1/9/2013 Topic 3: Evolution & Diversity of What are the protochordates? Vertebrates
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1/9/2013 Topic 3: Evolution & Diversity of Vertebrates What are the protochordates? Protostomes What are the protochordates? A phylogenetic perspective Relationship to craniates What are the key characteristics of chordates? What are the main Protochordate clades? What are the differences between craniates and vertebrates? Deuterostomes Hemichordata Chordata Protochordates are ______________ Hemichordata Echinoderms Pterobranchia Enteropneusta Urochordata Cephalochordata Pterobranchia Enteropneusta – acorn worms Urochordata Cephalochordata Tunicates Lancelets Craniata Modified: Liem et al. 2001, Fig. 2-1 What are the protochordates? Protostomes Protostomes Echinoderms Urochordata Cephalochordata Craniata Modified: Liem et al. 2001, Fig. 2-1 What sort of phylogenetic group are protochordates? Pterobranchia What does this mean? ________________ ________________ ________________ ________________ Enteropneusta Echinoderms Urochordata Cephalochordata Deuterostomes Hemichordata Chordata Enteropneusta Deuterostomes Hemichordata Chordata Pterobranchia What are the protochordates? What insights might the study of protochordates give us? Craniata Modified: Liem et al. 2001, Fig. 2-1 1 1/9/2013 What are the key chordate characteristics? To understand the evolution of chordates, we need an understanding of what makes up a chordate Hemichordates have some of these Chordates have all of these 5 key chordate characteristics: 1. 2. 3. 4. 5. 1. _______________________ ___________________ ___________________ ___________________ ___________________ ___________________ 2 What are the key chordate characteristics? Develops by invagination Results in a neural tube Develops from ectoderm, like the epidermis Becomes the spinal cord Ventral and solid in many nonchordates 1 1 3 5 4 Photo © C Arenz What are the key chordate characteristics? 2. _____________________ What are the key chordate characteristics? 2. Notochord Also dorsal in position, ventral to the nerve cord Develops from mesoderm, like muscles and skeleton Is a ___________________ Liem et al. 2001, Fig 2-9; Nature 2002; C Arenz Skeletal/support function Reduced and replaced by vertebrae in vertebrates Intervertebral discs Cells in fluid in a tough connective tissue sheath Allows flexion Resists compression Maintains body shape 2 2 Liem et al. 2001, Fig 2-9; Kardong 1998 Fig 2-5 A Harris; A Morton; Univ Maryland What are the key chordate characteristics? 3. ____________________ What are the key chordate characteristics? 3. Perforated pharynx - function Anterior end of gut Develops from endoderm, like the rest of the gut Allows ____________ of water for food particles Protochordates Fishes Primarily _______ (filtration) ___________ (gills, gill slits) Also in suction ___________ Tetrapods Slits disappear Pharyngeal structures contribute to jaws, ear bones, endocrine glands… 3 Liem et al. 2001, Fig 2-8D; C Arenz Photos © U Gille; C Arenz 1 1/9/2013 What are the key chordate characteristics? 4. _________________ 5. ____________ Seems intuitive What are the key chordate characteristics? Develops from endoderm A ciliated groove at the ventral end of the pharynx _________________ We define a “tail” this way Some animals have a tail-like structure with a gut inside Often has a ______________ Traps food particles Cilia move mucous posteriorly Transport mucous food to the for digestion and gut 5 4 Photos © M Himemiya; C Arenz Liem et al. 2001, Fig 2-8B; C Arenz What are the key chordate characteristics? What are the protochordate clades? Pterobranchia Controversial Enteropneusta Evidence for homology Urochordata Cephalochordata 5 Chordata Position Endostyle of larval lamprey metamorphoses into adult thyroid Both structures associated with iodine Tunicate (Urochordate) endostyle has similar genes expressed as a thyroid gland Protochordates Homologous to the thyroid gland in vertebrates Hemichordata 5. ________________ Craniata Ogasawara & Satou 2003; C Arenz What are the protochordate clades? ________________ Pterobranchia Enteropneusta (acorn worms) ~100 species Modified: Liem et al. 2001, Fig. 2-1 What are the protochordate clades? Pterobranchia Filter feeders Highly specialized morphology All are ___________ All are ___________ Pterobranchs are colonial, deepsea, and secrete a tube Acorn worms are shallower and fossorial