Experimental evidence that intra-specific competition in seagrass meadows reduces reproductive potential in the sea urchin Paracentrotus lividus (Lamarck)

To better understand the biological controls that regulate sea urchin dynamics, we studied the effects of potential inter- and intra-specific competition for food on several biological variables of the main sea urchin in the Mediterranean (Paracentrotus lividus). We carried out a caging experiment in which we manipulated sea urchin density (natural vs. high density) and herbivorous fish (Sarpa salpa) accessibility (free access vs. exclusion) in a Posidonia oceanica meadow. No evidence of competition between fish and urchins was detected. Neither density-dependent mortality nor changes in the somatic variables were found; however, we detected that intra-specific competition affected the reproductive potential of P. lividus. The gonad index of urchins at high population densities was ca. 30% lower than that of urchins at natural densities. As a spawning event had just occurred when urchins were collected, these differences probably reflect differences in reserve content, which may compromise the following reproductive period and decrease survival in the long term, as the gonads are also used as storage organs. For the time period studied, mortality rates appeared to be independent of local densities. The results indicate that a long-term negative feedback mechanism appears to take place in P. lividus in response to increased population density.

Comparative sensitivity of tumor and non-tumor cell lines as reliable approach for in vitro cytotoxicity screening of lysine-based surfactants with potential pharmaceutical applications

Surfactants are used as additives in topical pharmaceuticals and drug delivery systems. The biocompatibility of amino acid-based surfactants makes them highly suitable for use in these fields, but tests are needed to evaluate their potential toxicity. Here we addressed the sensitivity of tumor (HeLa, MCF-7) and non-tumor (3T3, 3T6, HaCaT, NCTC 2544) cell lines to the toxic effects of lysine-based surfactants by means of two in vitro endpoints (MTT and NRU). This comparative assay may serve as a reliable approach for predictive toxicity screening of chemicals prior to pharmaceutical applications. After 24-h of cell exposure to surfactants, differing toxic responses were observed. NCTC 2544 and 3T6 cell lines were the most sensitive, while both tumor cells and 3T3 fibroblasts were more resistant to the cytotoxic effects of surfactants. IC50-values revealed that cytotoxicity was detected earlier by MTT assay than by NRU assay, regardless of the compound or cell line. The overall results showed that surfactants with organic counterions were less cytotoxic than those with inorganic counterions. Our findings highlight the relevance of the correct choice and combination of cell lines and bioassays in toxicity studies for a safe and reliable screen of chemicals with potential interest in pharmaceutical industry.

Experimental evidence that intra-specific competition in seagrass meadows reduces reproductive potential in the sea urchin Paracentrotus lividus (Lamarck)

To better understand the biological controls that regulate sea urchin dynamics, we studied the effects of potential inter- and intra-specific competition for food on several biological variables of the main sea urchin in the Mediterranean (Paracentrotus lividus). We carried out a caging experiment in which we manipulated sea urchin density (natural vs. high density) and herbivorous fish (Sarpa salpa) accessibility (free access vs. exclusion) in a Posidonia oceanica meadow. No evidence of competition between fish and urchins was detected. Neither density-dependent mortality nor changes in the somatic variables were found; however, we detected that intra-specific competition affected the reproductive potential of P. lividus. The gonad index of urchins at high population densities was ca. 30% lower than that of urchins at natural densities. As a spawning event had just occurred when urchins were collected, these differences probably reflect differences in reserve content, which may compromise the following reproductive period and decrease survival in the long term, as the gonads are also used as storage organs. For the time period studied, mortality rates appeared to be independent of local densities. The results indicate that a long-term negative feedback mechanism appears to take place in P. lividus in response to increased population density.