I have been comparing the algal populations of two ponds over 6 months and I have run into some trouble differentiating two potentially different genera in one of my ponds. The algae I am trying to differentiate are a Desmodemsus species (with spines) and a Scenedesmus species (without spines). I know there has been much debate over whether or not the two genera actually belong within the same genera (Scenedemsus) and there have been instances of phenotypic plasticity where a Desmodesmus species presents without spines. In my first pond (Gilmore) I found no correlation/very weak correlation between the individuals with spines and individuals without spines (R2=0.13). In the second Pond (Peacock) I found a very strong correlation between the individuals with spines and those without spines (R2=0.85).

I have a few ideas as to what could be causing this:

-The genera are so similar that they may occupy the same niche and be competing for the same resources (therefore be related).

-I mistook another small round algae as Scenedesmus in my Gilmore samples (which is why there was no correlation)

-The Peacock Pond individuals are the same genera/species and are exhibiting phenotypic plasticity (absence/presence of spines), causing shifts in the population between months.

-This was an accident, correlation does not equal causation (how can I test this in an uncontrolled experiment?)

I think the easiest way to solve this problem would be to isolate the individuals and compare rRNA but the samples have been preserved in Lugols' and I do not have the equipment to run PCR.

Any ideas for other statistical analyses I could do to determine if the individuals from Peacock are in fact the same genus?

Again, the way I have labeled these for now are:

Scenedesmus = no spines

Desmodemsus = spines

Thanks!