Evolutionary ecology Parasitism

1 evolutionary ecology

1.1 coevolution , cospeciation
1.2 coevolution favoring mutualism
1.3 competition favoring virulence
1.4 modifying host behavior
1.5 parasite-stress theory
1.6 trait loss
1.7 secondary sex characteristics
1.8 parasite-host assemblages
1.9 extended phenotype
1.10 value
1.11 quantitative ecology

evolutionary ecology

restoration of tyrannosaurus holes possibly caused trichomonas-like parasite

parasitism has arisen independently many times. depending on definition used, many half of animals have @ least 1 parasitic phase in life cycles, , frequent in plants , fungi. free-living animals host 1 or more parasitic taxa. harder demonstrate fossil record, example holes in skulls of several specimens of tyrannosaurus may have been caused trichomonas-like parasites.

coevolution , cospeciation

a parasite undergoes co-speciation host. example between simian foamy virus (sfv) , primate hosts. phylogenies of sfv polymerase , mitochondrial cytochrome oxidase subunit ii african , asian primates found closely congruent in branching order , divergence times, implying simian foamy viruses co-speciated old world primates @ least 30 million years.

the presumption of shared evolutionary history between parasites , hosts can elucidate how host taxa related. instance, there has been dispute whether flamingos more closely related storks or ducks. fact flamingos share parasites ducks , geese taken evidence these groups more closely related each other either storks. however, evolutionary events such duplication or extinction of parasite species (without similar events on host phylogeny) erode similarities between host , parasite phylogenies. in case of flamingos, have similar lice of grebes. flamingos , grebes have common ancestor, implying cospeciation of birds , lice in these groups. flamingo lice switched hosts ducks, creating situation had confused biologists.

coevolution favoring mutualism

the gram-negative bacterium wolbachia within insect cell

long-term coevolution leads relatively stable relationship tending commensalism or mutualism, as, else being equal, in evolutionary interest of parasite host thrives. parasite may evolve become less harmful host or host may evolve cope unavoidable presence of parasite—to point parasite s absence causes host harm. example, although animals infected parasitic worms harmed, , therefore parasitized, such infections may reduce prevalence , effects of autoimmune disorders in animal hosts, including humans. in more extreme example, nematode worms cannot reproduce, or survive, without infection wolbachia bacteria.

lynn margulis , others have argued, following peter kropotkin s 1902 mutual aid: factor of evolution, natural selection drives relationships parasitism mutualism when resources limited. process may have been involved in symbiogenesis formed eukaryotes intracellular relationship between archaea , bacteria, though sequence of events remains largely undefined.

competition favoring virulence

competition between parasites can expected favor faster reproducing , therefore more virulent parasites, natural selection. parasites life cycle involves death of host, exit present host , enter next, evolve more virulent, , may alter behavior or other properties of host make more vulnerable predators.

however, among competing parasitic insect-killing bacteria of genera photorhabdus , xenorhabdus, virulence depended on relative potency of antimicrobial toxins (bacteriocins) produced 2 strains involved. when 1 bacterium kill other, other strain excluded competition. when caterpillars infected bacteria both of had toxins able kill other strain, neither strain excluded, , virulence less when insect infected single strain.

conversely, parasites reproduction largely tied host s reproductive success tend become less virulent or mutualist, hosts reproduce more effectively.

the protozoan toxoplasma gondii facilitates transmission inducing behavioral changes in rats through infection of neurons in central nervous system.


modifying host behavior

some parasites modify host behavior in order increase transmission between hosts, in relation predator , prey (parasite increased trophic transmission). example, in california salt marshes, fluke euhaplorchis californiensis reduces ability of killifish host avoid predators. parasite matures in egrets, more feed on infected killifish on uninfected fish. example protozoan toxoplasma gondii, parasite matures in cats can carried many other mammals. uninfected rats avoid cat odors, rats infected t. gondii drawn scent, may increase transmission feline hosts.

