8/19/2013 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 1 8/19/2013 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 1 8/19/2013 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 1 8/19/2013 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 1 8/19/2013 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 1 8/19/2013 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 2 8/19/2013 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 3 8/19/2013 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