Adam G. Marsh

Larval dispersal potential of the tubeworm Riftia pachyptila at deep-sea hydrothermal vents

Hydrothermal vents are ephemeral because of frequent volcanic and tectonic activities associated with crust formation. Although the larvae of hydrothermal vent fauna can rapidly colonize new vent sites separated by tens to hundreds of kilometres, the mechanisms by which these larvae disperse and recruit are not understood. Here we integrate physiological, developmental and hydrodynamic data to estimate the dispersal potential of larvae of the giant tubeworm Riftia pachyptila. At in situ temperatures and pressures (2 °C and 250 atm), we estimate that the metabolic lifespan for a larva of R. pachyptila averages 38 days. In the measured flow regime at a fast-spreading ridge axis (9° 50′ N; East Pacific Rise), this lifespan results in potential along-ridge dispersal distances that rarely exceed 100 km. This limited dispersal results not from the physiological performance of the embryos and larvae, but instead from transport limitations imposed by periodic reversals in along-ridge flows and sustained episodes of across-ridge flow. The lifespan presented for these larvae can now be used to predict dispersal under current regimes at other hydrothermal vent sites.

Effect of food type and ration on growth of juvenile Capitella sp. I (Annelida: Polychaeta): macro- and micronutrients

Growth rates of juvenile Capitella sp. I were determined on different rations of six food types: Gerbers mixed cereal, TetraMin fish flakes, benthic diatoms, Ulva sp., spring detritus, and summer detritus. A simple growth model estimated maximum growth rate and maintenance ration for each food. There were differences in the growth response among foods relative to nitrogen content. As juveniles increased in size, differences in growth between foods became more pronounced. For all juveniles, growth rates were correlated with levels of the amino acids histidine, phenylalanine, threonine, and valine, and the polyunsaturated fatty acid 20:5w3; correlations with histidine and phenylalanine levels were the most significant. Regressions of growth rates as a function of these two amino acids suggest a daily maintenance ration of 300 pg histidine and phenylalanine mg-1 nitrogen biomass. Juvenile worms grew on spring detritus but not on summer detritus, indicating the probable importance of micronutrients (polyunsaturated fatty acids, amino acids) for growth of juvenile Capitella sp. I in the field.

Short-term reproductive responses of capitella sp. I (Annelida: Polychaeta) fed on different diets

Abstract We measured short-term reproductive responses (15 days) of Capitella sp. I (Annelida: Polychaeta) at 20 °C for six daily ration levels (0.13–1.30 mg of organic N per cup) of four food sources (diatoms, Ulva , Tetramen fish food and Gerbers mixed cereals). Both food ration and food type influenced the size of the females and their reproductive characteristics (number of fertile segments, fecundity, number of eggs per fertile segment, and reproductive output). Daily food rations also affected the proportion of brooding females. The amount and the source of the food available affected both the periodicity and the intensity of reproduction. We used simple linear regression models to describe the relationships between reproductive characteristics (fecundity and reproductive output) and daily (N, C, and calories) rations. We ran an experiment allowing us to account for differential losses of hydrosoluble molecules by leaching from the different food types. This correction increased the correlation coefficients. In all cases, N ration best described both fecundities and reproductive outputs.

Nucleotide sequence variability in the nontranscribed spacer of the rRNA locus in the oyster parasite Perkinsus marinus.

We examined the sequence variability of the nontranscribed spacer (NTS) and internal-transcribed spacer (ITS1 and ITS2) domains of the rRNA locus of Perkinsus marinus from Maryland, Florida, and Louisiana. The sequence of P. marinus DNA including the 5S rRNA, NTS, small subunit (SSU) rRNA, ITSI, and ITS2 regions confirmed their contiguity in the rRNA locus and revealed differences at 28 positions with the SSU rRNA sequences published earlier. The 307-bp polymerase chain reaction (PCR)-amplified fragments from the NTS domain of the various P. marinus isolates revealed the presence of 2 distinct sequences, designated as types I and II, that differed at 6 defined nucleotide positions. Based on these differences, nested PCR and restriction enzyme digests were used to distinguish between the 2 types. Sequences of the ITS1 and ITS2 domains of samples from either NTS type I (n = 3) or type II (n = 3) showed no variation and were identical to published sequences. Frequencies of the P. marinus NTS sequence types I and II in infected oysters varied with the geographic origin of the samples. All Maryland samples examined (n = 19) corresponded to the NTS type I sequence, the type II was the most frequent in the Florida samples (n = 17), and both types were about equally represented in the Louisiana samples (n = 19), with both sequence types found in individual oyster specimens. Although it has been suggested that P. marinus is diploid, it remains to be determined if both NTS sequence types can be present in a single P. marinus trophozoite.

