Population responses to acute and chronic cadmium exposure in sexual and asexual estuarine gastropods

The acute lethal and chronic sublethal responses of sexual (Hydrobia ventrosa) and asexual (Potamopyrgus antipodarum) gastropod populations to cadmium exposure were examined. Three questions were addressed: (i) are there differences in responses of sexual and asexual populations; (ii) are the response patterns similar in lethal and sublethal exposure conditions; and (iii) how does preexposure to cadmium influence these responses. No differences between the two species in mean acute tolerance (LC₅₀) could be detected, but a significant difference was found between the slopes of the concentration-response curves. The steeper slope for P. antipodarium indicated a more uniform response for the asexual species than for H. ventrosa. In the sublethal experiment there was a significant difference in mean growth rate where, in general, P. antipodarum grew faster than H. ventrosa. P. antipodarum was more affected by cadmium at the low cadmium exposure, whereas growth rates were reduced equally for the two species at the high cadmium concentration. Pre-exposure to cadmium did not increase the tolerance to chronic exposure in either of the species, but P. antipodarum exhibited a tendency toward increased tolerance to acute cadmium stress after pre-exposure. The results show that there are differences between these closely related sexual and asexual species in response to cadmium, and that these differences are more pronounced under chronic sublethal exposure conditions.