#pleodorina

"You've got your gonium, looking like several of those little green algae stuck together. And then there's this active pandorina, also packing together several green cells in its colony body as it moves around. And then we see the Eudoria... and then the pleodorina, which looks increasingly like the orderly sphere of the Volvox. In fact, this combination of footage feels less like a family portrait and more like a series of yearbook photos taken from kindergarten through senior year. Expect instead of the striking passage of time documented through the changes in a child's face, this is the striking passage of multicellular evolution documented through the changes in on algal family."

Journey to the Microcosmos- How Did Multicellularity Evolve?

"Multicellularity is one of those things that is so entwined with notions of complexity and the forward marching of evolution that it might feel like it has to be one of those singular evolutionary events: a moment that occurred once or maybe twice, and was maybe too difficult to ever replicate again. But it turns out that making the jump from unicellular to multicellular life has actually happened quite a few times in our planet's history. It's maybe surprisingly not htat difficult a transition. But finding a way to study it is."

Journey to the Microcosmos- How Did Multicellularity Evolve?

Images Originally Captured by Jam's Germs

"And that leaves us with a gradient of cellular complexity that starts with the unicellular Chlamydomonas, transitions to the colonial gatherings of cells that make up the gonium through pleodorina, and that leads us to the multicellular Volvox. That ordering though is a little misleading in its simplicity. Evolution isn't nearly so neat to work in a straight line across a whole family. But laying out the organisms in this way helps us to understand that steps are involved in taking the species from unicellular to multicellular."

Journey to the Microcosmos- How Did Multicellularity Evolve?

"Many of these jumps [in evolution] happened too long ago, and evolution has removed the organisms whose bodies contain the story of how they or their ancestors went from living on their own to teaming up with others. But fortunately, the volvocine algae went about this transistion much more recently--likely around 200 million years ago."

Journey to the Microcosmos- How Did Multicellularity Evolve?

Images Originally Captured by Jam's Germs

"But multicellular is more than just getting big. The big step to taking the volvocine algae from colony to multicellular life involves putting all those cells to work--specialized work. You can see the early days of specialization in the colonial algae through the development of organismal polarity, which is a fancy way of saying that we can define a front and back of the colony. The cells in front are generally large with big eyespots. And as you go to the back, the cells and eyespots get smaller. These differences create a gradient not just in characteristics, but in function. The larger eyespots in front mean those cells will be more sensitive to light, making them responsible for directing the colony."

Journey to the Microcosmos- How Did Multicellularity Evolve?