Jeffrey S. Levinton

Ecology of Deposit-Feeding Animals in Marine Sediments

Deposit-feeding animals acquire food by swallowing large volumes of sediment. Possible food sources include organic debris and sediment-associated microbes. The relative importance of these classes of food is currelty an area of active research. The idea that microbes attached to sediment and detritus particles constitute the major food source for deposit feeders is being replaced by more complex models that incorporate interactions between animals and the food sources in the sedimentary matrix. Many deposit feeders appear to require both microbial and detrital foods. Deposit feeders display many adaptations appear to be cosistent with the energy maximization principle of optimal foraging theory, but rigorous testing of foraging models has proven to be difficult. Elucidation of deposit-feeding strategies may develop as optimal foraging theory is integrated with physiological energetics.

Molecular evidence for deep precambrian divergences among Metazoan phyla

A literal reading of the fossil record suggests that the animal phyla diverged in an “explosion” near the beginning of the Cambrian period. Calibrated rates of molecular sequence divergence were used to test this hypothesis. Seven independent data sets suggest that invertebrates diverged from chordates about a billion years ago, about twice as long ago as the Cambrian. Protostomes apparently diverged from chordates well before echinoderms, which suggests a prolonged radiation of animal phyla. These conclusions apply specifically to divergence times among phyla; the morphological features that characterize modern animal body plans, such as skeletons and coeloms, may have evolved later.

Rapid Evolution of Metal Resistance in a Benthic Oligochaete Inhabiting a Metal-polluted Site

We identified a case of very rapid evolution of resistance in a common freshwater benthic invertebrate, to sediment with extremely high levels of cadmium and nickel. Limnodrilus hoffmeisteri from metal-polluted sites in Foundry Cove (New York) was significantly more resistant than conspecifics from a nearby control site, to both metal-rich natural sediment and metal-spiked water. Resistance differences were also found among sites within Foundry Cove. The elevated resistance in Foundry Cove worms was genetically determined, as it was still present after two generations in clean sediment. Resistance had evolved rapidly (within 30 years). A laboratory selection experiment and estimates of the heritability of this resistance in L. hoffmeisteri from the control site, indicated that the resistance could have evolved in 1 to 4 generations. The laboratory selection resulted in a large increase in resistance after two generations of selection, while we demonstrated that most of the phenotypic variation was additiv...

Latitudinal Differentiation in Copepod Growth: An Adaptation to Temperature

We demonstrate the presence of significant differentiation in development rate, adult body length, and stomatic growth rate in the estuarine harpacticoid copepod Scottolana canadensis (Willey) collected from a broad range of latitudes (27°—43° N) and reared in the laboratory for several generations under the same conditions (15 g salts per 1000 g seawater, and 15°, 20°, 25°, or 28°C). The changing pattern of differential growth with increased temperature suggests local adaptation to maximize scope for growth under prevailing temperatures conditions; northern—derived individuals grew faster at low but not at high temperatures. See full-text article at JSTOR

The effect of grazing by the detritivore Orchestia grillus on Spartina litter and its associated microbial community

SummaryOrchestia grillus efficiently feeds upon microorganisms attached to ingested Spartina alterniflora litter, but does not digest litter itself. Microorganisms respond to Orchestia grazing with increased metabolic activity, reflected in accelerated decomposition of the nitrogen fraction of litter and increased microbial biomass. Increased microbial activity may be partly a function of ammonia excretion and higher diffusion rate due to animal movement, but mainly it is a direct response to grazing. Microbial biomass increases with grazing because the pool of available nitrogen becomes larger. A model postulating interactions between Orchestria, Spartina litter and attached microorganisms is presented.

