What’s New in the Third Edition of Kingdoms of Life Connected? January 12 2023, 1 Comment

Last fall, I completed the third edition of my book, Kingdoms of Life Connected: A Teachers’ Guide to the Tree of Life. This came only six years after the second edition, which in turn came eight years after the first edition. “Why all this change?” you may ask.

I found that updates were needed because of changes in biologists’ view of the diversity of life. The data about how organisms are related continue to pour in, and because of this, the details of lineages and relationships change. You may be tempted to wait until the field stabilizes and stick with older ideas. Children, however, need a useful view of the diversity of life, even if it will be somewhat amended later. They cannot build on a foundation that is clearly obsolete. Specifically, it is no longer useful to present children with Five or Six Kingdoms, and those charts need to go in your history-of-science file.  

I updated Kingdoms of Life Connected from cover to cover. I redid the lists of learning resources – books and websites; I purged links that no longer worked and added new ones. Publishers and authors have brought forth valuable new books in recent years, and I added titles to the lists while retaining older but useful books. I revised all the text, including the activities and lesson suggestions. I fact-checked the information to make sure it was as up to date as I could make it.

There is one especially important addition, a new lesson for introducing to the Tree of Life chart to beginning elementary children. This lesson gives older children important concepts as well, particularly if they have not yet had this overview. The introductory lesson leads children to the idea that all life shared a common ancestor and is connected. It shows them the relationships between the major branches of life. For example, they learn that the animals and fungi are sister lineages and that plants are only distantly related to fungi.

I’ll give a brief summary of some of the changes below. For more information, see the book, which is available at https://big-picture-science.myshopify.com/collections/biology/products/kingdoms-of-life-connected-third-edition (printed version). The ebook (pdf) is at https://big-picture-science.myshopify.com/collections/biology/products/kingdoms-of-life-connected-third-edition-ebook.

There are no big changes in the prokaryotes. I have kept a very basic approach because it takes extensive knowledge of biochemistry to understand the many branches of bacteria and archaea. Introductory college biology texts present a few basic lineages, and I felt that this approach would be good for children as well.  

In the protists, I rearranged the Excavata lineage on the Tree of Life chart. Now, the euglenazoa and kinetoplastids are sister lineages and the metamonads are the first branch. I expect that Excavata will be split apart and redone in the future. It probably won’t be a eukaryotic supergroup, but studies continue to confirm the other supergroups – Archaeplastida, SAR, and Amorphea.

Scientific terminology evolves, and I was happy to see a complicated name go away. The branch of the stramenopiles and alveolates was previously called Chromalveolata, but that term has fallen out of favor. It originally described a lineage that included two branches I didn’t show, the cryptophytes and haptophytes; these are now placed elsewhere on the Tree of Life. The branch of the stramenopiles and alveolates may get a new name, but it seems best to leave that branch blank for now.  

The fungi were the major branch that changed the most. The former Zygomycota lineage is now divided into two main lineages, the Mucoromycota and the Zoopagomycota. On my Tree of Life chart, I show the larger one, Murcoromycota. Its branches include the pin molds or Mucoromycotina (black bread mold, for example) and the arbuscular mycorrhiza fungi or Glomeromycotina (AM fungi). The AM fungi were previously placed on their own branch, but they have been added back to Mucoromycota. I didn’t add the Zoopagomycota to the Tree of Life chart, but if you have children who are interested in learning more, Fungarium by Katie Scott and Ester Gaya, is a good book for launching their explorations.

In the animal kingdom, studies have clarified some relationships in the protostome branch. You can give children the term “Spiralia” for the lineage previously called Lophotrochozoa. The whole branch is called Spiralia; “Lophotrochozoa” still refers to the mollusks and annelids. It is another of the situations where it is useful to know an older and newer term. “Lophotrochozoa” has been used for the Spiralia branch for about 20 years, and it appears in a number of websites. I recommend looking to the future and using “Spiralia” primarily. It is certainly easier to say and spell.

In the plant kingdom, studies have resolved several questions about the bryophytes. They are a single branch of life, a monophyletic lineage. The first branch was recently determined to be the hornworts. The mosses and liverworts are sister lineages. The older story was that the liverworts were the first branch because they do not have stomata. It appears that their ancestors lost their stomata rather than never having them.

The virus chapter now has suggestions for making a model of a coronavirus. I published this chapter as a stand-alone pdf in 2020. Note that if you have the third edition of Kingdoms of Life Connected, you already have the content of “What Is a Virus?”.

