One way to assess if genetic variation in the production of males and sexual females exists, and whether this variation is strongly environment dependent, is to expose a number of different individuals to several, different environmental stressors, and document respective responses of each of the individuals in response to the applied conditions(s).
Here, we exposed different clones of Daphnia pulex that either originated from ephemeral and permanent ponds in the UK (see Figure) to different environments that varied in the amount of food availability (i.e. different algae concentrations), different day length (mimicking either winter or summer conditions), and different population densities, i.e. using different numbers of individuals that share the same space. We then assessed the timing and total number of males or ephippia produced in the different environmental conditions.
Our phenotypic assessment suggests that a contribution of both genetic and environmental factors contribute to the switch from asexual to sexual reproduction in the investigated Daphnia clones.
In order to identify the molecular mechanisms that may drive the production of males and sexual females, we then looked at how the DNA is expressed in different clones under different conditions. Expression of genes is one of the first steps in turning an environmental signal into a distinct phenotype like the production of males or sexual females. Since we identified clonal clusters with clones that showed i) no sex investment, ii) male investment only, iii) sexual female investment only, and iv) investment in males and sexual females. While we expect that the genes that are expressed in these clonal clusters differ among the four groups, we are currently awaiting confirmation from our molecular analyses to proof this. In a final step, we will be looking at which genes are expressed together when the environment changes. Such co-expression generates networks of genes, somewhat like the network of connections among people on social networks. Ultimately, this analysis, we allow us to then look at whether there are certain genes that control expression patterns in other parts of the network.