Allocation of nutrient resources to body components by regenerating Luidia clathrata (Say) (Echinodermata: Asteroidea)

Abstract Intact Luidia clathrata (Say) and individuals with two adjacent arms amputated were fed on a maintenance-level diet or starved for 3 months during the gametogenic period. The radius of the intact arms did not change significantly in any of the groups. The radius and the amount (g dry weight) of regenerating arms of fed individuals were 3- to 4-fold as great as those of starved individuals. The amount of pyloric caeca and gonad in an intact arm increased in fed individuals and the amount of pyloric caeca decreased in starved ones independently of regeneration. The amount of pyloric caeca in an intact arm increased more in fed, regenerating individuals than in fed, intact individuals; the total amount of increase in the pyloric caeca was equivalent in the two groups. Absorbed nutrients are allocated primarily to growth of the pyloric caeca and gonads of the intact arms and secondarily to regeneration. This increase in functional capacity in terms of nutrient storage (pyloric caeca) and reproduction (gonads) may be more important than an increase in capacity for locomotion.

Fecundity and energy partitioning in Capitella capitata type I (Annelida: Polychaeta)

Three sets of experiments were carried out between April and September 1987 to assess reproductive energetics in a laboratory population of the capitellid polychaete Capitella capitata type I. In the first experiment, the population was sampled intensively over a short period of 3 wk. Weight-specific reproductive output did not differ significantly between females and hermaphrodites. However, because hermaphrodites were significantly bigger than females, their fecundity was significantly higher. In the second experiment, fecundity and weight-specific reproductive output were monitored weekly over the oscillation cycle of the population (30 wk). Both fecundity and weight-specific reproductive output varied drastically (40 to 80 eggs per female and 17 to 57%, respectively). In the third experiment, non-sexed juveniles were reared for 15 d on six ration levels (normalized on the basis of organic nitrogen) of four different food sources. The maximum weight-specific reproductive output was 70% (for females). Both fecundity and weight-specific reproductive output were positively correlated with food ration and varied with food type. The data on weight-specific reproductive output recorded in the present study have been compared with those of other iteroparous polychaetes in the literature. Reproductive output in C. Capitata type I varies more widely and is greater than in other iteroparous polychaetes. In this species, reproductive output and population dynamics vary concomitently with the level of organic matter in the habitat.

DNA methylation and temperature stress in an Antarctic polychaete, Spiophanes tcherniai

Epigenetic modifications of DNA and histones are a primary mechanism by which gene expression activities may be modified in response to environmental stimuli. Here we characterize patterns of methyl-cytosine composition in the marine polychaete Spiophanes tcherniai from McMurdo Sound, Antarctica. We cultured adult worms at two temperatures, −1.5°C (ambient control) and +4°C (warm treatment), for 4 weeks. We observed a rapid capacity for S. tcherniai organismal respiration rates and underlying catalytic rates of citrate synthase at +4°C to return to control levels in less than 4 weeks. We profiled changes in the methylation states of CpG sites in these treatments using an NGS strategy to computationally reconstruct and quantify methylation status across the genome. In our analysis we recovered 120,000 CpG sites in assembled contigs from both treatments. Of those, we were able to align 28,000 CpG sites in common between the two sample groups. In comparing these aligned sites between treatments, only 3000 (11%) evidenced a change in methylation state, but over 85% of changes involved a gain of a 5-methyl group on a CpG site (net increase in methyation). The ability to score CpG sites as partially methylated among gDNA copies in a sample opens up a new avenue for assessing DNA methylation responses to changing environments. By quantitatively distinguishing a “mixed” population of copies of one CpG site, we can begin to identify dynamic, non-binary, continuous-response reactions in DNA methylation intensity or density that previously may have been overlooked as noise.