It is easy to become overwhelmed by all the names and branches of life. I recommend that you concentrate on the larger branches on the Tree of Life and continue to other branches as children (and you) learn about these and are interested in pursuing more. For in-depth studies at the elementary level, I recommend the digging further into the animal and plant kingdoms.

Start with the big overview of the Tree of Life. After that, my learning material, Sorting Branches on the Tree of Life: Vertebrates and Plants, is a good place to go. It is available as a pdf that you can print https://big-picture-science.myshopify.com/collections/biology/products/sorting-branches-on-the-tree-of-life-vertebrates-and-plants or as a printed material https://big-picture-science.myshopify.com/collections/biology/products/copy-of-sorting-branches-on-the-tree-of-life-vertebrates-and-plants-file-for-printing.  

Enjoy your explorations of the Tree of Life!  

How do you divide the eukaryotes? September 19 2019, 0 Comments

If I asked you how you would divide the eukaryotes into groups, what would you say? Many people would say protists, fungi, animals, and plants. This is the idea presented in Five (or Six) Kingdoms classification. There is a more enlightening way to divide the eukaryotes, one that students currently see in introductory college courses.

The DNA revolution and the development of systematics rather than plain classification have given us a new view. Systematics includes the relationships between taxonomic categories instead of listing them with no information about their shared ancestors. It is a young science that has produced many changes and will likely produce many more.

This is not to say that we don’t have useable information right now. The largest categories of eukaryotes have been defined, and they are called the eukaryotic supergroups. There are four of them presently, and so the eukaryotes can be divided into four groups. Here’s an introduction to the archaeplastida, SAR, excavata, and unikonts aka Amorphea.

Archaeplastida is the lineage that acquired the first chloroplast. Its name means “ancient plastids.” A plastid is a type of organelle in a eukaryotic cell, and the category includes the chloroplast, whose name means “green body.” The archaeplastida lineage includes red algae and green algae, along with the embryophytes or land plants, which evolved from a green alga. This lineage is the only one that incorporated an ancient cyanobacterium into its cells. The origin of the chloroplasts in other lineages is a more complicated story.

The SAR lineage is named for the three main branches within it, stramenopiles, alveolates, and rhizarians. These lineages were defined independently and then researchers gathered enough evidence to conclude that they share a common ancestor. The stramenopiles (aka chromists or heterokonts) include brown algae, golden algae, diatoms, and water molds. Alveolates include dinoflagellates, apicomplexans (parasites such as malaria), and ciliates. The rhizarians include foraminiferans and radiolarians, single cell organisms that build amazing outer shells called tests.

And where did these branches of life get their chloroplasts? It seems that chloroplasts are NOT easy to acquire. Apparently, it is easier to take one from another cell than to acquire one by eating a cyanobacterium. An ancestor of the stramenopiles and alveolates probably ate a red alga and kept its chloroplasts. Euglenas, which we meet below, got their chloroplasts from a green alga.

The third eukaryotic supergroup is the excavata, also called the excavates, but I see potential for confusion between the word as a noun vs. a verb. The lineage is named for a groove that looks like it has been excavated from the cells of some members. The excavata include the euglenas, which are free-living, and the trypanosomes, which are parasites. Other members of this group include the parasite Giardia and organisms that live in the guts of termites and help them break down cellulose. These have reduced mitochondria, so small that they were first described as lacking mitochondria.

I know you have been waiting for the last of the four supergroups, our own lineage, the unikonts (“single flagellum”) also known as the Amorphea (“having no form”). “Wait a minute,” you may be thinking, “we definitely have form.” The amoebas that belong to this lineage do not, however. The Amoebozoa lineage includes most of the slime molds or social amoebas as well as the single cell ones. Some of the latter build hard coverings (tests) for themselves. The other members of the unikonts are the fungus kingdom and the animal kingdom, which are sister kingdoms, having shared a common ancestor right before they branched off. There are other single cell organisms that are related to animals and fungi as well.

As you can see, the old protist kingdom had many different lineages of life shoe-horned into it, and the kingdoms that developed from its members were chopped off and boxed separately from it in the Five (or Six) Kingdoms scheme.

Why should you or your children learn about the supergroups of eukaryotes? It gives you a richer view of life and one that your children will see in their future studies. Will the names stay the same? Maybe, or maybe not, but these are the names in current college biology books, and it is worthwhile to learn about them and their members now.  

Enjoy your explorations of the living world!

Priscilla