POTENTIAL, REALIZED, AND ACTUAL FECUNDITY IN THE CRAYFISH ORCONECTES IMMUNIS FROM SOUTHWESTERN ONTARIO

Data on crayfish life history are limited to a few populations of only a few species. Herein we examine the size-specific fecundity of a pop ulation of Orconectes immunis from southwestern Ontario. We compare lo g-log regressions of ovarian egg counts, abdominal egg counts, and the number of independent stage IV juveniles with the size of females to estimate reproductive losses associated with egg extrusion and hatchin g. We contrast these results with data from a Michigan population. Slo pes of the three allometric regressions for the Ontario population wer e significantly greater than zero (P < 0.05); however, the slope for t he ovarian egg counts was significantly less than the hypothesized val ue of 3.0 (P < 0.05), suggesting that ovarian egg counts did not scale volumetrically with size of females. An analysis of covariance indica ted that the slope for the ovarian egg counts differed significantly f rom the slopes for abdominal egg counts and the number of juveniles (P < 0.05), but the latter two regressions were parallel. The proportion al decline in fecundity between ovarian and abdominal egg counts could not be estimated unequivocally because the slopes differed. By contra st, the Michigan population exhibited a 35% decline between these stag es. A comparison of size-adjusted abdominal egg counts and the number of juveniles revealed a decline of 58% for the Ontario population. The observed differences in size-specific fecundity at each reproductive stage support the hypothesis that each of these parameters summarizes distinct life-history features. The roles of biotic and abiotic factor s on crayfish life history warrant further study.