EFFECT OF TEMPERATURE AND SALINITY ON LARVAL DEVELOPMENT OF SIBLING SPECIES OF ECHINASTER (ECHINODERMATA: ASTEROIDEA) AND THEIR HYBRIDS

Adult Echinaster Type 1 and Type 2 were collected along the west coast of Florida (25° C, 32‰S) and induced to spawn in the laboratory. Two-day old larvae of Type 1, Type 2, and their hybrids were subjected to temperature (T) and salinity (5) combinations (20, 25, 30°C; 25, 32, 39‰S). Response surface isopleths indicate that Type 1 and Type 2 larvae exhibit different developmental and growth rates in response to T/S combinations. Salinity was a dominant factor affecting development and growth. High and low salinities inhibited spine development. Developmental rates were directly related to temperature. Type 2 larvae exhibited a greater tolerance to temperature changes than did Type 1. Hybrids showed intermediate development and growth responses at the apparent optimal conditions and exhibited maternal characteristics.

eXPatGen: generating dynamic expression patterns for the systematic evaluation of analytical methods

MOTIVATION Experimental gene expression data sets, such as those generated by microarray or gene chip experiments, typically have significant noise and complicated interconnectivities that make understanding even simple regulatory patterns difficult. Given these complications, characterizing the effectiveness of different analysis techniques to uncover network groups and structures remains a challenge. Generating simulated expression patterns with known biological features of expression complexity, diversity and interconnectivities provides a more controlled means of investigating the appropriateness of different analysis methods. A simulation-based approach can systematically evaluate different gene expression analysis techniques and provide a basis for improved methods in dynamic metabolic network reconstruction. RESULTS We have developed an on-line simulator, called eXPatGen, to generate dynamic gene expression patterns typical of microarray experiments. eXPatGen provides a quantitative network structure to represent key biological features, including the induction, repression, and cascade regulation of messenger RNA (mRNA). The simulation is modular such that the expression model can be replaced with other representations, depending on the level of biological detail required by the user. Two example gene networks, of 25 and 100 genes respectively, were simulated. Two standard analysis techniques, clustering and PCA analysis, were performed on the resulting expression patterns in order to demonstrate how the simulator might be used to evaluate different analysis methods and provide experimental guidance for biological studies of gene expression. AVAILABILITY http://www.che.udel.edu/eXPatGen/

Dietary effects on oocyte yolk-composition inCapitella sp. I (Annelida: Polychaeta): Fatty acids and sterols

In 1988, immatureCapitella sp. I (initial biomass 80µg dry wt) were raised on four diets: Gerber cereal, TetraMin fish food,Ulva sp., and benthic diatoms. After 2 wk of culturing different populations on these diets, eggs were dissected from gravid females, frozen and analyzed for fatty acid and sterol composition. Eggs produced by worms on different food types were discriminated by fatty acid composition in a principal component analysis (PCA), with 18:19, 18:2, 20:5 and 20:4 fatty acids showing the greatest differences between experimental groups. The sterol profiles of all eggs were dominated by cholesterol (cholest-5-en-3β-ol) and cholest-5,24-dien-3β-ol (>60%). A PCA of egg sterols discriminated between adult diets with cholesterol, 23,24-dimethyl-cholesta-5-en-3β-ol, cholest-5,24-dien-3β-ol and a C-29 stenol showing the greatest differences. In field populations ofCapitella sp. I, oocytes produced at different times of the year may have different levels of lipids depending on their dietary availability during vitellogenesis. Variations in oocyte composition may influence larval growth and development and thus have an impact on population dynamics. Alternatively, variations in fatty acid and sterol composition of oocytes may allow us to identify the food resources utilized by this species.