Topic 13.pdf

1 Biology 3030 Evolution and Systematics Topic 13: Coevolution Coevolution ?There are about 750 species of figs ?Each fig species is polinated exclusively by a minute, agaonid wasp ?Each wasp depends on a single species of fig ?Wasp and fig phylogenies are highly congruent ?So it apears they speciated in paralel The Nature of Coevolution ?Coevolution = reciprocal genetic change in interacting species, owing to NS imposed by each other ?Includes several forms ?Specific coevolution - evolutionary arms race betwen predators and prey 2 The Nature of Coevolution ?Guild (difuse) coevolution - several species involved and their efects are not independent ?Like genetic variation in resistance to two diferent species of parasite ?Escape-and-radiate coevolution - a species evolves a defense against enemies and forms a diverse clade ?Plants evolved chemical defenses against insects and diversified ?Insects diversified to eat them Phylogeny ?Coevolution also aplied to history of paralel diversification ?Revealed by concordant phylogenies ?Endosymbiotic bacteria and aphids ?Highly concordant ?Rarely is it this neat Phylogeny ?Chewing lice and pocket gophers ?Largely concordant ?But some host switching ?Discordance can also be caused by extinction of parasite lineages ?May just reveal ancient asociations ?Leaf betles, long-horn betles and wevils mainly fed on cycads and conifers ?They are primitive groups feding on pri itive plants 3 Enemies and Victims ?Predators and parasites have wonderful things to capture prey ?Equaly impresive are the countereasures ?You can imagine a never- ending ars race, ?But, defenses have costs ?Secondary compounds in plants can take up 10% of energy budget ?Cucurbitacins enhance resistance of cucumbers to spider mites but atract cucuber-feding betles Examples of Predator-Prey Coevolution ?The Mesozoic saw an increase in efective molusc predators ?And thicker shels and spines in the moluscs ?Rough-skined newts can have tetrodotoxin ?Garter snakes have resistance in sympatric populations Examples of Predator-Prey Coevolution ?Plants in the carot family have toxic furanocouarins ?Black swalowtail buterflies have high activity of detoxifying enzymes and can fed on the ?Hosts wil expel cucko eggs ?So cuckos have evolved eg mi icry ?And prefer to lay egs in their genotype match HostCuckoo Artificial 4 Infectious Disease and Virulence ?Parasites are pased verticaly - to ofspring ?Or Horizontaly - betwen individuals via ?Environment - rhinoviruses and snezing ?Contact betwen hosts - venereal diseases ?Or vectors (cariers) such as mosquitoes and malaria ?Efects vary ?Virulent - reduce survival or reproduction ?Degre varies and evolves Infectious Disease and Virulence ?European rabits were introduced into Australia ?The myxoma virus from a South Aerican Rabit was introduced to kil them ?Rabits gained resistance ?But virulence of virus also decreased ?A limit to virulence because a parasite doesn?t want to kil host before it is transmited Virulence in Natural Populations ?Daphnia parasitized by microsporidian ?In pairs of infected and uninfected Daphnia ?The more parasites in one, the more likely the other wil be parasitized ?Produced more spores and caused greater mortality from their own or close populations ?The oposite of what you would think 5 Virulence in Natural Populations ?New Zealand freshwater snail has sexual and parthenogenic individuals ?Trematodes sterilize the snail ?Trematodes beter able to infect snails from their own populations ?In a lake with mostly asexual snails, diferent clonal genotypes varied over five years ?Infection rate peaked a year after genotype peaked ?Rare snail genotypes are more resistant to prevalent parasite genotype Mutualisms ?Interactions betwen species that benefit both species ?Symbiotic mutualisms - inately asociated over much of their lifeties ?Think of flowers and their polinators Darwin predicted their must be a moth on Madagascar to match this orchid with a 30 cm nectar spur. A century later, sphinx moths were found with 24 cm tongues Mutualisms ?Yuca Moths lay egs on Yucas ?Larvae consume some of the seds ?Adults spread polen ?Moths usualy lay just a few egs in each flower ?Plants can only produce seds in about 15% of flowers ?Rest are aborted ?So, moth can?t lay to many egs or egs wil be aborted with seds 6 Mutualisms ?But, mutualisms are prone to cheating ?Some orchids secrete no nectar but atract polinators with pheromones ?Two lineages of yuca moths do not polinate ?And lay enough egs to consume al seds ?Circumvent abortion response by laying egs after the critical abortion period Competitive Interactions ?Darwin sugested that competition would cause selection for divergence in resource use ?A major reason in the origin and divergence of species ?Sympatric species difer in resource use ?Probably evolved, at least in part, due to competition Competitive Interactions ?If individuals difer in a trait like bil depth ?Two species are variable and overlap a lot ?Intra- and interspecific competition ?If there is a broad range of resources available ?Extremes phenotypes have les intraspecific competition ?Diversifying selection 7 Competitive Interactions ?Character displacement - species more diferent when together ?Ecological Release - a species has greater variation in resource use and phenotype when alone ?Only wodpecker on Hispaniola has greater sexual dimorphism in bil length ?Than related continental species that live with other wodpeckers ?The sexes difer in where they forage Multispecies Interactions ?Thre-species selection mosaic - crosbils, pines, squirels ?Squirels eat pine seds - prefer narow cones with lots of seds ?Impose selection on wider cones with fewer seds Multispecies Interactions ?Red crosbils fed only on pine seds with their weird bils ?They are much more abundant in the few mountain ranges where squirels are absent ?Crosbils les efective in larger, wider cones with thicker scales ?Which is what is sen in these places ?Crosbils in these places have larger, deper bils 8 Multispecies Interactions ?Defensive mi icry is where one or more species gain protection from predators from their reseblance to one another ?Batesian Mimicry - palatable species resembles an unpalatable one ?Mülerian Mimicry - two or more unpalatable species resemble one another Red-spotted Purple Butterfly Palatable Pipevine Swallowtail Butterfly Unpalatable Multispecies Interactions ?Mimicry rings - groups of species that benefit from defensive mi icry ?Include strongly unpalatable and mildly unpalatable species ?May include some palatable Batesian mi ics ?May be several rings in one area ?Batesian mi ics may be polymorphic, each resembling a diferent unpalatable odel ?Mülerian mi ics almost never polymorphic within a population, but can be betwen populations Multispecies Interactions ?Predators more likely to avoid a phenotype if it recently had a bad experience ?If it just had a god experience with a phenotype, it wil be more likely to eat that phenotype again ?The more Batesian mi ics, the more likely predators wil atack ?So, Batesian mi ics are rare and polymorphic ?A new, rare, mi ic coloration wil be selected for in Batesian mi ics - frequency dependent selection ?Strong stabilizing selection for Mülerian mi ics Jonathan Armbruster Topic13 Coevolution.ppt