Evolution of Jaws Derived Fish Skull Components Jaw Suspension Jaw Protrusability and Feeding

Evolution of Jaws Derived Fish Skull Components Jaw Suspension Jaw Protrusability and Feeding

Evolution of Jaws Derived Fish Skull Components • Earliest forms – No jaws – Cartilage cranium – 8 Cartilage arches support gill slits • Derived forms – Jaws – Bony cranium – 5 arches support gills • Two theories • Neurocranium – – Serial • Suspensocranium (suspensorium) – – Composite • Bronchial Skeleton – Jaw suspension Jaw Protrusability and Feeding • Autostylic • Suction feeding – Palatoquadrate atriculated with neurocranium – Hyoid arch not involved in jaw suspension • Ram feeding – Hyomandibula -> inner ear bones – All non-fish vertebrates • Hyostylic • Suction feeding and Jaw Protrusion – Palatoquadrate hangs from ethmoid and hyomandibula – Hyoidmandibula attached to upper and lower jaws – Modern sharks and teleost fishes • Holostylic – Palatoquadrate fused with neurocranium, no hyomandibula in hyoid arch – Chimera 1 Feeding Habits and Gut Morphology Digestive Tract • Feeding Guilds • Esophagus – Detritivores • Stomach – Herbivores • Small intestines – Carnivores – Pyloric caeca – Omnivores • Most fish euryphagous carnivores, ontogenetic shifts common • Digestive tract anatomy – Low quality prey – – High quality prey – Chemoreception Sensory Epithelium • Olfactory reception • Composed of: – receptor neurons: high densities • 25,000/mm2 in salmonids • 500,000/mm2 in cyprinodontids • Taste – supporting cells – basal cells • Receptor neurons: – ciliated – 8 cilia – microvillous – 80 microvilli 2 Taste Chemoreception Examples • Taste buds • Salmon imprinting of natal stream, return migration – Detection limits: • Recognize smell of juveniles (Pheromone hypothesis) for parental care – Pimephales - p-chlorophenol <0.0005 ppm – Oncorhynchus - morpholine 1x10-6 ppm • Kin recognition, mitigates aggressive interactions – Catfish - amino acids 10-7 – 10-9 ppm • Schooling aggregation • Palatal organ: • Elasmobranchs: • Schreckstoff • Examples: • Food location – Ion concentrations detected by gill parasite catfish – sharks Detecting sound, vibration and water movement Variability in lateral line • Lateral line • Jawless fishes: • Open vs Closed Canals: – Neuromasts – • Habitat indicator – Cupula – 3 Inner ear Swim bladders and hearing • Embryologically related to the • Swim bladder as hearing receptor lateral line – Clupeidae - hollow ducts extend • Two parts: from gas bladder to inner ear – semicircular canals – otolith organs • Elephant fish have gas bubble in head • Perception • Weberian aparatus – Otophysan fishes (e.g., catfish, minnow) – Connected to air bladder Electroreception • External pit organs on teleosts • Ampullae of Lorenzini •In some ways, fish vision is better than our own. •UV, tetrachromic vision in some species • Weakly electric fishes - gymnotiformes • Communication, prey detection, navigation 4 Fish vs Terrestrial Eyes Rods, cones, photomechanical movement and light accommodation • Focusing • Pupils • Other structures Reproduction Reproduction continued • Gender System • Site of fertilization – Gonochoristic – Internal – Gynogenic – Hermaphroditic – External • Simultaneous • Fate of Eggs • Sequential – No parental care – Protandrous • Broadcast spawners – Protogynous • Sex determination – Pelagic – Genetic – Benthic – Environmental • Brood hiders • Mating System – Eggs guarded – Promiscuous • Substrate spawners – Monogamy – Polyandry • Nest builders – Polygyny – Bearers • Secondary traits • Internal bearers – Monomorphic – Ovovivipary – Dimorphic • Seasonally dimorphic – Vivipary • Permanently dimorphic • External bearers • Number of reproductive acts – Semelparous – Iteroparous 5.

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