26.4 Monday, Jan. 5 Accelerated mtDNA evolution in microcrustaceans (Daphniidae) that lack an ultraviolet-radiation refugium CONNELLY, SJ*; TAYLOR, DJ; Rochester Institute of Technology; University at Buffalo email@example.com
Ultraviolet radiation (UV-R) has been shown to negatively affect exposed organisms through induced DNA mutations, the formation of DNA photolesions, and an overall decreased fitness. Most zooplankton can reduce UV-R exposure by behavioral changes (vertical migration), acquisition of UV-filtering pigments and DNA repair processes. Nevertheless, these defenses may be overwhelmed or costly in high UV-R environments, leading to genomic evolution that minimizes DNA damage. Scapholeberis (Daphniidae) are potential candidates for UV-R mediated evolution because they spend much of their lives suspended from the waters surface. Predicted genomic changes in response to high UV-R are altered base composition (GC rich), reduced bipyrimidine sites and an increased mutation rate results in changes in the UV-R target sites of the DNA. Seventy Scapholeberis populations and representatives of each daphniid genus were sequenced for the mitochondrial regions comprised of 12s, 16s rDNA and tRNAVal (~1200 base pairs). Analysis revealed a significant increase in percent GC (%GC) base composition in several Scapholeberis species and a reduction of CC (a reported diagnostic UV mutation site) in one Scapholeberis sp. Additionally, relative rate tests showed a marked increase in the evolutionary rate between Scapholeberis and other daphniids. The results are consistent with the theory that extreme UV-R conditions can lead to genomic evolution in zooplankton. Additional daphnids are being assessed for similar genomic patterns under controlled UV conditions.