Parasite Adaptation

Comprehensive practice flashcards covering morphological, reproductive, physiological, life cycle, and behavioral adaptations of human endoparasites from BIOL 4091 Lecture 13.

How is parasitism defined in terms of species interaction and environment?

A symbiotic relationship between two different species where one organism (the parasite) benefits at the expense of the other (the host), with the host's body serving as the parasite's environment.

According to J.D. Smyth in Introduction to Animal Parasitology, what defines an "ideal" parasite, and which organism comes close to this description?

An "ideal" parasite transitions from a parasitic relationship to a commensal relationship where it benefits while causing no harm to the host; Taenia saginata is cited as being close to this relationship.

What are the three primary functional categories of parasite adaptations?

1. Behavioral adaptations (responses that aid survival/reproduction)

2. Physiological / Life Cycle adaptations (body processes aiding survival/reproduction)

3. Structural / Morphological adaptations (physical body features aiding survival/reproduction)

How do the body sizes of parasitic nematodes generally compare to free-living nematodes?

Parasitic nematodes are significantly larger than free-living nematodes, largely due to the development of their reproductive systems; free-living species reach up to $5\text{ cm}$, whereas parasitic species can reach up to $1\text{ m}$ (e.g., Caenorhabditis elegans vs. Ascaris lumbricoides).

How does habitat dictate body shape in Dracunculus medinensis, Fasciolopsis buski / Taenia solium, and Wuchereria bancrofti?

• Dracunculus medinensis: Long and thin for residing in dense connective tissue.
• Fasciolopsis buski / Taenia solium: Flat and broad to cling to host tissue surfaces.
• Wuchereria bancrofti: Round for lumen dwelling.

Which parasitic nematode is shown being extracted from the lower extremity, and what shape adaptation enables it to live in dense connective tissue?

Dracunculus medinensis; its long, thin thread-like body allows it to migrate through and inhabit dense connective tissue.

What are the primary functions of suckers and acetabula in cestodes and trematodes?

They act as biological holdfasts to anchor the parasite and prevent expulsion from the host gut, as well as aid movement within the circulatory system.

What specialized holdfast structure is utilized by the flagellated protozoan Giardia to adhere to the small intestine?

A ventral adhesive disk (sucking disk).

What parasitic taxon is identified by the thorny proboscis armed with curved hooks shown under the microscope?

An acanthocephalan (thorny-headed worm).

What morphological adaptation covers the outer surface of nematodes to protect against host immunity?

A tough cuticle that confers resistance to host natural and specific immune responses.

How do tapeworms (cestodes) absorb nutrients and eliminate waste without a digestive tract or circulatory system?

Across their specialized syncytial tegument covered in microtriches via active transport, facilitated diffusion, simple diffusion, and potentially pinocytosis.

How does the reproductive timing of endoparasites differ from most free-living animals?

Parasites produce eggs and sperm year-round without a seasonal reproductive cycle, dedicating nearly all physiological resources continuously to reproduction.

What is the daily egg production rate of a female Ascaris lumbricoides worm?

$200{,}000\text{ eggs per day}$.

What reproductive adaptation allows Taenia saginata to generate extensive quantities of offspring in the human intestine?

Hermaphroditism, with each mature proglottid containing both male and female reproductive organs along a body chain of up to $75\text{ feet}$ of reproductive tissue.

Which two homologous recombination genes are expressed during the encystation cycle of Entamoeba histolytica?

EhRad51 and EhDmc1.

What are four major physiological adaptations exhibited by human endoparasites?

1. Anti-enzyme production (chemical inhibitors that neutralize stomach acid and digestive enzymes)
2. Anaerobic respiration (enabling survival in oxygen-poor gut and tissue environments)
3. Osmoregulation (maintaining internal pressure equal to or slightly below the host environment to facilitate nutrient absorption)
4. Immune evasion (immunomodulation, antigenic variation, and molecular mimicry)

What evolutionary advantages do parasites gain by maintaining complex life cycles with intermediate hosts?

• Increased biotic potential by combining sexual and asexual reproduction
• Expanded geographic spatial range (e.g., bridging aquatic and terrestrial environments)
• Channeling of the parasite toward the definitive host through ecological food webs
• Tissue migration to continually evade localized host immune responses

What life cycle stage of the fish tapeworm (Diphyllobothrium latum) accumulates in fish musculature, leading to bioaccumulation in predators?

The plerocercoid larva.

Where do asexual reproduction and sexual reproduction occur in the life cycle of human schistosomes?

• Asexual reproduction: Inside intermediate snail hosts via successive generations of sporocysts producing cercariae.
• Sexual reproduction: Inside the human definitive host where paired adult worms mate in mesenteric or bladder venules.

What unique reproductive and life cycle features are characteristic of Strongyloides stercoralis?

It can alternate between free-living and parasitic generations, performs autoinfection (rhabditiform larvae developing into infective filariform larvae within the gut), and adult parasitic females reproduce via parthenogenesis.

What behavioral adaptation does this graph demonstrate regarding Wuchereria bancrofti transmission?

Nocturnal periodicity: microfilariae migrate to peripheral host blood vessels at night to coincide with the nocturnal peak biting activity of their mosquito vectors.