T08 Body Shape wrksht.ppt - Clark University
Transcript of 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…
Why is body shape important?
� Consider what aspects of body shape are variable
� _______________
� _______________
� _______________
� _______________
� _______________
Photos © PJ Bergmann
Why is body shape important?
� 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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Why is body shape important?
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
What are some common patterns in body shape evolution?
� 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
What are some common patterns in body shape evolution?
StockyElongate
What are some common patterns in body shape evolution?
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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
Hypotheses for the evolution of a snake-like body shape
� 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
Hypotheses for the evolution of a snake-like body shape
� Adaptation to aquatic habitat
Modified from Lee & Caldwell, 2000
Serpentes
Marine snakes
with legs
Hypotheses for the evolution of a snake-like body shape
� Adaptation to aquatic habitat
� Other analyses suggest they are nested within snakes
Modified from Tchernov et al., 2000
Marine snakes
with legs
Serpentes
Hypotheses for the evolution of a snake-like body shape
� 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
Hypotheses for the evolution of a snake-like body shape
� 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
Hypotheses for the evolution of a snake-like body shape
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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
Photos © PJ Bergmann
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
Morphological evolution of a snake-like form
� 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
Brandley et al. 2008
Morphological evolution of a snake-like form
� Transition from lizard to snake-like body can take _________________
� Intermediate body shapes can persist for ___________ _______________ of years
� _______________________ digits has occurred at least 6 times
Brandley et al. 2008
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
Morphological evolution of a snake-like form
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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?
Photos © ?, PJ Bergmann
How has a stocky body form evolved?
� 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 ______________
Photos © ?, PJ Bergmann
How has a stocky body form evolved?
� What body parts are involved in the evolution of stockiness?
Photos © PJ Bergmann
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
How has a stocky body form evolved?
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
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90
66
95
8177
57
70
99
78
58
57
52
*
61
92
95
82
Horned Lizards
Sand Lizards
Fence
Lizards
How has a stocky body form evolved?
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?
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© PJ Bergmann© CSIRO, Brad Maryan
Lerista Phrynosomatinae
What are the functional implications of body shape evolution?
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
What are the functional implications of body shape evolution?
� 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
What are the functional implications of body shape evolution?
� 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)
Photos © PJ Bergmann
Horned
Lizards
Sand
Lizards
Fence
Lizards
What are the functional implications of body shape evolution?
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
What are the functional implications of body shape evolution?
Photos © PJ Bergmann
� In horned lizards:
�
�
What are the functional implications of body shape evolution?