Population responses of the freshwater amphipod Gammarus pulex (L.) to an environmental estrogen, 17α-ethinylestradiol
✍ Scribed by Matthew M. Watts; David Pascoe; Kathleen Carroll
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 110 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0730-7268
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✦ Synopsis
Abstract
The effects of the environmental estrogen 17α‐ethinylestradiol (EE) on mixed populations of 90 individual Gammarus pulex were examined following a 100‐d exposure in a flow‐through system. Counts of total animal numbers revealed that, in all treatment groups, population size dramatically increased due to recruitment, with neonate and juvenile gammarids the most abundant. At concentrations of 1 and 10 μg/L EE, the recorded mean population sizes of 385 and 411, respectively, were significantly greater (p = 0.018) than the control (169). Mean population sizes in the solvent control (257) and 100 ng/L EE treatment (267) were not significantly different (p > 0.05) from the control. In addition to total counts, detailed image analysis of each individual animal allowed the assessment of length—frequency distributions, adult sex ratio, number of precopula pairs/ovigerous females, and measurement of secondary antenna and gnathopod length (secondary sex characteristics). The sex ratio of adults at 100 ng, 1 μg, and 10 μg/L EE was greater than 2:1 (female:male), and significantly more females (p = 0.008) were recorded at these concentrations compared with the control. The number of male adults, precopula guarding pairs, and ovigerous females did not differ between treatments (p > 0.05). Secondary antennal and gnathopod length in males was consistently greater than in females (p ≤ 0.001), but comparison between groups revealed no difference in these parameters.