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Transcript
Compara've Ocular Morphology of Troglomorphic Fish: Implica'ons for Evolu'on? Chuck Schobert, DVM Plan • Non‐vertebrate chordate eyes, agnatha • Congo blind fish: Lamprologus lethops • Travelogue: Congo River Habitats • Ocular Anatomy (also, Hot Off the Press!) • • • • • Mexican blind cave fish: Astyanax mexicanus Travelogue: Habitat Model system Ocular Anatomy So what?: Conclusions, specula'ons, and ques'ons Teleost Fish Eye Anatomy The Chordates in Evolu'on Cladogram: Hagfish & Lampreys Comparison Hagfish and Lampreys • • • • • No paired pectoral (shoulder) or pelvic (hip) fins Notochord persists for life. They have no scales. The axons of their neurons are unmyelinated. Lampreys have both an innate immune system and an adap've immune system, but the laVer is en'rely different from that found in the jawed vertebrates. Hagfish • Eat dead whales • Secrete copious amounts of thick slime (mucous) • Live in deep oceanic trenches (>100meters) • Recommenda'on: YouTube: “Eddie and the Hagfish” Hagfish Eyes No cornea No lens 2‐layered re'na (neuronal) No melanin Primi've photoreceptors Wired to the brain like a pineal gland • No pineal gland • Photoreceptors synapse directly onto ganglion cells • • • • • • Eye Transverse Sec'ons Hagfish Specimen courtesy of Dr Ivan Schwab Lamprey Eye: Larval • Larval form to adult form: Five Years! • Mostly buried in mud • No lens ini'ally • Larva details – Similar to hagfish eye – Eye covered in skin Lamprey Larval Eye Lamprey Adult •Cornea largely con'nuous with the skin •No muscles of accommoda'on •Has most of the structures of the vertebrate eye: –Lens –3 neuronal layers in re'na –Extraocularmuscles –Wired to brain like a visual eye –Melanin in choroid and RPE Color vision and pineal gland Lamprey Adult Eye: Five Years Later Photoreceptor Evolu'on Hagfish Lamprey From Lamb, TD et al. Evolu?on of the Vertebrate eye: opsins, photoreceptors, re?na and eye cup. 2007. Nature Reviews: Neuroscience, 8: 960‐975. Take Home? • A window to the earliest development of the vertebrate eye – Hagfish: circadian func'on – Lamprey: image‐forming eye, vertebrate‐like – Evolu'onary controversy about rela'onship between hagfish and lamprey: – If hagfish diverged earlier than lampreys from a common ancestor, opportunity to see the earliest examples of vertebrate ocular evolu'on – If hagfish diverged from the lamprey clade, then ocular differences are perhaps degenerate • And of course, weird food Hagfish‐Slime Cheddar‐Gruyere Scones 4 cups all‐purpose flour 2 tablespoons baking powder 4 teaspoons sugar 1/2 teaspoon salt 1 cup (two s'cks) chilled unsalted buVer, cut into 1/2‐inch cubes 2 cups (packed) coarsely grated extra‐sharp yellow cheddar cheese (about 9 ounces), or a mix of 6 ounces cheddar and 3 ounces gruyere. 1‐1/2 cups chilled heavy whipping cream 6 tablespoons hagfish slime Preheat oven to 375F In a food processor, blend flour, baking powder, sugar, and salt. Cut in the buVer using quick pulses un'l the mixture resembles coarse meal. Add cheese and cut in using quick pulses. In a small bowl, whisk together the cream and hagfish slime. With the food processor running, add cream mixture through feed tube. Process un'l dough just holds together – donÂ’t overmix! Turn dough out onto a lightly floured work surface. Gather the dough together and divide into quarters. Pat each quarter into a round just short of 1 inch high (it should be about 6‐7 inches in diameter). Using a clean, sharp knife, cut each round into six wedges. Transfer half the wedges to ungreased baking sheets lined with parchment paper, spacing them about 2 inches apart. Bake the first batch of scones un'l the edges just start to brown and a toothpick comes out clean, about 20 minutes. Transfer them, s'll on their parchment paper, to a wire rack to cool at least 10 minutes, during which 'me put in the second batch of scones. Serve warm or at room temperature. The scones will stand for about 8 hours. Do not refrigerate. If you want to reheat them, warm them in a 350F oven for about 5 minutes Lamprey Bordelaise For : 6 servings Time : 2 h 50 Difficulty : medium Ingredients for Lamprey Bordelaise : • 1 