Biogeography of Microalgae

Page 1: Aquatic Botany BR25820

Title: Biogeography of Microalgae

Page 2: Overview of Biogeography

Key Topics

  • Microalgae phylogeny.

  • Species concept for microalgae.

  • Baas Becking Hypothesis.

  • Dinoflagellates:

    • Alexandrium tamarense ?

    • Symbiodinium spp.

  • Diatoms:

    • Pseudo-nitzschia pungens.

Page 3: Microalgae Phylogeny

Definition of Microalgae

  • Microalgae are a polyphyletic group, meaning they lack a common ancestor.

    • Includes groups like Euglenids, Dinoflagellates, and various algae types such as Green algae, Red algae, Brown algae.

Classification

  • Various groups:

    • Euglenids

    • Chlorophyta (Green algae)

    • Rhodophyta (Red algae)

    • Bacillariophyceae (Diatoms)

    • Dinophyceae (Dinoflagellates)

    • Other groups include Slime molds, Fungi, and Animals.

Page 4: Plastid Evolution

Evolution of Plastids – Estimated Numbers

  • Chlorophytes: 20,000 species, 1,602 described.

  • Charophytes: 120,000 species, 3,215 described.

  • Rhodophytes: 20,000 species, 5,781 described.

  • Phaeophytes: 2,000 species, 1,718 described.

  • Diatoms: 200,000 species, 6,423 described.

  • Other groups include Haptophytes, Cryptophytes, and Euglenophytes with varying descriptions.

  • more estimated number of species compared to the amount described.

Page 5: Species Concepts for Microalgae

Defining 'Species'

  • The term species is contentious with 30 different proposals in history.

  • Two meanings of species:

    • A taxonomic category (used by taxonomists)

    • A 'natural' unit (used by ecologists/evolutionary biologists).

Approaches to Species Identification in microalgae

  • Morphology: Generally shows low diversity but includes cosmopolitan generalist species.

  • Phylogenetic Techniques: Suggests substantial cryptic diversity, focusing on OTUs from genetic markers (SSU/ITS/rbcL).

Page 6: Baas Becking Hypothesis

Background

  • Proposed by Lourens Baas Becking (1895-1963).

Central Idea

  • Translates to: "Everything is everywhere, but the environment selects."

  • Indicates that free-living microbes have the ability to colonize globally.

  • Their distribution is facilitated where conditions are suitable, irrespective of geographical barriers.

Page 7: Factors Influencing Distribution

Key Considerations

  • Body/Cell Size: Smaller taxa (100 µm - 10 mm) have wide distributions.

  • Population Size: Larger populations ensure deeper global reach.

  • Dispersivity: Smaller sizes and abundant populations enhance long-distance dispersal likelihood.

  • Survival Stages: Large quantities of resting spores enable long-term dispersal.

  • Speciation and Extinction Dynamics: Reduced geographical barriers and gene transfer lead to minimal extinction rates.

Page 8: Challenges in Microbial Biogeography

Current Issues

  • Microbial biogeography is still developing; molecular techniques are also emerging.

  • Need to explore driving factors of spatial or temporal distribution.

  • Concept adaptation: “Some things are everywhere, some are not, and sometimes the environment selects.”

Page 9: Long Distance Dispersal

Mechanisms

  • Mixing Dynamics: Freshwater mixing and ocean currents promote algae distribution.

  • Air Transport: Disseminates propagules and spores over varying distances.

  • Factors Affecting Distribution:

    • Motion of currents.

    • Surface variabilities.

    • Short distance dispersal connects to long-distance dispersal.

Page 10: Dinoflagellates

Characteristics

  • Essential unicellular algae characterized by two unequal flagella.

  • Exhibit significant plastid diversity, with unique evolutionary histories.

Ecological Importance

  • Mixotrophic nature allowing flexible nutritional strategies.

  • Role in harmful algal blooms (HABs).

  • Intricate endosymbiotic relationships.

Page 11: Alexandrium tamarense

Distribution

  • Cosmopolitan but question arises how cosmopolitan it is, with a reference link for further investigation.

Page 12: Biogeographical Complexity of Alexandrium tamarense

Colonization Insights

  • Natural and anthropogenic migration observed.

  • Evidence of trans-Atlantic movement via the Northwest Passage.

  • Use of modern molecular techniques revealed complexities, identifying it as a species complex.

Page 13: Alexandrium species taxonomy

Specific Clades

  • Related classifications of Alexandrium species illustrate their genetic variability and potential cryptic diversity indicating variations not immediately evident morphologically.

Page 14: Symbiodinium Overview

Ecological Role

  • Found in diverse hosts such as sponges, jellyfish, and corals.

  • Crucial in photosynthesis and nutrient exchange with hosts.

  • Loss of these organisms leads to coral bleaching phenomena.

Page 15: Early Investigations of Symbiodinium

Research Insights

  • Early molecular classifications revealed host-specificity but no co-evolution between corals and zooxanthellae.

  • Identified six distinct genotypes with restrictive group assignments.

Page 16: Later Investigations of Symbiodinium

Dynamic Communities

  • Subsequent research demonstrated that zooxanthellae function as dynamic communities, adapting to environmental pressures.

  • Study specific corals identified diverse Symbiodinium genotypes enhancing ecological relationships.

Page 17: The Symbiodinium Species Complex

Genetic Discoveries

  • Research identified eight clades of Symbiodinium; notable clades D and F segregating into sub-clades based on host interactions.

Page 18: Evolutionary Insights

Genetic Techniques

  • More comprehensive sampling of various Symbiodinium clades leading to explicit phylogenetic insights and the reliability of genetic techniques.

Page 19: Biogeography of Symbiodinium

Coral Associations

  • Variability of Symbiodinium within coral regions indicating features like species richness across different environments (e.g., GBR, Caribbean).

Page 20: Diatoms Overview

Importance in Ecology

  • Comprises approximately 200,000 species with intricate silica-based structures (frustules).

  • Reproduction mainly asexual, with occasional sexual processes.

Page 21: Freshwater Diatom Research

Study Findings

  • Identified 83 morphospecies across various global regions highlighting cryptic diversity.

  • Critique of earlier studies leading to reassessments of abundance claims by notable researchers.

Page 22: Pseudo-nitzschia pungens

Cosmopolitan Status

  • Analysis of clades illustrating global distribution, established presence in diverse marine regions.

Page 23: Summary

Challenges in Defining Microalgae

  • Morphological definitions lead to cryptic diversity issues.

Biogeographical Insights

  • Microalgae often expected to be cosmopolitan but display distribution restrictions aligning with the Baas Becking Hypothesis.

  • Notable examples include:

    • Alexandrium tamarense as a species complex.

    • Symbiodinium variability within hosts.

    • Misinterpretations of diatom populations.

    • Confirmation of Pseudo-nitzschia pungens’ extensive global presence.