Parasites and Evolution

Defensive Symbionts

  • Defensive symbionts act to protect their partners from threats, including:
    • Parasites
    • Predators
  • This form of interaction is termed "protection mutualism."
  • Includes various cleaning relationships, where one species cleans or removes harmful organisms from another.

Oxpecker Birds Relationship

  • Oxpecker birds feed on ticks found on ungulates in Africa.
  • There are questions regarding the nature of this relationship; while oxpeckers do consume ticks, they also consume blood and tissue from the mammals, suggesting a more complex interaction.
  • Nunn et al. (2011) found that the primary focus of the relationship between oxpeckers and ungulates is on tick consumption, classifying it as mutualism despite the additional negative aspects.

Seagrasses and Coralline Algae

  • Seagrasses, such as Thalassia (Turtle Grass), are grazed by sea turtles.
  • The presence of coralline algae can reduce grazing by sea turtles, as shown in the study by Leemans et al. (2020).

Ant Plants

  • Ant plants provide shelter and sometimes food for ants.
  • In return, ants offer protection to the plants.
  • Examples include the Acacia and Myrmecodia species.

Parasitism: Success or Dead End?

  • The success of parasitism can be evaluated from two perspectives:
    • The perspective of the parasite
    • The perspective of the host

Evaluating Success in Biodiversity

  • Definitions of success can vary:
    • For individuals, success may be linked to fitness levels.
    • For species, one must consider:
    • Number of species in a lineage (monophyletic group).
    • Longevity of the lineage.
    • Spatial distribution.
    • Resource and ecological dominance.
  • It has been estimated that nearly half of all species may be parasitic, raising questions regarding their overall success and distribution in the tree of life.

Origins of Parasites Across Animal Taxa

  • Data from Weinstein & Kuris (2016) indicates:
    • Significant variation in the percentage of parasitic species across animal taxa.
    • Examples:
    • Porifera: 0% parasitic
    • Cnidaria: ~7 species with 100% parasitic
    • Arthropoda: 143+ species with many parasitic.

Case Study: Orchids as Parasites

  • Orchids exhibit unique parasitic traits:
    • Successful as seedlings when parasitic.
    • When transitioning to fully parasitic states, success tends to decline.

Orchid Seed Structure

  • Structure includes important components:
    • Non-micropylar endosperm
    • Cotyledons
    • Embryo
    • Endosperm
    • Micropylar endosperm
    • Seed coat (testa)
    • Radicle

Leafless and Succulent Orchids

  • Leafless orchids are often found in specialized environments and exhibit mutualistic behavior with fungi.
  • Examples include temperate Monotropoids.
  • Many orchids are "cheaters," exploiting fungal relationships without reciprocation.