

Emerald Tree Boas and

Green Tree Pythons show a

remarkable level of

convergence

Photos © KP Bergmann, Philadelphia Zoo (adult ETB)

What is convergence?

� Several patterns are conflated into convergence:

� _____________

� _____________

� _____________

� “True” _______________

� All mean slightly different things

� Being clear on definitions is important

Photos © KP Bergmann, Philadelphia Zoo

What is convergence?

� ________________

� Phylogenetic term

� Previously defined as the similarity of a character between taxa due to convergence

� However, it includes:� True convergence

� Reversal

� Parallelism

� These have similar effects on phylogeny reconstruction

Pough et al. 2004, Fig 3-1

Snake-like Adults with gill slits

What is convergence?

� _____________

� When evolution switches _______________

� A recently evolved character is lost

� A recently lost character is re-evolved

� Example:

� Bachia digit loss and re-evolution

� Derived species tend to have _______________

� 5 digits is ancestral

Kohlsdorf & Wagner 2006; Photo © E Alzate

Digit loss

Digit gain

What is convergence?

� ________________

� Independent evolution of similar traits in related lineages whose common ancestor did not share that trait (Futuyma 1986)

� Parallelism generally involves a homologous ____________________

� Generally closely related lineages (not always)

� This has not been tested in Lerista, but is likely

Lerista (Scincidae)

Greer 1990

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What is convergence?

� __________________

� Independent evolution of similar traits in independent lineages, often by ___________ ______________

� Difference from parallelism can be blurred

� “when two taxa evolve to be more similar to one another than their ancestors were to each other” (Stayton 2008)

Stayton 2008

DE

H

G

F

C

B

A

Root

What is convergence?

Stayton 2008

DE

H

G

F

C

B

A

A B C D E F G H� How is convergence viewed?

� Phylogeny� _______________� _______________� Confounds ability to accurately reconstruct phylogeny

� A mistake in coding?

� Biology in general� ____________________� ____________________� Adaptation by different taxa to similar situations

� A phylogenetic perspective is important to studying it

How can convergence be detected?

� What kinds of patterns does convergence result

in?

� Pattern 1: Two different

taxa converging ________ _____________

� What we typically think of as convergence

Stayton, 2006; Photos © KP Bergmann, Philadelphia Zoo

Trait 1

Trait 2

� Pattern 2: Two ________ ____________________ ____________________

� The two taxa may be quite different in some ways, similar in others

Stayton, 2006; Photo www.digimorph.org

Trait 1

Trait 2

How can convergence be detected?

� Pattern 3: Two different taxa evolving _________ ____________________

� Parallel evolution, but NOT necessarily parallelism

� The ____________ ______________ are convergent, even if the phenotype is not

� More typical of very unrelated taxa (?)

Stayton, 2006; Photos ??, PJB

Trait 1

Trait 2

Pufferfishes and horned lizards?

How can convergence be detected?

� What pattern of convergence are each of these examples? Why?

Photos © PJB, KP Bergmann, Philadelphia Zoo

Tail as a fat

storage organSuite of morphological

& behavioral traits

Do we see convergence?

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Do we see

convergence?

� What are the herp examples?

� Snake-like body form (BE & LR) in squamates

� Has evolved __________ independently

� Has occurred in two ways, but within each, we still have convergence

� What pattern of convergence?

Brandley et al. 2008; Bergmann 2013

Do we see

convergence?

� Fossoriality

� Fusion of skull

� _________________

� Small relative head size

� Limited cranial kinesis

� Feed on smaller prey than non-fossorial relatives

� __________________

� __________________

� Examples:

� Gymnophiona

� Amphisbaenia

� Scolecophidia

� What pattern is this?

www.digimorph.org

Do we see convergence?

� Adhesive pads on digits

� Evolved 3 times in squamates

� Scales modified to have fine keratinous hairs called ____________

� Same mechanism of action (________________ forces)

� Also seen in some inverts, like tarantulas

� What pattern is this?

Gekkonidae

Anolis

Prasinohaema

Photos: KP Bergmann, USDA, Afco Zoo Supplies; SEMs: Williams and Peterson, 1982.

Do we see convergence?

� Clinging ability increases with ____________ & ___________

� Skinks are poor clingers for their body mass – pads are smaller, less effective

Photos: KP Bergmann, USDA, Afco Zoo Supplies; Graph: Irschick et al. 1996

Do we see convergence?

� Iguanidae and “Agamidae”

� ____________________

� New & Old World, respectively

� Ecological analogs look very similar

� Many instances of convergence

� Adaptation to _____________

� Perhaps a lizard’s shape can be modified in only certain ways

� e.g. a laterally flattened tail may be the easiest way for a

lizard to adapt to swimming

Photos © K Bergmann, K Derby

Do we see convergence?

� Iguanidae and “Agamidae”

� More examples

� What pattern do we see here?

Photos: PJB, K Bergmann, Pough et al., E Rudolph

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Do we see convergence?

� Iguanidae vs. “Agamidae”

� Most of these examples are relatively slight examples of convergence

� Phrynosoma & Moloch horridus is more complex

� _________________

� _________________

� Slow-moving

� ____________________

� Have micro-grooves that allow them to gather water in dry deserts

Photos: © PJB, J Meyers

Do we see convergence?

� Phrynosoma vs. Moloch

� Similar morphology

� Both eat ants

� _________________ _________________

� _________________ _________________

� Different from generalist lizards

� No body lunge

� Faster tongue

protrusion

� Faster feeding cycle

� Don’t process prey

Meyers and Herrel 2005

Do we see convergence?

� Reduction in shell defenses in insular giant tortoises

� Independent evolution of a saddle-backed shell in the Mascarine islands

� Similar patterns on Galapagos, Aldabra

Austin and Arnold 2001

Do we see convergence?

� Herbivory in lizards

� Comparison of skull shape

� Comparing ___________ to non-herbivore sister group

� Herbivores tend to “move” towards a common area of morphospace, relative to sister groups

� Herbivores tend to evolve skulls with higher mechanical advantage

� __________________

� __________________

� What pattern is this?

Stayton 2006

Do we see convergence?

� Unrelated rock-dwelling lizards have a flat body and long limbs

� Live on vertical rock surfaces

� Seen in:

� Petrosaurus (Phrynosomatinae)

� Platysaurus (Cordylidae)

� Pseudocordylus (Cordylidae)

� Anolis bartschi (Polychrotinae)

� Some tropidurines

� Has this body shape evolved along the branch on the phylogeny that also led to saxicoly?

Photos © Branch, Kober

Do we see convergence?� Convergence in

saxicolous lizards

� In general, saxicolous taxa have evolved:

� ________________

� ________________

� Petrosaurus has evolved a shallower head, but not longer limbs

Revell et al. 2007

PC-1: Limb length

PC-2: Head depth

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Do we see Convergence?

� _______________________

� mtDNA sequence phylogeny

� Ecomorphs evolved multiple times on different Greater Antillean islands

� Does this represent convergence?

� Need to look at the morphology

From Losos et al., 1998

Do we see Convergence?

� Anolis ecomorphs

� Morphometric data, distance clustering

� Each ecomorph clusters separately from others in morphospace

� Convergence is going on, but what pattern?

From Losos et al., 1998

Do we see

Convergence?

� Anolis ecomorphs

� ___________________ plays a role

� Same ecomorphs, but different sequence of evolution

� _________________ do not fall into ecomorphs

Irschick et al. 1997; Losos et al., 1998