Integrating life history and molecular responses to arsenic and heavy metals in a basal consumer (Rotifera: Plationus patulus) in a riverine food web
One aquatic system that has been dramatically degraded by human impact is the Rio Grande. Few studies have been published concerning water quality in the El Paso-Ciudad Juárez stretch of the river, and fewer still focus on the health of the ecosystem. Reports by government agencies such as the International Boundary Water Commission (IBWC) and the United States Geology Survey (USGS) have identified numerous chemical contaminants in the river, including heavy metals. While heavy metals have been detected in the river, their effects on the aquatic food web are largely unknown. Rotifers, basal consumers, have been used as bioindicators in freshwater systems due to their life history characteristics and cosmopolitan distribution. I determined the effects of arsenic and heavy metals in the rotifer, Plationus patulus at both the molecular (HSP60 induction) and the population level. Specifically, the following questions were addressed: (1) What are typical ambient concentrations of arsenic and heavy metals in the Rio Grande, (2) How do metals at environmental concentrations impact the population dynamics of basal consumers (rotifers), (3) Are stress proteins (HSP60) induced by metals as a molecular mechanism to prevent cellular damage? ^ Most metals were found at low concentrations in sediments and water, although Zinc and Pb were above the EPA chronic freshwater water criteria concentrations at 4 of the 7 sites. Results from this survey were used to define experimental exposure concentrations for both population dynamics and HSP60 induction experiments. Rotifers were exposed to different concentrations and combination of metals to develop statistical models that predict the effects of As and heavy metal in population dynamics. Seven population end points were measured: intrinsic rate of increase (r), relative cumulative reproduction (RCR), mictic ratio, fertilization ratio, resting egg production, mortality ratio, and deformed rotifers. ^ Exposure to metal mixtures resulted in several significant changes in population dynamics. Intrinsic rate of increase was lower in all treatments as compared to controls. Cu treatments produced the lowest population growth rates and highest mortality ratios. Mortality ratios are strongly affected by the presence of Cr as well. Zn results in decreased RCR and a decrease in resting egg production. Deformities in rotifers are induced by the presence of Ni and Pb in the media. HSP60 induction in response to As and heavy metal exposure (singly or in combination) depended on metal type and concentration as well as exposure time. Heavy metals in single exposures induced HSP60 while As did not. Mixtures of As and metals was did not always induce HSP60 or affect population end points additively. End points may be increased or inhibited when interactions between metals occur. Although responses to metal mixtures are complex and difficult to predict, our results show that even low concentrations of metals and arsenic can dramatically alter the short-term physiology and population dynamics of rotifers. Since rotifers are at the base of the aquatic food web, any effect caused by toxicants will have important implications for higher trophic levels. ^
Health Sciences, Toxicology|Environmental Sciences|Biology, Limnology
Rios, Judith Virginia, "Integrating life history and molecular responses to arsenic and heavy metals in a basal consumer (Rotifera: Plationus patulus) in a riverine food web" (2003). ETD Collection for University of Texas, El Paso. AAI3118501.