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Evolution of Venom Definition 5/27/14 Evolution of Venom Definition !! A poisonous fluid produced in a specialized gland !! “Delivered to a target organism through the infliction of a wound” !! “Contains molecules that disrupt normal physiological or biochemical processes” (Casewell et al., 2013) Function Venom: “A complex cocktail” !! Foraging adaptation (e.g., in snakes, some lizards, !! A mixture of proteins and peptides (a.k.a toxins), salts, scorpions) amino acids and neurotransmitters. !! Defensive adaptation (e.g., most venomous fish) !! Defensive venoms: streamlined, highly conserved; primary function: immediate, extreme localized pain !! Intraspecific conflict (e.g., platypus) !! Predatory venoms: more complex, highly variable in composition and physiological effects. (Casewell et al., 2013) (Casewell et al., 2013) Venom Across the Venom Evolution Animal !! Evolved several times throughout the animal kingdom Kingdom ! Various structures evolved for its delivery: barbs, beaks, !! Red branches: ! Predatory role fangs or modified teeth, harpoons, sprays, stingers,... !! Blue branches: Defensive role ! Convergent evolution of venom genes !! Green branches: A ! role in intraspecific competition (Casewell et al., 2013) (Casewell et al., 2013) 1 5/27/14 Origin of Venom Controversy Controversy: 1) Independent origin hypothesis: Two opposite hypotheses: Lizard evolved venom independently of snake: 1) Independent origin Hypothesis 1.1) Distant phylogenetic relatedness: !! Front fanged and non-front fanged caenophidians contained Duvernoy’s gland 2) Toxicofera Hypothesis !! Front fanged snakes ( atractaspidnes, elapids, and viperids) are three independent lineages among caenophidia) (Fry et al., 2006, 2009, 2010) Fry et al., 2006, 2009, 2010 Controversy Controversy 2)! Toxicofera Hypothesis 1.2) Significant difference in anatomy of venom delivery system ! Venom gene evolved in the common toxicofera ancestor ! !! Caenophidian Snakes -single compartment venom glands and !! Lizard and snake venom systems are homologous but highly differentiated delivery teeth are housed in the upper jaw descendants of an early evolved venom system in squamates !! Oral glands form a clade, indicate a single origin of the venom system in lizards !! Venomous lizards in the genus Heloderma- multi-compartmentalized and snakes glands on the lower jaw !! Seven toxin types are shared between lizards and snakes ! Later recruitment event facilitated diversification into complex and varied venom ! Fry et al., 2006, 2009, 2010 Fry et al., 2006, 2009, 2010 Diet and Location Diet and Geographic Variation !!Primary function of snake venom: to aid in the immobilization and/or digestion of prey !!Some prey confer greater resistance to snake venom !!Heritable variation of resistance to venom: co-evolutionary arms races between selection for increased venom toxicity in snakes and resistance in their prey. !!Venom composition subject to strong natural selection; venom diversity results from adaptation to specific diets. (Barlow et al., 2009;Daltry et al., 1996) 2 5/27/14 Venom Composition in Malayan Experimental Analysis Pitviper 1. Variation is explained by the geographical distance !!Researchers investigated intraspecific variation in venom between groups. composition among Malayan pitvipers. !!67 wild adult Malayan pitvipers were captured and venom 2. Variation in venom is due to close phylogenetic was collected. relationships among groups. !!Test subjects were collected from 36 separate locations 3. Variation in venom is associated with the geographical across Vietnam, Thailand, Malaysia, and Java. variation in diet. !!All samples were then used to create electophoretograms to draw comparisons. " (Daltry et al., 1996) (Daltry et al., 1996) " " " " !"#$%&#'' !! Neither spatial distance nor close phylogenetic relationships strongly Venomous or Toxic correlated with the variation in venom Venom: !! A strong correlation between venom composition & diet considering !! Requires a type of delivery system as mentioned: barb, geographical variation teeth, fangs, etc !! The evolution of venom highly influenced by the prey available to predators !! Venom/prey relationship heritable & not strictly influenced by environment: venoms of captive-bred pitvipers identical to their parents’ while on a different diet !! Venom is prey specific: Venom of arthropod-feeding snakes more toxic to scorpions than that of vertebrates-feeding snakes " " !! #$%&'()"*+"%',-".