Eukaryotic Supergroups: Exploring Protist Diversity: Study with Video Lessons, Practice Problems & Examples

Protists are a diverse group of eukaryotes, including lineages like Excavata, SAR clade, and Archaeplastida. Excavata features organisms like diplomonads and parabasalids, often lacking mitochondria. The SAR clade encompasses stramenopiles, alveolates, and rhizarians, with diatoms and dinoflagellates playing key roles in photosynthesis. Archaeplastida includes green algae and land plants, showcasing primary endosymbiosis. Apicomplexans, such as Plasmodium, exhibit complex life cycles involving multiple hosts. Ciliates utilize cilia for movement and feeding, while amoebozoans, including slime molds, demonstrate unique reproductive strategies, highlighting the evolutionary significance and ecological roles of protists.

Overview of the Four Supergroups of Eukaryotes

This video, we're going to continue to explore protist diversity as we introduce and overview the 4 supergroups of eukaryotes. And so, since protists are super diverse, their phylogeny is also super diverse, and this makes protists extremely difficult to be able to group and organize in terms of their evolutionary relationships. Although the evolutionary relationships of protists are heavily debated and actively being researched by experts today, one current hypothesis states that there are 4 supergroups of eukaryotes upon which all eukaryotes can be grouped into, including all of the protists. These 4 supergroups are the Excavata, the SAR, the Archaeaplastida, and the Uniconta. The primary benefit of these 4 supergroups is that they help to group the protists based on their evolutionary relationships.

These 4 supergroups are grouped based on both genetic and morphological studies, although they're primarily based on genetic studies. Notice down below in this phylogenetic tree, you can see these 4 supergroups are very nicely color-coded, and moving forward in our course in separate videos, we're going to explore examples of protists in each of these 4 supergroups. But before we do that, there are a few things that you should take note of. The first is that the group SAR is actually an acronym for these three lineages of protists, which are the Stramenopiles, the Alveolates, and the Rhizarians. Next, the group Archaeaplastida in some textbooks is referred to as Plantae since, of course, it includes the land plants.

Next, notice that these two lineages here, the Charophytes and Chlorophytes have a little asterisk next to them. That's because some authors actually classify these species as plants and not as protists, like we're doing here. And so this goes to show that there's not yet consensus on the groupings of these protists, and there's still much work and research to be done on protists to fully solidify these hypotheses. Next, the group Uniconta includes the animals, which, of course, includes you and I, and the fungi as well. Now, the term Uniconta is slowly becoming abandoned, and the term Amorpha is slowly becoming the more preferred term, which is why we include it here, although it's not likely your professors will test you on that.

Again, moving forward in our course, we're going to explore these groups even further, but for now, this here concludes our introduction and overview, and we'll be able to apply some of these concepts and problems moving forward. So I'll see you all in our next video.

Which of the following answer options lists the 4 supergroups of eukaroytes?

• A. Excavata, SAR, Amoebozoa, Archaeplastida.
• B. Unikonta, Plantae, Excavata, Rhizaria.
• C. Excavata, SAR, Archaeplastida, Opisthokonta.
• D. Stramenopila, Alveolata, Rhizaria, Unikonta.
• E. Excavata, SAR, Archaeplastida, Unikonta.

Using the phylogenetic tree below, which of the following groups is most closely related to animals?

• A. Archaea.
• B. Nucleariids.
• C. Parabasalids.
• D. Charophytes.

How does the eukaryotic supergroup classification system differ from the traditional taxonomic hierarchy (Domain, Kingdom, Phylum, etc.)?

• A. Supergroups emphasize evolutionary relationships based on genetic evidence, while the traditional hierarchy often relies on observable traits.
• B. Supergroups are not rank-based and do not conform to the rigid levels of the traditional hierarchy.
• C. The supergroup classification system is designed to accommodate updates as new phylogenetic discoveries are made.
• D. All of the above.

What is the biggest benefit to the eukaryotic supergroup framework?

• A. It clearly reflects the genetic & evolutionary relationships between different protists.
• B. It clearly reflects the genetic & evolutionary relationships between different animals.
• C. It clearly reflects the genetic & evolutionary relationships between different plants.
• D. It clearly reflects the genetic & evolutionary relationships between different fungi.

Here’s what students ask on this topic:

What are the key characteristics of the Excavata lineage in protists?

Excavata is a major group of unicellular eukaryotes, many of which lack mitochondria and reproduce asexually. Key subgroups include Diplomonads, which have two nuclei and reduced mitochondrial structures, and Parabasalids, which also lack mitochondria and use flagella for movement. Another subgroup, Euglenozoans, includes Kinetoplastids with large mitochondria and Euglenids, which can be mixotrophs, combining photosynthesis and heterotrophy. These characteristics highlight the diversity and adaptability of the Excavata lineage.

How do diatoms contribute to Earth's photosynthesis and carbon cycle?

Diatoms are unicellular photosynthetic organisms encased in protective silica shells. They play a significant role in Earth's photosynthesis, contributing to a large portion of global oxygen production. Diatoms also impact the carbon cycle by absorbing carbon dioxide during photosynthesis. When diatom populations bloom, they can cause noticeable reductions in atmospheric carbon levels in their vicinity, thus playing a crucial role in regulating Earth's climate and carbon balance.

What is the significance of secondary endosymbiosis in the SAR clade?

Secondary endosymbiosis is a process where a eukaryotic cell engulfs another eukaryotic cell that has already undergone primary endosymbiosis. In the SAR clade, this process is significant as it led to the acquisition of chloroplasts in groups like Stramenopiles and Alveolates. This event likely involved the engulfment of red algae, enabling these protists to perform photosynthesis. This evolutionary step has allowed SAR clade members to become major contributors to marine and freshwater ecosystems' primary productivity.

How do apicomplexans like Plasmodium exhibit complex life cycles?

Apicomplexans, such as Plasmodium, have intricate life cycles involving multiple hosts. Plasmodium, the parasite causing malaria, reproduces sexually in mosquitoes and asexually in humans. In mosquitoes, gametocytes form zygotes, which develop into sporozoites. When a mosquito bites a human, sporozoites enter the bloodstream, infect liver cells, and then blood cells, producing more gametocytes. These gametocytes are taken up by another mosquito, continuing the cycle. This complex life cycle ensures the parasite's survival and transmission between hosts.

What are the unique reproductive strategies of slime molds in the Amoebozoa group?

Slime molds in the Amoebozoa group exhibit unique reproductive strategies. Plasmodial slime molds form large, multinucleate cells that create fruiting bodies for spore dispersal. In contrast, cellular slime molds consist of individual cells that aggregate to form fruiting bodies. These aggregates of cells work together to reproduce, highlighting a form of cooperative behavior. Both types of slime molds demonstrate the diverse and adaptive reproductive strategies within the Amoebozoa group, contributing to their ecological success.