| The principal life cycle characteristics of Capitella capitata Type I (Annelida: Polychaeta) were measured under five experimental regimes: high temperature, high salinity (18 degrees C., 30 ppt); high temperature, low salinity (18 degrees C., 20 ppt); control or mid-range (15 degrees C., 25 ppt); low temperature, high salinity (12 degrees C., 30 ppt); low temperature, low salinity (12 degrees C., 20 ppt). The square root of the total number of offspring per female, mean number of offspring per brood, interval between broods and mean brooding time all showed significant treatment effects at a probability level of .05 or less (ANOVA). Experimental regime had no significant effect on the number of broods per female. Survivorship curves and life tables were prepared for all conditions except low temperature, low salinity in which very few individuals survived. Length of life in decreasing order was as follows: control (59 weeks); high temperature, high salinity (43 weeks); low temperature, high salinity (33 weeks); high temperature, low salinity (17 weeks). Net reproduction (Ro) and intrinsic natural increase (r) were calculated from the life tables; the latter using Euler's equation. There is no presumption that these experimental conditions resulted in maximum values of these parameters; the internal evidence, including brood size and number of offspring, suggests food was not limiting. Net reproduction in the several conditions was 36.69 (HTHS); 2.19 (HTLS); 41.75 (C); 2.16 (LTHS). Intrinsic rate of natural increase was 0.261 (HTHS); 0.070 (HTLS); 0.194 (C); and 0.039 (LTHS).; Hermaphroditic individuals were included among the parental animals and functioned as females; occasional hermaphrodites appeared among the progeny.; Of the life history traits that have been suggested to be important from an evolutionary point of view, mean offspring per brood, brood interval, incubation time, square root of total number of offspring, r, Ro, mortality and relation of reproductive effort to adult mortality have been shown in this study to be significantly influenced by environmental change. |
