The biotical interrelation of living organisms

SIMBIOSIS – Any organism that spends at least a portion of its life very closely

associated with another living organism of a different spieces is known as a

symbiont or symbiote, and the relationship is known as symbiosis.

There are four types of symbiosis: commensalism, phoresis, mutualism, parasitism.

Commensalism - A type of symbiosis in which spatial proximity allows the

commensal to feed on substances captured or ingested by the host, but the two

partners can survive independently.

Phoresis - In this type of symbiotic relationship, the phoront, usually smaller than

the host, is mechanically carried by the host, but unlike in commensalism there is no

dependence in procurement of food between the partners.

Mutualism – This category of symbiosis is an association in which the mutualist and

the host depend on each other physiologically – ties of bilateral interdependence.

Parasitism – A parasite is an organism that is physiologically dependent on the

host. Parasites derive the nutrients they need directly from the host, usually from

blood, lymph, cytoplasm and tissue fluids, or host-digested food. For many

parasites, their host is also their home, in some cases temporary, and permanent in

others.

Commensalism - a type of symbiosis in which spatial proximity

allows the commensal to feed on substances captured or ingested by

the host, and it literally means 'eating at the

same table'.

The relationship between hermit

crab and sea-anemone is an

excellent example of

Commensalism. Hermit crab lives

inside empty shell of mollusc. The

sea-anemone inhabits the outer

surface of shell. Sea-anemone is

transported form place to place to

get food by crab. The sea-anemone

also gets food captured by crab. The

stinging cells of sea-anemone

protect the hermit crab from

enemies. Thus, both partners are

benefited.

Hermit crab and sea-anemone

The commensal shrimp Periclimenes imperator on

Chromodoris tinctoria,

Emperor shrimp on a

large sea-slug

A titan triggerfish creates feeding

opportunities for smaller fish by moving

large rocks too big for them to shift

themselves

Moss is considered a type of

commensalism because it benefits

from the trees it grows on but the

tree is not affected by the moss.

Moss growing on trees benefits

from being raised above the forest

floor and can easily grow and

spread on the trees.

An emperor shrimp

(Periclimenes imperator)

hitches a ride on a purple-

edged large seaslug

ceratosoma nudibranch

(Ceratosoma tenue).

Lembeh Strait, Indonesia.

Shark and remora fish

Phoresis - In this type of symbiotic relationship, the phoront,

usually smaller than the host, is mechanically carried by the host, to

the places, where are better conditions to live and to feed but unlike

in commensalism there is no dependence in procurement of food

between the partners. The host is required to serve as ‘transporter’

only . Sometimes the host can accidentally protect phoront from

potential enemies.

The mites on the head and body of

the Nicrophorus beetle

Mutualism – This type of symbiosis is an association in which the

mutualist and the host depend on each other physiologically – and

each individual derives a fitness benefit (nutritional, hygienic

(sanitary), protectional).

Clown anemonefish in sea-

anemone, Pacific Ocean.

Parazitizmas – A symbiotic

relationship in which one

organism (the parasite) benefits

and the other (the host) is

generally harmed. Parasites

derive nutrition from their host

and may also gain other benefits

such as shelter and a habitat in

which to grow and reproduce.

The Forms of Parasitism. Classification of Parasites

Plasmodium malariae Dust mite

According to the parasites’ level of dependence

on the host ---

They can be grouped into obligate and facultative.

• Obligate parasites are physiologically dependent

on their hosts and cannot live and/or breed

independently.

• Facultative parasites are essentially free-living

organisms that are capable of becoming parasitic

if placed in a situation conductive to such a mode.

Entamoeba histolytica

Hartmannella vermiformis

Infection of Acanthamoeba sp.

May cause ocular keratitis

Acanthamoeba sp.

Larvae visible after manual

opening of the eye.

Oral myiasis caused by the invasion of

tissues by maggots. It is attributed to

poor oral hygiene, alcoholism, senility.

The larvae of common

(House) fly may cause

myasis

Furuncular myiasis

Common (house) fly, Green fly,

Sarcophage (flesh) fly Larvae (maggots)

Mosquito female

Trichinella spiralis

According to the duration of time the parasites interact with

the host ---

They are classified into temporary and permanent

• Temporary (or periodic) parasites –

include blood-sucking arthropoda. They

spend only a part of their lifetime interacting

with the host, most commonly when feeding.

•Permanent parasites are closely

connected to the host for all or most

of their life cycle and cannot

develop freely away from the host.

Head lice Pork tapeworm

According to the location of the parasites in the host ---

they may be classified as ectoparasites or endoparasites

• Ectoparasites act on the surface of the host, or superficially

embedded in it. Some actualy reside there, while others only come

thereto feed.

• Endoparasites live inside the host, in its internal cavities, organs,

tissues and cells.

• location well-defined

• location is not well-defined

According to the specificity of their life cycle,

parasites – especially helminths - are classified into three groups:

bioparasites, geoparasites, contact parasites.

• Bioparasites (biohelminths) – change their hosts, with different

developmental stages occuring in different host species.

• Geoparasites (geohelminths) – do not usually change host

species as they develop, but a certain stage of the parasite must

develop in the outside environment (soil).

