Vet/Med Ent. 1/29

Definition: Parasitism is described as a mode of life where one organism, the parasite, benefits at the expense of another organism, the host.
Focus on the adaptive adaptations that have occurred in parasitic organisms, particularly in arthropods.
Discussion on the historical implications of parasitism in various lineages, including frequent independent evolutions.

Parasitism in arthropods has evolved long ago and on multiple occasions.
Evidence suggests that:
- Different lineages (e.g., arachnids and insects) have evolved parasitic behaviors.
- Specific lineages within arachnids are entirely parasitic, indicating a common ancestor with parasitic traits.
- Mites show a mix of parasitic and non-parasitic characteristics.
In insects, parasitism has also presumably developed several times:
- Some sublineages are entirely parasitic, and others are partially parasitic.

Types of Feeding Behaviors:
- Most parasites are blood feeders, accessing the circulatory system of their hosts.
- Other feeding strategies include:
- Feeding on skin
- Feeding on feathers
- Targeting organs and tissues
Examples of parasitic orders within insects:
- Thoraptora (e.g., lice): 100% parasitic.
- Siphonaptera (e.g., fleas): 100% parasitic and deeply related.

Depicts evolutionary pathways highlighting disparate evolutionary trajectories.
Graphical Representation:
- A diagram outlines relationships among various orders within Insecta.
- Orders with significant parasites marked with asterisks.
Suggests that parasitism could have independently evolved multiple times based on the presence of non-parasitic orders.

Evidence of early parasitic forms:
- Soft Ticks: Evolved over 92 million years ago.
- Lice: Evolved about 175 million years ago.
- Fleas: Approximately 150 million years ago.
- Mosquitoes: Originating around 75 million years ago.
Early parasitic forms likely targeted host organisms that have since evolved (e.g., ancient birds and mammals).

Historical speculation on hosts for parasitic lineages:
- Early arthropod parasites did not primarily feed on modern birds and mammals, which evolved later.
- Speculated early hosts could include dinosaurs, amphibians, and reptiles.

Adaptive Pathways:
- Evolution from free-living organisms feeding on different diets to parasitic organisms.
- Transition mechanism exploration from non-parasitic ancestors to parasitic forms supported by feeding adaptations.
Example of Butterflies:
- Various feeding styles may lead towards parasitism:
- Nectar feeders evolving into forms that can exploit host resources (e.g., butterfly feeding on bird tears).
- Vampire Moths: A specific group that feeds on the blood of their hosts, reliant on coiled proboscises to pierce skin.

Discovery of previously undocumented populations further illustrates adaptive evolution:
- Vampire moths feed on nectar primarily but have adapted structures for blood feeding.
- Male moths possibly using blood feeding to convey nutritional benefits during reproduction, representing a mid-step evolutionary trait (nutritional requirements).

Discussion on how small adaptations lead arthropods towards parasitic lifestyles:
- Behaviorally, some species may develop closer relationships with potential hosts, turning into parasites.
- Various lines of evolution could converge on similar parasitic lifestyles through different routes, leading to:
- Behavioral changes, morphological adaptations.
Discussion on mosquito evolution parallels:
- Mosquito evolution highlighting nectar feeding transitions leading to blood feeding requirements for reproductive purposes.

Morphological and Physiological Adaptations Needed:
- Reduction in size may help with effective parasitism.
- Mouthpart modifications for blood feeding versus previous forms of feeding modes.
- Increased ability to sense hosts through novel adaptations (i.e., heat sensors).
Addressed the steps from a free-living organism to a successful parasite:
- Importance of locating host and extending survival strategies, overriding innate host defenses.