Development Timing & Interspecific Interactions

Community Ecology

  • Overview of Key Questions:

    • How can changes in gene expression lead to evolutionary change?

    • What is symbiosis?

    • Distinguish between different types of community interactions: positive vs. negative.

Gene Expression and Evolutionary Change

  • Gene Functions:

    • Not all genes code for proteins; some affect the expression of other genes.

    • Genes influence which portions are treated as introns during RNA splicing in eukaryotes.

  • Development Timing:

    • Changes in gene expression or timing can lead to evolutionary adaptations.

Developmental Timing Changes

  • Heterochrony:

    • Definition: Evolutionary change in the rate or timing of developmental events.

    • Examples:

      • Slowing the rate of bone development in whales leads to limb reduction.

      • Speeding up the development of reproductive organs in comparison to the body leads to paedomorphosis—sexually mature adults resembling juvenile forms.

Examples of Paedomorphosis

  • Species demonstrating changes in development timing include:

    • Axolotl: Retains juvenile features in adults.

    • Sand Cat: Example of developmental timing variations.

Gene Regulation and Evolution

  • Homeotic Genes:

    • Master regulatory genes that control the spatial organization of body parts.

  • Significance of Hox Genes:

    • A single change can result in major morphological changes, e.g., insects evolving pairs of wings instead of legs.

    • Changes in gene regulation can result in phenotypic changes like loss of spines in stickleback fish.

Community Definitions

  • Community:

    • Group of populations from different species interacting with one another.

    • Boundaries defined by:

      • Ecological roles of species (like producers or decomposers).

      • Geographic area or habitat type (e.g., riparian vs. grassland).

Symbiosis and Interspecific Interactions

  • Symbiosis:

    • Individuals of two or more species living in direct contact, can lead to three kinds of interactions: positive, negative, or neutral.

  • Types of Interactions:

    • Commensalism (+/0): One species benefits without affecting the other.

      • Example: Cattle egrets benefiting from water buffalo.

    • Facilitation (+/0): One species positively affects another's survival/reproduction without a symbiotic relationship.

      • Example: Rhizobacteria aiding soil chemistry.

Mutualism in Communities

  • Mutualism:

    • All species benefit from the interaction (+/+).

    • Obligate Mutualism: One species cannot survive without their symbiote.

      • Example: Siboglinid tube worms and microorganisms.

    • Facultative Mutualism: Species can live independently of each other.

      • Example: Ants and acacia trees.

Parasitism

  • Definition:

    • One species (the parasite) extracts energy from another (the host) (+/-).

  • Types of Parasites:

    • Endoparasites: Live inside the host (e.g., liver flukes).

    • Ectoparasites: Feed on the outside of a host (e.g., ticks, mosquitoes).

    • Parasitoid Insects: Lay eggs inside hosts leading to host eventual demise.

Parasites and Host Interactions

  • Effects on Host:

    • Parasites can weaken immune systems, depriving hosts of nutrients, and affecting survival and reproduction.

    • Transmission of diseases (such as malaria) can also occur, impacting host behavior.