POECILOGONY AS A REPRODUCTIVE STRATEGY OF MARINE-INVERTEBRATES

Poecilogony is a polymorphism of sexual development in some marine inv ertebrates, in which both feeding and non-feeding or planktonic and be nthic larvae are produced. Since the original report on poecilogony by Gaird in 1905, a good number of such species have been recognized. Up on close examination, however, Hoagland and Roberston (1988) have foun d that almost all the 64 species reported to be poecilogonous are in f act a result of miss-identification of species or due to laboratory di sturbance. To be a poecilogonous species, a different mode of developm ent has to be found from sibling offspring of a single female, or from different individuals of a single biological species, and the differe nt modes of development cannot be altered by disturbance in laboratory handling. This being the case, there are only a few known species whi ch are poecilogonous. As a reproductive strategy poecilogony appears t o have the advantages of both the commonly recognized patterns of deve lopment, short planktonic or benthic development (without planktonic l arvae) and long planktonic development (broadcaster, with planktonic l arvae). The former allows immediate recruitment to the parental habita ts for fast population growth and the latter provides some degree of d ispersal and gene flow. In this paper, we briefly review the reproduct ion and larval development of three poecilogonous species (Haminaea ca llidegenita, Streblospio benedicti and Capitella sp.) and pose the fol lowing questions: 1) Why are the currently known examples of poecilogo nous species found only in polychaetes and opisthobranchs? 2) Why are poecilogonous animals predominately located on mud flats? 3) If poecil ogony is such a good reproductive strategy, why don't we see it in mor e species? We reasoned that polychaetes and opisthobranchs may be gene tically predisposed for more flexible reproduction, and that the mud f lat is among the most dynamic marine habitat, exerting greater selecti ve pressure favoring polymorphism of reproduction than that of other h abitats. We reasoned also that there may be more such species which ca n only be discovered through intensive and long term research on the r eproductive biology of invertebrates on mud flats.