parasitism relationship between two organisms, where the parasite benefits at the expense of the...
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Parasitism
Relationship between two organisms, where the parasite benefits at the expense of the host (ant. mutualism)
50% of all living species are parasites
Every organism is susceptible to parasite infection once in its lifetime
Microparasites
Very small, often intracelluar, have short generation times, high rates of reproduction within the host, tendency to induce immunity. Typical infections are of short duration in relation to the normal life-span of the host.
Bacteria, viruses, protozoa, fungi
Macroparasites
Much larger than microparasites with much longer generation times. Reproduction occurs but reproductive products are shed. Immune response is usually density dependent and of short duration. Such infections are persistent with hosts often being continuously reinfected.
Ectoparasites
On the outside of the host feather, skin, hair, gills (permanent, temporarily)
No complete parasite existence (oxygen from outside the host)
Ticks, fleas, lice, mites, mosquitoes, bugs
Effect of parasites on their hosts: morbidity and mortality
Microparasites Acute infections over a short term, can have a
major influence on host mortality Macroparasites
More commonly chronic infections, cause less mortality but more morbidity (i.e. pathogenicity leading to reduced fitness)
Mortality in intermediate hosts
Biological invasions – an introduction
Closely connected to human travel and trade (increased by 50% since 1990)
Biggest threat to worldwide biodiversity besides habitat loss and fragmentation
Cause for 40% of historic extinctions
Special danger to island ecosystems
Clavera & García-Berthou 2005
Introduced species: nonindigenous to a given area, transported by human
activity usually localized distribution, possibly rare can include garden and farm animals
Invasive species: non-indigenous species (NIS) that can maintain an
established population causes economic or ecological harm or is likely to do
so in the future
Biological invasions – an introduction
Typical introduction routes: Intentional introductions:
Domestic, farming or hunting animals Farm or ornamental plants Biological control experiments
Unintentional introductions: Transport of plant seeds, small insects and other
invertebrates with other goods Marine organisms via ballast water, fouling Pathogens
Biological invasions – an introduction
Biological invasions – an introduction
100 of the worst invaders, selected by the Invasive Species Specialist Group (ISSG) of the IUCN:
Lowe et al. 2004
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Ecological consequences – Lake Victoria Nile perch (Lates niloticus)
introduction 1954 Massive spread in
1980s Extinction of >200
endemic fish species (mainly cichlids)
Nile perch
Endemic cichlids
Altered fish industry: smoking instead of sun drying
Deforestation, soil erosion, desertification
Increased nutrient levels promoted water hyazinth (Eichhornia crassipes) invasion
Ecological consequences – Lake Victoria
Ecological consequences – Hawaii Avian malaria (Plasmodium
relictum) introduced with pet birds
But: vector necessary for spread
1826: introduction of the southern house mosquito (Culex quinquefasciatus)
Malaria spread among bird populations
Honeycreeper with malaria-transmitting mosquitos
nucleus
Plasmodium
High mortality due to lack of resistance
Contributed to the extinction to >10 native bird species
Limits geographic distribution of birds
Hawaiian honeycreepers
Ecological consequences – Hawaii
Control difficult due to remote habitats
Mosquitos benefit from another invader: feral pigs (Sus scrofa)
Water-filled wallows serve as breeding locations for mosquitos
Ecological consequences – Hawaii
Anguillicoloides crassus
Der Nematode ist der Parasit:Anguillicola crassus
Natürliche Bedingungen: saugt Blut in der Schwimmblase des Japanischen Aals (Anguilla japonica).
Globalisierung: hat Aalarten anderer Kontinente, die mit dem Parasitenkeine Koevolution durchlaufen haben, als naive Neuwirte
kolonisiert. Wurde selbst nicht als Wirt von Parasiten oder Pathogenen beschrieben.
Natural and introduced range of A. crassus. Red area: distributional range of Anguilla- species naturally infected by A. crassus (Anguilla japonica) and colonized eel species in Europe, America and Africa
Biogeographical studies: examine native and introduced
populations of invaders
Community studies: compare native and introduced
species within the same community
How is invasion success determined?The enemy release hypothesis (ERH):
Confirmed release from
enemies, impact on invasion
suggested
Invaders do not have less
enemies than the native species
Colautti et al. 2004
Hypotheses opposing the ERH: Propagule/sampling bias Community interactions or abiotic factors
reverse/reduce enemy effects Effects of newly acquired enemies:
NIS are naive hosts Genetic bottleneck leads to higher susceptibility
How is invasion success determined? The enemy release hypothesis (ERH):
Ticks: Acari, Ixodida
About 900 species in two major families: Argasidae (ca. 180 spp.) and Ixodidae (ca.720 spp.)
Almost all species spend much more time free-living in the environment than on their hosts
About 5-10% of species are of medical or veterinary significance
Three families
Argasidae The soft ticks (Lederzecken)
Ixodidae The hard ticks (Schildzecken)
Nuttalliellidae A monospecific family (Nuttalliella namaqua)
The lifecycle of ixodid ticks
Three-host ticks
Larvae Nymphs Adults
Transstadial transmission
Transovarial transmission
Eggs
Ticks as vectors
Ticks are the most important vectors of pathogens to domestic animals and the second most important to humans
Tick-borne diseases
Viral (e.g. CCHF, TBE) Bacterial (e.g. Borrelia, Ehrlichia,
Rickettsia) Protozoan (e.g. Babesia, Theileria)
Environment and hosts
Tick distribution appears to be largely controlled by the environmental conditions available to the free living stages (eggs, larvae, nymphs and adults), especially temperature and humidity
Host availability may also play a role but many economically and medically important species use a wide variety of hosts (e.g. Ixodes ricinus, Amblyomma variegatum)
Tick distributions and global change Substantial changes in various species, e.g.
I. ricinus in Europe Evidence that these may be due to climatic
changes (e.g. Finland, Czech Republic) Also suggestions that political, social and
habitat changes may be involved (Randolph 2004)
Food-borne trematodes
Opistorchis viverrini, the small liver fluke Mekong area: Thailand, Laos, Cambodia, Vietnam 10 million people infected in Thailand and Laos
alone Infection by eating uncooked freshwater fish from
the cyprinid family
At the taxonomic level: how many species are present?
Pathogenicity
Causes liver and bile duct problems; blockage
One of the two species classifies by WHO as a carcinogen
Long-term infection can lead to cholangiocarcinoma (bile duct and later liver cancer)
Problem
Symptoms and disease prevalence in the human population in the northeast of Thailand and southern Laos vary geographically
Does this variation have a population genetic basis: i.e. due to variation in O. viverrini