THE LATITUDINAL COMPENSATION HYPOTHESIS: GROWTH DATA AND A MODEL OF LATITUDINAL GROWTH DIFFERENTIATION BASED UPON ENERGY BUDGETS. I. INTERSPECIFIC COMPARISON OF OPHRYOTROCHA (POLYCHAETA: DORVILLEIDAE)

A northern (North Carolina) sibling species of Ophryotrocha grew more rapidly than a southern sibling species (Florida); this presumed advantage, however, diminished to zero as temperature increased from 15 to 30°C. Survival of the northern sibling species was low at 30°C. The differential response probably had a genetic basis since both species had been reared for 2-3 generations under the same conditions. The effect lasted in laboratory populations reared for a year in the laboratory at 25°C (ca. 10 generations). My results are consistent with a graphical model that suggests an evolutionary shift of metabolism-temperature curves and feeding efficiency curves for the two sibling species. These shifts predict a changing advantage of growth of one species relative to the other as temperature increases.

Ecology of Marine Deposit Feeders

1 Deposit Feeding and Coastal Oceanography.- 2 Examining Relationships Between Organic Carbon Flux and Deep-Sea Deposit Feeding.- 3 Early Diagenesis of Organic Matter and and the Nutritional Value of Sediment.- 4 The Nature and Determination of Non-Living Sedimentary Organic Matter as a Food Source for Deposit Feeders.- 5 Digestion Theory Applied to Deposit Feeding.- 6 Time-Dependent Absorption in Deposit Feeders.- 7 Radiotracer Methods for Determining Utilization of Sedimentary Organic Matter by Deposit Feeders.- 8 The Lnportance of Size-Dependent Processes in the Ecology of Deposit-Feeding Benthos.- 9 The Relationship Between Ingestion Rate of Deposit Feeders and Sediment Nutritional Value.- 10 Modeling Deposit Feeding.- 11 The Effects of Sediment Transport and Deposition on Infauna: Results Obtained in a Specially Designed Flume.- 12 Small-Scale Features of Marine Sediments and Their Importance to the Study of Deposit Feeding.- 13 On Some Mechanistic Approaches to the Study of Deposit Feeding in Polychaetes.- 14 Some Ecological Perspectives in the Study of the Nutrition of Deposit Feeders.

The availability of microorganisms attached to sediment particles as food for Hydrobia ventrosa Montagu (Gastropoda: Prosobranchia)

SummaryThe deposit-feeding prosobranch Hydrobia ventrosa Montagu feeds most rapidly upon sediment particles that pass through a 10 μm sieve. Ingestion rate decreases with particles 80–125 μm, then increases with larger particles, which are fed upon by scraping fine material from their surfaces. Hydrobia is capable of digesting diatoms and bacteria from sediment particles, but with generally lower efficiencies than reported when fed pure cultures. Digestion of microorganisms appears to be constrained by ability of the snail to detach cells from sediment particles; only those cells detached from sediment seem to be available for digestion. In contrast, the amphipod Corophium volutator is capable of utilizing most of the diatoms not digested by Hydrobia. For a given sediment, a constant number of microorganisms appear to be safe from digestion by H. ventrosa, and bacteria and microalgae over this amount constitutes the available food.

The effect of density upon deposit-feeding populations: Movement, feeding and floating of Hydrobia ventrosa Montagu (Gastropoda: Prosobranchia)

SummaryCrawling rate, feeding rate and floating frequency were measured for laboratory populations of the deposit-feeding snail Hydrobia ventrosa at densities of 0.3–16 snails cm-2. Both movement and feeding were depressed with increasing density. However, floating increased with increasing density. Crowding effects are thus important in deposit-feeding populations and must be considered along with resource-renewal in considerations of population control. Floating may be an adaptation to escape crowded conditions.

Site of particle selection in a bivalve mollusc

Bivalve molluscs form dense populations that exert profound effects on the particle loads and phytoplankton composition of coastal waters. It has long been known that bivalves can select among different particle types, including selecting against those of poor nutritional value, but because of difficulties in observing particle transport processes in the pallial cavity in vivo, the mechanism of selection was not known. We now use a combination of video endoscopy and flow cytometry to show that oysters can select living particles from non-living detritus on the gills. Our methods could aid the study of suspension feeding in many animal groups.