//012%'+&3"*+"%',-"40056" " Venomous or Toxic Odd examples Poisonous Feathers in Hooded Pitohui “Rubbish Toxic skin: Birds” ! Poison glands throughout the skin of some animals. ! !! The only case of a poison defense found !! Level of toxicity can be environmentally affected (dart frogs raised in amongst birds: Pitohuis. captivity aren’t toxic because they have a different diet than wild dart frogs). !! Poison found both in skin and feathers, not !! Selection pressures (i.e. predation) can also increase level of toxicity. much internally. Examples are dart frogs, rough skinned newts. !! Studies show that the toxin in the skin and feathers is very similar to that of dart frogs, found only in those two groups, yet arose independently in completely different areas of the world. (Brodie, 1968) (Dumbacher et al., 1992) 3 5/27/14 Homobatrachotoxin Venom in Mammals !! Shrews and other insectivores - have !! Very complex structure !! Randomly appeared in two genus of species: venom developed in saliva gland, pitohuis and dart frogs. poison through biting ! Small amounts can cause numbness and irritation ! in humans if passed through mucous membrane (like sucking on a scratch caused by the bird after !! Hedgehogs use a mix of saliva and capture). frog toxin to make some of their !! Homobatrachotoxin can kill smaller animals. spines toxic (secondarily venomous) !! It works by polarizing nerve and muscle cells by activating Na+ channels. !! Monotremes (Platypus) - males have poison sac and spur (Dumbacher et al., 1992) (Dufton, 1992) Oddest example - The Slow Loris !! Only known primate to form any type of toxin. Theory of !! Arguably venomous in that it uses it’s tongue to move toxin from gland on arm to combs (pockets) in teeth and poisons the origin predators by biting. !! Toxin is similar to cat allergens. of Slow !! Protect their young by coating them in the toxin. Loris Venom (Nekaris et al., 2013) (Nekaris et al., 2013) Molecular Evolution of Venom Change in Bioactive Surfaces • Cysteine rich support ! Scorpions: ~350 million years with no changes in ! ! structure anatomy •! “Molecular Lever” !! Venom active on gated sodium channels •! Disulfide bonds allow plasticity !! Multiple sites in neuromuscular system • Amino acid substitutions ! •! Formation of new #78&*9:+;"*+"%'-".//46" molecular exteriors #78&*9:+;"*+"%'-".//46" 4 5/27/14 Conclusion Questions !! Snakes: Role of Natural Selection as a driving force in the evolution of 1) Why does homobatrachotoxin’s ability to keep Na+ channels open disrupt venom remains contentious the action potential? Why would this lead to numbness, and possible !! Strong correlation between venom variation in the Malayan pit viper and death? variation in the diet of the species: adaptation for feeding on local prey !! “Red Queen Hypothesis”: resistance to venom among preys & predators 2) Kordis and Gubensek state, "At the molecular level, venom-encoding genes show extremely high rates of sequence evolution and an excess of nonsynonymous over synonymous of snakes; reciprocal selective pressure substitutions" !! Venom: A metabolically expensive resource: What does this statement suggest about the type of selective pressure these "! Several rattlesnakes: the amount of venom injected correlates with venom-coding genes may be under? the size of the prey "! Spiders & scorpions: evolved venom metering (Different amount of 3) Why did various organisms evolve different mechanisms and structures for venom injected based on the intensity/ duration of prey movement) delivery of venom? and pre-venom (metabolically inexpensive, pain inducing predator deterrent) (Casewell et al., 2013) Citation !! Barlow, A., C. E. Pook, R. A. Harrison, and W. Wüster. "Coevolution of Diet and Prey-specific Venom Activity Supports the Role of Selection in Snake Venom Evolution." Proceedings of the Royal Society B: Biological Sciences 276.1666 (2009): 2443-449. Web Of Science. Web. 23 May 2014. Image Citation !! Brodie, Jr, E. (1968) Investigations on the Skin Toxin of the Adult Rough-Skinned Newt, Taricha granulosa. Copeia, Vol. 1968 (2) 307-313 http://1.bp.blogspot.com/-rAkgLtmrOaw/T2cMLU2MaDI/AAAAAAAAAlU/iKSLbnLf9Aw/s1600/King-Cobra-Download-Wallpaper.jpg !! Casewell, N. R., Wuster, W., Vonk, F. J., Harrison, R. A., & Fry, B. G. (April 01, 2013). Complex cocktails: the evolutionary novelty of http://cherokeebillie.files.wordpress.com/2012/02/scorpion.jpg venoms. Trends in Ecology & Evolution, 28, 4, 219-229. http://soer.justice.tas.gov.au/2003/image/559/ilw/p-platypus_m.jpg !! Daltry, Jennifer C., Wolfgang Wüster, and Roger S. Thorpe. "Diet and Snake Venom Evolution." Nature 379.6565 (1996): 537-40. Web http://www.rosamondgiffordzoo.org/assets/uploads/animals/pdf/GreenBlackPoisonDartFrog.pdf of Science. Web. 23 May 2014. http://3.bp.blogspot.com/_2vua2t6H-5o/TK9bfsWdnkI/AAAAAAAAD_o/fqaz8dAUJIM/s1600/WASP+01.jpg !! Dufton, Mark J. (1992) Venomous Mammals. Pharmacology & Therapeutics, Volume 53 (2), 199–215 http://animalkingdomwonders.blogspot.com/2013/01/the-duck-billed-platypus.html, http://www.medtogo.com/scorpion-stings.htm http://archies.info/animals/green-poison-dart-frog/,
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