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.