t08 body shape wrksht.ppt - clark university

8/19/2013

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Topic 8: The Evolution of Body Shape

� Why is body shape important?

� What are some common patterns in body shape evolution?

� How has a snake-like form evolved?� What are the main hypotheses for its evolution?� What is the developmental basis of body elongation and

limb reduction?

� What are some morphological patterns in its evolution?

� How has a stocky form evolved?� What are some clade-specific hypotheses?

� What does it mean to evolve stockiness?

� What are the functional implications of body shape evolution?

Why is body shape important?

� Body shape is a key aspect of ________

� Species within clades differ in body shape

� True for almost all clades

� This variation can have far-reaching consequences

Photos © PJB, KP Bergmann

Think about how different these organisms are…


� Consider what aspects of body shape are variable

� _______________

� _______________

� _______________

� _______________

� _______________

Photos © PJ Bergmann


� Body shape is a key aspect of diversity

� Expect differently shaped animals to:

� ___________________

� ___________________

� ___________________

� Different body shapes will be better at doing different things

Functional Aspects of

Body Shape

Organismal

Function

Organismal

Ecology

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Aspects of Body Shape

� Small limbs

� Tail

� Sprawling

� Long hind limbs

� Light bodied

� Adhesive pads

� Equal-sized limbs

� “Mid” bodied

� Upright

� Short limbs

� Heavy bodied

� Large mouth

Functional Aspects

Photos © PJB, KP Bergmann

Salamander

Tree Frog

Toad

Ceratophrys

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What are some common patterns in body shape evolution?

� A _________________ body shape� “Body _______________ and limb

________________”

� Has evolved many times

� Examples:

� Fishes: Bichirs, eels, gobies, gar

� Mammals: Mustelids

� Birds: Hesperornis?

� Amphibians: Sirenidae, Amphiumidae, Gymnophiona

� Squamates: Snakes, Amphisbaenia, Pygopodidae, some Anguidae, Gymnophthalmidae, Scincidae, Gerrhosauridae

� A snake-like body shape

� Evolved several times in Amphibia

� Evolved >25 times in the Squamata

� Never in the ____________

� In some clades, there are only snake-like species

� In others, there are intermediate forms

� Degrees of BE & LR

Photos PJB, Pough et al. 2004


� A _____________ body shape

� Has evolved multiple times

� Poorly studied

� Some clades are all stocky, others have intermediates

� Examples:

� Fishes: Tetraodontiformes

� Amphibians: Anura� Also has evolved within Anura

� Examples?

� Testudines

� Squamata: Phrynosoma

Photos ?, PJB


StockyElongate


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How has a snake-like body form evolved?

� Body elongation and limb reduction

� Studied the most

� Primarily in Squamata

� Several hypotheses for its evolution

� Studies of development

� Studies of morphology

Photo © PJ Bergmann

Hypotheses for the evolution of a snake-like body shape

� Adaptation to ______________

� Adaptation to _________________

� Adaptation to ______ _________________ _________________

� Adaptation to _________________

Photos PJB, Pough et al 2004

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� Adaptation to _______________� Premise: A snake-like body allows

easy making of and travel through tunnels

� Examples: Some snakes, Amphisbaenia, many lizards

� Evidence:

� Many elongate lizards are fossorial

� Other adaptations coincide with snake-like body

� Basal snakes are all fossorial

� Reduced eyes in many burrowing animals and the lack of ciliary muscles in snake eyes � re-evolution?

� Traditional hypothesis

Photos Pough et al 2004, www.digimorph.org


� Adaptation to ______________

� Premise: An elongate body is good for propulsion in water through __________________ ________________________

� Examples: Sea snakes, water snakes, Sirenidae, eels, lots of elongate fishes

� Evidence:

� Fossil snakes with small legs that were marine

� Maybe related to marine

mosasaurs

� Some phylogenies suggest

that they are sister to all snakes

Photos Pough et al 2004, www.paleopolis.com


� Adaptation to aquatic habitat

Modified from Lee & Caldwell, 2000

Serpentes

Marine snakes

with legs


� Adaptation to aquatic habitat

� Other analyses suggest they are nested within snakes

Modified from Tchernov et al., 2000

Marine snakes

with legs

Serpentes


� Adaptation to ______________ __________________________

� Premise: Legs get in the way in dense grass and shrubs. No legs allows the animals to wriggle through _____________

� Examples: Some pygopodids, many skinks, elongate reef fishes?

