Meeting Abstract
S4-1.5 Thursday, Jan. 5 Sipunculan Larvae and “Cosmopolitan” Species SCHULZE, A.*; MAIOROVA, A.; TIMM, L.E.; RICE, M.E.; Texas A and M University at Galveston; Institut of Marine Biology; Texas A and M University at Galveston; Smithsonian Marine Station at Fort Pierce schulzea@tamug.edu
Sipuncula are a relatively small taxon with roughly 150 recognized species. Many species are geographically widespread or “cosmopolitan”. The pelagosphera larvae of some species are estimated to spend several months in the plankton. However, recent molecular evidence suggests that many of the “cosmopolitan” species actually represent species complexes, some not even monophyletic. Here we present data on three sipunculan species with different developmental modes that occur both in the Sea of Japan and in the Northeast Pacific. The development of the three species – Thysanocardia nigra, Themiste pyroides and Phascolosoma agassizii – is exceptionally well studied in both regions of the Pacific, owing to the extensive work of Mary Rice at the Friday Harbor Laboratories since the 1960s and that of Adrianov and Maiorova at the Institute of Marine Biology in Vladivostok. Interestingly, significant differences have been observed between the two regions with respect to reproductive and developmental timing, gametogenesis and developmental rate. In general, egg sizes are larger and development slower in the Northeast Pacific as compared to the Sea of Japan. These differences have been explained as a result of phenotypic plasticity exhibited under different environmental conditions, in particular temperature, but we show that the populations are also remarkably distinct genetically. Against our expectations, the largest genetic differentiation occurs in P. agassizii with the longest pelagic larval duration and the least in T. pyroides with the most abbreviated development. We are currently examining whether these counter-intuitive results are a product of over-conserved taxonomy by re-evaluating the morphological characters in each of these species.
