Arthropod Adaptation to Parasitism

Parasitic arthropods

several independent lineages of arthropods have evolved to be parasites of vertebrates

Parasitism

organism (parasite) derives some benefit from a relationship with and to the detriment of another organism (host)

Host provides…

food (blood, lymph, body secretions, skin debris, hair, feathers)

suitable environment (warmth, moisture, protection)

Obligatory parasite

dependent on the host for continued life or to complete life cycle

time spent on host may vary

needs host no matter what

Facultative parasite

may feed or live only occasionally on a host

not entirely dependent on the host for survival

Parasitism may occur in…

one or more life stages

Parasitic arthropods

chiggers, mosquitoes, ticks

Chiggers

only feed on vertebrates as larvae

Mosquitoes

only feed on vertebrates as adults

Ticks

feed on vertebrates during each life stage

Internal parasites

spend at least part of their life in a body tissue of a host

Myiasis-producing flies

calliphoridae (blow flies, screwworms); sacrophagidae (flesh flies); oestridae (cattle grubs, sheep nose bots); gasterophillidae (horse bots); cuterebridae (rodent bots)

External parasites

obtain nourishment from the host on the skin surface - sucking blood or bodily fluids, and feeding on skin debris, hair or body secretions

some burrow beneath the skin surface - sarcoptic mange

Duration time on host

varies; some parasites live continuously associated with host and are highly dependent on host for survival (lice, some mites, sheep keds)

most have intermittent contact (ticks, mosquitoes, biting flies)

Host specificity

highly variable - some exhibit mild preferences, others are very specific

ticks will feed on multiple

blood-feeding flies may be less selective

Pest control programs

obligate vs facultative, host specificity, time on vs off host

Arthropod-borne disease management

zoonotic pathogens - transmission to humans

wildlife as reservoirs of infection - transmission from wildlife to domestic animals

Body shape

facilitates movement on the host and to enable them to hide in tight spaces when off the host

blood feeders that have brief contact with host do not show flattening (biting flies, mosquitoes, biting midges)

Dorsoventral flattening

flattening of body from top to bottom (lice, house flies and keds, ticks)

Bilateral flattening

squished to the side (fleas)

Wings

indispensable for many parasitic insects required to reach vertebrate hosts

wings may become secondary or completely lost (fleas, lice, sheep ked)

may have functional wings as an adult that are shed one host reached leaving a wing stump (deer ked)

Legs

modified for grasping and holding on

allows them to stay attached during grooming by host

flea hind leg highly modified for movement between hosts - enlarged muscular femur, elastic protein in the integument called resilin allows them to jump

Sensory structures

important for host location and recognition

detect motion, vibrations, temp, moisture, CO2, and chemical substances produced by potential hosts

Eyes

compound eye made of thousands of ommatidia

each has its own lens and light sensing cells at the back

Antennas

role varies with species, when present attached to the head

used primarily for olfaction but can also be sued for sensing tactile stimuli

vibrations in air can be detected and interpreted as sound

may be reduced (flea) or entirely absent (ticks, mites)

Flea sensillum

specialized for detecting host-associated cues such as vibrations and temp gradients

Ticks

cavity on first pair of legs

detection of temp, air movements, host odors, and other host and environment cues

no eyes, no antennas, reach arms out when they sense something

Mouthparts

essential for survival and adapted to food source and manner of feeding

vary in size and shape all contain variations of the same parts (building blocks)

acari have diff mouthparts to insecta

mouthparts adapted to securing specific kind of food

Evolution of blood feeding

greater than 15,000 species from 400 genera are hematophagous (feed on blood)

Type of blood feeding: Telmophagy

pool feeders (bigger mouthpart, more painful)

ticks, black flies, horse and deer flies

bites from these insects typically cause immediate pain

damage to surrounding skin and related tissues results in a great risk of secondary infections

Type of blood feeding: Solenophagy

highly specialized piercing - sucking mouthparts that pierce individual capillaries and then feed directly from them through highly modified, styliform (slender, sharp) mouthparts

mosquitoes, bed bugs, kissing bugs, sucking lice

typically leave little to no evidence of an actual puncture of the skin at the bite site