VARIABLE DEVELOPMENT IN THE SPIONID BOCCARDIA PROBOSCIDEA (POLYCHAETA) IS LINKED TO NURSE EGG PRODUCTION AND LARVAL TROPHIC MODE

摘要

Boccardia proboscidea has poecilogonous development, i.e., it produces more than one type of offspring. Patterns of larval development within one population (La Jolla, CA) vary both among broods produced by different females, and also within a single brood, as some females produce both planktotrophic larvae and benthic juveniles within a single egg capsule. The mode of larval development is linked to the production of nurse eggs, non-viable eggs that are ingested by developing larvae (a process called adelphophagy). Not all females produce nurse eggs and most observed here produced only developing oocytes (Type 1 development). Type I females produce offspring that hatch at an early larval stage (3-setiger) and are planktotrophic for 30 d before metamorphosing. Type 2 females are similar to Type I, but similar to 15% of the eggs per brood are non-developing nurse eggs. Type 2 offspring ingest the nurse eggs, larvae are slightly more advanced at hatching (3-5 setigers), and have a shorter planktotrophic period (19 d) than do Type 1 larvae. Type 3 females differ in that they produce broods in which most eggs (similar to 90%) are nurse eggs. Offspring in Type 3 broods are either adelphophagic (ingest nurse eggs, have accelerated development, and hatch as juveniles) or non-adelphophagic (do not ingest nurse eggs and are similar to Type 1 planktotrophic larvae). Adults of each type are morphologically and ecologically similar and offspring of Type 1 and Type 3 females are interfertile. Although larval development varies among females, a single female will consistently produce broods of the same type. Poecilogony has been reported previously in B. pro boscidea, but this is the first report of three developmental morphs within one population. [References: 32]