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Topic 8: The Evolution of Body Shape Why is body shape important?
Why is body shape important? Body shape is a key What are some common patterns in body shape aspect of ______evolution? Species within Think clades differ in about how How has a snake-like form evolved? body shape What are the main hypotheses for its evolution? different True for almost all What is the developmental basis of body elongation and these limb reduction? clades What are some morphological patterns in its evolution? organisms This variation can have far-reaching are… How has a stocky form evolved? consequences What are some clade-specific hypotheses? What does it mean to evolve stockiness?
What are the functional implications of body shape evolution?
Photos © PJB, KP Bergmann
Why is body shape important? Why is body shape important?
Consider what Body shape is a key Functional Aspects of aspects of body aspect of diversity Body Shape shape are variable Expect differently ______shaped animals to: ______ ______Organismal ______ ______Function ______ ______ ______ Different body shapes will be better at doing Organismal different things Ecology
Photos © PJ Bergmann
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Photos © PJB, KP Bergmann
Why is body shape important?
Aspects of Body Shape Functional Aspects Small limbs Tail Salamander Sprawling
Long hind limbs Light bodied
Tree Frog Tree Adhesive pads
Equal-sized limbs “Mid” bodied Toad Upright
Short limbs Heavy bodied
Ceratophrys Large mouth
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What are some common patterns in body shape evolution? What are some common patterns in body shape evolution?
A ______body shape A snake-like body shape “Body ______and limb ______” Evolved several times in Has evolved many times Amphibia
Examples: Evolved >25 times in the Fishes: Bichirs, eels, gobies, gar Squamata
Mammals: Mustelids Never in the ______
Birds: Hesperornis? In some clades, there are only snake-like species Amphibians: Sirenidae, Amphiumidae, Gymnophiona In others, there are intermediate forms Squamates: Snakes, Amphisbaenia, Pygopodidae, some Anguidae, Degrees of BE & LR Gymnophthalmidae, Scincidae, Gerrhosauridae Photos PJB, Pough et al. 2004
What are some common patterns in body shape evolution? 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 Elongate Stocky Also has evolved within Anura Examples?
Testudines
Squamata: Phrynosoma
Photos ?, PJB
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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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Hypotheses for the evolution of a snake-like body shape Hypotheses for the evolution of a snake-like body shape
Adaptation to ______ Premise: A snake-like body allows Adaptation to ______easy making of and travel through Premise: An elongate body is tunnels good for propulsion in water through ______ Examples: Some snakes, ______Amphisbaenia, many lizards
Examples: Sea snakes, water Evidence: snakes, Sirenidae, eels, lots of Many elongate lizards are fossorial elongate fishes Other adaptations coincide with snake-like body Evidence: Basal snakes are all fossorial Fossil snakes with small legs Reduced eyes in many that were marine burrowing animals and the lack of ciliary muscles in snake eyes Maybe related to marine re-evolution? mosasaurs Some phylogenies suggest that they are sister to all Traditional hypothesis snakes
Photos Pough et al 2004, www.digimorph.org Photos Pough et al 2004, www.paleopolis.com
Hypotheses for the evolution of a snake-like body shape Hypotheses for the evolution of a snake-like body shape
Adaptation to aquatic habitat Adaptation to aquatic habitat Other analyses suggest they are nested within snakes
Marine snakes Marine snakes with legs with legs
Serpentes Serpentes
Modified from Lee & Caldwell, 2000 Modified from Tchernov et al., 2000
Hypotheses for the evolution of a snake-like body shape Hypotheses for the evolution of a snake-like body shape
Adaptation to ______ Adaptation to ______ Premise: Pushing off with whole Premise: Legs get in the way in body displaces the substrate less dense grass and shrubs. No than limbs (higher SA), so legs allows the animals to locomotion is more ______wriggle through ______
Examples: Sidewinders, Lerista Examples: Some pygopodids, skinks, other elongate sand- © Britannica many skinks, elongate reef fishes? dwellers
Evidence: Evidence: Studies that show that shorter Observational limbed species inhabit more Maybe not well supported closed habitats (Bergmann & Irschick 2010) Horned lizards move slower in patches of invasive buffle grass © PJB Photos © PJB
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Developmental basis of body elongation and limb reduction Developmental basis of limb reduction
The two traits (BE & LR) LR has received most have been studied attention separately
Observation of varying They are highly ______numbers of digits and with one another phalanges
The same Hox genes are How would this arise? involved in patterning ______of ______development ______ Loss of digits with decreasing ______ Other things as well Some other mechanism
Photos © PJ Bergmann Greer 1990
Developmental basis of limb reduction Developmental basis of body elongation
Early experiments with Elongate vertebrates tend ______to have: Development is truncated experimentally Reduced limbs Get digit pattern as seen A long thoracic region in nature
More recent molecular In snakes, expansion of developmental studies Hox gene domains has: Development is not Over-run the location of simply truncated the ______ Phalangeal numbers don’t match Expanded area of Duration of ______identity ______gene expression Hox C6 marks the location regulates cell proliferation of the ______Hox B5 Hox C8 Hox C6 in many vertebrates
Shapiro et al. 2003 Cohn & Tickle 1999
