Intersexuality is the abnormal condition when an organism displays characteristics of being both male and female. The study of intersexuality in wildlife provides excellent means for studying comparative biology of abnormal conditions in reproductive determination and/or differentiation. Intersex in crustaceans can occur through genetic abberations, parasitism, disrupted environmental sex determination (ESD) and through chemical exposure. The genetic knowledge of crustacean groups is currently very limited making the assessment of mechanisms behind environmental sex determination (ESD); feminsing parasites; and pollution very limited in this ecologically important group: thus hot-topics in environmental sciences such as endocrine disruption and climate change are difficult to assess without a clear understanding of the biology of ecologically relevant species. Considerable information exists at the physiological, individual and population level impacts of temperature, photoperiod, and parasitism on the sex determination in amphipods. In addition, several studies have suggested sexual disruption might also be occuring in this group following exposure to environmental contaminents. Following on from a NERC 454 pilot study into gene expression in normal and intersex gonadal tissues, this project would utilise high-throughput sequencing technologies to complete a suite of archived biological tissues for specific gene expression in male and female amphipods and two intersex phenotypes (intersex males and females); increasing substantially the genetic knowledge for this and crustacean groups in general. Intra and inter specific differences between organs of males, females, intersex males and intersex females would be compared by digital transcriptmics. Following some evidence that suggests that male crustaceans maybe impacted by pollution in a way that effects their male hormones and cause demasculinisation (a more female-like appearance). Further studies would experimently induce de-masculinisation in an intertidal amphipod using three methods; firstly, physically dissecting the male (androgenic) glands; secondly, through infection with feminising parasites; and thirdly, through chemical exposure to some known endocrine disrupting chemicals. These experiments would be used to examine comparisons in the genes being up/down regulated following each experimental manipulation. Key genes would be selected and utilised to develop assays to assess whether demasculinisation is occuring in field collected specimens from clean and polluted sites. All genetic data acquired during these studies would be made publically available through a specially designed database entitled AmphiBASE.