REPRODUCTIVE ISOLATION - INTERANNUAL VARIABILITY IN THE TIMING OF REPRODUCTION IN SYMPATRIC SEA-URCHINS, GENUS PSEUDECHINUS

Reproductive cycles of 3 sympatric species of the echinoid genus Pseud echinus, found in southeastern New Zealand, were examined over 27 mont hs from October 1989 to December 1991. Analysis of periodic changes in relative gonadal size was used to help define the reproductive cycle of each species, Although P. huttoni reproduced primarily during the e arly (austral) summers of 1990 and 1991 (December-January), mature gam etes were present in the gonads throughout much of the year. Conversel y, P. novaezealandine reproduced primarily during the autumn and early winter (May-July). P. albocinctus had an extended reproductive period in 1990, which peaked in late spring/early summer (December-January), followed by a gradual spawn-out to late autumn (May-June). The patter n was different in 1991, with a secondary peak in reproductive potenti al noted in late autumn (June). For all 3 species, males tended to be competent to spawn gametes for a longer period than were females. Thes e observations were all corroborated by analysis of changes in overall gonad histology and in the distribution of oocyte sizes in the ovarie s of each species throughout the year. P. huttoni and P. novaezealandi ae thus appeared to exhibit temporal reproductive isolation from each other. Intraspecific as well as interannual variability in the timing of reproduction, however, suggests that such temporal isolation may no t always be complete. In contrast, P. albocinctus was not temporally i solated from either of its 2 sympatric congeners. These results were e xamined in the context of seasonally variable environmental conditions .