� Evidence:

� Studies that show that shorter limbed species inhabit more closed habitats

� Horned lizards move slower in patches of invasive buffle grass

Photos © PJB


� Adaptation to ________________

� Premise: Pushing off with whole body displaces the substrate less than limbs (higher SA), so locomotion is more ___________

� Examples: Sidewinders, Leristaskinks, other elongate sand-dwellers

� Evidence:

� Observational

� Maybe not well supported (Bergmann & Irschick 2010)

© PJB

© Britannica


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Developmental basis of body

elongation and limb reduction

� The two traits (BE & LR) have been studied separately

� They are highly _________ with one another

� The same Hox genes are involved in patterning

� ____________________

� ____________________

� Other things as well


Developmental basis of limb reduction

� LR has received most attention

� Observation of varying numbers of digits and phalanges

� How would this arise?

� ___________________ of development

� Loss of digits with decreasing ______________

� Some other mechanism

Greer 1990

Developmental basis of limb reduction

� Early experiments with _____________________� Development is truncated

experimentally

� Get digit pattern as seen in nature

� More recent molecular developmental studies� Development is not

simply truncated

� Phalangeal numbers don’t match

� Duration of __________ _______ gene expression regulates cell proliferation

Shapiro et al. 2003

Developmental basis of body elongation

� Elongate vertebrates tend to have:

� Reduced limbs

� A long thoracic region

� In snakes, expansion of Hox gene domains has:

� Over-run the location of the __________________

� Expanded area of ____________ identity

� Hox C6 marks the location of the ________________ in many vertebrates

Cohn & Tickle 1999

Hox B5 Hox C8 Hox C6

Developmental basis of body elongation

� But how do snakes get so MANY vertebrae?

� Vertebrae form from paraxial mesoderm tissue

� Paraxial mesoderm subdivides __________________ during development

� Faster division of tissue results in ________________________________ _________________________________________________

Gomez et al. 2008

Morphological patterns of evolution of a

snake-like body form

� Early studies lined up the morphologies �

� Created “______________”

� No phylogenies were available or used

� Appreciated variation, but not patterns of evolution

Greer 1990# Phalanges

# Vertebrae

035

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Morphological evolution of a snake-like form

� Evolutionary approach

� What is ancestral?

� How many times has BE & LR evolved?

� Is it reversible?

� How fast do these traits evolve?

� Phylogenies are available

� Statistics for accounting for phylogeny are available

Greer 1990

Lerista (Scincidae)� Bachia (Gymnophthalmidae)

limb evolution

� Clade has hind limbs more reduced than front

� Found that in Bachia, derived species have _____________ ______________

� Evidence is stronger in hind limb than front

� Example of the re-evolution of a complex structure

Kohlsdorf & Wagner 2006

Morphological evolution

of a snake-like form

� A broad look at squamates

� Evidence for two ecomorphs:

� _______________________________________

� _______________________________________

Brandley et al. 2008


� Short-tailed

� Some are fossorial, like Amphisbaenia

� Some are sand swimming

� Long tailed

� Tend to live in dense vegetation

� Thresholds

� ___________ completely disappear when BE reaches a certain point

� There are ____________ when degree of BE reaches a certain point



� Transition from lizard to snake-like body can take _________________

� Intermediate body shapes can persist for ___________ _______________ of years

� _______________________ digits has occurred at least 6 times


Morphological evolution

of a snake-like form

� Snake like ecomorphs have evolved many times

� Biogeographic explanation

� They do not disperse inter-continentally

� Isolated evolution allows __________________ in different places

� Each ecomorph has evolved several times on each continent

Wiens et al. 2006


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� Stockiness has evolved several times independently

� Pufferfishes

� Frogs

� Horned lizards

� Largely neglected area of study

� Different hypotheses for each instance?

