In the American West, increased development, agriculture, and large hydrologic and irrigation projects have strongly impacted aquatic ecosystems by contributing to habitat fragmentation and altered environmental conditions. Understanding impacts on biotic communities requires multidimensional research that incorporates population genetics and landscape ecology, preferably over multiple time scales to capture historical and current eco-evolutionary processes.
We have focused our study on the benthic invertebrate Daphnia pulicaria, which produces ephippia that survive in sediments for decades. Our study system includes the lakes and canal system of the Columbia Basin Project (CBP) in southeast Washington State, which built 6 dams and >480 km of canals for irrigation, flood protection, and power and as one of the earliest (c. 1945) projects provides the opportunity for historical comparison of native Daphnia populations, which occur throughout the region.
Our objectives are to examine the genetic structure of populations across the CBP over time. We will use sediment core data from 16 lakes within and 7 outside of the boundaries of the CBP, completed in the 2015 and 2016 field seasons, for these analyses. We have conducted a literature review of ephippial morphometrics to assist in identifying ephippia extracted from sediment. Population genetic analysis combined with environmental data collected from the study lakes will enable us to infer eco-evolutionary patterns in this system.
We have sampled D. pulicaria ephippia in multiple CBP lakes for genetic analysis through surface sediment and sediment coring. Ephippia extracted from the sediment cores, sectioned at 1-cm intervals, have hatched at a 10% overall success rate, which is comparable to other paleolimnological hatching studies. Morphometric assessment of ephippia indicated that species from our study region are similar to ephippia from other regions, suggesting that we can use prior study results to identify D. pulicaria.
Sediment cores from two lakes, one from within and one from outside of the boundaries of the CBP, were submitted to an independent laboratory for 210Pb dating to determine a timeframe for sediment deposition. These analyses determined that sediment deposition occurs relatively slowly in our study region, such that our target time frame of 10 years prior to the initiation of the CBP (c. 1945) occurs at ~8 to 18 cm depth in different lakes. The upper 1 cm of sediment reflects our contemporary populations. We will employ landscape genetic models that use known and simulated data that describe landscape differences between sampling locations.