Photos © Discovery Channel, A Artour, E Balser Liem et al. 2001, Fig 2-2; Sinauer Associates, 2001 2 1/9/2013 What are the protochordate clades? Enteropneusta What are the protochordate clades? Enteropneusta Locomotion More generalized Worm-like ______________ Mucous is used to trap food on ________ Cilia then transport the food and mucous into the mouth Have some chordate characteristics Liem et al. 2001, Fig 2-3 ____________________ What are the protochordate clades? Chordates ___________ (tunicates) What does this tell you? All are marine __________________ Pharyngeal slits Dorsal, hollow nerve cord formed by invagination Liem et al. 2001, Fig 2-3 What are the protochordate clades? Anchoring with collar Probing with proboscis Pulling body along No notochord Have all chordate characteristics at some point in life cycle Larva Dorsal hollow nerve cord Notochord Pharynx with slits is rudimentary, not used Post-anal tail Endostyle is rudimentary Pelagic, mobile Non-feeding Finds a place to settle __________________ Sessile, attached to substrate Filter feeding Covered in tough tunic Photos © C Arenz, I Frank, I Sayers, USGS Liem et al. 2001, Fig 2-7, C Arenz What are the protochordate clades? Urochordata (tunicates) Have all chordate characteristics at some point in life cycle Adult _____________________ _____________________ Other characteristics are lost due to sessile nature What are the protochordate clades? _________________ Liem et al. 2001, Fig 2-6, N Hobgood Future anus near excurrent siphon Also chordates Ciliated neurula larva Filter feeding, burrowing adult Both stages are motile Lancelets/Amphioxus ~45 species Liem et al. 2001, Fig 2-10; C Arenz 3 1/9/2013 What are the differences between craniates and vertebrates? What are the protochordate clades? Dorsal Hollow Nerve Cord __________________ Pterobranchia Enteropneusta Urochordata Endostyle Perforated Pharynx Cephalochordata Chordata Post-anal Tail Protochordates Notochord All chordate characteristics Feeding: Wheel organ and velar tentacles create current Endostyle secretes mucous Pharynx filters out food Water exits through atriopore Hemichordata Craniata Modified: Liem et al. 2001, Fig. 2-1 Liem et al. 2001, Fig 2-8B; C Arenz What are the differences between craniates and vertebrates? Myxiniformes (Hagfishes) Petromyzontiformes (Lampreys) Gnathostomata Amniotes Modified: Liem et al. 2001, Fig. 3-1 Tetrapoda Amphbians Craniata Vertebrata Dipnoi (Lungfishes) _______________ Chondrichthyes (Sharks and Rays) Actinopterygii (Ray-Finned Fishes) Craniata and Vertebrata What are the differences between craniates and vertebrates? Which is more inclusive? What are hagfishes? What are lampreys? Both are highly specialized parasites of fishes Hagfishes Tear parts off dead and dying fishes Use clamping mouth parts Use a knot behavior to gain leverage Little is known about them Non-vertebrate craniates Cartilaginous brain case No vertebrae Segmental muscles, like amphioxus and vertebrates Photo © C Ortlepp What are the differences between craniates and vertebrates? ____________________ Lampreys ___________________ Freshwater larvae Marine adults Feed on fish body fluids Rasping mouth parts Basal vertebrates Cartilaginous brain case Cartilaginous arcualia Arcualia Notochord Photos © U Thomas, EPA, Tree of Life 4 1/9/2013 An Evolutionary Perspective Pterobranchs Allows us to consider the evolution of many structures Enteropneusts Cephalochordates Lampreys Other Vertebrates Chordata Hagfishes Craniata Vertebrata 1. Pharyngeal slits 2. Dorsal hollow nerve cord 3. Notochord 4. Post-anal tail 5. Endostyle 6. Segmentation 7. Brain case 8. Vertebrae (arcualia) Urochordates Protochordates Protochordates allow us to study the evolution of vertebrates Hemichorata 1 1/9/2013 Myxiniformes Craniates and Vertebrates Petromyzontif. Chondrichthyes Actinopterygii Vertebrates are very diverse and the focus of this course Some major nested groups: ____________ _____________ Sarcopterygii ___________ _________ Diapsida Archosauria Mammalia Actinistia Dipnoi Lissamphibia Testudines Lepidosauria Crocodylia Aves Monotremata Metatheria Eutheria Liem et al. 2001, Fig 3-1 Craniates and Vertebrates Morphological diversity will be one course focus Also appreciate the species richness: ~48,000 Vertebrates ~25,000 are Fishes ~4,000 Amphibians ~15,000 Reptiles ~6,000 Crocs, Turtles, Lepidosauria ~9,000 Birds ~4,000 Mammals 5 Hominids Vertebrate Life, Fig. 1-1 1
