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Evolution Lecture 28 Chapter 18 Topics for today: Coevolution • Enemy-victim • Predator-prey • Fossil record • Extant populations • Host-parasite • Mutualism • Competition Evolution in Enemy-Victim relationships Evidence for predator-prey coevolution 1. Predator-prey from fossil record o Mesozoic fish evolved ability to crush and rip shells o Diversity of shell form in molluscs increased o Thicker shell margins 1. Protected aperature o Fig. 18.9 2. Predator-prey from extant populations o Potent neurotoxin TTX in skin o One newt has enough toxin to kill 25,000 mice o Population on Vancouver Island has almost no TTX o Garter snakes that are sympatric with toxic newts feed on them Predictions regarding resistance? o Garter snake o Rough-skinned newt o Garter snakes in sympatry with toxic newts have higher resistance to TTX Fig. 18.10 Evidence for predator-prey coevolution Infectious disease and their hosts o Level of virulence depends on both host and parasite o Common idea is virulence should decline Why? o Evolution of resistance o Loss of virulence Ro = bN v+d+r Ro = fitness of parasite (number of new hosts infected) b = probability of infection N = number of hosts available v = mortality rate of hosts due to disease d = mortality rate of hosts due to other causes r = rate of recovery of hosts Example: Coevolution in contemporary time o European rabbit introduced in to Australia in1859 o By 1880’s became major pest o 1950 myxoma virus introduced o Mosquito vectors spread across continent o Rabbit population drastically declined Test for evolution of resistance? o Rabbits tested against original virus strain for susceptibility after each disease epidemic r Fig. 18.12 Test for loss of virulence? o Virus sampled from field over time and tested on susceptible rabbits o Original virus killed rabbit in 6-10 days o Less-virulent virus kills rabbit in 21-28 days o Milder strain more effective in infecting rabbits ( v) o Spreads more rapidly than virulent strains ( Ro) Fig. 18.12 Is the hypothesis of the evolution of benign parasite naïve? o Gut parasite o Spores released in feces o Tested pairs Local Nonlocal o Parasites locally adapated o Contradicts prevailing hypothesis Fig. 18.13 Evolution of mutualisms o Benefit both species o Can result in extreme adaptations Movie clip: Nice example of: 1. Coevolution leading to extreme adaptation 2. Diffuse coevolution that involves multiple participants 3. Coevolution in competitive interactions Hover fly How do mutualisms evolve? Example of yucca and yucca moth o Female pollinates with specialized mouth parts o Lays a few eggs in each flower o Leaves scent marking o Larvae survive only in pollinated flowers o Hatch, consume developing seed, pupate Many incremental changes over time o Parasitize flower for larval resources o Pollinate incidentally o Those that pollinate have higher larval survival o Evolve structures to aid in intentional pollination o Plant protects itself from over utilization o Moths evolve cheating How can this be tested? o Map traits onto a phylogeny o Includes more ancestral moths Evolution of competitive interactions o Competition for resources drives evolution of divergence in resource use o Major cause of origin and divergence of species Fig. 18.18 Example of resource partitioning through spatial segregation o Bumble bees use that use flowers of same corolla length are spatially segregated by elevation Fig. 18.17 Example of character displacement o Divergence due to competition o Sympatric populations of two species differ more than allopatric populations Fig. 9.27 Example of ecological release from character displacement o Bill size correlated with feeding behavior and resource use o Competition with other woodpecker species on continent o No competition on island Fig. 18.19 Is character displacement predictable? Not always o 56 species of lizard in co-occur in the Great Victoria Desert of Australia o 20 species in Kalahari semidesert of southern Africa o 6-17 species in similar North America deserts Sometimes o Species on different islands have evolved similar ways to avoid competition Fig. 18.20