Consequences of water quality on genetic variation on the brackish water rotifer Brachionus plicatilis

Background/Question/Methods

Impacts of water quality on the genetic structure of freshwater zooplankton have not been well characterized. Unfavorable conditions may result in loss of species diversity and/ or select for tolerant genotypes. We investigated whether aquatic pollutants affect the genetic diversity of a model invertebrate, the rotifer Brachionus plicatilis. We predict that the genetic diversity of B. plicatilis will decrease with lower water quality. An urban population (Ascarate Lake, El Paso Co., TX) was compared with a remote, non-impacted population (Figure 8 Lake, Bottomless Lakes, NM). Basic water chemistry parameters (e.g., pH, salinity, conductivity) were measured in the field and additional samples were taken for heavy metal analyses. Nutrients, alkalinity, hardness, and turbidity were measured using a YSI photometer and kits. Metals were measured using ICP-OES following EPA protocols. Genetic variation was determined by cloning individual Brachionus plicatilis, and amplifying and sequencing the mitochondrial COI, 16S rRNA genes and the nuclear non-coding ITS region. Microsatellites will also be used to assess genetic variation, if other gene regions do not provide sufficient resolution.

Results/Conclusions

Most water chemistry parameters for Ascarate Lake fell within the EPA freshwater chronic criteria except for conductivity, salinity, and TDS. The results were similar for Figure 8 Lake.  However, Ascarate Lake exceeded criteria for several metals including; Aluminum (174 ppb), Cadmium (5 ppb), Chromium (36 ppb), Copper (55 ppb), and Selenium (157 ppb). Thus, Ascarate Lake will be used as the impacted site for this study. Figure 8 Lake only exceeded the criteria for Selenium (230 ppb), so this site will be used as the non-impacted site. Preliminary analyses of 16S rRNA genes showed no genetic variation among 16 individuals from Ascarate Lake. Although, the 16S rRNA did not provide sufficient level of variation for population analysis we were able to assign the B. plicatilis to the Brachionus sp. Almenara lineage which was originally isolated from a saline pond in Spain. Individuals from Figure 8 Lake are being cultured from diapausing eggs found in sediment samples. Determination of genetic variation within and between populations using genetic distances and haplotype frequencies are underway.