Sara M. Lindsay

Diet of Worms Emended: An Update of Polychaete Feeding Guilds

Polychaetes are common in most marine habitats and dominate many infaunal communities. Functional guild classification based on taxonomic identity and morphology has linked community structure to ecological function. The functional guilds now include osmotrophic siboglinids as well as sipunculans, echiurans, and myzostomes, which molecular genetic analyses have placed within Annelida. Advances in understanding of encounter mechanisms explicitly relate motility to feeding mode. New analyses of burrowing mechanics explain the prevalence of bilateral symmetry and blur the boundary between surface and subsurface feeding. The dichotomy between microphagous deposit and suspension feeders and macrophagous carnivores, herbivores, and omnivores is further supported by divergent digestive strategies. Deposit feeding appears to be limited largely to worms longer than 1 cm, with juveniles and small worms in general restricted to ingesting highly digestible organic material and larger, rich food items, blurring the macrophage-microphage dichotomy that applies well to larger worms.

Frequency of Injury and the Ecology of Regeneration in Marine Benthic Invertebrates

Many marine invertebrates are able to regenerate lost tissue following injury, but regeneration can come at a cost to individuals in terms of reproduction, behavior and physiological condition, and can have effects that reach beyond the individual to impact populations, communities, and ecosystems. For example, removal and subsequent regeneration of clams siphons, polychaetes segments, and brittlestars arms can represent significant energetic input to higher trophic levels. In marine soft-sediment habitats, injury changes infaunal bioturbation rates and thus secondarily influences sediment-mediated competition, adult-larval interactions, and recruitment success. The importance of injury and regeneration as factors affecting the ecology of marine invertebrate communities depends on the frequency of injury, as well as on individual capacity for, and speed of, regeneration. A key question to answer is: How frequently are marine benthic invertebrates injured? Here, I review the sources and the frequencies of injury in a variety of marine invertebrates from different benthic habitats, discuss challenges, and approaches for accurately determining injury rates in the field, consider evidence for species-specific, temporal and geographic variation in injury rates, and present examples of indirect effects of injury on marine invertebrates to illustrate how injury and regeneration can modify larger-scale ecological patterns and processes.

Feeding responses to particle-bound cues by a deposit-feeding spionid polychaete, Dipolydora quadrilobata (Jacobi 1883)

In marine soft-sediment habitats, chemical sensing by deposit-feeding organisms most likely plays a critical role in feeding behavior, yet, few specifics about this role and its ecological implications are known. We show that several particle-bound chemical cues stimulate feeding activity of a spionid polychaete Dipolydora quadrilobata (Jacobi 1883). Using glass beads as a proxy for sediment, we tested for feeding responses to a selected number of potential cues that might be used to indicate food availability or quality. We presented two sets of beads to individual intact worms: one with and one without covalently bound compounds such as single amino acids, mixtures of amino acids, and single simple sugars. Worms were exposed to the beads under slow flowing seawater so that any dissolved cues were flushed from the test chamber. Each worm was videotaped for 15 min immediately following the addition of beads, and these records were scored for the time the worm spent in a variety of behaviors. Responses to beads with and without cues were compared to identify compounds as stimulatory, inhibitory, or inactive. Five of the seven particle-bound cues tested significantly increased feeding activity, and none of those tested were found to be inhibitory.

Immunolocalization of a Gαq protein to the chemosensory organs of Dipolydora quadrilobata (Polychaeta: Spionidae)

Chemoreception in marine invertebrates mediates a variety of ecologically important behaviors including defense, reproduction, larval settlement and recruitment, and feeding. The sensory pathways that regulate deposit-feeding activity by polychaetes living in sedimentary habitats are of particular interest because such feeding has profound effects on the physical and chemical properties of the habitat. Nevertheless, little is known concerning the molecular mechanisms of chemical signal transduction associated with deposit feeding and other behaviors in polychaetes. Chemosensory-based feeding behaviors are typically regulated by G-protein-coupled signal transduction pathways. However, the presence and role of such pathways have not been demonstrated in marine polychaetes. Methodologies involving degenerate primer-based reverse transcription with the polymerase chain reaction and rapid amplification of cDNA ends were used to identify and characterize a Gαq subunit expressed in the feeding palps of the spionid polychaete Dipolydora quadrilobata. The D. quadrilobata Gαq protein had high sequence similarity with previously reported Gαq subunits from both invertebrate and vertebrate taxa. Immunhistochemistry and immunocytochemistry were used with confocal laser scanning microscopy and transmission electron microscopy to visualize the distribution of a Gαq antibody in whole worms and in cilia of the feeding palps. Gαq immunoreactivity was concentrated in the nuchal organs, food-groove cilia, and lateral/abfrontal cilia of the feeding palps. Because these structures are known to be involved in chemoreception, we propose that Gαq isolated from D. quadrilobata is a key component of chemosensory signal transduction pathways in this species.