Local site differences in survival and parasitism of periwinkles (Littorina sitkana Philippi, 1846)

Parasitism enhances gastropod feeding on invasive and native algae while altering essential energy reserves for organismal homeostasis upon warming

Marine bioinvasions are of increasing attention due to their potential of causing ecological and economic loss. The seaweed Gracilaria vermiculophylla has recently invaded the Baltic Sea, where, under certain conditions, it was found to outcompete the native alga Fucus vesiculosus. Parasites of grazers and temperature are among the potential factors which might indirectly modulate the interactions between these co-occurring algae through their single and combined effects on grazing rates. We tested the temperature and parasitism effects on the feeding of the gastropod Littorina littorea on F. vesiculosus vs. G. vermiculophylla. Uninfected and trematode-infected gastropods were exposed to 10, 16, 22, and 28 °C for 4 days while fed with either algae. Faeces production was determined as a proxy for grazing rate, and HSP70 expression, glycogen and lipid concentrations were used to assess the gastropod's biochemical condition. Gracilaria vermiculophylla was grazed more than F. vesiculosus. Trematode infection significantly enhanced faeces production, decreased glycogen concentrations, and increased lipid concentrations in the gastropod. Warming significantly affected glycogen and lipid concentrations, with glycogen peaking at 16 °C and lipids at 22 °C. Although not significant, warming and trematode infection increased HSP70 levels. Increased faeces production in infected snails and higher faeces production by L. littorea fed with G. vermiculophylla compared to those which fed on F. vesiculosus, suggest parasitism as an important indirect modulator of the interaction between these algae. The changes in the gastropod's biochemical condition indicate that thermal stress induced the mobilization of energy reserves, suggesting a possible onset of compensatory metabolism. Finally, glycogen decrease in infected snails compared to uninfected ones might make them more susceptible to thermal stress.

Diversity and Distribution of Bacteria Producing Known Secondary Metabolites

There is an increasing interest in the utilisation of marine bioactive compounds as novel biopharmaceuticals and agrichemicals; however, little is known about the environmental distribution for many of these molecules. Here, we aimed to elucidate the environmental distribution and to detect the biosynthetic gene clusters in environmental samples of four bioactive compounds, namely violacein, tropodithietic acid (TDA), tambjamine and the antibacterial protein AlpP. Our database analyses revealed high bacterial diversity for AlpP and violacein producers, while TDA-producing bacteria were mostly associated with marine surfaces and all belonged to the roseobacter group. In contrast, the tambjamine cluster was only found in the genomes of two Pseudoalteromonas species and in one terrestrial species belonging to the Cupriavidus genus. Using a PCR-based screen of different marine samples, we detected TDA and violacein genes associated with the microbiome of Ulva and Protohyale niger and tambjamine genes associated with Nodilittorina unifasciata; however, alpP was not detected. These results highlight the variable distribution of the genes encoding these four bioactive compounds, including their detection from the surface of multiple marine eukaryotic hosts. Determining the natural distribution of these gene clusters will help to understand the ecological importance of these metabolites and the bacteria that produce them.

Local site differences in survival and parasitism of periwinkles (Littorina sitkana Philippi, 1846)

The periwinkle, Littorina sitkana, is found throughout the intertidal zone, often in isolated subpopulations. The majority of trematode parasites use snails as intermediate hosts, and decreased survivorship is often observed in snails infected with trematodes. Sampling L. sitkana from four sites in Barkley Sound, British Columbia, Canada, we test the effects of parasitic infection on snail survival using maximum likelihood and Bayesian approaches using the software MARK and WinBUGS. We found that survival of periwinkles and trematode community composition differed among sites, but survival and trematode prevalence were uncorrelated. WinBUGS performed better than MARK in two ways: (1) by allowing the use of information on known mortality, thus preventing survival overestimation; and (2) by giving more stable estimates while testing the effect of body size on snail survival. Our results suggest that snail survival depends heavily on local environmental factors that may vary greatly within a small geographical region. These findings are important because the majority of experimental studies on survival are done on snails from a single location.