• Contact parasites (contact helminths) – develop inside a single

host, and are passed from host to host through direct contact

between hosts.

The adult flukes deposit fully developed

eggs that are passed in the feces (1).

After ingestion by a suitable snail (first

intermediate host) (2), the eggs release

miracidia (2a), which undergo in the snail

several developmental stages

(sporocysts (2b), rediae (2c), cercariae

(2d). Cercariae are released from the

snail (3) and penetrate freshwater fish

(second intermediate host) (4), encysting

as metacercariae in the muscles or

under the scales (4a). The mammalian

definitive host (cats, dogs, and various

fish-eating mammals including humans)

become infected by ingesting

undercooked fish containing

metacercariae. After ingestion, the

metacercariae excyst in the duodenum

(5) and ascend through the ampulla of

Vater into the biliary ducts, where they

attach and develop into adults, which lay

eggs after 3 to 4 weeks (6). The adult

flukes (O. felineus: 7 mm to 12 mm by 2

mm to 3 mm) reside in the biliary and

pancreatic ducts of the mammalian host,

where they attach to the mucosa.

4

4a

Life cycle of Biohelminths

Adult worms (1) live in the lumen of the

small intestine. A female may produce

approximately 200,000 eggs per day,

which are passed with the feces

(2). Unfertilized eggs may be ingested

but are not infective.

Fertile eggs embryonate and become

infective after 18 days to several weeks

(3), depending on the environmental

conditions (optimum: moist, warm,

shaded soil).

After infective eggs are swallowed (4),

the larvae hatch (5), invade the

intestinal mucosa, and are carried via

the portal, then systemic circulation to

the lungs (6). The larvae mature further

in the lungs (10 to 14 days), penetrate

the alveolar walls, ascend the bronchial

tree to the throat, and are swallowed

(7). Upon reaching the small intestine,

they develop into adult worms

(1). Between 2 and 3 months are

required from ingestion of the infective

eggs to oviposition by the adult

female. Adult worms can live 1 to 2

years.

Life cycle of Geohelminths

Eggs are deposited on perianal folds (1). Self-

infection occurs by transferring infective eggs to

the mouth with hands that have scratched the

perianal area (2).

Person-to-person transmission can also

occur through handling of contaminated

clothes or bed linens.

Enterobiasis may also be acquired through

surfaces in the environment that are

contaminated with pinworm eggs (e.g., curtains,

carpeting). Some small number of eggs may

become airborne and inhaled. These would be

swallowed and follow the same development as

ingested eggs. Following ingestion of infective

eggs, the larvae hatch in the small intestine (3)

and the adults establish themselves in the colon

(4). The time interval from ingestion of infective

eggs to oviposition by the adult females is about

one month. The life span of the adults is about

two months. Gravid females migrate nocturnally

outside the anus and oviposit while crawling on

the skin of the perianal area (5). The larvae

contained inside the eggs develop (the eggs

become infective) in 4 to 6 hours under optimal

conditions (1).

Retroinfection, or the migration of newly hatched

larvae from the anal skin back into the rectum,

may occur but the frequency with which this

happens is unknown.

Life cycle of Contact helminths

Hosts and Their Classification

A host is an organism in or on which a parasite lives, and at

whose expense the parasite feeds.

Some species of parasites move from one host to another in

the course of their development. This is named as host change.

In terms of host

change, hosts can be

classified into:

• Definitive or main

• Intermediate

• Transfer or paratenic

• Reservoir

• Accidental or unsuitable.

Definitive host(Fish eating animals and birds)

Adult fish tapeworm

Egg

Free-swimming

ciliated

Coracidia

1-st Intermediate

host(Crustacean)

Procercoid

2-nd Intermediate

host(Small fish)

Plerocercoid

Transfer (paratenic) host(Predatory fish)

Plerocercoid

Example of

Parasite life cycle

Definitive host( Dog, cat)

Adult helminth

Egg(in faeces)

Raidos ciklo

pavyzdys

External environment

Mature egg

Accidental

host(Human)

Larval stageLarval stage

Adult lancet fluke

Dicrocoelium dendriticum –

Sexually mature stage – marita

Definitive hosts are those in which the parasite can

attain sexual maturity and/or multiply sexually

Intermediate hosts are essential to the parasites’

development, but in them the parasites do not

become sexually mature, though asexual

reproduction may take place.

miracidium

I-st sporocyst

II-nd sporocyst

cercaria

Cercaria in snail

slime balls

metacercariaI-st intermediate host –

terrestrial snail

(Zebrina, Helicella gen.)

II-nd intermediate host –

ant

(Formica gen.)

egg

Transfer (paratenic) host, is not obligate to

the parasite life cycle, but serves simply as a

convenient vehicle towards the definitive

host under otherwise unfavorable

circumstances.

Larva stage

in fish A

Larva stage

in fish B

Fish B

Larva stage transfer

from fish A into fish B

Reservoir hosts are those in which parasites do not

reproduce, but in which parasites can reside,

survive, and be passed on to other hosts.

Accidental hosts are those in which a parasite

enters by accident rather than by design. There it

can neither normally develop nor complete its life

cycle.