Brown trout as biomonitor of heavy metal pollution: effect of age on the reliability of the assessment

Brown trout (Salmo trutta L.) is a native fish of the rivers of northern Spain. It is the dominant fish species in these rivers, and it is widespread over all the range of freshwater ecosystems in the area, including ecosystems potentially polluted with heavy metals. In this study, the potential of brown trout as biomonitor of heavy metal pollution and the effect of fish age on the reliability of the assessment are analyzed. Copper, lead, and cadmium concentrations of both abiotic compartments (water and sediments) and brown trout (S. trutta) from three northern Spanish rivers were analyzed. Significant correlations were found between sediment lead content and lead concentration in trout liver. One-year-old juvenile trouts were demonstrated to be useful as a biomonitor of copper and lead pollution, revealing between-location differences. Older trouts do not seem adequate to properly monitor heavy metal pollution. The effect of aging on the reliability of this species as biomonitor is discussed.     

Chemical Ecology of the host searching behavior in an Egg Parasitoid: are Common Chemical Cues exploited to locate hosts in Taxonomically Distant Plant Species?

Parasitoids are known to exploit volatile cues emitted by plants after herbivore attack to locate their hosts. Feeding and oviposition of a polyphagous herbivore can induce the emission of odor blends that differ among distant plant species, and parasitoids have evolved an incredible ability to discriminate them and locate their hosts relying on olfactive cues. We evaluated the host searching behavior of the egg parasitoid Cosmocomoidea annulicornis (Ogloblin) (Hymenoptera: Mymaridae) in response to odors emitted by two taxonomically distant host plants, citrus and Johnson grass, after infestation by the sharpshooter Tapajosa rubromarginata (Signoret) (Hemiptera: Cicadellidae), vector of Citrus Variegated Chlorosis. Olfactory response of female parasitoids toward plants with no herbivore damage and plants with feeding damage, oviposition damage, and parasitized eggs was tested in a Y-tube olfactometer. In addition, volatiles released by the two host plant species constitutively and under herbivore attack were characterized. Females of C. annulicornis were able to detect and significantly preferred plants with host eggs, irrespectively of plant species. However, wasps were unable to discriminate between plants with healthy eggs and those with eggs previously parasitized by conspecifics. Analysis of plant volatiles induced after sharpshooter attack showed only two common volatiles between the two plant species, indole and β-caryophyllene. Our results suggest that this parasitoid wasp uses common chemical cues released by many different plants after herbivory at long range and, once on the plant, other more specific chemical cues could trigger the final decision to oviposit.