In this study, Lee looks at how populations of Daphnia pulex and how their morphological and genetic changes occur depending on season and environmental predictability.  Lee hypothesizes that there should be more genetic polymorphism at the site of genes responsible for morphological adaptations  in unpredictable environments than in predictable areas. 

He took Daphnia from two different areas, TSL and Rash Pond, a small 2m deep abandoned gravel pit at the UM Botanical Gardens.  Over a three year period between June 1976 and July, 1979, zooplankton in both sites were sampled.  In TSL, they were sampled using plankton nets and vertical hauls down to 10 m depth.  Females were isolated and parthenogenetic clones were established from them.  Daphnia were grown on Ankistodesmus algae.  Laboratory experiments involved placing 10 adult Daphnia from the same clone together and subjected to either a summer or a winter condition treatment.  The summer condition was 22 C, 16 h light to 8 h darkness while the winter condition was 8 h light to 16 h darkness at 6 C.  Cultures were grown for over 14 days and population densities were kept constant by the daily removal of any progeny. 

Measurements were taken at the end of the experiment on several morphological traits including carapace length, max carapace width, length of tail spine, etc. Protein analysis was conducted by sacrificing 1 female per sample after removal of gut contents.  Gel electrophoresis was then conducted on the proteins and the resulting differences in number and position of polypeptide spots were analyzed.  

Lee found that the seasonal treatments caused significant morphological differences between individuals from the same clone for nearly all characters measured.  This seasonal difference was true for both clones from TSL and Rash Pond.  Summer treatments caused Daphnia to have smaller and less conspicuous measurements of all characters besides spine length, which increased in summer treatments.  Few differences existed between TSL and Rash Pond, although the tail spine was always longer in TSL and in summer, most characters were smaller for Rash Pond Daphnia. 

For the protein analysis, 4 clones were analyzed from TSL (all summer populations) and five from Rash Pond (3 in summer and 2 in winter).  Gel analysis revealed that there were many polypeptide spots common to all clones regardless of season or locality.  Lee found that about 30% of polypeptides did not change and 70% were plastic depending on the seasonal treatment.  Traits were more likely to be plastic in summer than in winter.  Variation between clones was higher in Rash Pond clones than in TSL clones. 

Lee explains that summer plasticity in Daphnia allows them to escape the predators associated with the summer environments of both TSL and Rash Pond.  Lee claims that the protein analysis suggests that these large variations between seasons represent switching between different genetic pathways and not just the expression of alternate alleles.  The author continues to note that Rash Pond has greater seasonal variability and unpredictability, hence their clones having more plasticity than TSL clones. 

Significance to TSL:  Lee also notes that in Summer, Daphnia individuals exhibit spatial variation where those individuals who live below the thermocline are conspicuous and have short tail spines while those individuals in the epilimnion are more susceptible to predation and thus are smaller and have longer tail spines. 

Overall Literature Significance: Cited by 4, most recently in 1997 by: Khan, A.A and A. Alam. Cyclomorphosis, the Morphological Responses to Certain Environmental Factors in Cladocera (Water Fleas): A Review. Recent Advances in Ecobiological Research, 1997.