Variable Development in the Spionid Boccardia proboscidea (Polychaeta) Is Linked to Nurse Egg Production and Larval Trophic Mode

Abstract

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 1 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 1, but -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 (-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. proboscidea, but this is the first report of three developmental morphs within one population. Additional key words: poecilogony, larval ecology, adelphophagy, nurse egg, dispersal Benthic marine invertebrates exhibit a broad diversity in their life-history patterns, including the type of larvae produced (recently reviewed by Levin & Bridges 1995) and the larval trophic mode (feeding, nonfeeding) and habitat (planktonic, benthic). The mode of larval development has major significance in terms of fecundity, dispersal, recruitment, demography, and evolution (Christiansen & Fenchel 1979; Jablonski & Lutz 1983; Graham & Branch 1985; Strathmann 1993), and diversity is often manifested even between closely related species. However, a few species of marine invertebrates have poecilogonous development, producing more than one kind of offspring within a single species (Giard 1905). Poecilogonous species are not common, but several examples have been well described, and include both polychaetes (Blake 1969; a Present address: Dept. of Biology, Acadia University, Wolfville, Nova Scotia, BOP lXO Canada. E-mail: glenys.gibson @ acadiau.ca Blake & Kudenov 1981; Levin 1984; Qian & Chia 1991, 1992) and opisthobranch molluscs (West et al. 1984; Bouchet 1989; Gibson & Chia 1989; Carroll & Kempf 1990; Chester 1995). Although they are unusual, poecilogonous species present interesting systems in which to compare alternate life-history modes, while excluding inter-specific differences. Some species which have previously been thought to be poecilogonous have since been demonstrated to be cryptic species (Hoagland & Robertson 1988) making it essential to attempt to clarify if individuals thought to be poecilogonous actually represent one species. The objective of this paper is to examine developmental variability in Boccardia proboscidea HARTMAN 1940, a spionid polychaete. Larval development in B. proboscidea has been described by several authors, each examining a different population and most reporting a different development mode. Hartman (1941) first described development of B. proboscidea as including the release of both planktotrophic larvae and adelphophagic (nurse-egg ingesting) juveniles. SubseThis content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 06:39:39 UTC All use subject to http://about.jstor.org/terms