In May 2002, I set out to test the central tenet of evolutionary theory
about phenotypic plasticity. Briefly stated the theory predicts that
plastic phenotypes evolve in variable environments whereas non-plastic
phenotypes evolve in constant environments. Freshwater snails (Helisoma
trivolvis) and their predators (i.e. water bugs, Belostoma
flumineum) provided an excellent opportunity to empirically test
this evolutionary theory. Using outdoor mesocosms, I reared snails in
three treatments: 1) constant no-predator, 2) constant predator, and
3) variable predator (predator added and removed every three months).
For each of the outdoor mesocosms, I have conducted annual assessments
of the populations' trait changes to track the course of evolution.
The funding provided by the Malacological Society of London Centenary
Research Grant has provided the resources necessary to continue my annual
assessments of trait evolution for the past two summers. The 2005 assessment
demonstrated that the snail populations exposed to constant no-predator
environments were less responsive to water bugs and tended to constantly
produce poorly defended phenotypes (i.e. narrow shells). However, there
was no indication that snail populations exposed to constant water bug
environments were becoming canalized for well defended phenotypes (i.e.
wider shells). This past September I conducted the final assessment
of the snail populations. Over the next several months, I will complete
the measurements on the snails and data analysis. Although the data
from the past assessments is encouraging, it would be premature to reach
conclusions about the experiment without the results from the final
assessment.
In summary, I would like to thank the Malacological Society of London
for their support on this long-term project.