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