This is the first in series of posts which will work through David Attenboroughs Life on Earth series, taking interesting parts and going into them in greater depth, to try and explain, and make accessible, what it is that excites me about nature, and about the history of life on Earth.
Previously I have written about cyanobacteria, and the theories on how eukaryotes arose, so this series will start with protists and micro-algae. This clip shows the amazing differences in structure among these organisms, as well as the reproductive differences.
In this video there are a number of different single celled organisms, so let’s take a peek into the structure of some of them:
Dinoflagellates (Dinophyta) are the organisms responsible for the “red tide” effects when some species undergo rapid growth in numbers due to a change in conditions. They come in a variety of different shapes, and I often mistake some of them for diatoms, which are a different group of organisms. They are also responsible for the colours in coral, and for many forms of food poisoning from fish and shellfish
Image from http://www.mnh.si.edu/highlight/sem/dinoflagellates.html (Also a LOAD more amazing photos of dinoflagellates on there) VERY recommended viewing for awesome pictures!
(Image from http://www.biologycorner.com/resources/dino.jpg )
Dinoflagellates also produce the bioluminescence you see at night on the ocean….this alone makes them fairly awesome in my opinion, but I really love their structure, it is so unexpected. They have a whole range of shapes and forms, and many appear almost man-made. One group is responsible for the colours in coral, where they live in symbiosis with the colonial organisms which make up the coral….there is discussion about whether the coral is actually parasitic towards the dinoflagellates, as the benefits to the coral are clear, but because they capture the dinoflagellates, incorporate them into their own systems, and then reject them when conditions change, it appears that the coral is the dominant partner in this relationship (Much more to come on this when I get to corals)
Dinoflagellates can be autotrophic (Generating their own carbohydrates from photosynthesis), heterotrophic (obtains carbohydrates from other organisms, like us), or, mixotrophic (This means they can do both, so depending on environmental conditions, they use photosynthesis, or are predators)
During their life cycles, some species are able to form cysts if conditions are not suitable for growth, these cysts fall to the bottom of the lake or ocean where the organsism is, and can be transported by currents to a more suitable location, or can lay dormant until conditions are favourable. When conditions improve, the cysts germinate, causing the blooms that we see in our lakes and oceans. (see http://www.whoi.edu/redtide/page.do?pid=18215 for more details on the general life-cycle of dinoflagellates, with an interactive image)
There is one species of dinoflagellate, Pfisteria piscidia, which is thought to have a particularly complex and interesting life cycle. When it is in cyst form, the presence of fish appears to trigger germination, and the organism then produces a toxic substance which paralyzes the respiratory system of the fish, causing it to suffocate. As the fish decomposes, the cells extend a tube, and digest the fish flesh. Once the fish is consumed, they turn back into cysts, and sink to the ocean floor once again. Investigation into this, and whether there are other organisms involved in the process, and the exact nature of the toxin used is still ongoing, and the subject of debate among researchers.
Finally, I will leave you with an image of bioluminescence from dinoflagellates. This is caused when the water around them is disturbed. They release a chemical known as luciferin. Further information on how bioluminescence occurs is here http://www.sciencebuddies.org/science-fair-projects/project_ideas/BioChem_p033.shtml