live 2 kg lamprey • 1 dl oil • 100 g buVer • 1 boVle red Bordeaux wine • 1 small glass Armagnac • 4 shallots • 8 onions • 15 leeks • 4 garlic cloves • 600 g Bayonne ham • 2 tablespoons flour • 1 glass broth • 2 cloves • 1 bouquet garni • 6 slices country‐style bread • salt • Pepper Technical stages for Lamprey Bordelaise : • • • • • • • • • Bleed the lamprey by hanging it by the head and cuqng the tail over a container to collect the blood. When there's no blood dripping anymore, dip the lamprey in boiling water for 1 minute. Take it out and peel it. Cut in 4 cm‐thick (1,57 inches) slices. Put the slices in the container of blood. Cut the white part of the leeks into 7‐8 cm‐long (2,76‐3,15 inches) whistles and steam them in buVer. Add the diced ham, the shallots and minced onions. Sprinkle with flour and roast. Moisten with the wine and broth. Add the cloves and bouquet garni. Add pepper, salt a liVle. Add two crushed garlic cloves. Bring to a boiling point, then cook for 45 minutes over low heat. 45 minutes later, add the pieces of lamprey in the sauce, cover and cook again for 45 minutes. Remove the slices of fish, and flamb them in another pan or skillet with Armagnac. Pour the equivalent of a glass of warm sauce over the blood in order to dilute it, and poor in the skillet. S'r well. Put back the lamprey, season and cook for 10 minutes with the lid on. Beat the sauce with buVer. Meanwhile, toast the bread and rub it with the remaining garlic.Put the lamprey in a shallow dish, on the slices of bread. Put the leeks all around. Coat with the sauce. L. lethops and L. ?gripic?lis Benthic Fish: gas bubble disease “mondelli bureau” Congo River • Short film What is cool about the Congo River? • Many, many microhabitats • Evolu'on occurring all the 'me! • Weird river=weird fish Sighted vs Blind L. Lethops histology images L. ?gripic?lis Immunohistochemistry: opsins Hot off the press! Mastacembelus brichardi Mastacembelus brichardi • one specimen is fully depigmented and eyeless • second specimen is a slightly pigmented morph with 'ny eyes: fully developed lens, re'na, incomplete cornea, eyes dorsally displaced toward midline • intraspecific comparison or is the ves'gial eyed morph a hybrid between the eyeless brichardi and an eyed congener • collected at the same locality, in shallow water under rocks and boulders. Astyanax mexicanus • Blind and sighted in same species • Divergence 1 mya • Model system for development, molecular gene'cs • Differences in ocular anatomy A Mature Adult Sighted Blind Cave habitat Model system in evo devo • Molecular gene'cs well known • Embryological development easily studied: eye begins to develop, lens cells undergo apoptosis, degenera'on • 4‐6 month genera'on 'me • Lens transplant experiments show eye development genes s'll present: lens from sighted into blind, vice versa • Pleiotropy: single gene controls two or more phenotypic traits that may seem unrelated: on‐ off switch …. Ocular anatomy • Comparison montage A. Mexicanus images: blind A. mexicanus: sighted Implica'ons for evolu'on? • Evolu'on not always construc've • Regressive evolu'on occurs • Different habitats produce varied selec'on pressures • Fish adapts to darkness through selec'on of “numerous grada'ons” leading to increased olfac'on, enhanced mechanorecep'on, altered craniofacial structure Phenotypic Plas'city • Phenotype=genotype + environment • Light‐dark experiments with epigean Astyanax fasciatus larvae • Eyes of larvae raised in darkness for 30d are much less developed than those raised in light • Alternate developmental pathways based on environmental condi'ons…….. Spin‐offs • Why develop a morphological catalog of blind/par?ally‐sighted fish? • Relate these morphological differences to genome differences to aid understanding of eye evolu'on, development and disease • Use well‐studied systems such as Zebra fish and Astyanax spp to understand the rela'onship between gene'cs and morphology when looking at wild fish Many thanks! • • • • • • • • • Dr Dick Dubielzig Dr Melanie S'assny and colleagues, AMNH Dr William R. Jeffery, UMD Dr Ivan Schwab Dr Leandro Teixeira Dr Jen Dreyfus Mr ScoV Earnest Ms Kate Lieber Ms. Janice Lokken Ques'ons, specula'ons?
