THE GENERATIONAL EFFECTS OF TEMPERATURE AND VISCOSITY ON FRESHWATER COPEPOD BODY SIZE

Bergmann’s Rule is an ecogeographical theory that states that closely related organisms will be larger in higher latitudes than those of lower latitudes. Copepods, small crustacean zooplankton that live at Intermediate Reynolds Numbers, closely follow this trend. While temperature is often stated to be the major driver behind this trend in body size, one little studied variable linked to temperature is viscosity. To test the effects of viscosity on copepod body size, two lineages of subtropical, freshwater Mesocyclops sp. copepods were grown for five generations in cultures of differing temperatures, 30C and 18C, and viscosities, natural and altered to mimic 18C while at 30C. Adult females were collected and measured, and their nauplii used to begin the next culture, the process repeated for each generation. It was found that copepods grown at 30C were on average 13.20% smaller than those grown at 18C, regardless of viscosity. Copepods grown in 30C cultures with the viscosity of 18C had no body size differences when compared to copepods grown at 30C and natural viscosity. Additionally, Mesocyclops sp. reached sexual maturity after 9 days while grown at 30C, and 11 days while grown at 18C, with viscosity playing no role in maturation time. This study provides further support for temperature driving copepod body size, with the physics of the environment playing no role in the body size of these small organisms. This is especially surprising due to copepod movement, feeding, and sensory ecology being reliant on the viscous properties of water. 

Presentation Preference: Poster

Primary Presenter: Zachary Wagner, Georgia Institute of Technology (zwagner7@gatech.edu)

Authors:

Zachary Wagner, Georgia Institute of Technology  (zwagner7@gatech.edu)

David Fields, Bigelow Laboratory for Ocean Sciences  (dfields@bigelow.org)

Jeannette Yen, Georgia Institute of Technology  (jeannette.yen@biosci.gatech.edu)