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Coevolution : The joint evolution of two species with close ecological relationships. -- evolution of each is partly dependent on the other. -- includes parasite-hosts, mutualisms -- endo and ectoparasites. Parasites include: viruses bacteria fungi invertebrates
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Coevolution: The joint evolution of two species with close ecological relationships • -- evolution of each is partly dependent on the other -- includes parasite-hosts, mutualisms -- endo and ectoparasites
Parasites include: viruses bacteria fungi invertebrates vertebrates (social parasitism) Many are highly specialized to only one host species e.g, bird lice, botflies Plant mite Human head lice
Host defenses against parasites --Biochemical (e.g., antibodies) --tissue growth to contain parasite (e.g., galls)
Galls have many forms and shapes Over 2000 gall-forming insects in U.S., most are gall wasps Most galls are on oaks (60%) Insect feeds mainly on gall tissue
To eradicate parasites -- gene-for-gene response -- multiple defenses at once (not really possible) -- turn it into a mutualism
Social parasitism in birds cuckoos cowbirds some ducks warbler nest with two cowbird eggs Brown-headed cowbird
Oropendolas and Cowbirds parasitism to mutualism
Mutualisms: coevolved systems where two species interact to the benefit of both -- e.g., Rhizobium, Mycorrhiza • -- symbiotic and nonsymbiotic -- obligate and facultative Landmark paper on coevolution and mutualism in ecology: Erhlich, Paul and Peter Raven. 1964. Butterflies and plants: a study in coevolution. Evolution 18: 586-608.
Mutualisms can be dynamic and switch to parasitism under certain environmental circumstances e.g., Rhyzombium bacteria
Ants and acacia trees: a symbiotic obligate mutualism These ant-acacia mutualisms are found primarily in tropical South and Central America, Africa 32 species of ants have this relationship in tropical forests in South America
Thorns to deter herbivory but hollow to provide home for the ants Nectar glands or food bodies provided to feed ants In return, ants attack herbivores, parasites, and other plant competitors
Research on this system suggests that the ants were ‘trapped’ into servitude by the sugary nectar Makes them addicted to only that nectar, so stay and protect the plant Also has been shown that one ant species can replace another on a tree over time, a dynamic system Pollination occurs by keeping ants off the flower
Honey badger and honeyguide: a nonsymbiotic facultative mutualism
Pine cone seeds have co-evolved with predators Pine seeds evolved from small, wind dispersed form to larger, heavier form (bird dispersed)
Many species of pines have co-evolved with jays as ‘scatter hoarders’ who now disperse the large seeds long distances Pensendorfer et al. 2016
Crossbills have found a way to get the seeds first https://www.allaboutbirds.org https://www.bbc.co.uk/programmes/p00m8cl6
Dodo Mauritius Island Calvaria trees Nonsymbiotic obligate mutualism (for tree)
Mutualisms are not always ideal -- not always a ‘happy’ relationship -- e.g., yucca moths pollinate plants, larvae feed on seeds -- too many larvae, flower dies and both species lose out -- puts constraints on fecundity
Now know that mutualisms and other co-evolved systems are common in nature -- functional links above ground to below ground -- nutrient cycling and ecosystem function often dependent on these relationships Plant interactions above and below ground
Quiz • What is co-evolution? What types of interspecific interactions would this include? • Why can’t hosts always eradicate a parasite and what is the gene-for-gene response? • What is social parasitism and give an example? • What is meant by obligate and facultative mutualisms, and those that are symbiotic and nonsymbiotic? • How might a parasite-host relationship eventually become a mutualism? Give an example.
Specialist flowers: large nectar reward Columbine and hummingbirds
Specialist flowers: use smell to pollinate Orchid and flies
Orchid using smell and sugary nectar to attract bats
