Demir Neslihan

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Demir
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Neslihan
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  • Article
    Response of the American lobster to the stress of shell disease
    (National Shellfisheries Association, 2005-10) Laufer, Hans ; Demir, Neslihan ; Biggers, William J.
    Shell disease is a problem affecting lobsters in eastern Long Island Sound causing disfiguration of the shell, decreasing the lobsters' value, and whereas mild and medium levels of the disease are not lethal, ultimately, severe cases result in mortality. Levels of the molting hormone, ecdysone, were quantitated, using a radioimmunoassay (RIA), in hemolymph of animals exhibiting shell disease. Our results indicate that levels of ecdysone were increased in the hemolymph of shell-diseased lobsters, with a medium level of expression of the disease to 89 ± 32 ng/mL (n = 76), whereas unaffected, presumably healthy ones had 57 ± 16 ng/mL (n = 210). In 7 of 10 months of the year shell-diseased animals had higher ecdysone levels in their hemolymph than unaffected animals. In addition, ecdysone levels were abnormally high, 165 ± 53 ng/mL (n = 5), in shell-diseased ovigerous lobsters, whereas normal unaffected ovigerous ones had low levels of this hormone, 13 ± 4 ng/mL (n = 7). These results indicate that shell disease may induce lobsters to alter the systemic levels of ecdysone, possibly serving as a defensive measure, allowing the animals to ward off the effects of shell disease through induced molting.
  • Article
    The effect of alkylphenols on lobster shell hardening
    (National Shellfisheries Association, 2012-06) Laufer, Hans ; Chen, Ming ; Johnson, Michael ; Demir, Neslihan ; Bobbitt, James M.
    Alkylphenols, anthropogenic estrogenic endocrine disruptors in vertebrates, have been found in lobsters (Homarus americanus) in New England sites. We hypothesize that alkylphenols interfere in the shell hardening during molting. We used an in vitro cuticle bioassay to investigate the effects of 2 alkylphenolic compounds—2,4-bis-(dimethylbenzyl) phenol (compound 3) and bisphenol A (BPA; 4,4′-dihydroxy-2,2-diphenylpropane (also referred to as 4,4′-(propan-2-ylidene) diphenol)) on tyrosine incorporation during the hardening of new cuticle following lobster molting. During sclerotization, both alkylphenols and cold tyrosine competed with C14-tyrosine incorporation in a concentration-dependent manner. This process was also phenoloxidase dependent, as treatment with phenylthiourea (PTU; a phenoloxidase inhibitor) significantly decreased C14-tyrosine incorporation. We also found that incorporation of C14-2,4-bis-(dimethylbenzyl) phenol during the shell hardening process was inhibited by cold alkylphenol, cold tyrosine, or PTU, and competition was concentration dependent. Furthermore, incorporation of tyrosine and derivatives into new cuticle decreased with time after molting from 27% incorporation 1 day after a molt to 6% by 4 days after a molt. In nonmolting cuticles, there was no incorporation of alkylphenol or tyrosine derivatives. When lobsters were injected with 2,4-bis-(dimethylbenzyl) phenol during the premolt stage, it took the shells 12 ± 1 days to harden sufficiently to resist deflection by 5 lb pressure exerted by a pressure gauge, compared with 7 ± 1 days for control shells. Thus, shell hardening is delayed significantly by the presence of 2,4-bis-(dimethylbenzyl) phenol. The effects of this compound on shell hardening may result in lobsters' susceptibility to microbial invasion and, therefore, may contribute to the onset of shell disease.