Morphological patterns of evolution of a Developmental basis of body elongation snake-like body form
But how do snakes get so MANY vertebrae? Vertebrae form from paraxial mesoderm tissue Early studies lined up the Paraxial mesoderm subdivides ______during development morphologies Faster division of tissue results in ______ Created “______” No phylogenies were available or used Appreciated variation, but not patterns of evolution # Vertebrae #
35 0 Gomez et al. 2008 # Phalanges Greer 1990
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Morphological evolution Morphological evolution of a snake-like form of a snake-like form
Lerista (Scincidae) Evolutionary approach Bachia (Gymnophthalmidae) What is ancestral? limb evolution How many times has BE & LR evolved? Clade has hind limbs more reduced than front Is it reversible? How fast do these traits evolve? Found that in Bachia , derived species have ______ Phylogenies are available Evidence is stronger in hind limb than front Statistics for accounting for
phylogeny are available Example of the re-evolution of a complex structure
Greer 1990 Kohlsdorf & Wagner 2006
Morphological evolution of a snake-like form Morphological evolution of a snake-like form
A broad look at squamates Thresholds Evidence for two ecomorphs: ______completely ______disappear when BE ______reaches a certain point
Short-tailed There are ______ Some are fossorial, like when degree of BE Amphisbaenia reaches a certain point Some are sand swimming Long tailed Tend to live in dense vegetation
Brandley et al. 2008 Brandley et al. 2008
Morphological evolution of a snake-like form Morphological evolution of a snake-like form
Snake like ecomorphs have evolved many times Biogeographic explanation
Transition from lizard to They do not disperse inter-continentally snake-like body can take Isolated evolution allows ______in different places ______ Each ecomorph has evolved several times on each continent
Intermediate body shapes can persist for ______of years
______digits has occurred at least 6 times
Brandley et al. 2008 Wiens et al. 2006
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How has a stocky body form evolved? How has a stocky body form evolved?
Why might stockiness have evolved in Stockiness has evolved these taxa? several times independently Pufferfishes Pufferfish: Frogs Related to ______ Horned lizards
Anura: Largely neglected Facilitates ______area of study Need a short rigid body to maintain control during big jumps
Different hypotheses for each instance? Phrynosoma : Thermoregulation? Crypsis? Defenses?
Photos © ?, PJ Bergmann Photos © ?, PJ Bergmann
How has a stocky body form evolved? How has a stocky body form evolved?
What body parts are A stocky body shape has costs: involved in the evolution of stockiness? These animals seem to have Variable Stockiness ______Snout-Vent Length -0.326
Puffers with fewer vertebrae are Head Length -0.326 able to bend their bodies less Head Height 0.275 (Brainerd & Patek 1998) Head Width 0.116
Puffers and horned lizards seem Front Limb Length -0.321 to move rather ______Hind Limb Length -0.574 Body Width 0.514 Body Height 0.047 Photos © ?, PJ Bergmann Bergmann et al. 2009 Photos © PJ Bergmann
How has a stocky body form evolved? What are the functional implications of body shape evolution? The Phrynosomatinae and Lerista skinks * Phrynosoma douglassi ** Phrynosoma hernandesi have incredible variation in body shape * Phrynosoma ditmarsi 61 Phrynosoma orbiculare Phrynosoma modestum 82 59 Phrynosoma solare * PhrynosomaHorned mcallii Lizards 58 Phrynosoma platyrhinos Phrynosoma asio Phrynosoma taurus Phrynosoma cornutum * Uma notata Uma scoparia 92 CophosaurusSand texanus Lizards L e r i s t a P h r y n o s o m a t i n a e Callisaurus draconoides 95 Holbrookia maculata Uta stansburiana Urosaurus ornatus Sceloporus variabilis * Sceloporus magister Sand 78 Sceloporus orcutti Sceloporus malachiticus Horned * Sceloporus formosus Lizards * Sceloporus mucronatus Fence Lizards * Sceloporus horridus * Sceloporus spinosus Do these Lizards SceloporusFence graciosus 57 Sceloporus jarrovi 66 different body 52 51 Sceloporus grammicus * SceloporusLizards olivaceus 95 57 Sceloporus clarki shapes do things 70 Sceloporus scalaris 81 * Sceloporus poinsetti differently? 77 Sceloporus cyanogenys 99 Sceloporus minor Sceloporus occidentalis Sceloporus virgatus Bergmann et al. 2009 *90 Sceloporus undulatus Bergmann & Irschick 2010
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What are the functional implications of body shape evolution? Lerista Phrynosomatinae What are the functional implications of body shape evolution? Functional Aspects •Degree of elongation of Body Shape •Relative limb length
•Axial angle •Limb angles •Velocity •Stride length ______•Stride frequency
•Substrate ______•Particle size •Load-bearing capacity © CSIRO, Brad Maryan © PJ Bergmann
What are the functional implications of body shape evolution? What are the functional implications of body shape evolution?
Horned Lizards More elongate skinks ______ Going back to the study of Phrynosomatines only… Sand Lizards Species with longer limbs: Looked for evolutionary ______correlation of: Fence Lizards Take longer & quicker strides Stockiness Bend less (skinks) Relative horn size Absolute sprint speed Species did not perform differently Relative sprint speed on sand paper versus sand % ants in diet (Volume)
Species did not select habitats based on body shape
Bergmann & Irschick 2010 Photo © PJ Bergmann Photos © PJ Bergmann
What are the functional implications of body shape evolution? What are the functional implications of body shape evolution?
Found a complex pattern of co-evolution among these traits In horned lizards:
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
Bergmann & Irschick 2009 Photos © PJ Bergmann
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