Linking intraspecific trait variation to community assembly dynamics in newly formed ponds

Background/Question/Methods

Phenotypic variation within a population results from a combination of genetics and the environment, and understanding the relative contribution of each is useful in predicting the outcome of interspecific interactions. In the freshwater crustacean Daphnia pulex, there is both significant genetic variation as well as phenotypic plasticity in several ecologically relevant traits. We seek to understand the consequences of this variation on patterns of community assembly. Using a combination of laboratory assays and observational data we quantified how ecologically relevant life history traits differ among genotypes of D. pulex that were stocked into newly created experimental ponds in 2011. Replicate individuals of six genotypes were grown under ecological conditions found to differ in the field (pH, food quality, and predator presence). We measured size at birth, size and age at maturity, and clutch size through the first four clutches.  These data were used to calculate juvenile growth rate for each clone.

Results/Conclusions

In the laboratory assays, clonal growth rate ranged from 0.3-0.7 day^-1 depending on the genotype. Some genotypes, however, showed more plasticity in growth rate than did others.  Clutch size ranged from 2-37 individuals / clutch and size at maturity ranged from 1.2 mm to 3.0 mm.  Adult females collected from 30 ponds in years 2011 and 2012 also exhibited a large range in mean body size (from 0.6 mm to 2.6 mm).  These differences in ecologically relevant traits will likely lead to differences in community structuring over both time and space.  Individuals collected from the ponds in May 2013 are currently being genotyped to assess at the genetic structure of these populations in each pond. This will allow us to determine the degree to which clones have dispersed from the ponds in which they were stocked. Continued analysis of the importance of intraspecific variation in ecologically relevant traits will help disentangle the relative contribution of life history variation and interspecific interactions on patterns of community assembly in natural systems.