I thought I would resume my blog by writing about a topic that is both different yet similar to my earlier posts. I have written extensively about Daphnia, the parthenogenetic crustacean common to vernal pools (and lakes but that will have to be discussed at another time). A few years ago, (okay, more like 15 years) I realized that there was more to a vernal pool than just being a home for animals that can make clones. Vernal pools can also be the homes for plants that make clones. That vernal pools host such a diversity of organisms that require sex rarely, if ever, is interesting in itself but I’ll save that discussion for later as well.
First, I thought I would introduce everyone to the world’s smallest flowering plant, Wolffia (water meal; and you thought it was Lemna, or duck weed). As small as duck weed is, Wolffia is even smaller (a nice comparison photo is at http://www.uwgb.edu/BIODIVERSITY/herbarium/wetland_plants/wolcol_aspect01.jpg). What is interesting about both of these genera is that you only need one individual to start a population. I have to admit that while growing duck weed is pretty easy I have had little luck with Wolffia although it grows in vernal pools so how can it be to grow? Anyway, unlike Daphnia which use eggs to produce clones, the plants do so by producing buds which separate from the parent. Like Daphnia, at some point the population is induced to become sexual and flowers are formed (see http://waynesword.palomar.edu/plaug96.htm for some cool pictures of the flowers and seeds).
My interest in Wolffia came about while hunting for Daphnia around Floyd County, Georgia while a faculty member at Berry College. I came across a few ponds that were covered with the stuff and thought they might make an interesting study subject for those students that were not so much into Daphnia (I know that is hard to imagine). I tried to find guides and keys to the species, but this was before the internet made it so easy to find information. I learned there are a few species and they could be identified, in part, by the number of stomata on the surface of the plant. For those of you that have forgotten your botany, stomata are the openings on leaves that allow plants to breath. They are necessary because plants are covered with a waxy cuticle that restricts water loss but also limits gas exchange. Plants need carbon dioxide for photosynthesis and need to get rid of oxygen, the waste product of that process.
I set a couple of students to look for the same sorts of clonal indicators used with Daphnia using allozyme electrophoresis. We had marginal luck and nothing that I would feel comfortable using for a study of population genetics. As I mentioned, I had read that the species could be distinguished by the number of stomata on the surface so I had students counting these openings on samples from the different habitats. As it turned out, we had more than one species growing in the area and the populations each consisted of a single species.
That is sort of interesting but not what caught my attention. What caught my attention is the topic for tomorrow. Glad to be back.
“Glad to be back.”
VERY glad to have you back!