parasite-stress theory

parasites infect hosts within same geographical area (sympatric) more effectively. phenomenon supports red queen hypothesis, states interactions between species, such host , parasites, lead constant natural selection coadaptation. parasites track locally common hosts phenotypes, parasites less infective allopatric hosts, different geographical regions. when populations of lake snails exposed 2 pure parasites (digenetic trematode), whether sympatric parasites, allopatric parasites or mixture, parasites more effective in infecting sympatric snails allopatric snails. parasites apparently adapted infect local populations of snails.

trait loss

bed bug, cimex lectularius, flightless, many insect ectoparasites.

parasites able exploit hosts variety of functions. many insect ectoparasites including bedbugs, batbugs, lice , fleas have lost ability fly, relying instead on hosts transport. trait loss more widespread among parasites.

secondary sex characteristics

parasitism has been suggested part of explanation of evolution of secondary sex characteristics in breeding male animals, such plumage of peacocks , manes of male lions. argument female hosts select males breeding based on such characteristics because act honest signals of costly handicaps. possible mechanism this, suggested ivar folstad , andrew karter, male hormone testosterone encourages growth of secondary sex characteristics such manes, @ price of reducing animal s immune defences.

the parasitic barnacle sacculina carcini (highlighted) attached crab

parasitic crustaceans such peltogaster carvatus , sacculina cause damage gonads of host crabs. in case of sacculina, testes of on 2 thirds of crab hosts had degenerated sufficiently these male crabs have gained female secondary sex characteristics such broader abdomens, smaller claws (chelae) , egg-grasping appendages. trematode zoogonus lasius causes parasitic castration of intertidal snail ilyanassa obsoleta; other trematodes directly or indirectly castrate other species of snail.

parasite-host assemblages

parasite ecology complex, involving hosts have multiple parasites (multi-parasite hosts), parasites have multiple hosts (multi-host parasites), , competition within host. these interactions affect parasite , host reproduction , therefore evolution, including of virulence of parasites , of methods of transmission. reviewing field, t. rigaud , colleagues noted in 2010 among outcomes demonstrated empirically multiple infection can affect virulence, , can trigger evolutionary change; parasites involved in same host may have contrasting transmission modes; , assemblages of multiple parasites can more virulent expected each individual parasite. rigaud , colleagues consider trade-offs of virulence among hosts (that adaptation higher virulence in 1 host means lower virulence in others), predicting when there many hosts, outcome non-specialist parasites relatively low virulence. hosts differ in quality, rigaud , colleagues predict parasites should become optimally virulent in primary host. on other hand, predict more diverse host community, lower incidence of parasites should be, because infecting hosts unsuitable or resistant means loss of parasites (wasted transmission).

extended phenotype

the evolutionary biologist richard dawkins argued in 1989 book organisms have extended phenotype consists not of expression of own genes, but, among other things (such artefacts), of of parasites. this, suggested, apply not endoparasites such cuckoos briefly come contact hosts.

value

although parasites considered harmful, eradication of parasites not beneficial. parasites account @ least half of life s diversity; perform important ecological role (by weakening prey) ecosystems take time adapt to; , without parasites, organisms may tend asexual reproduction, diminishing diversity of sexually dimorphic traits. parasites provide opportunity transfer of genetic material between species. on rare, significant, occasions may facilitate evolutionary changes not otherwise occur, or otherwise take longer.

although parasites omitted in depictions of food webs, occupy top position. parasites can function keystone species, reducing dominance of superior competitors , allowing competing species co-exist.

many parasites require multiple hosts of different species complete life cycles , rely on predator-prey or other stable ecological interactions 1 host another. in sense, parasites in ecosystem reflect health of system.

quantitative ecology

a single parasite species has aggregated distribution across host individuals, means hosts harbor few parasites, while few hosts carry vast majority of parasite individuals. poses considerable problems students of parasite ecology, renders parametric statistics invalid. log-transformation of data before application of parametric test, or use of non-parametric statistics recommended several authors, can give rise further problems, quantitative parasitology based on more advanced biostatistical methods.