Influence of body size and gender on valve movement responses of a freshwater bivalve to uranium.

Body size, age, and gender (male or female) are important variables influencing many aspects of the ecology, physiology, and survival of animals. However, no data are available on the influence of these variables on bivalves exposed to sublethal metal concentrations. This study tested whether the valve movement responses (measured in terms of the duration or frequency of valve opening) of the Australian tropical freshwater unionoid bivalve, Velesunio angasi, exposed to sublethal uranium (U) concentrations in a standard synthetic water (pH, 6.0; hardness and alkalinity, 4 mg/L as CaCO(3)) were influenced by body size (shell length, shell breadth, or dry tissue weight), age, and/or gender. The valve movement responses of V. angasi to U were independent of gender; the sensitivity of males to U was not significantly (p > 0.05) different from that of females. In contrast, the valve movement responses of V. angasi to U were size- and age-dependent; smaller and younger individuals (median shell length = 36.8 mm; median age = 0.7 years) were 22% more sensitive (p </= 0.05) than larger and older individuals (median shell length = 61.3 mm; median age = 14 years). By correcting for differences in body size, age, and/or gender among individuals, using multiple linear regression analyses, the mean variability in valve movement responses was reduced by 81%. Consequently, errors (95% confidence limits) associated with valve movement response (EC(50)) values were substantially reduced (75%). Hence, the ability to demonstrate statistically significant (p </= 0.05) differences in valve movement responses between U exposure concentrations was enhanced. This, in turn, may permit better estimates of the risk of the effects of U exposures to bivalve populations. Copyright 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 126-136, 2003