Photos © ?, PJ Bergmann

How has a stocky body form evolved?

� Why might stockiness have evolved in these taxa?

� Pufferfish:� Related to ________________________

� Anura:� Facilitates ________________________

� Need a short rigid body to maintain control during big jumps

� Phrynosoma:� Thermoregulation?

� Crypsis?

� Defenses?



� A stocky body shape has costs:

� These animals seem to have ________________________

� Puffers with fewer vertebrae are able to bend their bodies less (Brainerd & Patek 1998)

� Puffers and horned lizards seem to move rather ______________



� What body parts are involved in the evolution of stockiness?


Variable Stockiness

Snout-Vent Length -0.326

Head Length -0.326

Head Height 0.275

Head Width 0.116

Front Limb Length -0.321

Hind Limb Length -0.574

Body Width 0.514

Body Height 0.047

Bergmann et al. 2009


Bergmann et al. 2009

Phrynosoma douglassi

Phrynosoma hernandesi

Phrynosoma ditmarsi

Phrynosoma orbiculare

Phrynosoma modestum

Phrynosoma platyrhinos

Phrynosoma mcallii

Phrynosoma solare

Phrynosoma asio

Phrynosoma taurus

Phrynosoma cornutum

Uma notata

Uma scoparia

Cophosaurus texanus

Callisaurus draconoides

Holbrookia maculata

Uta stansburiana

Urosaurus ornatus

Sceloporus variabilis

Sceloporus magister

Sceloporus orcutti

Sceloporus malachiticus

Sceloporus formosus

Sceloporus mucronatus

Sceloporus horridus

Sceloporus spinosus

Sceloporus graciosus

Sceloporus jarrovi

Sceloporus grammicus

Sceloporus olivaceus

Sceloporus clarki

Sceloporus scalaris

Sceloporus poinsetti

Sceloporus cyanogenys

Sceloporus minor

Sceloporus occidentalis

Sceloporus virgatus

Sceloporus undulatus

51

59

*

*

*

****

*

*

*

*

*

*

90

66

95

8177

57

70

99

78

58

57

52

*

61

92

95

82

Horned Lizards

Sand Lizards

Fence

Lizards


The Phrynosomatinae and Lerista skinks have incredible variation in body shape

Bergmann & Irschick 2010

What are the functional implications of body shape evolution?

L e r i s t a P h r y n o s o m a t i n a e

Fence

Lizards

Sand

Lizards Horned

Lizards

Do these

different body shapes do things

differently?

8/19/2013

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© PJ Bergmann© CSIRO, Brad Maryan

Lerista Phrynosomatinae


Functional Aspects

of Body Shape

__________ __________

__________

•Degree of elongation

•Relative limb length

•Axial angle

•Limb angles

•Stride length

•Stride frequency

•Velocity

•Substrate

•Particle size

•Load-bearing

capacity


� More elongate skinks __________

� Species with longer limbs:

� _______________

� Take longer & quicker strides

� Bend less (skinks)

� Species did not perform differently on sand paper versus sand

� Species did not select habitats based on body shape

Photo © PJ BergmannBergmann & Irschick 2010


� Going back to the study of Phrynosomatines only…

� Looked for evolutionary correlation of:

� Stockiness

� Relative horn size

� Absolute sprint speed

� Relative sprint speed

� % ants in diet (Volume)


Horned

Lizards

Sand

Lizards

Fence

Lizards


Found a complex pattern of co-evolution among these traits

Bergmann & Irschick 2009

Trait 1 Trait 2 N R BF

Stockiness Abs speed 28 -0.491 4.72

Stockiness Rel speed 28 -0.148 4.50

Stockiness % ants 16 0.630 9.91

Abs speed % ants 10 -0.817 9.32

Horn size Rel speed 18 -0.422 8.34

Horn size % ants 16 0.625 15.26



� In horned lizards:

�

�


t08 body shape wrksht.ppt - clark university

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